Anesthesia for Congenital Heart Surgery

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CHAPTER 20 Anesthesia for Congenital Heart Surgery

James A. DiNardo, Avinash C. Shukla and Francis X. McGowan, Jr.

This chapter describes the perioperative management of major forms of congenital heart disease (CHD) that require surgery with the use of cardiopulmonary bypass. Congenital cardiac lesions that are primarily addressed in the catheterization laboratory or without CPB are discussed in Chapter 21, Congenital Cardiac Anesthesia: Non-Bypass Procedures.

Congenital anomalies of the heart and cardiovascular system occur in 7 to 10 per 1000 live births. Congenital heart disease is the most common congenital disease, accounting for approximately 30% of all congenital diseases. CHD has become the principal cause of pediatric heart disease as the incidence of rheumatic heart disease has declined. Ten percent to 15% of children with CHD have associated congenital anomalies of the skeletal, genitourinary, or gastrointestinal system. The U.S. population of adults with CHD, surgically corrected or uncorrected, is estimated to exceed 1 million and is increasing steadily. As a result, it is not uncommon for adult patients with CHD to present for noncardiac surgery (see Chapter 21, Congenital Cardiac Anesthesia: Non-Bypass Procedures).

Transthoracic and transesophageal echocardiography has facilitated early, accurate diagnosis of congenital heart disease. Unlike in adults, who may have limited transthoracic echocardiographic windows, high-quality echocardiographic images in pediatric patients are easily obtained. Most neonates with CHD can have sufficient and thorough evaluation of their cardiac lesions by echocardiography and thus avoid catheterization studies for diagnosis and management. In some instances, catheterization and angiography are necessary to clearly delineate coronary or aortopulmonary collateral anatomy and other intracardiac defects, to assess pressure gradients, and to potentially intervene for palliative or reparative purposes. Fetal cardiac ultrasonography has permitted antenatal diagnosis of congenital heart defects, allowing subsequent perinatal management in specialized tertiary care centers. Imaging modalities such as cardiac magnetic resonance imaging (MRI) and three-dimensional echocardiography are being used with increasing frequency.

Advances in molecular biology have provided a new understanding of the genetic basis of CHD. Chromosomal abnormalities are associated with an estimated 10% of congenital cardiovascular lesions. Two thirds of these lesions occur in patients with trisomy 21; the other one third of lesions are found in patients with other chromosomal abnormalities, such as trisomy 13 and trisomy 18, and in patients with Turner’s syndrome. Conotruncal lesions (tetralogy of Fallot, interrupted aortic arch, truncus arteriosus, ventricular septal defects) are commonly associated with a 22q11.2 chromosomal deletion. This defect is associated with DiGeorge syndrome, velocardiofacial syndrome, and conotruncal anomaly face syndromes. These syndromes can be associated with hypocalcemia, immunodeficiency, facial dysmorphia, palate anomalies, velopharyngeal dysfunction, renal anomalies, and developmental, speech, and feeding disorders. The remaining 90% or so of congenital cardiovascular lesions are currently without defined genetic association and are postulated to be the results of interactions of one or more genes with external or environmental factors (e.g., rubella, ethanol, lithium, maternal diabetes mellitus, folate deficiency).

Signs and symptoms of congenital heart disease in infants and children often include dyspnea, poor feeding, poor growth, delayed physical development, and the presence of a cardiac murmur. The diagnosis of CHD is apparent during the first week of life in about 50% of patients, and before 5 years of age in virtually all remaining patients. Echocardiography is the initial diagnostic step if CHD is suspected.

Congenital heart disease can be associated with specific complications. For example, infective endocarditis is a risk associated with most congenital cardiac anomalies. Sudden death occasionally occurs in patients who undergo surgical correction of CHD, presumably reflecting the effects of chronic abnormal hemodynamic loads, myocardial scarring and fibrosis, damage to the cardiac conduction system, or underlying (and presently occult) abnormal molecular and ion channel defects. Cardiac dysrhythmias are not usually a prominent presenting feature of CHD but can be more common as patients age and pathophysiologic sequelae of abnormal cardiac structure, function, and surgery accrue (see later and Chapter 21, Congenital Cardiac Anesthesia: Non-Bypass Procedures). Table 20-1 summarizes the pathophysiology and clinical picture associated with a wide variety of congenital heart defects. Table 20-2 summarizes the surgical repair options for each type of lesion.

TABLE 20-1 Pathophysiology and Clinical Picture of Congenital Heart Defects

Lesion Type	Pathophysiology	Clinical Signs and Symptoms
Shunt Lesion without Outflow Tract Obstruction
• Atrial septal defects • Ventricular septal defects • Atrioventricular canal defects • Patent ductus arteriosus • Aortopulmonary window	• Intracardiac L-R shunt • Increased pulmonary blood flow	• CHF (systemic and pulmonary vascular congestion) • No cyanosis (unless high pulmonary blood flow leads to increased left atrial pressure, pulmonary edema, and intrapulmonary V/Q mismatch and shunt)
Shunt Lesions with Right Ventricular Outflow Tract Obstruction
• Tetralogy of Fallot • Ebstein’s anomaly • Pulmonary stenosis with atrial or ventricular septal defects • Eisenmenger’s syndrome	• Intracardiac R-L shunt • Decreased pulmonary blood flow	• Cyanosis
Transposition Physiology (Intercirculatory mixing)
• Dextro-transposition of the great arteries	• Intracardiac L-R and R-L shunts are equal	• Cyanosis
Single Ventricle Physiology
*One-Ventricle Lesions*	• Mixing of systemic and pulmonary venous blood • Parallel distribution of pulmonary and systemic blood flow determined by relative circuit resistances	• CHF (systemic and pulmonary vascular congestion) • Cyanosis
• Hypoplastic left heart syndrome • Tricuspid atresia • Double inlet left ventricle
*Two-Ventricle Lesions*
• Truncus arteriosus • Tetralogy of Fallot with pulmonary atresia • Severe neonatal aortic stenosis
Left Ventricular Obstructive Lesions
*Mitral Stenosis*	• Left ventricular pressure overload from aortic lesions • Increased left atrial pressure from left ventricular systolic and diastolic dysfunction OR obstruction to left atrial emptying	• CHF (if high left atrial pressure leads to pulmonary vascular congestion) • No cyanosis (unless high left atrial pressure leads to pulmonary edema and intrapulmonary V/Q mismatch and shunt)
• Valvular
• Cor triatriatum
*Aortic Stenosis*
• Valvular
• Subvalvular (subaortic membrane)
• Supravalvular (Williams-Beuren syndrome)
*Coarctation*
• Shone’s syndrome (mitral stenosis, aortic stenosis, coarctation)
Mixing of Systemic and Pulmonary Venous Blood with Series Circulation
• Partial anomalous pulmonary venous return (PAPVR) • Total anomalous pulmonary venous return (TAPVR)	• Mixing of systemic and pulmonary venous blood • Increased pulmonary blood flow	*CHF* • Systemic and pulmonary vascular congestion; pulmonary vascular congestion is severe if pulmonary venous obstruction • No cyanosis *PAPVR* • Cyanosis *TAPVR* • Exacerbated if pulmonary venous obstruction leads to pulmonary edema and intrapulmonary V/Q mismatch and shunt

CHF, Congestive heart failure; PAPVR, partial anomalous pulmonary venous return; TAPVR, total anomalous pulmonary venous return.

TABLE 20-2 Classification of Congenital Heart Lesions and Associated Repairs

Lesion Type	Repair
Shunt Lesions
*Left-to-Right*
• Atrial septal defects	Complete repair
• Ventricular septal defects	Complete repair
• Atrioventricular canal defects	Complete repair
• Patent ductus arteriosus	Complete repair
• Aortopulmonary window	Complete repair
*Right-to-Left*
• Tetralogy of Fallot	Complete repair
• Ebstein’s anomaly	Complete repair
• Pulmonary stenosis in conjunction with atrial or ventricular septal defects	Complete repair
• Eisenmenger’s syndrome	No repair
Transposition Physiology
• Dextro-transposition of the great arteries	Complete repair
Single-Ventricle Physiology
*One-Ventricle Lesions*
• Hypoplastic left heart syndrome	Staging to Fontan
• Tricuspid atresia	Staging to Fontan
• Double inlet left ventricle	Staging to Fontan
*Two-Ventricle Lesions*
• Truncus arteriosus	Complete repair
• Tetralogy of Fallot with pulmonary atresia	Complete repair
• Severe neonatal aortic stenosis	Complete repair
Left Ventricular Obstructive Lesions
*Mitral Stenosis*
• Valvular • Cor triatriatum	Complete repair
*Aortic Stenosis*
• Valvular • Subvalvular (subaortic membrane) • Supravalvular (Williams-Beuren Syndrome)	Complete repair
*Coarctation*
• Shone’s syndrome (mitral stenosis, aortic stenosis, coarctation)	Repair with likely residual lesions
Mixing of Systemic and Pulmonary Venous Blood with Series Circulation
• Partial anomalous pulmonary venous return (PAPVR) • Total anomalous pulmonary venous return (TAPVR)	Complete repair

Pathophysiology of congenital heart disease

Although some congenital heart defects involve purely obstructive or regurgitant valvular lesions, shunts (both physiologic and anatomic) are a hallmark of CHD. The concepts of shunting (both physiologic and anatomic), single-ventricle physiology, and intercirculatory mixing require discussion.

Shunting

Shunting is the process whereby venous return into one circulatory system is recirculated through the arterial outflow of the same circulatory system. Flow of blood from the systemic venous atrium or right atrium (RA) to the aorta produces recirculation of systemic venous blood. Flow of blood from the pulmonary venous atrium or left atrium (LA) to the pulmonary artery (PA) produces recirculation of pulmonary venous blood. Recirculation of blood produces a physiologic shunt. Recirculation of pulmonary venous blood produces a physiologic left-to-right (L-R), whereas recirculation of systemic venous blood produces a physiologic right-to-left (R-L) shunt.

Effective blood flow is the quantity of venous blood from one circulatory system reaching the arterial system of the other circulatory system. Effective pulmonary blood flow is the volume of systemic venous blood reaching the pulmonary circulation, whereas effective systemic blood flow is the volume of pulmonary venous blood reaching the systemic circulation. Effective pulmonary blood flow and effective systemic blood flows are the flows necessary to maintain life. Effective pulmonary blood flow and effective systemic blood flow are always equal, no matter how complex the lesions. Effective blood flow is usually the result of a normal pathway through the heart, but it may occur as the result of an anatomic R-L or L-R shunt, as in transposition physiology.

Total pulmonary blood flow () is the sum of effective pulmonary blood flow and recirculated pulmonary blood flow. Total systemic blood flow () is the sum of effective systemic blood flow and recirculated systemic blood flow. Total pulmonary blood flow and total systemic blood flow do not have to be equal. Therefore, it is best to think of recirculated flow (physiologic shunt flow) as the extra, noneffective flow superimposed on the nutritive effective blood flow. These concepts are illustrated in Figures 20-1 to 20-3.

FIGURE 20-1 Blood flows in a nonrestrictive atrial septal defect (ASD). Effective pulmonary and effective systemic blood flows are equal (2.0 L/min/m²). The (ratio of total pulmonary to total systemic blood flow) is 2:1. (4.0 L/min per meter-squared) is the sum of the effective pulmonary blood flow (2.0 L/min/m²) and a L-R physiologic shunt (2.0 L/min/m²). This L-R shunt is recirculation of pulmonary venous blood into the pulmonary artery that imposes a volume load on the left atrium, right atrium, and right ventricle.

FIGURE 20-2 Saturations, pressures, and blood flows in tricuspid atresia with a mildly restrictive atrial septal defect (ASD), a small restrictive ventricular septal defect (VSD), and mild pulmonic stenosis (PS). Complete mixing or blending occurs at the atrial level. This complete mixing is the consequence of an obligatory physiologic and anatomic R-L shunting across the ASD. Effective pulmonary and effective systemic blood flows are equal (1.5 L/min/m²). Effective systemic blood flow occurs via a normal pathway through the heart. Effective pulmonary blood flow is the result of an anatomic R-L shunt at the atrial level, and an anatomic L-R shunt at the ventricular level. This illustrates the concept that when complete outflow obstruction exists and there is obligatory anatomic shunting, a downstream anatomic shunt must exist to deliver blood back to the obstructed circuit. Total pulmonary blood flow () is 2.8 L/min/m² and is the sum of effective pulmonary blood flow (1.5 L/min/m²) and a physiologic and anatomic L-R shunt (1.3 L/min/m²) at the VSD. Total systemic blood flow () is 3.3 L/min/m² and is the sum of effective systemic blood flow (1.5 L/min/m²) and a physiologic and anatomic R-L shunt (1.8 L/min/m²) at the ASD. Here, there is a small pressure gradient at the atrial level and a large pressure gradient at the ventricular level. In addition, there is a small additional gradient at the level of the pulmonic valve.

FIGURE 20-3 Saturations, pressures, and blood flows in transposition of the great arteries with a nonrestrictive atrial septal defect and a small left ventricular outflow tract gradient. Intercirculatory mixing occurs at the atrial level. Effective pulmonary and effective systemic blood flows are equal (1.1 L/min/m²) and are the result of a bidirectional anatomic shunt at the atrial level. The physiologic L-R shunt is 9.0 L/min/m²; this represents blood recirculated from the pulmonary veins to the pulmonary artery. The physiologic R-L shunt is 1.2 L/min/m²; this represents blood recirculated from the systemic veins to the aorta. Total pulmonary blood flow () is almost five times the total systemic blood flow (). The bulk of pulmonary blood flow is recirculated pulmonary venous blood. Here, pulmonary vascular resistance is low (approximately 1/35 of systemic vascular resistance) and there is a small (17 mm Hg, peak to peak) gradient from the left ventricle to the pulmonary artery. These findings are compatible with the high pulmonary blood flow shown.

Single-Ventricle Physiology

Single-ventricle physiology describes the situation in which there is complete mixing of pulmonary venous and systemic venous blood at the atrial or ventricular level, and the ventricle (or the ventricles) then distribute output to both the systemic and pulmonary beds. As a result of this physiology (1) ventricular output is the sum of pulmonary blood flow () and systemic blood flow (), (2) distribution of systemic and pulmonary blood flow is dependent on the relative resistances to flow (both intracardiac and extracardiac) into the two parallel circuits, and (3) oxygen saturations are the same in the aorta and the pulmonary artery. This physiology can exist in patients with one well-developed ventricle and one hypoplastic ventricle, as well as in patients with two well-formed ventricles.

In the case of a single anatomic ventricle, there is always obstruction to either pulmonary or systemic blood flow as the result of complete or near-complete obstruction to inflow or outflow (or both) from the hypoplastic ventricle. In this circumstance, there must be a source of both systemic and pulmonary blood flow to assure postnatal survival. In some instances of a single anatomic ventricle, a direct connection between the aorta and the pulmonary artery via a patent ductus arteriosus (PDA) is the sole source of systemic blood flow (e.g., hypoplastic left heart syndrome [HLHS]) or of pulmonary blood flow (e.g., pulmonary atresia with intact ventricular septum). This is known as ductal dependent circulation. In other instances of a single anatomic ventricle, intracardiac pathways provide both systemic and pulmonary blood flow without a PDA. This is the case when tricuspid atresia occurs along with normally related great vessels, a nonrestrictive ventricular septal defect (VSD), and minimal or absent pulmonary stenosis.

In certain circumstances, single-ventricle physiology can exist in the presence of two well-formed anatomic ventricles: (1) tetralogy of Fallot (TOF) with pulmonary atresia (in which pulmonary blood flow is supplied via a PDA or multiple aortopulmonary collateral arteries), (2) truncus arteriosus, and (3) severe neonatal aortic stenosis and interrupted aortic arch (in which a substantial portion of systemic blood flow is supplied via a PDA).

Table 20-3 lists a number of single-ventricle physiology lesions. All patients with single-ventricle physiology who have severe hypoplasia of one ventricle will ultimately undergo the staged surgeries that comprise the single-ventricle pathway and result in Fontan physiology (described later). Patients with single-ventricle physiology and two well-formed ventricles are usually able to undergo a two-ventricle repair. In some cases, the two-ventricle repair will be complete. In others, significant residual lesions (VSD, aortopulmonary collaterals) will remain. In patients with single-ventricle physiology, the arterial oxygen saturation (Sao₂) is determined by the relative volumes and saturations of pulmonary venous and systemic venous blood flows that have mixed and reach the aorta (see Fig. 20-1).

TABLE 20-3 Anatomic Subtypes of Single-Ventricle Physiology

	Aortic Blood Flow from:	Pulmonary Artery Blood Flow from:
HLHS	PDA	RV
Severe neonatal aortic stenosis	PDA	RV
IAA	LV (proximal)PDA (distal)	RV
PA with IVS	LV	PDA
Tetralogy of Fallot with pulmonary atresia	LV	PDA, MAPCAs
Tricuspid atresia, NRGA, with pulmonary atresia (type 1A)	LV	PDA, MAPCAs
Tricuspid atresia, NRGA, with restrictive VSD and pulmonary stenosis (type 1B)	LV	LV thru VSD to RV
Tricuspid atresia, NRGA, with non-restrictive VSD and no pulmonary stenosis (type 1C)	LV	LV thru VSD to RV
Truncus arteriosus	LV and RV	Aorta
DILV, NRGA	LV	LV thru BVF

BVF, Bulboventricular foramen; DILV, double-inlet left ventricle; HLHS, hypoplastic left heart syndrome; IAA, interrupted aortic arch; LV, left ventricle; MAPCAs, multiple aortopulmonary collateral arteries; NRGA, normally related great arteries; PA with IVS, pulmonary atresia with intact ventricular septum; PDA, patent ductus arteriosus; RV, right ventricle; VSD, ventricular septal defect.

Intercirculatory Mixing

Intercirculatory mixing is the unique situation that exists in transposition of the great arteries (TGA) (see Fig. 20-2). In TGA, there are two parallel circulations because of the existence of atrioventricular concordance (right atrium to right ventricle [RA-RV], and left atrium to left ventricle [LA-LV]) and ventriculoarterial discordance (right atrium to aorta [RV-Ao], and left ventricle to pulmonary artery [LV-PA]). This produces a parallel rather than a normal series circulation. In this arrangement, parallel recirculation of pulmonary venous blood in the pulmonary circuit and systemic venous blood in the systemic circuit occurs. Therefore, the physiologic shunt or the percentage of venous blood from one system that recirculates in the arterial outflow of the same system is 100% for both circuits.

Thus, this lesion is incompatible with life unless there are one or more communications (atrial septal defect [ASD], patent foramen ovale [PFO], VSD, PDA) between the parallel circuits to allow intercirculatory mixing. In the presence of mixing, arterial saturation (Sao₂) is determined by the relative volumes and saturations of the recirculated systemic and effective systemic venous blood flows reaching the aorta (see Fig. 20-3).

Fontan Physiology

Fontan physiology (see also later) is a series (i.e., “normal”) circulation in which one ventricle has sufficient diastolic, systolic, and atrioventricular valve function to support systemic circulation (Figs. 20-4 and 20-5). This ventricle must in turn be in unobstructed continuity with the aorta and pulmonary venous blood return; there must also be unobstructed delivery of systemic venous blood to the pulmonary circulation (total cavopulmonary continuity).

FIGURE 20-4 Total cavopulmonary connection (Fontan) using an intraatrial lateral tunnel or baffle. The tunnel is prosthetic graft material such as Gore-Tex. A fenestration has been placed in this prosthetic material allowing a physiologic R-L shunt to exist when baffle pressure exceeds common (pulmonary venous) atrial pressure. This pop-off allows systemic cardiac output to be maintained (at the expense of arterial saturation) when the resistance to pulmonary blood flow is high.

(Redrawn from Children’s Hospital Boston, Boston, Mass.)

FIGURE 20-5 Total cavopulmonary connection (Fontan) using an extracardiac conduit or baffle. The conduit is prosthetic graft material such as Gore-Tex. In this example, no fenestration or pop-off is present to allow physiologic R-L shunting when baffle pressure exceeds common (pulmonary venous) atrial pressure.

(Redrawn from Children’s Hospital Boston, Boston, Mass.)

General Approach to Anesthetic Management

Preparation for Anesthesia

Preparation for anesthesia begins with a thorough assessment of the patient’s medical and surgical conditions (as with any preoperative assessment). Also necessary is a complete understanding of the patient’s “original” cardiac anatomy and physiology, any previous surgical or catheterization procedures and complications, the present status of the patient’s anatomy and pathophysiology, current medications, and involvement of other organ systems (e.g., renal insufficiency). Also necessary is detailed knowledge of the anatomic and functional information contained in the most recent diagnostic studies (echocardiography or Doppler on most patients, and often catheterization and cardiac MRI data as well), as well as of the planned procedure and its acute physiologic consequences and potential complications.

Basic operating room preparation begins with the considerations common to all pediatric anesthesia, including the presence of appropriately sized airway; ventilator; monitoring; cardioversion, defibrillation, and external pacing (including external pads or paddles and internal paddles of appropriate sizes); temperature control (capability for warming and cooling); blood and fluid administration; and vascular access equipment and supplies. In addition, an extra blood pressure cuff and pulse oximeter should be on hand in case the need arises for some specific lesions. Size-appropriate equipment and supplies (including vascular ultrasound devices and pressure monitoring transducers) to perform peripheral and femoral arterial and central venous cannulation and pressure monitoring are necessary. In addition to standard drugs, one should have predrawn and hence immediately available syringes containing weight-appropriate concentrations of emergency drugs including epinephrine, calcium (gluconate or chloride salt), phenylephrine, and atropine. Other agents, such as sodium bicarbonate, glucose, potassium chloride, antiarrhythmics (e.g., adenosine, procainamide), β-blockers, heparin, and inotropes and other vasoactive drugs for infusion (e.g., dopamine, dobutamine, epinephrine, phenylephrine, milrinone, vasopressin, nitroglycerin, nitroprusside, esmolol) should be immediately available. Many find it helpful to complete a patient-specific emergency card for each patient that contains weight-based concentrations, dosages, and bolus volumes or infusion rates for the most frequently used agents before starting the case.

No one anesthetic induction technique is suitable for all patients with congenital heart disease. The patient’s age, cardiopulmonary function, degree of cyanosis, and emotional state all play roles in the selection of an anesthetic technique. Intravenous administration of induction agents clearly affords the greatest flexibility in terms of drug selection and drug titration and allows prompt control of the airway. We believe that intravenous induction is the preferred technique in the majority of patients, including those with significantly impaired ventricular systolic function, significant obstruction to blood flow (e.g., severe aortic stenosis), and systemic or suprasystemic pulmonary artery pressures. In all patients, ensuring adequacy of the airway and gas exchange is a preeminent consideration.

Sevoflurane, halothane, isoflurane, and fentanyl plus midazolam do not change the ratio of pulmonary-to-systemic blood flow () in children with atrial and ventricular septal defects when cautiously administered with 100% oxygen (Laird et al., 2002). Sevoflurane (1 minimum alveolar concentration [MAC]) and fentanyl plus midazolam have no significant effect on myocardial function in patients with a single ventricle (Ikemba et al., 2004). Halothane (1 and 1.5 MAC) depresses cardiac index and contractility more than comparable levels of sevoflurane, isoflurane, and fentanyl plus midazolam anesthesia (Rivenes et al., 2001). In addition, halothane anesthesia may result in more severe hypotension and emergent drug use than sevoflurane anesthesia in children with CHD (Russell et al., 2001).

Specific lesions

Atrial Septal Defect

Atrial septal defect accounts for about one third of the congenital heart disease detected in adults, with the frequency in women two to three times that in men. See related video online at www.expertconsult.com.

Strictly speaking, an ASD is a communication between the left and right atrium resulting from a defect in the intraatrial septum, which consists of a central membranous portion and a thicker inferior and superior fatty limbus. The central membranous portion is formed by tissue of the septum primum, ultimately forming the fossa ovalis. This membrane lies posterior to the superior aspect of the fatty limbus.

ASDs are classified by their location (Fig. 20-6). There are four morphologic types: ostium secundum defects, ostium primum defects, inferior and superior sinus venosus defects, and coronary sinus (CS) defects. Although they are classified as ASDs, sinus venosus and CS defects are not truly defects in the intraatrial septum. Secundum ASDs account for 80% of all ASDs. Whereas a PFO results from incomplete fusion of an intact fossa ovalis membrane with the superior aspect of the fatty limbus, an ostium secundum ASD is the result of actual deficiencies in the membrane (septum primum) of the fossa ovalis. Isolated ostium primum ASDs, also known as partial atrioventricular canal defects, are discussed later (see Atrioventricular Canal Defects). The isolated ostium primum defect extends from the inferior intraatrial septum fatty limbus, to the crest of the intact ventricular septum.

FIGURE 20-6 Location of atrial septal defects (ASDs). ASD 1°, primum ASD; ASD 2°, secundum ASD. Superior and inferior sinus venous defects are shown.

(Redrawn from Children’s Hospital Boston, Boston, Mass.)

Both types of sinus venous defects are associated with partially anomalous pulmonary venous return. In the case of the superior defect, anomalous drainage of the right upper pulmonary vein into the junction of the superior vena cava (SVC) and the RA is the most common finding. In the case of the inferior defect, scimitar syndrome (anomalous drainage of the right upper and lower pulmonary veins to the junction of the inferior vena cava [IVC] and RA, aortopulmonary collaterals to the right lower lobe, and hypoplasia of the right lung) can be seen.

Clinical Presentation

The physiologic consequences of ASDs are the same regardless of the anatomic location and reflect the shunting of blood from one atrium to the other; the direction and magnitude of the shunt are determined by the size of the defect and the relative compliance of the ventricles. A small defect (less than 0.5 cm in diameter) is associated with a small shunt and no hemodynamic sequelae. When the diameter of the ASD approaches 2 cm, it is likely that left atrial blood is being shunted to the right atrium (the right ventricle is more compliant than the left ventricle), resulting in increased pulmonary blood flow. A systolic ejection murmur audible in the second left intercostal space may be mistaken for an innocent flow murmur. The electrocardiogram (ECG) may reflect right axis deviation and incomplete right bundle branch block. Atrial fibrillation and supraventricular tachycardia may accompany an ASD that remains uncorrected into adulthood. The chest radiograph is likely to reveal prominent pulmonary arteries. Echocardiography is the mainstay of diagnostic imaging for these patients, with catheterization usually reserved for assessment of pulmonary artery pressures when indicated.

Because they initially produce no symptoms or striking findings on physical examination, ASDs may remain undetected for years. Symptoms resulting from large ASDs include dyspnea on exertion, supraventricular dysrhythmias, right heart failure, paradoxical embolism, and recurrent pulmonary infections. Prophylaxis against infective endocarditis is not recommended for patients with an ASD unless a concomitant valvular abnormality (mitral valve prolapse or mitral valve cleft) is present. Supraventricular dysrhythmias and pulmonary hypertension can increase in frequency, even for moderately sized defects, as patients enter the second and third decades of life.

Some small ostium secundum ASDs can be primarily closed, whereas larger defects are patched, usually with pericardium. An alternative is nonoperative device closure of secundum ASDs in the cardiac catheterization laboratory (see Chapter 21, Congenital Cardiac Anesthesia: Non-Bypass Procedures). Primum ASDs generally require patch closure and suture closure of the anterior leaflet mitral cleft. Sinus venous defects without partially anomalous pulmonary venous return can be closed primarily with a patch. An alternative procedure is performed when the pulmonary vein or veins anomalously enter the SVC. The SVC is transected above the origin of the anomalous vein or veins, and the SVC orifice is directed across the defect into the LA with a pericardial patch. The distal end of the SVC is then anastomosed in an end-to-end fashion to the roof of the RA appendage, recreating SVC-to-RA continuity.

Management of Anesthesia

The goals of anesthetic management for patients with ASD before cardiopulmonary bypass (CPB) follow from the aforementioned principles and are outlined in Box 20-1. The goals for these patients after CPB are outlined in Box 20-2.

Box 20-1 Anesthesia Management Goals for ASD, VSD, AVC Defect, and PDA before Cardiopulmonary Bypass (CPB)

1. Maintain heart rate, contractility, and preload to maintain cardiac output.

• A reduction in cardiac output compromises systemic perfusion, despite a relatively high pulmonary blood flow.

2. Avoid maneuvers that decrease the PVR-to-SVR ratio.

• The increase in pulmonary blood flow that accompanies a reduced PVR-to-SVR ratio necessitates an increase in cardiac output to maintain systemic blood flow, thereby compromising systemic (e.g., coronary, cerebral, GI, renal) perfusion.

3. Maintain normoxia and normocarbia or mild hypercarbia.

• Some patients overcirculate (excessive pulmonary blood flow) despite these measures, and it may be necessary to support systemic perfusion prior to CPB, with additional volume expansion or inotropes (or both).

• The right pulmonary artery can be partially or completely occluded to mechanically control the magnitude of a left-to-right shunt and thus support systemic perfusion once adequate surgical exposure is attained.

4. Avoid large increases in the PVR-to-SVR ratio.

• A substantial increase may result in production of a right-to-left shunt.

5. When a right-to-left shunt exists, ventilatory measures to decrease PVR should be entertained, and SVR must be maintained or increased.

• These measures will reduce the magnitude of the right-to-left shunt.

ASD, Atrial septal defect; AVC, atrioventricular canal; GI, gastrointestinal; PDA, patent ductus arteriosus; PVR, pulmonary vascular resistance; SVR, systemic vascular resistance; VSD, ventricular septal defect.

Box 20-2 Management Goals for ASD, VSD, and AVC Defect after Cardiopulmonary Bypass (CPB)

1. Maintain heart rate (preferably sinus rhythm) at an age-appropriate rate.

• Cardiac output is likely to be more heart rate dependent in the post-CPB period.

2. Reduce PVR through ventilatory interventions.

• This is particularly important if PVOD is present.

3. Inotropic support of the right ventricle may be necessary, particularly if PVR is high. In patients with VSD or AVC, the left ventricle will no longer contribute to ejection of blood via the pulmonary artery, and the right ventricle will face a high afterload.

• Dobutamine (5 to 10 mcg/kg per minute) or dopamine (5 to 10 mcg/kg per minute) provide inotropic support without increasing PVR.

• Milrinone (0.5 to 1.0 mcg/kg per minute) after a loading dose of 50 mcg/kg has more-direct PVR-reducing effects in addition to inotropic, lusitrophic, and SVR reducing effects.

4. Infants with large VSDs or AVC defects, particularly in association with trisomy 21, are candidates for development of severe pulmonary hypertension and hypertensive crises after CPB.

• Consider inhaled nitric oxide (iNO) when pulmonary hypertension and resultant RV dysfunction and low cardiac output persist.

ASD, Atrial septal defect; AVC, atrioventricular canal; PVOD, pulmonary vascular occlusive disease; PVR, pulmonary vascular resistance; SVR, systemic vascular resistance; VSD, ventricular septal defect.

From Bizzarro M, Gross I: Inhaled nitric oxide for the postoperative management of pulmonary hypertension in infants and children with congenital heart disease, Cochrane Database Syst Rev (4):CD005055, 2005.

Ventricular Septal Defect

Ventricular septal defect is the most common congenital cardiac abnormality in infants and children. See related video online at www.expertconsult.com.

A large number of VSDs close spontaneously by the time a child reaches 2 years of age. VSDs can be classified by their location in the septum (Fig. 20-7).

FIGURE 20-7 Locations of ventricular septal defects.

(Redrawn from Children’s Hospital Boston, Boston, Mass.)

Subpulmonary or supracristal defects are located in the infundibular septum just below the aortic valve. Subpulmonary lesions may be associated with aortic insufficiency due to a lack of support for the right coronary cusp of the aortic valve and prolapse of this leaflet. Membranous or perimembranous defects comprise approximately 80% of all VSDs and are located in the subaortic region of the membranous septum, near or under the septal leaflet of the tricuspid valve, and they communicate with the LV just below the aortic valve. These defects are commonly partially closed by a collection of tricuspid valve and membranous septal tissue, giving an aneurysmal appearance to the septum. Conoventricular defects involve the same area as perimembranous defects, but they extend anteriorly and superiorly in the septum. Inlet- or canal-type defects involve the posterior septum near the atrioventricular (AV) valves. Muscular defects are located in the lower trabecular septum and may appear deceptively small on inspection from the right ventricular aspect of the septum because of heavy trabeculation. These defects may be apical, midmuscular, anterior, or posterior.

Clinical Presentation

The physiologic significance of a VSD depends on the size of the defect and the relative resistance in the systemic and pulmonary circulations. Restrictive VSDs have a substantial pressure gradient across them (i.e., left ventricular pressure significantly greater than the right) and, as the name suggests, are sufficiently small to limit the amount of flow (and pressure) entering the RV via the defect. In contrast, flow through unrestrictive VSDs is largely based on the relative resistance in the systemic and pulmonary circulations. If the defect is small, there is minimal functional disturbance, as pulmonary blood flow is only modestly increased. The newborn infant with a large VSD may have near-normal pulmonary blood flow as a result of the high PVR present at birth. However, by the second week of life and continuing into the second month, PVR begins to fall to near-normal levels and pulmonary blood flow increases dramatically. Continued decreases in PVR after birth may be delayed by the elevated left atrial pressure that accompanies increased pulmonary blood flow (PBF).

Patients with large VSDs present with one or more signs and symptoms of pulmonary overcirculation and congestive heart failure (CHF) that increase as PVR falls. These include tachypnea, other signs of increased work of breathing (including retractions and nasal flaring), poor feeding, poor growth, diaphoresis, delayed capillary refill, diminished pulses, and hepatomegaly. Patients can be managed medically with diuretics, at times in combination with digoxin; however, significant symptoms usually result in early surgery.

Large VSDs also predispose to the development of pulmonary vascular occlusive disease (PVOD) during the first few years of life as a result of exposure of the pulmonary vasculature to high flows and systemic blood pressures. The increases in PVR that accompany PVOD ultimately produce bidirectional and right-to-left shunts. Patients with advanced PVOD and markedly increased PVR (Eisenmenger’s complex) are not generally candidates for VSD closure, because closure will result in an enormous increase in RV afterload and RV-afterload mismatch. For this reason, large VSDs (> 2:1) are corrected early in childhood. Whether to close smaller, more restrictive VSDs (i.e., when the is < 1.5:1) remains controversial. Here, the major long-term risk is most likely subacute bacterial endocarditis, and much less likely the development of CHF or PVOD, which must be balanced against the risks of CPB and surgery.

The murmur of a moderate to large VSD is holosystolic and is loudest at the lower left sternal border. The ECG and chest radiograph remain essentially normal in the presence of a small VSD. When the VSD is large, there is evidence of left atrial and ventricular enlargement on the ECG. The chest radiograph in patients with larger VSDs typically demonstrates cardiomegaly and increased PBF; increased interstitial markings, enlarged central pulmonary arteries, and hyperinflation may also be seen, particularly as CHF worsens. If pulmonary hypertension develops, the QRS axis shifts to the right, and right atrial and ventricular enlargement are noted on the ECG. A significant finding on physical examination is a loud second single heart sound. Here again, echocardiography is the major diagnostic imaging modality. Cardiac catheterization is usually reserved to assess other potential lesions and the degree of pulmonary hypertension and its responsiveness to pulmonary vasodilators.

Treatment

VSDs are generally closed with a patch by a variety of approaches, depending on their location. To avoid postoperative compromise of a small ventricle, with its poor compliance and limited capacity for tension development, a ventriculotomy to approach and correct VSDs is usually avoided. Many defects are approachable through the right atrium and tricuspid valve, aorta, or pulmonary artery.

Management of Anesthesia

The before-CPB goals of anesthetic management for patients with VSD are outlined in Box 20-1. The goals for these patients after CPB are outlined in Box 20-2.

Atrioventricular Canal Defects

Embryologically, four endocardial cushions contribute to the development of the lower ostium primum portion of the atrial septum and the upper, posterior inlet portion of the intact ventricular septum (IVS), where the AV valves insert. See related video online at www.expertconsult.com.

The endocardial cushions also contribute to the tissue that forms the septal leaflets of the mitral and tricuspid valves. Therefore, cushion defects, or atrioventricular canal (AVC) defects, can include abnormalities in all these structures. The terminology of these lesions can be confusing and is summarized as follows:

Partial AVC. This is an ostium primum ASD in association with a cleft mitral valve. There are two separate AV valve (mitral and tricuspid) annuli. No inlet VSD is present.

Transitional AVC. This is an ostium primum ASD, common AV valve orifice, common anterosuperior and posteroinferior bridging leaflets, with dense chordal attachments to the crest of the IVS creating functionally separate mitral and tricuspid valves. There is a very small or absent inlet VSD.

Complete AVC. This is an ostium primum ASD, common AV valve orifice, common anterosuperior and posteroinferior bridging leaflets, with varying chordal attachments to the crest of the IVS. There is a moderate to large inlet VSD.

Clinical Presentation

These defects can result in communication between all four heart chambers as well as in abnormalities of the mitral and tricuspid valves. Approximately 50% occur in patients with trisomy 21. Because the orifice between the four chambers is large, as with large VSDs, this results in (1) production of a large left-to-right shunt, (2) increased pulmonary blood flow, (3) transmission of systemic pressures to the right ventricle and pulmonary arteries, and (4) volume overloading of the right and left ventricles. The signs and symptoms are related mainly to pulmonary overcirculation and the development of CHF, and they are similar to those outlined previously for large VSD.

As with large VSDs, complete AVC defects predispose to the early development of PVOD. Advanced PVOD may increase the PVR:SVR ratio so that a bidirectional or right-to-left shunt develops. This is a particular concern for patients with trisomy 21, who appear to develop earlier and more significant irreversible PVOD than the patient without trisomy 21 who has a similar hemodynamic disturbance. In some complete AVC defects, the presence of severe mitral insufficiency results in regurgitation of left ventricular blood directly into the right atrium (LV to RA shunt). This increases the left-to-right shunt. In addition, mitral regurgitation increases the volume work of the LV. Use of echocardiography and catheterization are generally similar to that outlined for ASDs and VSDs.

Treatment

Repair of AV canal defects involves closure of the ostium primum ASD and inlet VSD, and septation of the common AV valve tissue into two separate, competent, nonstenotic tricuspid and mitral valves. This can usually be accomplished using a one-patch technique, wherein a single patch is used to close both the VSD and the ASD, and the reconstructed AV valves are resuspended by sutures to the patch. When the VSD is large and extends to other areas of the septum, two patches (atrial and ventricular) may be necessary. When the inlet VSD component is small, the AV valve tissue can be sutured down to the crest of the ventricular septum, essentially closing the VSD. A patch is then sutured to the crest of the ventricular septum and is used to close the ASD.

Management of Anesthesia

The before-CPB goals of anesthetic management for patients with AVC are outlined in Box 20-1. The goals for these patients after CPB are outlined in Box 20-2.

Tetralogy of Fallot

Tetralogy of Fallot is the most common cyanotic congenital heart defect. See related video online at www.expertconsult.com.

It is characterized by a VSD, an overriding aorta, a right ventricular hypertrophy, and pulmonic stenosis (infundibular or subvalvular, valvular, supravalvular, or a combination thereof) (Fig. 20-8). The critical pathophysiologic malformation is underdevelopment of the right ventricular infundibulum and displacement of the infundibular septum, which together result in right ventricular outflow tract (RVOT) stenosis. Patients with TOF have displacement of the infundibular septum in an anterior, superior, and leftward direction. The posterior wall of the right ventricular outflow tract is formed by the infundibular septum, and its abnormal displacement results in narrowing of the right ventricular outflow tract. In addition, displacement of the infundibular septum creates a large malalignment VSD, with the aorta overriding the intraventricular septum. Abnormalities in the septal and parietal attachments of the outflow tract further exacerbate the infundibular stenosis.

FIGURE 20-8 Anatomy of tetralogy of Fallot (TOF). The following features are notable: malalignment ventricular septal defect (VSD), overriding aorta (Ao), infundibular pulmonic stenosis, and small pulmonary arteries. There is a right aortic arch with mirror-image arch vessel branching, as occurs in 25% of patients with TOF.

(Redrawn from Children’s Hospital Boston, Boston, Mass.)

Seventy-five percent of TOF patients have both infundibular and valvular stenosis. A small proportion of patients will have multiple muscular VSDs. The pulmonary valve is almost always bi-leaflet. At one end of the spectrum of TOF, the pulmonary valve may be mildly hypoplastic (reduced annulus size), with minimal fusion of the pulmonary valve leaflets. At the other end of the spectrum, the pulmonary annulus may be very small, with near fusion of the valve leaflets. In addition, there are varying degrees of main pulmonary artery and branch pulmonary artery hypoplasia. The most common associated lesion, present in 25% of patients, is a right aortic arch with mirror-image arch vessel branching (the innominate artery gives rise to the left carotid and left subclavian, and the right carotid and right subclavian arise separately).

In most patients with TOF, there is both a fixed and a dynamic component to RV outflow obstruction. The fixed component is produced by the infundibular, valvular, and supravalvular stenosis. The dynamic component (subvalvular pulmonic stenosis) is produced by variations in the caliber of the RV infundibulum. In patients with TOF, magnitude of the right-to-left shunt and resultant arterial saturation are a direct reflection of the effects of these fixed and variable obstructions on pulmonary blood flow. A small subset of TOF patients (“pink tet” patients) have minimal obstruction to pulmonary blood flow at the right ventricular outflow and pulmonary artery level and may have normal oxygen saturation. Some of these patients have a left-to-right shunt with increased pulmonary blood flow and symptoms of CHF. Another subset where the pulmonary valve is completely or largely absent (“tetralogy-absent valve”) can have massive pulmonary artery enlargement and resultant prominent airway symptoms because of airway compression and tracheobronchomalacia.

Diagnosis

Echocardiography is used to establish the diagnosis and assess the presence of associated abnormalities, the level and severity of the obstruction to right ventricular outflow, the size of the main pulmonary artery and its branches, and the number and location of the VSDs. Right-to-left shunting through the VSD is visualized by color Doppler imaging, and the severity of the RVOT obstruction can be determined by spectral Doppler measurement. Cardiac catheterization and angiography is necessary only when echocardiography cannot rule out coronary artery abnormalities. Approximately 8% of patients have either the left main coronary artery or the left anterior descending artery as a branch of the right coronary artery. In these cases, a right ventriculotomy to enlarge the RVOT will endanger the left coronary artery. In such cases, an extracardiac conduit (RV to main PA) may be necessary to bypass the outflow tract obstruction and avoid injury to the coronary artery.

Clinical Presentation

Most patients with tetralogy of Fallot have cyanosis, frequently progressive, from shortly after birth or beginning during the first months to 1 year of life. The most common ausculatory finding is an ejection murmur heard along the left sternal border resulting from blood flow across the stenotic pulmonic valve. CHF rarely develops because of the RVOT obstruction limitation to PBF, and the large VSD permits equilibration of intraventricular pressures and cardiac workload. Chest radiographs show evidence of decreased lung vascularity, and the heart is “boot shaped” with an upturned right ventricular apex and a concave main pulmonary arterial segment. The ECG is characterized by changes of right axis deviation and right ventricular hypertrophy. Squatting is a common feature of in older children with tetralogy of Fallot. It is speculated that squatting increases the systemic vascular resistance by kinking the large arteries in the inguinal area. The resulting increase in systemic vascular resistance tends to decrease the magnitude of the right-to-left intracardiac shunt, which leads to increased pulmonary blood flow and subsequent improvement in arterial oxygenation.

Hypoxic or Hypercyanotic Episodes (“Tet Spells”)

The occurrence of hypoxic episodes in TOF patients may be life threatening and should be anticipated in every patient, even those who are not normally cyanotic. Spells occur more frequently in cyanotic patients, with the peak frequency of spells between 2 and 3 months of age. The onset of spells usually prompts urgent surgical intervention, so it is not unusual for the anesthesiologist to care for an infant who is at great risk for spells during the preoperative period.

The etiology of spells is not completely understood, but infundibular spasm or constriction may play a role. Crying, defecation, feeding, fever, and awakening can all be precipitating events. Paroxysmal hyperpnea is the initial finding. There is an increase in rate and depth of respiration, leading to increasing cyanosis and potential syncope, convulsions, or death. During a spell, the infant appears pale and limp secondary to poor cardiac output. Hyperpnea has several deleterious effects in maintaining and worsening a hypoxic spell. Hyperpnea increases oxygen consumption through the increased work of breathing. Hypoxia induces a decrease in SVR, which further increases the right-to-left shunt. Hyperpnea also lowers intrathoracic pressure and leads to an increase in systemic venous return. In the face of worsening infundibular obstruction, this results in an increased RV preload and an increase in the right-to-left shunt. Thus, episodes seem to be associated with events that increase oxygen demand while simultaneous decreases in PO₂ and increases in pH and Paco₂ are occurring. Treatment of a Tet spell includes the following points:

• Administration of 100% oxygen.

• Compression of the femoral arteries or placing the patient in a knee-to-chest position, which transiently increases SVR and reduces the R-L shunt. Manual compression of the abdominal aorta is particularly effective for the anesthetized patient. After the chest is open, the surgeon can manually compress the ascending aorta to increase impedance to ejection through the LV.

• Administration of morphine sulfate (0.05 to 0.1 mg/kg), which sedates the patient and may have a depressant effect on respiratory drive and hyperpnea.

• Administration of 15 to 30 mL/kg of a crystalloid solution. Enhancing preload increases heart size, which may increase the diameter of the RVOT.

• Administration of sodium bicarbonate to treat the severe metabolic acidosis that occurs during a spell. Correction of the metabolic acidosis will normalize SVR and reduce hyperpnea. Bicarbonate administration (1 to 2 mEq/kg) in the absence of a blood gas determination is warranted during a spell.

• Phenylephrine in relatively large dosages (5 to 10 mcg/kg IV as a bolus, or 2 to 5 mcg/kg per minute as an infusion) increases SVR and reduces R-L shunting. In the presence of severe RV outflow obstruction, phenylephrine-induced increases of PVR have little or no effect in increasing RV outflow resistance. It is important to point out that treatment with α-adrenergic agents to increase SVR does nothing to treat the underlying cause of the spell, although the decrease in unstressed venous volume induced by these agents may augment preload.

• β-Adrenergic agonists are absolutely contraindicated. Increasing contractility will further narrow the stenotic infundibulum.

• Administration of propranolol (0.1 mg/kg) or esmolol (0.5 mg/kg followed by an infusion of 50 to 300 mcg/kg per minute) may reduce infundibular spasm by depressing contractility. In addition, slowing of heart rate may allow improved diastolic filling (increased preload), increased heart size, and an increase in the diameter of the RVOT.

• Resuscitation by extracorporeal membrane oxygenation (ECMO) in refractory episodes, when immediate operative intervention is not possible.

Cerebral Complications

Cerebrovascular accidents are common in older children with severe tetralogy of Fallot. Cerebrovascular thrombosis or severe arterial hypoxemia may be the explanation for these adverse responses. Dehydration and polycythemia may contribute to thrombosis. Hemoglobin concentrations exceeding 20 g/dL are common in these patients. A cerebral abscess is suggested by the abrupt onset of headache, fever, and lethargy, followed by persistent emesis and the appearance of seizure activity. The most likely cause is arterial seeding into areas of prior cerebral infarction.

Infective Endocarditis

Infective endocarditis is a constant danger in patients with tetralogy of Fallot and is associated with a high mortality rate. Appropriate antibiotics should be administered whenever dental or surgical procedures are planned in these patients.

Treatment

Without surgery, mortality exceeds 50% by 3 years of age. Currently, most patients with TOF have an elective full correction between the ages of 2 and 10 months. In some centers, surgery is delayed as long as possible within this time interval, with the precise timing of repair dictated by the onset of cyanotic episodes. Definitive repair for TOF is being accomplished in neonates in some centers if favorable anatomy is present. Surgery is aimed at relieving the outflow obstruction by resection of hypertrophied, obstructing muscle bundles and augmentation and enlargement of the RVOT with a pericardial patch. In a somewhat older approach, unless the pulmonic annulus was near normal size, and the pulmonary valve only mildly stenotic, enlargement of the RVOT frequently included extension of the patch across the pulmonary valve annulus and into the main pulmonary artery (transannular patch). Because a transannular patch creates pulmonic insufficiency, which has been associated with a negative impact on long-term RV function and outcome, more recent data suggest it is best avoided when possible; as a result, the current approach for many is to enlarge the infundibular area with a patch (and resect interfering muscles bundles) and repair the pulmonary stenosis to the extent possible, thereby relieving most if not all of the outflow obstruction (and resultant RV hypertension) without creating significant pulmonary regurgitation. If stenosis of the pulmonary artery extends to the bifurcation of the pulmonary artery, a pericardial patch can be placed beyond the bifurcation of the pulmonary arteries (either de novo or as a continuation of the transannular patch). Finally, the VSD is closed. In neonates, this is usually done through the right ventriculotomy created for resection of RVOT obstruction, and with placement of the infundibular, pulmonary artery, or transannular patch. In infants and older children, the VSD can be closed via a trans–tricuspid valve approach, thereby avoiding the likely deleterious consequences of a right ventriculotomy. The overall goals of the surgery are to reduce RV pressure (ideally to below one half to three fourths of the systemic pressure), to avoid inducing RV volume overload (pulmonary regurgitation), and to successfully close the VSD (Apitz et al., 2009; Jonas, 2009; Khairy et al., 2009).

In the past, infants underwent palliative procedures that involved anastomosis of a systemic artery to a pulmonary artery in an effort to increase pulmonary blood flow and improve arterial oxygenation. These palliative procedures were the Waterston shunt (side-to-side anastomosis of the ascending aorta and the right pulmonary artery), the Potts shunt (side-to-side anastomosis of the descending aorta to the left pulmonary artery), the Blalock-Taussig shunt (end-to-side anastomosis of the subclavian artery to the pulmonary artery), and the modified Blalock-Taussig shunt (interposing a length of Gore-Tex tube graft between the subclavian or innominate artery and the branch pulmonary artery). Often, however, these procedures were associated with long-term complications such as pulmonary hypertension, left ventricular volume overload, distortion of the pulmonary arterial branches, reduced RV function, ventricular dysrhythmias, and sudden death.

Management of Anesthesia

The anesthetic management goals for patients with tetralogy of Fallot are summarized in Box 20-3. Preoperatively, it is important to avoid dehydration by maintaining oral feedings in infants and young children or by providing intravenous fluids before the patient’s arrival in the operating room. Crying associated with intramuscular administration of drugs used for preoperative medication can lead to hypercyanotic spells in those prone to do so. β-Adrenergic antagonists (now used infrequently) should be continued until the induction of anesthesia in patients receiving these drugs, for prophylaxis against hypercyanotic attacks.

Box 20-3 Goals of Anesthesia Management for Tetralogy of Fallot

1. Maintain heart rate, contractility, and preload to maintain cardiac output.

• Euvolemia prevents exacerbation of dynamic RVOT obstruction from hypovolemia and reflex increases in HR and contractility.

2. Avoid increases in the PVR-to-SVR ratio.

• Increases in PVR relative to SVR, and decreases in SVR relative to PVR, will increase R-L shunting, reduce pulmonary blood flow, and produce or worsen cyanosis.

3. Use ventilatory measures to reduce PVR.

• Minimize mean airway pressure to avoid mechanical obstruction of pulmonary blood flow and effects to decrease preload.

4. Maintain or increase SVR.

• This is particularly important when RV outflow obstruction is severe and changes in PVR have little or no effect on shunt.

5. Treat hypercyanosis promptly.

6. Avoid RV contractility depression with severe fixed RV outflow obstruction except in patients with dynamic infundibular obstruction (tet spell).

• Reducing contractility during tet spells may reduce RV outflow obstruction via relaxation of the infundibulum.

HR, Heart rate; PVR, pulmonary vascular resistance; RV, right ventricle; RVOT, right ventricular outflow tract; SVR, systemic vascular resistance.

An IV induction may be desirable, particularly in patients with significant outflow obstruction. In patients without a preexisting intravenous catheter, IV placement may be facilitated by administration of adequate premedication (see earlier).

Mask induction of anesthesia with either sevoflurane or halothane (if still available) is usually effective, as there is a parallel decrease in PVR and SVR. Interestingly, halothane may better attenuate the dynamic component of RVOT obstruction than sevoflurane, because of halothane’s more potent negative inotropic effect. Regardless of induction technique, systemic hypotension should be avoided or treated promptly. Systemic hypotension is particularly likely to cause or increase right-to-left shunting when RV outflow obstruction is severe, because anesthesia-induced decreases in PVR have little effect on decreasing RV outflow resistance. Hypotension responds to intravascular volume expansion, and, if necessary, markedly reduced SVR and worsening hypoxemia can be treated with phenylephrine (0.5- to 1.0-mcg/kg intravenous boluses).

Ketamine is a useful induction agent in patients with TOF. Ketamine has been shown to cause no significant alteration in in these patients. Fentanyl or sufentanil provide very stable induction and maintenance hemodynamics and will blunt stimulation-induced increases in PVR. Maintenance of anesthesia with fentanyl or sufentanil, a muscle relaxant (perhaps avoiding pancuronium because of tachycardia, and because of its effects on RV preload and contractility), and modest amounts of benzodiazepine or inhalation agent is appropriate.

Regardless of the mode of induction, volume expansion with 10 to 15 mL/kg (or greater) of 5% albumin or normal saline should be initiated once intravenous access is obtained. This is particularly necessary in patients who have received nothing by mouth for a long interval before induction. This is the most effective first-line therapy in preventing and treating dynamic RVOT obstruction. In addition to the peri-induction period, pericardial incision and retraction and aortic and pulmonary artery manipulation are other frequent points of acute hypoxemia and tet spell–like behavior prior to CPB. In addition to aggressive volume expansion, phenylephrine may be needed to reverse precipitously declining systemic oxygen saturations; at times, rapid institution of CPB is the effective therapy.

After definite repair for TOF, several factors may contribute to impaired RV systolic and diastolic function. First, there is likely to be preexisting dysfunction as a result of hypertrophy, and perhaps cyanosis. Myocardial preservation of the RV in TOF is widely felt to be insufficient for several reasons, including difficulties protecting hypertrophic muscle, increased tendency to free radical injury, and increased washout of cardioplegia due to collaterals. There is likely to be a mechanical component of RV dysfunction because of the use of a right ventriculotomy and RVOT patch. Finally, there may be new or residual abnormal hemodynamic loads because of pulmonary regurgitation, created by enlargement of the RVOT with a transannular patch, which imposes a new volume load on the RV, or residual pressure load because of RVOT obstruction below (infundibular), at, or distal to (main or branch PA stenosis) the pulmonary valve.

A residual VSD is likely to be very poorly tolerated in the patient with TOF, with the most likely manifestation being low cardiac output syndrome associated with elevated central venous pressure, left atrial pressure (LAP), and pulmonary arterial pressure (PAP). RVOT obstruction should be nearly completely eliminated after repair. PVR is likely to be low and the pulmonary vasculature very compliant. As a result, there will be potential for a large left-to-right intracardiac shunt with a residual VSD. This will place a large volume load on the LV and RV. An acute volume load will not be well tolerated by the RV, which is likely to be concentrically hypertrophied and poorly compliant in response to the chronic pressure overload that existed preoperatively. The presence of pulmonary insufficiency will further exacerbate RV dysfunction by imposing an additional volume load. Any distal pulmonary artery stenoses, high mean airway pressures, and elevated PVR will all increase the regurgitant volume and subsequent RV volume load.

After complete repair of TOF with no residual lesions and minimal intrapulmonary shunt, the Sao₂ should be 100%, and most patients require only modest to moderate degrees of inotropic support with dopamine or dobutamine (3 to 10 mcg/kg per minute). The need for substantially higher levels of support should raise the suspicion of a residual anatomic defect. In infants and small children, particularly those left with pulmonary insufficiency as the result of a transannular patch and those expected to have RV dysfunction as a result of a ventriculotomy or extensive RV hypertrophy (this may be an especially prominent problem in repairs in infants < 3 to 4 months old), the surgeon may choose to leave a pop-off valve by leaving the PFO open or by creating a small (3 to 4 mm) atrial-level fenestration. This will allow physiologic intracardiac R-L shunting (there will be direct delivery of some desaturated venous blood to the LA), with the ability to augment systemic cardiac output at the expense of systemic oxygen saturation in the setting of RV dysfunction. In these patients, a Pao₂ of 40 to 50 mm Hg and a Sao₂ of 70% to 80% is acceptable until RV function improves over the course of days. A right bundle branch block is common. Rarely, heart block requiring temporary (or permanent) pacing can occur as a consequence of the VSD closure; a large VSD patch can also occasionally be associated with LV outflow tract obstruction.

Ebstein’s Anomaly

Ebstein’s anomaly is an abnormality of the tricuspid valve in which the septal and often the posterior valve leaflets are displaced downward into the right ventricle (Fig. 20-9). See related video online at www.expertconsult.com.

In addition, the anterior tricuspid valve leaflet is abnormal. It is generally elongated and sail-like, with chordal attachments to the RV free wall. There may be RV outflow obstruction from the anterior leaflet. The result is a dilated right atrium with atrialization of the proximal RV and reduced effective RV cavity size and function. The tricuspid valve is usually regurgitant but may also be stenotic. Most patients with Ebstein’s anomaly have an interatrial communication (ASD, PFO), through which there may be right-to-left shunting of blood, the magnitude of which depends on the severity of the tricuspid valve abnormality and degree of RV dysfunction.

FIGURE 20-9 Anatomy of Ebstein’s anomaly. There is apical displacement of the posterior and septal leaflets of the tricuspid valve. As a result, there is an atrialized right ventricle and an enlarged right atrium. The anterior tricuspid valve leaflet is not shown. An atrial septal defect or patent foramen ovale would be present.

(Redrawn from Children’s Hospital Boston, Boston, Mass.)

Clinical Presentation

The severity of the hemodynamic derangements in patients with Ebstein’s anomaly depends on the degree of displacement and the functional status of the tricuspid valve and RV. As a result, the clinical presentation varies from congestive heart failure in neonates to the absence of symptoms in adults in whom the anomaly is discovered incidentally. Neonates often manifest systemic venous congestion and cyanosis that worsens after ductus arteriosus closure reduces pulmonary blood flow. Older children with Ebstein’s anomaly may be diagnosed as a result of an incidental murmur, whereas adolescents and adults are likely to present with supraventricular dysrhythmias that lead to CHF, worsening cyanosis, and occasionally syncope. Patients with Ebstein’s anomaly and an interatrial communication are at risk for paradoxical embolization, brain abscess, CHF, and sudden death.

The severity of cyanosis depends on the magnitude of the right-to-left shunt. A systolic murmur caused by tricuspid regurgitation is usually present at the left lower sternal border. Hepatomegaly resulting from passive hepatic congestion due to increased right atrial pressures may be present. The ECG is characterized by tall and broad P waves (resembling right bundle branch block), and first-degree atrioventricular heart block is common. Paroxysmal supraventricular and ventricular tachydysrhythmias may occur; and as many as 20% of patients with Ebstein’s anomaly have ventricular preexcitation by way of accessory electrical pathways between the atrium and ventricle (Wolff-Parkinson-White syndrome). In patients with severe disease (marked right-to-left shunting and minimal functional right ventricle), marked cardiomegaly is present that is largely the result of right atrial enlargement.

Echocardiography is used to assess right atrial dilation, distortion of the tricuspid valve leaflets, and the severity of the tricuspid regurgitation or stenosis. The presence and magnitude of interatrial shunting can be determined by color Doppler imaging studies. Enlargement of the right atrium may be so massive that the apical portions of the lungs are compressed, resulting in restrictive pulmonary disease.

Treatment

Treatment of neonatal Ebstein’s anomaly is controversial and varies with the specific subtype of abnormality. Approaches range from tricuspid valve repair (for patients whose valve is amenable to repair and in whom the RV is likely to be able to support normal cardiac output), staging to a Fontan procedure (for those with significantly reduced RV size and function), and transplantation. In older patients, treatment is based on the prevention of associated complications, including antibiotic prophylaxis against infective endocarditis and administration of diuretics and digoxin for the management of CHF. Patients with supraventricular dysrhythmias are treated pharmacologically or with catheter ablation if an accessory pathway is present. Repair or replacement of the tricuspid valve in conjunction with closure of the interatrial communication is recommended for older patients who have severe symptoms despite medical therapy. Complications of surgery to correct Ebstein’s anomaly include third-degree atrioventricular heart block, persistence of supraventricular dysrhythmias, residual tricuspid regurgitation after valve repair, and prosthetic valve dysfunction when the tricuspid valve is replaced (da Silva et al., 2007; Knott-Craig et al., 2007; Bove et al., 2009).

Management of Anesthesia

Delayed onset of pharmacologic effects can be expected after IV administration of an anesthetic, which may result in part from pooling and dilution in an enlarged right atrium. The major hazards during anesthesia in patients with Ebstein’s anomaly include depression of RV function and reduced forward flow into the pulmonary artery, accentuation of arterial hypoxemia because of increases in the magnitude of the right-to-left intracardiac shunt, and the development of supraventricular tachydysrhythmias (Lerner et al., 2003). Increased right atrial pressures may indicate the presence of right ventricular failure. Both ventilatory and pharmacologic measures should focus on minimizing mechanical and metabolic effects of ventilation on RV afterload and on maintaining RV contractility. In the presence of a PFO, an increase in right atrial pressure above the pressure in the left atrium can lead to a right-to-left intracardiac shunt through the foramen ovale. Unexplained arterial hypoxemia or paradoxical air embolism during the perioperative period may result from shunting of blood or air through a previously closed foramen ovale.

Tricuspid Atresia

Tricuspid atresia (TA) involves a lesion with single-ventricle physiology. See related video online at www.expertconsult.com.

These patients are staged to a Fontan procedure. Patients with TA have complete obstruction to RV inflow and variable obstruction to RV outflow. A communication (ASD or PFO) results in an obligatory right-to-left shunt at the atrial level with complete mixing of systemic and pulmonary venous blood in the left atrium. When the ASD or PFO is restrictive, there is a large right atrial to left atrial pressure gradient, which results in poor decompression of the RA and systemic venous congestion. Pulmonary blood flow can be provided by a downstream shunt from intracardiac (VSD) and extracardiac (PDA, multiple aortopulmonary collateral arteries) sources. Anatomic classification is based on the presence or absence of transposition of the great arteries, the extent of pulmonary stenosis or atresia, and the size of the VSD. Approximately 70% of all patients with TA are type 1, and 50% percent of all TA patients are type 1B (Fig. 20-10, and see Fig. 20-2 and Table 20-3).

FIGURE 20-10 Anatomy and blood flow in tricuspid atresia type 1. Type 1A: pulmonary atresia with pulmonary blood flow via patent ductus arteriosus or major aortopulmonary collateral arteries (MAPCAs). Type 1B: small ventricular septal defect and pulmonary stenosis. Type 1C: large ventricular septal defect and no pulmonary stenosis.

Treatment

Initial palliation depends on the anatomic variant. Infants with TA, adequate ASD, adequate VSD, and an “appropriate” amount of pulmonic stenosis can have a balanced circulation and require little or no intervention until later in infancy. Prostaglandin E₁ (PGE₁) is frequently necessary to augment PBF, and a balloon atrial septostomy may be necessary to allow adequate mixing and right atrial decompression. A Blalock-Taussig (BT) shunt may be required to provide a stable source of augmented pulmonary blood flow (e.g., TA with no VSD or with VSD but also with severe pulmonary stenosis or atresia). A staged approach to a Fontan procedure as described previously (see Figs. 20-4 and 20-5; Fig. 20-19) is the usual definitive treatment approach for TA.

FIGURE 20-19 Sequence of repairs in the surgical staging of hypoplastic left heart syndrome (HLHS) to a fenestrated lateral-tunnel Fontan. Upper left: HLHS. Upper right A: Initial repair performed shortly after birth involving atrial septectomy, Damus-Kaye-Stansel (DKS) anastomosis of main pulmonary artery to ascending aorta, homograft augmentation of the aortic arch, and a right modified Blalock-Taussig shunt (BTS) to supply pulmonary blood flow. Upper right B: Alternate initial repair performed shortly after birth involving atrial septectomy, DKS anastomosis of main pulmonary artery to ascending aorta, homograft augmentation of the aortic arch, and a right ventricle–to–pulmonary artery conduit to supply pulmonary blood flow. Lower left: Superior cavopulmonary shunt or bidirectional Glenn (BDG), generally performed at 6 to 8 months of age. The right modified BTS has been taken down and ligated. Lower right: The completed total cavopulmonary connection or Fontan procedure generally performed at 2 to 3 years of age. A lateral-tunnel Fontan with a fenestration is shown. The small arrows indicate flow from the systemic venous baffle to the common pulmonary venous atrium, causing a small right-to-left physiologic shunt.

Management of Anesthesia

Anesthetic management of patients with TA largely depends on their specific anatomy and where they are in their course of single-ventricle physiology. In general, IV induction techniques as outlined earlier are preferred for their reliability (e.g., uncertain uptake of inhaled agents in the presence of a “complete” right-to-left shunt) and hemodynamic stability; anesthetic maintenance typically uses “balanced” combinations of opioid, low-concentration inhaled agent, and muscle relaxation. The patient on PGE₁ presenting for balloon atrial septostomy or BT shunt creation is ductal dependent for PBF. As described previously, the major goals are to preserve overall cardiac contractility and output and to balance the relationship between PVR and SVR so that arterial oxygen saturations in the mid 70% to 80% range are maintained. Factors that raise PVR, decrease SVR, or reduce cardiac output can all contribute to increased hypoxemia by reducing ductal flow into the lungs. On the other hand, it may be possible to markedly compromise systemic perfusion by significantly reducing PVR (e.g., hyperoxic and hyperventilation or hypocarbia), thereby promoting increased left-to-right flow through the PDA. This occurrence may be signaled by increased arterial oxygen saturations, widened pulse pressure, and hypotension.

Considerations after BT shunt creation have been discussed. In brief, one typically expects arterial oxygen saturations in the range of 75% to 85%. Substantially lower values may indicate shunt obstruction (arterial BP will be close to normal or high), low cardiac output or SVR, and, occasionally, high PVR. Pulmonary overcirculation (high arterial oxygen saturations, hypotension) may be managed by ventilatory maneuvers to increase PVR; at times, partial clipping of the shunt may be necessary. Controlled ventilation and inotropes are frequently required for several hours to days, as these infants adapt to the shunt-dependent circulation. The patient with TA, VSD, and no obstruction to PBF can be prone to pulmonary overcirculation and systemic hypoperfusion as PVR falls in the postnatal period. Initial management considerations are the same as those for other situations of potential excessive PBF—support systemic cardiac output and attempt to prevent increases in PBF by avoiding increased fraction of inspired oxygen (Fio₂) and hypocarbia; some patients will require palliation with a pulmonary artery band to mechanically control PBF before more definitive surgery.

Total Anomalous Pulmonary Venous Return

Anatomy

Total anomalous pulmonary venous return (TAPVR) results in blood return from all of the pulmonary veins into the systemic venous system rather than directly into the left atrium. See related video online at www.expertconsult.com.

The individual pulmonary veins usually drain into a common pulmonary venous confluence that has no direct connection to the LA; this confluence connects to the systemic venous circulation via one of four anatomic variants (Fig. 20-11):

1. Supracardiac TAPVR. Drainage of the pulmonary vein confluence is into a supracardiac venous structure. This occurs in nearly 50% of TAPVR cases, most often employing a “vertical vein” that connects the pulmonary venous confluence with the innominate vein, which then drains into the SVC.

2. Infracardiac TAPVR. This next most frequent subtype, occurring in approximately 25% of patients, involves drainage of the pulmonary venous confluence into an infracardiac vessel, such as the IVC, portal vein, or hepatic vein, via an inferiorly directed vertical vein that goes through the diaphragm to connect to one of these infracardiac vessels.

3. Intracardiac TAPVR. Here, the pulmonary venous confluence drains directly into the RA via the coronary sinus.

4. Mixed TAPVR. In a small percentage (<10%) of patients, pulmonary venous drainage is some combination of types 1, 2, and 3.

FIGURE 20-11 Types of total anomalous pulmonary venous return (TAPVR). A, Supracardiac (46%). Pulmonary venous blood returns to common pulmonary vein; the common pulmonary vein drains via a left vertical vein to the innominate vein, the superior vena cava (SVC), and finally to the right atrium. B, Infracardiac (22%). A common pulmonary vein passes through the diaphragm at the esophageal hiatus. The common vein then drains into the portal vein, hepatic vein, or ductus venosus. Obstruction of flow into the inferior vena cava (IVC) and right atrium may be caused by obligatory passage through the liver. C, Cardiac (24%). A common pulmonary vein directly enters the right atrium via the coronary sinus. D, Mixed (8%). The mixed type involves components of supracardiac, infracardiac, and cardiac drainage. Illustrated here is a combination of cardiac and supracardiac connections. LA, Left atrium; RA, right atrium.

(Redrawn from Children’s Hospital Boston, Boston, Mass.)

Infracardiac TAPVR is most frequently associated with pulmonary venous obstruction, at least in part because of the long course of the vertical vein and its passage through the diaphragm. Some patients with supracardiac TAPVR exhibit compression of the vertical vein between the left main stem bronchus and left pulmonary artery.

Physiology

There is a complete mixing lesion where all of the systemic and pulmonary venous blood mixes in the right atrium. The return of all pulmonary venous blood to the right atrium results in a large L-R shunt. Thus, an anatomic R-L shunt (an ASD or a PFO) is necessary for left heart filing and postnatal survival. These patients usually have a nonrestrictive or only mildly restrictive atrial level defect; however, R-L flow across the atrial septum is usually hampered by poor LA and LV compliance, in part because the reduced blood flow to the left side of the heart in utero caused these chambers to be smaller and stiffer than normal.

Taken together, these factors have the following results. In the absence of pulmonary venous obstruction, newborn infants with TAPVR have a close to 1:1. The decrease of PVR that occurs shortly after birth, in combination with significantly decreased left-sided compliance, promotes delivery of the mixed systemic and pulmonary venous blood to the pulmonary circuit. Pulmonary artery pressures will then be near systemic because, although PVR is not markedly elevated, the is usually quite high (>2:1 to 3:1).

Compression of the vertical venous pathway produces obstructed TAPVR. This distinction and diagnosis are critical, because obstruction causes pulmonary venous hypertension, elevated PVR, and systemic or even suprasystemic RV and PA pressures. Some of these patients may develop PVOD in utero as well. In addition, pulmonary venous obstruction will produce pulmonary edema, further elevating PVR, much as it does with mitral stenosis. Obstructed TAPVR is a surgical emergency, one of the few remaining in the era of PGE₁ therapy

Clinical Presentation

Systemic cardiac output and organ perfusion can be severely compromised in these patients. Systemic or suprasystemic RV pressures can result in a leftward shift of the interventicular septum (known as ventricular interdependence) that pancakes the LV and further reduces the compliance and filling of the already small LV; a secondary effect of these alterations is to reduce R-L flow across the atrial septum (because the impedance to LA emptying has increased). There is also likely to be RV afterload mismatch, resulting in RV distention and tricuspid regurgitation. Thus, systemic cardiac output largely depends on a physiologic R-L shunt across the ductus arteriosus, but one that is supplied by a failing RV. These patients have a small heart and congested lungs on chest radiograph, the latter appearing worse in the case of obstructed TAPVR. The diagnosis is usually confirmed by surface echocardiography.

Patients with TAPVR are hypoxemic because of complete mixing; their degree of hypoxemia is further exacerbated by low cardiac output (which reduces mixed venous oxyhemoglobin saturation [Svo₂] and hence the Sao₂ that results from complete mixing), pulmonary edema (which causes intrapulmonary shunt and V/Q mismatch, leading to low pulmonary venous oxyhemoglobin saturation [Spvo₂]), and reduced PBF arising from increased PVR. Efforts to increase pulmonary blood flow in these patients will only worsen the pulmonary edema (thus, e.g., inhaled nitric oxide [iNO], as well as other inhaled pulmonary vasodilators, are clearly contraindicated).

Patients with obstructed TAPVR present at birth with hypoxemia and poor systemic perfusion. In many, there is an ongoing metabolic acidosis and evidence of end-organ (hepatic and renal) dysfunction. In patients with severe pulmonary venous obstruction leading to suprasystemic RV and PA pressures and R-L shunting across the ductus arteriosus, ductal patency is necessary to maintain cardiac output (i.e., use of PGE₁ for temporary palliation may be indicated); frequently, inotropic support is required. In patients with less severe obstruction and subsystemic RV and PA pressures, ductal flow will be bidirectional or L-R. In these patients, ductal patency may exacerbate pulmonary edema.

Surgical Therapy

Definitive repair involves anastomosis of the pulmonary venous confluence to the posterior LA, ligation of the vertical vein, and closure of the ASD (Boger et al., 1999; Wang et al., 2004; Lacour-Gayet, 2006; Siles and Lapierre, 2008).

Anesthetic Management

General Considerations

The infant with TAPVR is frequently extremely ill and demonstrates both severe respiratory and circulatory compromise. This is especially true of TAPVR infants with pulmonary venous obstruction, in whom emergency surgery is the only viable therapeutic option. Efforts to increase pulmonary blood flow by ventilatory interventions will worsen pulmonary edema in these patients.

Overall, it is important to maintain heart rate, contractility, and preload so as to maintain systemic cardiac output. As noted previously, decreased cardiac output reduces systemic venous oxygen saturation, which, in a complete mixing lesion, will reduce arterial oxygen saturation. For patients with increased pulmonary blood flow, decreases in the PVR-to-SVR ratio should be avoided. The increase in pulmonary blood flow that accompanies a reduced PVR-to-SVR ratio necessitates an increase in cardiac output to maintain systemic blood flow, which will be difficult if not impossible in these patients for the reasons discussed previously. For patients with increased pulmonary blood flow and right ventricular volume overload, ventilatory interventions should be used to increase PVR, reduce pulmonary blood flow, and decrease the volume load on the right ventricle.

Induction and Maintenance

Neonates with pulmonary venous obstruction generally arrive in the operating room intubated, ventilated, and on inotropic support. Nonintubated patients are probably best managed by intravenous induction with etomidate or high-dosage potent opioid and muscle relaxation. The primary goals are to maintain systemic cardiac output and gain rapid control of ventilation without adversely affecting the tenuous relationships that affect the PVR-to-SVR ratio, systemic venous return, and cardiac output. Management of ventilation prior to CPB is therefore based on the aforementioned principles. These patients are best anesthetized with a high-dosage-narcotic technique that includes fentanyl or sufentanil and muscle relaxation. Patients with TAPVR, particularly those with venous obstruction, have a highly reactive pulmonary vasculature. High dosages of fentanyl and sufentanil may be useful for blunting increases in PVR associated with surgical stimulation.

Post-CPB Management

After surgical repair, the primary problems in these patients relate to left-sided filling and output compromise related to (1) small and noncompliant LA and LV, along with superimposed acute myocardial ischemia–reperfusion injury, and (2) reactive pulmonary vasculature, pulmonary hypertension, right ventricular hypertension, and RV dysfunction. The initial goals are to maintain heart rate (ideally, sinus rhythm) at an age-appropriate rate, using temporary pacing if necessary. Cardiac output is likely to be more heart-rate dependent in the post-CPB period.

Pulmonary hypertension (frequently at systemic or even suprasystemic levels of PA pressure) and limited systemic cardiac output are the major challenges after CPB. For patients’ reactive pulmonary vasculature, blunting of stress-induced increases in PVR with narcotics is indicated. In addition, ventilatory interventions that reduce PVR and the use of selective pulmonary vasodilators such as iNO are frequently necessary; indeed, this group of patients with CHD are among those most likely to respond to iNO after CPB with a clinically significant decrease in PVR and improvement in cardiac function (Adatia and Wessel, 1994; Curran et al., 1995; Bizzarro and Gross, 2005; Roberts et al., 1993).

Despite maneuvers to decrease PVR, inotropic support of the RV may be necessary. Dobutamine (5 to 10 mcg/kg per minute) or dopamine (5 to 10 mcg/kg per minute) is useful in this instance because both agents provide potent inotropic support without increasing PVR. In the absence of systemic hypotension, milrinone (0.25 to 1.0 mcg/kg per minute after a 50-mcg/kg loading dosage, preferably administered on CPB) can be considered. Left-sided (e.g., LA) pressures are often high (∼12 to 20 mm Hg) because of the combination of intrinsic, poor left-sided compliance, acute myocardial injury, and RV distention. It is easy to both underfill (resulting in low output) and overfill (acute distention and mitral regurgitation) the left heart. One, thus, needs to keep up with ongoing blood loss and replacement of clotting factors, but volume administration needs to be done with significant caution. The overall goal is to keep LA pressures within a reasonable target range while maintaining a reasonable (e.g., ∼60 mm Hg systolic) blood pressure and evidence of adequate systemic perfusion (e.g., urine output, pH, cerebral oximetry, or SVC saturation).

Residual RV and PA hypertension can be caused by one or more of the following: (1) pulmonary venous obstruction, a technical (surgical) problem arising from the failure to construct a nonrestrictive anastomosis of the pulmonary venous confluence to the LA; (2) LA (and hence pulmonary venous) hypertension due to the small, noncompliant LA and LV and post-CPB LV dysfunction; and (3) labile increases in PVR due to reactive pulmonary vasoconstriction (capillary and precapillary). In the presence of postoperative pulmonary venous obstruction, efforts to increase pulmonary blood flow may worsen pulmonary edema. Surgical revision may be necessary (Lacour-Gayet, 2006).

The use of surgically placed PA and LA monitoring catheters, often in combination with echocardiography (surface “on-heart” or transesophageal echocardiography [TEE], depending on patient size and probe availability), can be helpful in sorting out these issues. For example, the presence of high PA pressure, elevated LAP, and a PA diastolic pressure of less than 5 mm Hg above the LAP suggests that LA hypertension is the primary cause of PA hypertension. In contrast, the presence of high PA pressure, low or normal LAP, and a PA diastolic pressure of greater than 15 to 20 mm Hg above the LAP suggests that reactive pulmonary vasoconstriction, PVOD, or anastomotic pulmonary venous obstruction exists. Similarly, the presence of reactive pulmonary vasoconstriction or PVOD is suggested by a pulmonary wedge pressure of less than 3 to 5 mm Hg above the LAP, whereas a wedge pressure of greater than 7 to 10 mm Hg above the LAP is consistent with pulmonary venous obstruction. Echocardiography can be helpful in assessing the status of the pulmonary venous connection to the LA, and in assessing ventricular function and filling.

Transposition of the Great Arteries

Anatomy

In patients with TGA, there is discordance of the ventriculoarterial connections and concordance of the atrioventricular connections. See related video online at www.expertconsult.com.

In other words, a right-sided RA connects via a right-sided tricuspid valve and RV to a right-sided and anterior aorta. A left-sided LA connects via a left-sided mitral valve and LV to a left-sided and posterior pulmonary artery (Fig. 20-12). The coronary arteries in dextro- (D-)TGA arise from the aortic sinuses that face the pulmonary artery. In normally related vessels, these sinuses are located on the anterior portion of the aorta, whereas in D-TGA they are located posteriorly. In the majority of D-TGA patients (70%), the right sinus is the origin of the right coronary artery, whereas the left sinus is the origin of the left main coronary artery. In the remainder of cases, there is considerable variability in this coronary anatomy. The exact coronary anatomy must be delineated; variants can contribute significantly to operative difficulty and the success of surgical repair.

FIGURE 20-12 Anatomy of dextro-transposition of the great arteries (D-TGA). The aorta is in continuity with the right ventricle, and the pulmonary artery is in continuity with the left ventricle, producing a parallel rather than a series circulation. Ao, Aorta; LV, left ventricle; RV, right ventricle.

(Redrawn from Children’s Hospital Boston, Boston, Mass.)

TGA can occur with an intact ventricular septum or with a VSD, with or without subpulmonic stenosis. In D-TGA, subpulmonic stenosis causes left ventricular outflow tract (LVOT) obstruction, which is present in about 25% of patients with VSD and is most often due to a subpulmonary fibromuscular ring or posterior displacement of the outlet portion of the ventricular septum (or both). In addition, the foramen ovale is almost always patent, whereas a true secundum ASD exists in only about 5% of patients; approximately 50% of patients with D-TGA present with a PDA. Although angiographically detectable VSDs may occur in 30% to 40% of patients, only about one third of these defects are hemodynamically significant. Thus, from a functional standpoint, 75% of patients will behave as if they have an intact ventricular septum (see later). Only 5% of patients with IVS have significant LVOT obstruction. Valvular pulmonary stenosis is rare in patients with TGA. Other less commonly seen lesions are tricuspid or mitral regurgitation (4% of each) and a coarctation of the aorta (5%). Bronchopulmonary collateral vessels arising from the aorta are visible angiographically in 30% of patients with D-TGA, more frequently and extensively to the right lung. These collaterals provide a site for intercirculatory mixing and have been implicated in the accelerated development of pulmonary vascular occlusive disease in TGA patients.

D-TGA produces two parallel circulations with recirculation of systemic and pulmonary venous blood. Short-term survival depends on the presence of one or more communications between the two parallel circuits to allow intercirculatory mixing; the potential sites in patients with D-TGA are both intracardiac (PFO, ASD, VSD) and extracardiac (PDA, bronchopulmonary collaterals). Several factors determine the amount of intercirculatory mixing and hence arterial oxygen saturation and delivery. One large, nonrestrictive communication provides better mixing than two or three restrictive communications. Reduced ventricular compliance and elevated systemic and pulmonary vascular resistance tend to reduce intercirculatory mixing by impeding flow across the anatomic communications. The location of the communications is also important. Poor mixing occurs even with large anterior muscular VSDs because of their unfavorable positions.

In TGA with VSD, some intercirculatory mixing can occur at the ventricular level, but there is predominantly anatomic R-to-L shunting (effective pulmonary blood flow) at the VSD (RV→LV→PA) and PDA (RV→Ao→PA) and anatomic L-to-R shunting (effective systemic blood flow) at the PFO or ASD (LA→RA→RV→Ao). Clearly, the more severe the LVOT obstruction, the more dependent the effective pulmonary blood flow will be on the presence of a PDA.

Patients with pulmonary stenosis sufficient to limit PBF may be hypoxemic despite a relatively large intercirculatory communication. Patients with high pulmonary blood flow, particularly those with a large VSD, are at risk of developing both overcirculation and congestive symptoms and PVOD. In the presence of a good-sized intercirculatory communication and no obstruction to PBF, most of these patients will not initially be hypoxemic but will have a large volume load imposed on the LA and LV and develop signs and symptoms of pulmonary overcirculation and CHF. However, the progressive development of PVOD can eventually reduce pulmonary blood flow and produce hypoxemia.

In TGA with an intact ventricular septum, the anatomic mixing sites are typically restricted to a PDA and a PFO. The factors determining the degree of intercirculatory mixing in TGA/IVS are complex and potentially problematic clinically. Anatomic shunting at the atrial level is mainly determined by the size of the atrial communication and the cyclic pressure variations between the left and right atrial chambers. The volume and compliance of the atria, ventricles, and vascular beds in each circuit, as well as heart rate and respiration, all influence the result. Shunting is from the right atrium to the left atrium during diastole as a result of the reduced ventricular and vascular compliance of the systemic circuit. In systole, the shunt is predominantly from the left atrium to the right atrium, primarily because of the large volume of blood returning to the left atrium as a result of the high volume of recirculated pulmonary blood flow.

The direction of shunting across the PDA largely depends on the PVR and the size of the intraatrial communication. When the PVR is low and the intraatrial communication is nonrestrictive, shunting is predominantly from the aorta to the pulmonary artery via the PDA, and predominantly from the left to right atrium (and hence into the systemic right ventricle) across the atrial septum. When the PVR is elevated, shunting across the PDA is likely to be bidirectional, which would in turn encourage bidirectional shunting across the atrial septum.

When the PVR is high and pulmonary artery pressure exceeds aortic pressure, shunting at the PDA will be predominantly from the pulmonary artery to the aorta. This causes a phenomenon known as reverse differential cyanosis, where the preductal arterial oxygen saturation is lower than the postductal arterial oxygen saturation. This is usually the result of a restrictive atrial communication producing left atrial hypertension and is associated with poor mixing and hypoxemia. A balloon atrial septostomy can be lifesaving in this setting. Decompression of the left atrium promotes mixing at the atrial level and also reduces PVR and pulmonary artery pressure, thereby promoting mixing (bidirectional shunting) at the level of the PDA.

The majority of neonates with D-TGA and IVS are hypoxemic (arterial saturation ≤ 70%) immediately after birth, with some patients demonstrating severely reduced effective pulmonary and systemic blood flow. This can result in severe hypoxemia (Pao₂ < 20 mm Hg), hypercarbia, and increasing metabolic acidosis secondary to the poor tissue oxygen delivery. PGE₁ (0.01 to 0.05 mcg/kg per minute) is administered to dilate and maintain the patency of the ductus arteriosus and facilitate mixing at this level. This maneuver increases effective pulmonary and systemic blood flow and can improve Pao₂ and tissue oxygen delivery if PVR is less than SVR (see earlier) and there is a nonrestrictive or minimally restrictive atrial septal communication. PGE₁ infusion is associated with apnea, pyrexia, fluid retention, and platelet dysfunction, which are largely dosage dependent.

If PGE₁ does not improve tissue oxygen delivery, then an emergent balloon atrial septostomy can be performed in the catheterization laboratory (using angiography) or in the intensive care unit (ICU) (using echocardiographic guidance). These patients require tracheal intubation and mechanical ventilation if not already in place. This allows reduction of PVR via induction of a respiratory alkalosis and elimination of pulmonary V/Q mismatch; in addition, we have noted significant numbers of apnea episodes when trying to provide procedural sedation to neonates receiving PGE₁ infusions. In rare circumstances, the combination of PGE₁, a balloon atrial septostomy, and mechanical ventilation with sedation and muscle relaxation may be ineffective at improving oxygen saturation and systemic oxygen delivery. In this circumstance, ECMO (either veno-arterial or veno-veno) support to improve tissue oxygenation and to reverse end-organ insult and lactic acidosis prior to surgery may be necessary.

Surgical Therapy

Two general types of procedures have been performed to repair D-TGA, namely intraatrial baffle and arterial switch procedures.

Mustard and Senning Procedures

Both the Mustard and the Senning procedures are atrial switch procedures, which surgically create discordant atrioventricular connections in the presence of the preexisting discordant ventriculoarterial connections. As a result of atrial baffling, systemic venous blood is directed to the LV, which remains in continuity with the pulmonary artery, and pulmonary venous blood is baffled to the RV, which is in continuity with the aorta. This arrangement results in physiologic but not anatomic correction of D-TGA. After these procedures, the right ventricle remains the systemic ventricle and the tricuspid valve remains the systemic AV valve (Fig. 20-13).

FIGURE 20-13 Interior of right atrium showing the baffle that rearranges and redirects atrial blood flow after the Mustard procedure. Pulmonary vein openings can be seen. CS, Coronary sinus; IVC, inferior vena cava; MV, mitral valve; TV, tricuspid valve.

(From Reed CC, Stafford TB, editors: Cardiopulmonary bypass, ed 2, Houston, 1985, Texas Medical Press, p 78.)

The Mustard procedure redirects pulmonary and systemic venous return via an intraatrial baffle made from pericardium or artificial graft material that is created after excision of the interatrial septum. The Senning version uses autologous right atrial tissue instead of pericardium or synthetic material. As a result of either procedure, pulmonary venous blood is essentially guided over the top of the baffle and across the tricuspid valve, while systemic venous blood is directed beneath the baffle to cross the mitral valve.

Both systemic and pulmonary venous obstruction by baffle material may occur as the result of either procedure. Because of the extensive atrial suture lines and at times atrial distention, dysrhythmias occur frequently after these procedures: about 60% to 70% of patients have some form of dysrhythmia, 30% of which are serious (bradycardia, sick-sinus syndrome, atrial flutter). Long-term exposure of the right ventricle and tricuspid valve to systemic pressure can result in progressive and severe right ventricular dysfunction (Horer et al., 2008).

Anatomic Repair or the Arterial (Jatene) Switch Procedure

The arterial switch operation (ASO) surgically reverses the discordant ventriculoarterial connections so that after repair, the right ventricle is connected to the pulmonary artery and the left ventricle is connected to the aorta. This is now the most common procedure performed for D-TGA (DeBord et al., 2007; Gottlieb et al., 2008; Quinn et al., 2008). In brief, the pulmonary artery and the aorta are transected distal to their respective valves. The coronary arteries are excised from the ascending aorta with 3 to 4 mm of surrounding tissue and these sites repaired either with pericardium or synthetic material. The coronary arteries are reimplanted into the proximal pulmonary artery (neoaorta), the distal pulmonary artery is brought anterior (LeCompte maneuver) and reanastomosed to the proximal aorta (right ventricular outflow), and the distal aorta is reanastomosed to the proximal pulmonary artery (left ventricular outflow) (Fig. 20-14). As mentioned earlier, variants in coronary anatomy can complicate this scenario. Although most patients with D-TGA have coronary anatomy that is suitable for coronary reimplantation, some variants, such as a single right coronary artery, are at risk for postoperative myocardial ischemia and death because reimplantation can result in distortion of the coronary ostia or narrowing of the artery itself. Inverted, intramural, or parallel coronary arteries can also be a problem.

FIGURE 20-14 Arterial switch procedure. A, The aorta is transected, and left and right coronary arteries and their bases are excised. B, An equivalent segment of pulmonary arterial wall is excised, and coronary arteries are sutured to the pulmonary artery. C, The distal pulmonary artery is brought anterior to ascending aorta, and the proximal pulmonary artery is anastomosed to the distal aorta. D, Sites of coronary artery extraction are repaired with use of either (a) a patch of prosthetic material or (b) a segment of pericardium. Finally, the proximal aorta is sutured to distal pulmonary artery.

(Modified from Castaneda AR, Norwood WI, Jonas RA, et al: Transposition of the great arteries and intact ventricular septum: anatomical repair in the neonate, Ann Thorac Surg 38:438, 1984, with permission from the Society of Thoracic Surgeons.)

The ASO was originally described in patients with D-TGA and a large VSD or a large PDA, in whom the LV (the pulmonary ventricle prior to ASO) is exposed to systemic pressures, and the LV mass remains sufficient to support the systemic circulation. This situation requires that the ASO be performed within the first few months (usually within the first few weeks) of life to avoid the development of progressive CHF or PVOD. The VSD is usually closed via the tricuspid valve to avoid a right ventriculotomy and resultant RV dysfunction. A brief period (<15 minutes) of deep hypothermic circulatory arrest is often used to facilitate closure of the ASD.

In patients with D-TGA and IVS, the ASO can be performed primarily or as the second phase of a staged procedure. A primary ASO procedure is usual for these patients and is usually performed within the first week of life. This is because the LV mass (and thus its ability to support the systemic circulation after ASO) in these patients declines as the elevated PVR that is characteristic of the normal fetus and newborn declines in the days to weeks after birth. Adequate LV mass to support the systemic circulation exists in these patients for only the first 2 to 3 months after birth, at most. Two-dimensional echocardiography is used to assess the LV-to-RV-pressure ratio and to quantify the adequacy of LV mass, size, and function.

A two-stage repair for D-TGA with IVS can be used for neonates and infants in whom significant regression of LV mass has occurred. These are generally infants on whom surgery was not performed during the first several weeks of life because of other factors (e.g., delayed diagnosis and referral, other anomalies, sepsis, or prematurity). To reestablish the ability of the LV to perform systemic workload, a pulmonary artery band is placed as a first stage; in addition, a BT shunt (one that enters the pulmonary artery distal to the band) is created to prevent hypoxemia. The goal of the band is to increase the LV (which is still the pulmonary ventricle) pressure to approximately one-half to two-thirds that in the systemic (right) ventricle to prevent further regression of LV mass and in fact promote a moderate degree of LV hypertrophy. These patients can initially be quite ill after the banding procedure, requiring mechanical ventilation and inotropic support as the adaptation occurs over several days; if the band is too tight, frank LV decompensation secondary to afterload mismatch can ensue.

After this first stage, the actual ASO can be performed as early as several days to 1 week after the pulmonary artery band procedure that was done to prepare the LV. The timing is often guided by noninvasive assessment of LV mass and function; somewhat surprisingly, a marked increase of LV mass can be seen within a week or less of pulmonary artery banding in most patients. Nonetheless, some degree of impaired LV function after ASO should be anticipated in these patients (see later), and at times a period of ECMO support and “training of the LV” (where ECMO flows and support are slowly and progressively weaned over several days after ASO) are needed. In addition to the difficulties of obtaining appropriate band tightness and of its effects on LV function, the systemic-to-pulmonary artery shunt can distort the pulmonary artery, making the subsequent ASO more difficult.

Rastelli Procedure

The ASO is generally not performed on patients with significant anatomic and fixed LVOT obstruction (subpulmonic stenosis; patients with dynamic LVOT obstruction are likely to have no gradient across the LV outflow tract after the ASO). Correction of some types and severities of anatomic LVOT obstruction is possible and these patients are also potential candidates for ASO. For patients with D-TGA, VSD, and severe anatomic LVOT obstruction (subpulmonary stenosis), a Rastelli procedure is performed (Fig. 20-15).

FIGURE 20-15 A, In the Rastelli procedure, closure of ventricular septal defect results in the left ventricle (LV) ejecting blood into the aorta (Ao). B, An external right ventricle (RV)–to–pulmonary artery (PA) conduit is placed to provide pulmonary circulation.

(From Strafford M: Transposition of the great vessels. In Lake CL, editor: Pediatric cardiac anesthesia, Norwalk, Conn, 1988, Appleton & Lange, p 237.)

Here, the VSD is closed via a right ventriculotomy using a more complicated patch, so that LV blood is directed through the aorta. The proximal pulmonary artery is ligated and a valved conduit is placed from the right ventriculotomy to the pulmonary artery, thereby bypassing the subpulmonic stenosis. Subaortic stenosis may result from placement of the complex VSD patch. Balloon dilations and eventual replacement of the valved RV-PA conduit are usually necessary because of calcification and patient growth.

Anesthetic Management

Several principles of anesthetic management pertain to all D-TGA infants, and some are specific for the individual subtypes. These will be discussed in turn.

For all patients, it is important to select drugs and other strategies that maintain cardiac output by their effects on heart rate, contractility, and preload. This is important because decreases in cardiac output decrease systemic venous saturation, with a resultant decrease in arterial saturation. Although this is true of all patients on PGE, it can be a critical consideration in patients with TGA and IVS, in whom optimizing preload and cardiac output may be the most reliable means to maintaining adequate intercirculatory mixing and avoid severe derangements in oxygen saturation (both systemic venous and arterial) and delivery.

When a patient has evidence of pulmonary overcirculation and congestive signs or symptoms, maneuvers (particularly ventilatory) that further decrease PVR should be avoided. It is also important to avoid significant increases in PVR relative to SVR, which will decrease pulmonary blood flow and reduce intercirculatory mixing. Similarly, reductions in SVR relative to PVR should also be avoided, because SVR promotes recirculation of systemic venous blood (and thus intercirculatory mixing) and decreases arterial saturation. Again, in general, promoting overall filling and ventricular output are the most reliable ways to maintain intercirculatory mixing, oxygenation, and oxygen delivery. Positive pressure ventilation needs to be sufficient to ensure adequate lung volume and gas exchange without promoting unwanted metabolic effects (e.g., hypocarbia and alkalosis in patients with already low PVR and evidence of pulmonary overcirculation) or substantial mechanical compromise of venous return, ventricular function, or mixing (e.g., increased PVR).

Induction and Maintenance

In prostaglandin-dependent neonates, the PGE₁ infusion (0.01 to 0.05 mcg/kg per minute) should be continued until shortly before CPB to ensure sufficient intercirculatory mixing. Anesthetic-related myocardial depression can occur on several counts and is more likely in these patients because of myocardial immaturity, the effects of positive pressure ventilation, and increased pulmonary blood flow with limited cardiac reserve. Therefore, this is another situation in which inhaled agent–based induction and maintenance techniques are not favored. Instead, anesthesia is usually induced and maintained using high-dosage fentanyl or sufentanil to provide hemodynamic stability and blunting of the stress response without adversely affecting intercirculatory mixing. In addition to muscle relaxation, judicious and divided doses of benzodiazepines (or low-concentration inhaled agent) can be added to promote amnesia.

In patients with reduced pulmonary blood flow or poor intercirculatory mixing, efforts to reduce PVR should be made to increase pulmonary blood flow and intercirculatory mixing (again with the caveat of not impeding PBF or cardiac output by excessive ventilatory maneuvers). Again, volume expansion and the addition of inotropic support (e.g., dopamine, 5 to 10 mcg/kg per minute) may be indicated to improve overall mixing and output and offset to some extent the alterations imposed by anesthetic agents and mechanical ventilation. In patients with PVOD, ventilatory measures to reduce PVR are useful if PVR is not fixed. Hypercarbia, acidosis, and hypoxemia further increase PVR and should be avoided because of limited myocardial reserve and deleterious effects on PVR (and therefore mixing as well). This is particularly true in neonates with TGA and IVS, where systemic oxygen delivery is tenuous, and in infants with TGA and VSD, in whom left ventricular volume overload is present. Indeed, it is not uncommon to see S-T segment changes on the ECG in these infants when systemic output and oxygenation are compromised, particularly in the face of LV volume overload. In addition, reactive increases in PVR are commonly seen in the immature pulmonary vasculature and may severely compromise pulmonary blood flow.

Post-CPB Management

After CPB and surgical repair, the most frequent problems include myocardial ischemia due to coronary insufficiency, decreased myocardial function, bleeding due to extensive and pressurized suture lines after neonatal CPB and hypothermia (i.e., clotting factor dilution, thrombocytopenia, and platelet dysfunction [see later]), and reactive pulmonary vasculature. Heart rate should be maintained at age-appropriate levels, using atrial pacing if necessary, as cardiac output is likely to be more heart-rate-dependent during the post-CPB period, particularly in these neonates and young infants. Although blood pressure should also be kept at age-appropriate norms (especially after hypothermic CPB or deep hypothermic circulatory arrest [DHCA] when cerebral autoregulation is likely to be impaired), at times reducing aortic or pulmonary artery pressure (or both) may be used to reduce suture line bleeding after the ASO. Systemic ventricular (RV after atrial baffle procedures and LV after arterial switch procedures) dysfunction may necessitate inotropic and vasodilator therapy to terminate CPB. Dobutamine (5 to 10 mcg/kg per minute) or dopamine (5 to 10 mcg/kg per minute) is most often used. Milrinone (0.25 to 1.0 mcg/kg per minute after a loading dose of 50 mcg/kg) may be used if SVR is high. Milrinone not only reduces LV afterload but may also contribute inotropic, lusitrophic, and PVR-reducing effects.

Obstruction of pulmonary or systemic venous return can occur after atrial baffle (Mustard or Senning) repairs. Systemic venous obstruction will produce evidence of systemic venous congestion and a measurable gradient between a catheter located in the SVC and one in the RA. Pulmonary venous obstruction may result in pulmonary venous and pulmonary arterial hypertension, pulmonary edema, and hypoxemia. Efforts to reduce SVR will reduce the RV afterload and help prevent tricuspid regurgitation. Therapy for atrial dysrhythmias also may be necessary. Echocardiography can help assess the presence of pulmonary or systemic venous obstruction, as well as atrial baffle leaks; any of these will require surgical revision if significant.

After the arterial switch procedure, there may be extensive bleeding from the aortic and pulmonary suture lines. Clotting factors (see later) and avoidance of hypertension are indicated. Myocardial ischemia after reimplantation of the coronary arteries is a potential and not infrequent problem after the ASO. In some circumstances, ischemia is caused by coronary air emboli and is transient. Maintenance of high perfusion pressures on CPB after aortic cross-clamp removal can promote distal migration and eventual dissipation of coronary air emboli. Echocardiography can help ensure adequate de-airing of the left atrium and ventricle prior to separating from CPB. It can also detect and distinguish between regional (i.e., potentially due to coronary insufficiency) and global (more likely due to ischemia–reperfusion injury) myocardial dysfunction and assess the presence of flow in the proximal portions of the reimplanted coronary arteries.

Evidence of myocardial ischemia after coronary reimplantation should be treated aggressively and should prompt immediate reevaluation of the anastomoses as well as the possibility of coronary kinking or external coronary compression by clot or hemostatic packing material. Such evidence is typically in the form of focal ECG abnormalities such as S-T/T wave changes, but it can also include various dysrhythmias and forms of AV block. Kinking of a reimplanted artery or obstruction of the implanted coronary ostia is likely to require immediate surgical intervention. If the quality of the repair is good and it was accomplished relatively swiftly (i.e., to limit myocardial ischemia–reperfusion damage), then it is unusual to require significant inotropic support or artificial pacing (for anything other than a relative sinus bradycardia) or experience much in the way of ECG abnormalities, dysrhythmias, or AV block. On the other hand, the need for AV pacing, the occurrence of dysrhythmias, or the need for unexpected degrees of vasoactive support (e.g., epinephrine) should lead to a search for a technical problem.

A sequence of LV dilation both initiating and exacerbating myocardial ischemia can occur in D-TGA patients after the ASO. Myocardial ischemia, afterload mismatch, or excessive volume infusion can result in LV distention and LA hypertension. This is particularly likely if there is mitral insufficiency from either (ischemic) papillary muscle dysfunction or dilation of the mitral valve annulus. LV distention may result in tension on and kinking of the coronary reanastomosis sites. LA hypertension produces elevations in pulmonary artery pressure and distention of the pulmonary artery. Because the LeCompte maneuver brings the distal pulmonary artery anterior to the ascending aorta, distention of the pulmonary artery may actually compress or place tension on the coronary ostia. The resulting myocardial ischemia produces further LV dilation, progressive elevations in LA and pulmonary artery pressures, and continuing compromise of coronary blood flow.

In some TGA patients, the LV may have limited ability to support the systemic circulation after the ASO. This may occur as the result of myocardial ischemia, inadequate LV mass, poor protection of the LV during aortic cross-clamping, or a combination thereof. Echocardiography can be useful in identifying both global and regional LV systolic dysfunction. It also detects mitral regurgitation, which may occur secondary to papillary muscle dysfunction or to dilation of the mitral valve annulus. Inotropic support of the LV and afterload reduction may be necessary to terminate CPB. Initial inotropic support is accomplished with dopamine (3 to 10 mcg/kg per minute). In rare instances when LV failure (that, again, has been proven not to be the result of a coronary problem) is severe, epinephrine (0.05 to 0.5 mcg/kg per minute) may have to be added. Milrinone (0.25 to 1.0 mcg/kg per minute after a 50-mcg/kg loading dose) can be a useful agent based on its inodilator properties (Hoffman et al., 2002, 2003). These patients are at particular risk for LV dysfunction in the immediate postoperative period secondary to afterload mismatch (insufficient contractility for the degree of systemic afterload). Although the vasodilation that accompanies milrinone administration in infants is substantially less than that seen in adult patients, it is nonetheless advisable to administer the loading dose of milrinone over 10 to 15 minutes or longer.

Truncus Arteriosus

Anatomy

A single great vessel arising from the base of the heart and giving rise to the pulmonary, coronary, and systemic arteries characterizes truncus arteriosus (Figs. 20-16 and 20-17). See related video online at www.expertconsult.com.

There is a single semilunar valve, which is usually abnormal, and invariably a large (nonrestrictive) conoventricular septal VSD is present. The truncus straddles this large VSD (see Fig. 20-16). Truncus arteriosus is classified based on the origin of the pulmonary arteries. In type 1, a short pulmonary trunk originates from the truncus and gives rise to both pulmonary arteries. In type 2, both pulmonary arteries arise from a common orifice of the truncus, whereas in type 3, the right and left pulmonary arteries arise separately from the lateral aspect of the truncus. The VSD is usually of the infundibular or perimembranous infundibular type. The truncal valve is tricuspid in most patients, but multiple cusps (four to seven) are common, and the valve itself may be regurgitant or stenotic. Extracardiac anomalies are seen in approximately 30% of patients.