Incidence

Congenital heart disease (CHD) represents the most common form of congenital pathology, with an estimated incidence of 0.3% to 1.2% of live births.¹ CHD is a major cause of morbidity and mortality during the neonatal period. However, with advances in medical and surgical management, including significant contributions related to anesthesia care, survival to adulthood is the expectation for most infants and children with CHD.^2–4

A bicuspid aortic valve (Video 14-1) is the most common cardiac defect, occurring in up to 1% of the population.^5,6 Ventricular septal defects (VSD) (Video 14-2) represent the next most common congenital pathology,^5,7–11 followed by secundum atrial septal defects (ASD) (Video 14-3).^5,12 Among cyanotic lesions, tetralogy of Fallot (TOF) predominates, affecting almost 6% of children with CHD (Fig. 14-1).¹³ In the first week of life, d-transposition of the great arteries (Fig. 14-2) is the most frequently encountered cause of cardiac cyanosis; TOF is sometimes not detected until later in life because cyanosis is absent or only mild desaturation is present.

FIGURE 14-1 The diagram depicts the anatomic features of tetralogy of Fallot. The abnormalities consist of right ventricular outflow tract obstruction (typically at any or a combination of valvar, subvalvar, and supravalvar levels), a large ventricular septal defect (VSD), aortic override, and right ventricular hypertrophy (RVH). Purple aorta indicates desaturation. The small size of the pulmonary artery is indicative of the right outflow tract obstruction.

FIGURE 14-2 Discordant ventriculoarterial connections are shown in the diagram of d-transposition of the great arteries. The right ventricle ejects blood into the pulmonary artery and the left ventricle ejects blood into the aorta. Mixing of blood must occur via an atrial septal defect, ventricular septal defect, or patent ductus arteriosus.

Segmental Approach to Diagnosis

Several classification schemes have been proposed to characterize and categorize various congenital cardiac defects.^14–20 The segmental approach to the diagnosis of CHD assumes a sequential, systematic analysis of the three major cardiac segments (i.e., atria, ventricles, and great arteries) to describe the anatomic abnormalities. The principle of this scheme is that specific cardiac chambers and vascular structures have characteristic morphologic properties that determine their identities, rather than their positions within the body.²¹ An organized, systematic identification of all cardiac structures or segments and their relationships (i.e., connections or alignments between segments) is carried out to define a child’s anatomy.²²

The initial approach is to determine the cardiac position within the thorax and the arrangement or situs of the thoracic and abdominal organs. The cardiac position can be described in terms of its location within the thoracic cavity (Fig. 14-3) and the direction of the cardiac apex. Although the cardiac position within the thorax may be considered independent of the cardiac base-apex axis, for simplicity the following terms are used: levocardia if the heart is in the left hemithorax (as is normally the case); dextrocardia if the heart is located in the right hemithorax; and mesocardia if the heart is displaced rightward but not completely in the right thoracic cavity. An abnormal location of the heart within the thorax (i.e., cardiac malposition) may result from displacement by adjacent structures or underlying noncardiac malformations (e.g., diaphragmatic hernia, lung hypoplasia, scoliosis).

FIGURE 14-3 Chest radiographs demonstrate various cardiac positions within the thorax. A, Levocardia (left-sided position). B, Dextrocardia (right-sided position). C, Mesocardia (centrally located cardiac mass).

The visceral situs, or sidedness, of the abdominal organs (i.e., liver and stomach) and atrial situs are considered independently (Fig. 14-4). Visceral situs is classified as solitus (i.e., normal arrangement of viscera, with the liver on the right, stomach on the left, and a single spleen on the left), inversus (i.e., inversion of viscera, with the liver on the left and stomach on the right), or ambiguous (i.e., indeterminate visceral position). Abnormal arrangements or sidedness of the abdominal viscera, heart, and lungs suggests a high likelihood of complex cardiovascular disease. The atrial situs, atrioventricular (AV) connections, ventricular looping (i.e., position of the ventricles as a result of the direction of bending of the straight heart tube in early development), ventriculoarterial connections, and the relationship between the great vessels are then delineated.

FIGURE 14-4 Three types of visceroatrial situs are shown. Situs solitus indicates a normal arrangement of the viscera and atria, with the right atrium (RA) on the right side and the left atrium (LA) on the left side. The stomach and spleen are on the left, and the liver is on the right. Situs inversus indicates inverted arrangement of viscera and atria, with the RA on the left side and the LA on the right side, as in a mirror image of situs solitus. In visceral situs inversus, the stomach and spleen are on the right, and the liver is on the left. Situs ambiguous denotes that the visceroatrial situs is anatomically uncertain or indeterminate because the anatomic findings are ambiguous.

(From Van Praagh R. The segmental approach to diagnosis in congenital heart disease. In: Bergsma D, editor: Birth defects: original article series. Vol 8. Baltimore: Williams & Wilkins; 1972, p. 23-44. Permission granted by March of Dimes.)

Associated malformations are described, including number and size of septal defects and valvar or great vessel abnormalities. Whereas many types of congenital defects fall neatly into this classification scheme, others (e.g., heterotaxy syndromes, conditions associated with malposition of the heart and abdominal organs) are often more difficult to precisely define.

Physiologic Classification of Defects

The wide spectrum of cardiovascular malformations in the pediatric age group presents a challenge to the clinician who does not specialize in the care of these children. Even for those with a focus or interest in cardiovascular disease, the range of structural defects and the varied associated hemodynamic perturbations can be overwhelming.

A physiologic classification system can facilitate understanding of the basic hemodynamic abnormalities common to a group of congenital or acquired lesions and assist in patient management (Table 14-1).^23,24 Several classification schemes have been proposed, including some that categorize structural defects as simple or complex lesions, consider the presence or absence of cyanosis, or consider whether pulmonary blood flow is increased or decreased.^25–27 The following approach groups pediatric heart disease into six broad categories according to the underlying physiology or common features of the pathologies.

TABLE 14-1 Physiologic Classification of Congenital Heart Disease (Representative Lesions)

Cardiomyopathies

The term cardiomyopathy usually refers to diseases of the myocardium associated with cardiac dysfunction.^31,32 They have been classified as primary and secondary forms. The most common types in children are hypertrophic, dilated or congestive, and restrictive cardiomyopathies. Other forms include left ventricular noncompaction^33–35 and arrhythmogenic right ventricular dysplasia.³⁶ Secondary forms of cardiomyopathies are those associated with neuromuscular disorders such as Duchenne muscular dystrophy, glycogen storage diseases (i.e., Pompe disease), hemochromatosis or iron overload, and mitochondrial disorders. Chemotherapeutic agents such as anthracyclines may result in dilated cardiomyopathy.³⁷ It is important to understand the hemodynamic processes behind the myocardial disease and implications for acute and chronic management.

Hypertrophic cardiomyopathy (HCM) is characterized by ventricular hypertrophy without an identifiable hemodynamic cause that results in increased thickness of the myocardium. This accounts for almost 40% of cardiomyopathies in children.^38–41 The condition represents a heterogenous group of disorders, and most of the identified genetic defects exhibit autosomal dominant inheritance patterns.^42,43 This is the most common cause of sudden cardiac death (SCD) in athletes.^44,45 Most children with HCM do not have systemic outflow tract obstruction (i.e., nonobstructive cardiomyopathy). It is unclear whether the few with hypertrophic obstructive cardiomyopathy, previously known as idiopathic hypertrophic subaortic stenosis, are at increased risk for SCD compared with children without obstruction.⁴⁴

Most children with HCM present for evaluation of a heart murmur, syncope, palpitations, or chest pain. Occasionally, an abnormal electrocardiogram (ECG) leads to referral. An accurate family history is essential. An apical impulse is often prominent. Auscultation may reveal a systolic ejection outflow murmur that becomes louder with maneuvers that decrease preload or afterload (e.g., standing, Valsalva maneuver) or increased contractility. The murmur decreases in intensity with squatting and isometric hand grip. A mitral regurgitant murmur may also be present. The ECG meets criteria for left ventricular hypertrophy in most children (Fig. 14-5). In some, the electrocardiographic findings may be striking (Fig. 14-6). A hypertrophied, nondilated left ventricle is a diagnostic feature determined by echocardiography (Video 14-4, A and B).⁴⁵ In many children, the hypertrophy may be asymmetric (Video 14-5, A and B). Echocardiography is the primary imaging modality for long-term assessment of wall thickness, ventricular dimensions, presence and severity of obstruction, systolic and diastolic function, valve competence, and response to therapy. Other diagnostic approaches such as cardiac catheterization and magnetic resonance imaging (MRI) may add helpful information in some cases.

FIGURE 14-5 The electrocardiogram from an adolescent with hypertrophic cardiomyopathy demonstrates left ventricular hypertrophy (i.e., deep S wave in V₁ and tall R waves over the left precordial leads). The ST-segment depression and T-wave inversion over the left precordial leads is related to repolarization changes associated with left ventricular hypertrophy, also known as a strain pattern. Reciprocal ST-segment elevation can be seen over the right precordial leads. This recording is consistent with sinus bradycardia (heart rate average of 50 beats per minute).

FIGURE 14-6 Pompe disease is an inherited disorder characterized by the accumulation of glycogen in cells. The electrocardiographic tracing for an infant with this glycogen storage disease and a severe form of hypertrophic cardiomyopathy displays dramatic right and left ventricular voltages, in addition to ST-segment and T-wave abnormalities. The recording is displayed at full standard (10 mm/mV), meaning that the electrocardiogram was not reduced in size to fit on the paper.

The care of children with HCM includes maintenance of adequate preload, particularly in those with dynamic obstruction. Diuretics are not indicated and often worsen the hemodynamic state by reducing left ventricular volume and increasing the outflow tract obstruction. Drugs that augment myocardial contractility (e.g., inotropic agents, calcium infusions) are not well tolerated. Patients usually undergo continuous electrocardiographic monitoring (i.e., Holter recording) and exercise testing for risk stratification.⁴⁶ β-Blockers and calcium channel blockers are the primary agents for outpatient drug therapy.⁴⁷ Therapies range widely and include longitudinal observation with medical management of heart failure and arrhythmias, implantation of cardioverter-defibrillators, surgical myotomy or myectomy, transcatheter alcohol septal ablation, and cardiac transplantation.

Dilated cardiomyopathy (DCM), also known as congestive cardiomyopathy, is characterized by thinning of the left ventricular myocardium, dilation of the ventricular cavity, and impaired systolic function.^48–50 The broad number of etiologies range from genetic or familial forms to those caused by infections,⁵¹ metabolic derangements, toxic exposures, and degenerative disorders.^52,53 Chronic tachyarrhythmias can also lead to DCM that may or may not improve after the rhythm disturbance is controlled.^54–56

Most children with DCM present with signs and symptoms of congestive heart failure (e.g., tachypnea, tachycardia, gallop rhythm, diminished pulses, hepatomegaly). The chest radiograph typically demonstrates cardiomegaly, pulmonary vascular congestion, and in some cases, atelectasis (Fig. 14-7). The ECG may identify the likely cause of the cardiac dysfunction in those with cardiomyopathy due to rhythm disorders or anomalous origin of the left coronary artery from the pulmonary root (ALCAPA). The echocardiogram can confirm the diagnosis by demonstrating a dilated left ventricle with decreased systolic function (Video 14-6, A and B).⁵⁷ Therapy in the acute setting is supportive and aimed at stabilization. Management may include afterload reduction, inotropic support, and mechanical ventilation. Unlike children with HCM, those with DCM have a volume-loaded, poorly contractile ventricle. Gentle diuresis is beneficial. The infusion of large fluid boluses may be poorly tolerated and result in hemodynamic decompensation and cardiovascular collapse. The outcomes of children with dilated cardiomyopathy vary. For most, recovery of left ventricular systolic function occurs, but others eventually require cardiac transplantation.⁵⁸ In a subset of children with severe disease, mechanical circulatory support may be necessary as a bridge to recovery or cardiac transplantation (Fig. 14-8) (see Chapter 19).^59–61

FIGURE 14-7 Chest radiographs of a young child with dilated cardiomyopathy in the posteroanterior (A) and lateral (B) projections demonstrate moderate to severe cardiomegaly and pulmonary vascular congestion. The lateral radiograph shows the heart bulging anteriorly against the sternum.

FIGURE 14-8 Some children with severe dilated cardiomyopathy (DCM) require mechanical circulatory assist devices. A, Chest radiograph of a child with end-stage DCM after placement of a Micromed DeBakey ventricular assist device for circulatory support as a bridge to cardiac transplantation. This miniaturized device includes a titanium pump, inlet cannula placed in the left ventricle, percutaneous cable, flow probe, and outflow graft placed in the aorta (not radiopaque). B, The Berlin Heart ventricular assist device allows paracorporeal placement and circulatory support in infants and small children.

Restrictive cardiomyopathy (RCM) is the least common of the major types of cardiomyopathies (5%) and portends a poor prognosis when it manifests during childhood.^62–67 The disorder is characterized by diastolic dysfunction related to a marked increase in myocardial stiffness resulting in impaired ventricular filling. Most cases are thought to be idiopathic. Presenting symptoms are nonspecific and primarily respiratory. Occasionally, the diagnosis is made after a syncopal or sudden near-death event. The physical examination may demonstrate hepatomegaly, peripheral edema, and ascites.

The echocardiographic hallmark of RCM is that of severe atrial dilation and normal- to small-sized ventricles (Video 14-7). The marked diastolic dysfunction leads to increased end-diastolic pressures, left atrial hypertension, and secondary pulmonary hypertension. Children with RCM are prone to thromboembolic complications, and anticoagulation therapy is frequently recommended. This is an important consideration during perioperative care because adjustments in the anticoagulation regimen may be necessary. Atrial and ventricular tachyarrhythmias may also occur. Optimal medical treatment is controversial because no specific agents or strategies have been shown to significantly alter outcomes.⁶⁷ Similar to children with HCM, diuretics often cause a decrease in the needed preload with detrimental effects on hemodynamics. Inotropic agents are not indicated because systolic function is preserved and the arrhythmogenic properties of inotropic drugs can induce a terminal event. In many centers, cardiac transplantation has been effectively used.^68,69

Myocarditis

Myocarditis is defined as inflammation of the myocardium, often associated with necrosis and myocyte degeneration. In the United States, it is most often caused by a viral infection. Over the past 20 years, the spectrum of viral pathogens causing myocarditis has changed, such that adenovirus, enteroviruses (e.g., coxsackievirus B), and parvovirus have become the most frequent causes of fulminant disease.^70–72

The overall incidence of myocarditis is unknown because it is frequently underdiagnosed and unrecognized as a nonspecific viral syndrome. A large, 10-year, population-based study on cardiomyopathy found an annual incidence of 1.24 cases per 100,000 children younger than 10 years of age; only a fraction of cases represented those with myocarditis.⁷³ The diagnosis is made using clinical history, physical examination, and imaging modalities. Myocarditis is highly suspected when a child presents with new-onset congestive heart failure or ventricular arrhythmias without evidence of structural heart disease. The ECG typically demonstrates low-voltage QRS complexes with tachycardia, which sometimes is ventricular in origin. Chest radiography often shows cardiomegaly with pulmonary vascular congestion (Fig. 14-9). Echocardiography displays ventricular dilation with decreased systolic function, similar to DCM, and it is useful in the exclusion of alternative diagnoses, such as pericardial effusion or anomalous origin of a coronary artery. Myocarditis is a clinical diagnosis because definitive confirmation requires the analysis of tissue obtained through myocardial biopsy in the catheterization laboratory or the operating room (rarely performed).⁷⁴

FIGURE 14-9 The chest radiograph of a child with acute myocarditis shows severe cardiomegaly and increased pulmonary vascularity.

Many children with myocarditis have subclinical or mild clinical disease, whereas others progress to overt heart failure or arrhythmias, or both. Among children with heart failure, approximately one third will regain full ventricular function, one third will recover but continue to demonstrate impaired systolic function, and one third will require cardiac transplantation.^75,76 A subset of children, not all of whom initially manifest severe symptoms in the acute period, will progress to have DCM.

Although no specific therapies have been identified to directly treat the myocardial injury, a variety of strategies have been employed.^77–80 The current paradigm includes diuresis and afterload reduction to improve myocardial performance without placing a large burden on an already failing heart.⁸¹ Rhythm disturbances are treated appropriately. Therapy with immune modulation or suppression with intravenous immunoglobulin is the standard of care at many centers.^81–83 Mechanical circulatory support may be required in fulminant disease.^84–89

Rheumatic Fever and Rheumatic Heart Disease

Acute rheumatic fever and rheumatic heart disease are leading causes of acquired cardiac disease in developing countries and still occur, albeit infrequently, in developed countries.⁹⁰ In the United States, the availability of antibiotic therapy for streptococcal pharyngitis has markedly reduced the incidence of this disease, but sporadic cases still occur.⁹¹ In children, the peak incidence occurs between 5 and 14 years of age.

Rheumatic fever results from infection by particular strains of group A β-hemolytic Streptococcus or Streptococcus pyogenes leading to a multisystemic inflammatory disorder. The incubation period for most strains of group A β-hemolytic Streptococcus is typically 3 to 5 days, although some children present with a more remote history of pharyngitis.

The clinical diagnosis of rheumatic fever is based on the modified Jones criteria.⁹² Major criteria include carditis, polyarthritis, chorea, subcutaneous nodules, and erythema marginatum. Without a history of rheumatic fever or echocardiographic evidence of typical valvular involvement, the diagnosis in children requires evidence of a prior streptococcal infection along with two major criteria or one major and two minor criteria. Fever and arthritis are common symptoms. The polyarthritis has a migratory pattern, typically affecting large joints. Cardiac involvement or carditis occurs in almost 50% of children with their first attack of rheumatic fever. Rheumatic heart disease represents a sequela of the acute process, and it most frequently affects the mitral and aortic valves.

Primary prevention of rheumatic fever and rheumatic heart disease begins with prompt recognition and appropriate treatment of the initial streptococcal infection.^93,94 Secondary prevention, with ongoing therapy in individuals with a known history of rheumatic fever, has been extremely effective in preventing recurrent attacks. Although there is debate regarding the optimal regimen, intramuscular injections of benzathine penicillin every 3 to 4 weeks appear to be most efficacious.⁹⁵

In a subset of children with severe cardiac involvement, elective or emergent surgery may be required.⁹⁶ Valvular disease, rather than global myocarditis, is often the cause of congestive symptoms; medical management therefore has limited efficacy. Valve repair is preferred to replacement.

Infective Endocarditis

Kawasaki Disease

Kawasaki disease (i.e., mucocutaneous lymph node syndrome) represents a fairly common and potentially fatal form of systemic vasculitis of unknown origin.^111–115 It is seen predominantly in infants and young children. The disease can affect the coronary arteries resulting in dilation and aneurysm formation.^116,117

The diagnosis relies on clinical features. To meet criteria, a child must have persistent fevers and at least four of the following findings^118,119:

Nonspecific findings may include irritability, hydrops of the gallbladder, sterile pyuria, arthritis, and aseptic meningitis. Acute-phase reactants and thrombocytosis are usually present.

Intravenous gamma globulin (IVIG) and high-dose aspirin are recommended during the acute phase of the disease. The incidence of coronary artery aneurysms is significantly reduced if IVIG is administered within the first 10 days of the illness.¹¹⁹ The presence of coronary artery aneurysms is considered diagnostic for Kawasaki disease (Fig. 14-10). In children with coronary artery aneurysms, low-dose aspirin therapy is administered, in some cases in combination with anticoagulants or antiplatelet drugs.¹²⁰ Myocardial ischemia and infarction, although uncommon, are important potential complications.^117,121 Anesthetic care in these children requires careful consideration regarding myocardial oxygen demand and supply; on rare occasions, coronary revascularization may be necessary.

FIGURE 14-10 Magnetic resonance reconstruction at the level of the great vessels in a child with Kawasaki disease demonstrates a large, fusiform coronary aneurysm (arrow). Ao, Aorta; MPA, main pulmonary artery.

Cardiac Tumors

Because cardiac tumors are rare in children, the natural history and optimal treatment strategies are often determined from limited case series.^122–124 Atrial myxomas represent more than 90% of cardiac tumors in adults, but in children, they tend to be rhabdomyomas or fibromas.¹²⁵ Less common types include hemangiomas, myxomas (Video 14-9), Purkinje cell tumors, and teratomas. In adults, most tumors are found in the left atrium, but cardiac tumors in children occur in all four cardiac chambers. Malignant primary tumors are rare, and data on their outcomes are limited. Other nonprimary cardiac tumors, such as neuroblastoma, can invade vascular structures and extend into the heart.

Rhabdomyomas are the most common primary cardiac tumors in children. They often involve the ventricular septum and left ventricle and are multiple in most cases.¹²⁶ Although they are considered benign, children may present with cardiomegaly, congestive heart failure, arrhythmias, or sudden death. The significance of a rhabdomyoma is determined largely by its size and any obstruction it may cause. Many tumors regress over time or completely resolve; surgery is not indicated unless symptoms are present.^127,128 Many children with cardiac rhabdomyomas have associated tuberous sclerosis.^129,130

Cardiac fibromas are the second most common type of pediatric primary cardiac tumors.¹³¹ They are typically single and involve the ventricular free wall. In a subset of fibromas, the tumor can invade the conduction system.¹³² Surgery or cardiac transplantation may be required.^133,134 The tumors can be very large, and complete surgical resection may result in severely depressed cardiac function. Partial resections have been found to result in an arrest in growth with good outcomes while sparing cardiac function.¹²⁸

The primary concerns in the perioperative care of children with cardiac tumors are the impact of the mass on hemodynamics and the associated abnormalities of cardiac rhythm.¹³⁵

Definition and Pathophysiology

Heart failure has become a major field of interest and investigation in pediatric cardiology and the subject of various publications,¹³⁶ scientific meetings, and several textbooks.^137,138 Pediatric heart failure results from markedly different causes from those reported in adults.¹³⁹ The cellular basis of heart failure, compensatory mechanisms, and therapeutic advances represent areas of interest in children.^{136–138,140,141} The following discussion highlights key concepts as they relate to anesthetic practice.

Heart failure is considered to be a pump failure and a circulatory failure involving neurohumoral aspects of the circulation.¹⁴² Several conditions may ultimately compromise the ability to generate an adequate cardiac output to meet the systemic circulatory demands. This disease state does not necessarily imply impairment of ventricular systolic function, but diastolic heart failure is an increasingly recognized clinical entity.

Etiology and Clinical Features

Causes of heart failure vary with age. In the perinatal period, cardiac dysfunction may be related to birth asphyxia or sepsis or may represent an early presentation of CHD. The neonate with heart failure frequently presents with clinical signs of a low cardiac output state. Causes include left-sided outflow obstruction (e.g., aortic stenosis, aortic coarctation, hypoplastic left heart syndrome), severe valve regurgitation (e.g., Ebstein anomaly), or absent pulmonary valve syndrome.

During the first year of life, most cases of heart failure are caused by structural heart disease. Other causes include cardiomyopathies due to inborn errors of metabolism or acute events such as myocarditis. In infants with heart failure, tachypnea, dyspnea, tachycardia, feeding difficulties, and failure to thrive are prominent symptoms.¹⁴³ Physical examination reveals grunting respirations, rales, intercostal retractions, a gallop rhythm, and hepatosplenomegaly. Frequently, a mitral regurgitant murmur is present.

Beyond the first year of life, heart failure is a consequence of previous surgical interventions, unpalliated or unrepaired cardiovascular disease, cardiomyopathies, myocarditis, or anthracycline therapy for a malignancy. Occasionally, a child may present with severe ventricular systolic impairment related to ongoing myocardial ischemia as a result of a coronary artery anomaly or rarely due to acquired pathologies such as Kawasaki disease. Older children with heart failure exhibit exercise intolerance, fatigue, and growth failure, whereas adolescents have symptoms similar to those of adults.

Treatment Strategies

Therapy is tailored to the cause of the cardiac dysfunction and may include supportive care, mechanical ventilation, inotropic support, afterload reduction, prostaglandin E₁ therapy to maintain pulmonary or systemic blood flow, maneuvers to balance the systemic and pulmonary circulations, catheter-based interventions, or surgery.^144–148 Maintaining organ perfusion is the main goal of therapy for acute heart failure. Pharmacologic agents include inotropes (used on a very-short-term basis, if necessary) and inodilators. Although the administration of digoxin was the mainstay of chronic therapy in the past, this is no longer the case. Favored agents for use in children include diuretics, angiotensin-converting enzyme inhibitors, and β-blockade.^149,150 Newer agents that have received increasing attention in the management of pediatric heart failure include nesiritide (a recombinant form of human B-type natriuretic peptide)^151–153 and carvedilol (a third-generation β-blocker).^154–156

Anesthetic Considerations

Anesthesia for children with heart failure can be quite challenging. The severity of the condition and degree of baseline decompensation can influence the likelihood of an untoward event and the potential for hemodynamic instability and a bad outcome. Several publications have addressed the risks associated with anesthesia in this setting.^157–159 It is important to first reexamine the risk–benefit ratio in these patients before going forward with the planned procedure. In most surgical settings, tracheal intubation and mechanical ventilation are indicated. The need for invasive monitoring should be based on the clinical situation, anticipated nature of the procedure, and impact on hemodynamic state.

Chromosomal Syndromes

Gene Deletion Syndromes

Williams Syndrome

Williams syndrome is a congenital disorder with an incidence of 1/20,000 live births. In most cases, the long arm of chromosome 7 is deleted, altering the elastin gene.^181,182 The absence of this gene is detected by fluorescence in situ hybridization (FISH). Features of Williams syndrome include characteristic elfin facies, outgoing personality, endocrine abnormalities (including hypercalcemia and hypothyroidism), mental retardation, growth deficiency, and altered neurodevelopment. Cardiovascular abnormalities can include valvar and supravalvular aortic stenosis (Fig. 14-11) and aortic coarctation.^183,184 This arteriopathy can also involve the origin of the coronary arteries or other vessels. Diffuse narrowing of the abdominal aorta may be associated with renal artery stenosis.

FIGURE 14-11 The angiogram displays the classic supravalvar aortic stenosis (SVAS, arrow) in a child with Williams syndrome.

Several reports have described unanticipated events during anesthesia for these children.^185–187 Two conditions can increase anesthetic morbidity and the potential for mortality: coronary artery stenosis leading to myocardial ischemia and severe biventricular outflow tract obstruction. A thorough cardiac evaluation of all children is advisable because the spectrum of disease and the potential devastating implications in affected individuals varies.¹⁸⁸ Children occasionally may require further evaluation before undergoing anesthetic care. Even asymptomatic children and those without evidence of clinical cardiovascular disease may be at risk for morbidity and death in the perioperative period.¹⁸⁷ Extreme vigilance and particular attention to signs of myocardial ischemia is warranted, as is a plan of action in the event of acute decompensation. This syndrome is one of the leading causes of cardiac arrest in the Pediatric Perioperative Cardiac Arrest (POCA) registry.¹⁸⁹

Children with Williams syndrome may exhibit some degree of muscular weakness, and the cautious use and application of muscle relaxants has been recommended.¹⁸⁸ Associated neurodevelopmental delay, attention-deficit disorder, and autistic behavior often requires adequate premedication. Subclinical hypothyroidism has a high prevalence among these children.¹⁹⁰ Renal manifestations include renovascular hypertension, reduced function, and hypercalcemia-induced nephrocalcinosis.

Single-Gene Defects

Marfan Syndrome

Marfan syndrome is a multisystem disorder with variable expression resulting from a mutation in the fibrillin gene, a connective tissue protein, located on chromosome 15.¹⁹⁹ Clinical manifestations typically involve the cardiovascular, skeletal, and ocular systems.^200,201 Cardiovascular pathology includes mitral valve prolapse and regurgitation, ascending aortic dilation (Fig. 14-12), and main pulmonary artery dilatation. The risk of aortic dissection rises considerably with increasing aortic size but may occur at any point in the course of the disease.²⁰² Cardiac arrhythmias may be related to valvular heart disease, cardiomyopathy, or congestive heart failure.

FIGURE 14-12 A severely dilated aortic root is displayed by magnetic resonance imaging in a patient with Marfan syndrome. There is a marked discrepancy between the diameters of the ascending and descending aorta.

β-Blocker therapy and aggressive blood pressure control has been the standard of care in children with aortic root dilation²⁰³ and should be continued perioperatively. Aortic root replacement in Marfan syndrome has been associated with a greater risk of repeat dissection and recurrent aneurysm compared with other children who have undergone similar interventions.²⁰⁴ It is wise to maintain hemodynamics near baseline values in the perioperative period. After aortic root surgery some individuals may require chronic anticoagulation therapy. Preoperative hospitalization may be necessary to adjust the anticoagulation regimen in anticipation of surgery in these children. In emergency cases, administration of coagulation factors and other blood products may be required. In addition to vascular pathology, children with Marfan syndrome have a predisposition for ventricular dilation and abnormal systolic function.^205,206

Several factors can result in pulmonary disease in these children.²⁰⁷ Chest wall deformities and progressive scoliosis can contribute to restrictive lung disease. The fibrillin defect may affect lung development and homeostasis, impairing pulmonary function. Development of a pneumothorax is relatively common.

Associations

Other Disorders

Tuberous sclerosis is a rare genetic disease with an autosomal dominant inheritance pattern and an incidence of approximately 1 case per 25,000 to 30,000 births.²¹⁸ In a relatively large number of children, it can be attributed to spontaneous mutations. This systemic disease primarily manifests as cutaneous and neurologic symptoms, but cardiac and renal lesions are frequent findings.

The presence of upper airway nodular tumors, fibromas, or papillomas in affected children may interfere with airway management. Developmental delay, autism, attention-deficit disorder, and aggressive behavior are common. Brain tumors and renal tumors (60% to 80%) may produce significant comorbidities. Cardiac pathology includes cardiac rhabdomyoma in 60% of children and coexisting CHD in 33% of cases.^219–221 Cardiac abnormalities with obstruction to flow, heart failure, arrhythmias, conduction defects, or preexcitation may affect the selection of anesthetic agents. Preoperative evaluation in most cases should include an ECG to assess arrhythmia, conduction defects, or preexcitation.²¹⁹ Blood pressure and renal function should also be assessed. Anticonvulsants should be optimized and continued until the morning of surgery. Baseline medical treatment should be resumed as soon as possible because seizures are the most common postoperative complication.²²² A child with mental retardation may require premedication with oral midazolam or ketamine, or both, to facilitate parental separation.

Aberrant Subclavian Arteries

An aberrant or anomalous subclavian artery usually arises from the descending aorta as a separate vessel distal to the usual last subclavian artery in a posterior location. In a left aortic arch, this arrangement is as follows. The first branch is the right carotid artery, followed by the left carotid artery and the left subclavian artery. The aberrant right subclavian artery, rather than arising proximally from the innominate artery as the first arch branch, originates distal to the last (left) subclavian artery as the fourth branch and courses behind the esophagus toward the right arm. This variant is one of the most common aortic arch anomalies. It occurs in 0.4% to 2% of the general population and may or may not be associated with CHD.²²³ This anomaly has a high incidence among children with Down syndrome and is associated with VSDs, TOF, and other lesions. In a right aortic arch, the anomalous left subclavian artery originates distal to the origin of the right subclavian artery (Fig. 14-13). This anomaly may be seen in the context of conotruncal malformations. The diagnosis of an aberrant subclavian artery is made by most currently available imaging modalities.

FIGURE 14-13 Anterior (A) and posterior (B) magnetic resonance images demonstrate a right aortic arch with an aberrant left subclavian artery (Ab LSA). The first arch vessel is the left carotid artery (LCA), followed by the right carotid artery (RCA), and right subclavian artery (RSA). The Ab LSA is the most distal branch originating from the descending aorta and coursing posterior to the esophagus toward the left arm. This vessel may be compressed by a transesophageal echocardiographic probe.

This anomaly has several implications:

Persistent Left Superior Vena Cava to the Coronary Sinus

A persistent left superior vena cava (LSVC) is a form of anomalous systemic venous drainage identified in 4.4% of children with CHD, most frequently those with septal defects.²²⁵ It represents a venous remnant that typically involutes during development. If it persists, it remains patent and drains into the right atrium through an enlarged coronary sinus. Bilateral superior vena cavae may be present (Fig. 14-14), or the right superior vena cava may be absent. Bilateral superior vena cavae may communicate through an innominate or bridging vein. This anomaly has several implications:

FIGURE 14-14 Bilateral superior vena cavae may exist separately or may communicate through an innominate or bridging vein. A, The angiogram depicts the superior vena cava, normally a right-sided structure, as it drains into the right atrium. B, In the same patient, an angiogram shows drainage of a large left superior vena cava into the coronary sinus. The catheter courses from the inferior vena cava into the right atrium, coronary sinus, and left superior vena cava. Contrast into the left superior vena cava demonstrates no innominate vein between the two cavae. The coronary sinus is dilated.

Basic Rhythms

Sinus Arrhythmia

Sinus arrhythmia represents cyclic changes in the heart rate during breathing. This is a normal finding in healthy children (Fig. 14-21).

FIGURE 14-21 The rhythm tracing displays the normal heart rate variability with respiration. There is a normal increase in heart rate during inspiration. This sinus arrhythmia is a natural response and is more commonly seen in children than adults.

Sinus Tachycardia

During sinus tachycardia, sinus rhythm occurs at a heart rate above normal for age (Fig. 14-22). In the perioperative setting this is often the result of surgical stimulation, stress, pain, hypovolemia, anemia, fever, medications (i.e., inotropic agents), malignant hyperthermia, or a high catecholamine state. Treatment is directed at the underlying cause. Prolonged periods of sinus tachycardia may impair diastolic filling time, limit ventricular preload, and compromise cardiac output. Children at risk for hemodynamic decompensation include those with significant degrees of ventricular hypertrophy or diastolic dysfunction, aortic stenosis, Williams syndrome, and HCM.

FIGURE 14-22 Electrocardiogram for a febrile infant with sinus tachycardia, characterized by a heart rate above normal for age and QRS complexes of normal appearance preceded by P waves, which are upright in leads I and aVF.

Junctional Rhythm

A junctional rhythm is characterized by QRS complexes of morphology identical to that of sinus rhythm without preceding P waves. This rhythm is slower than the expected sinus rate. When this rhythm completely takes over the pacemaker activity of the heart, retrograde P waves and AV dissociation may be seen. Junctional rhythm during cardiac surgery is frequently the result of manipulation or dissection near the right atrium. The central venous pressure contour typically demonstrates prominent v waves (i.e., right atrial pressure wave at the end of systole) due to the loss of AV synchrony (Fig. 14-23). The lack of atrial contribution to ventricular filling may result in decreases in the systemic arterial blood pressure.

FIGURE 14-23 The intraoperative tracing obtained during cardiac surgery at the time of right atrial dissection demonstrates the features of a junctional rhythm. Retrograde P waves are identified after the QRS complexes. The central venous pressure (CVP) tracing demonstrates prominent v waves (arrows) related to the loss of atrioventricular synchrony (scale of 0 to 30 mm Hg for CVP).

Conduction Disorders

Atrioventricular Block

First-Degree Atrioventricular Block

In first-degree AV block, there is prolongation of the PR interval beyond the normal range for age. Each P wave is followed by a conducted QRS. This may be found in healthy individuals but can also be seen in various disease states. First-degree AV block is a benign condition requiring no specific treatment.

Second-Degree Atrioventricular Block

There are two forms of second-degree AV block: Mobitz type I (Wenckebach) and Mobitz type II. They are characterized by a periodic failure to conduct atrial impulses to the ventricle (i.e., P wave without following QRS complex). In a type I, second-degree AV block, there is a gradual lengthening of the PR interval with eventual failure of conduction of the next atrial impulse to the ventricle. The RR intervals concomitantly shorten. The degree of AV block is expressed as the ratio of P waves per QRS complexes (i.e., 2 : 1, 3 : 2). This can occur during periods of high vagal tone or in the postoperative setting. It is usually a benign phenomenon that requires no therapy. In the less frequent type II second-degree AV block, there is a relatively constant PR interval before an atrial impulse that fails to conduct. This is considered a more serious conduction disturbance and merits further investigation.

Third-Degree Atrioventricular Block

Third-degree (complete) AV block is characterized by total failure of conduction of atrial impulses to the ventricle. It can be congenital or acquired. There is complete AV dissociation, with more atrial than ventricular contractions, and the ventricular rate is usually slow and regular (Fig. 14-24). Temporary pacing may be indicated in the acute setting.

FIGURE 14-24 Rhythm strip demonstrates independent atrial and ventricular activity (i.e., atrioventricular dissociation) and failure of any atrial impulses to conduct to the ventricles. These features characterize a complete atrioventricular block.

Cardiac Arrhythmias

Supraventricular Arrhythmias

Premature Atrial Contractions or Beats

Isolated premature atrial contractions (PACs) are relatively common in infants and small children. On the ECG, the early P waves exhibit a morphology and axis that are different from those in normal sinus rhythm. Premature atrial contractions may be conducted to the ventricles normally, blocked at the AV node, or conduct aberrantly (i.e., abnormal QRS morphology). They are usually benign and require no therapy. If a central venous catheter is present, the tip position should be evaluated.

Supraventricular Tachycardia

Supraventricular tachycardia (SVT) is the most common significant arrhythmia in infants and children.^238,239 It is characterized by a regular tachyarrhythmia (tachycardia heart rate is age dependent but typically more than 230 beats/min in children) with a narrow or usual complex QRS morphology. Supraventricular tachycardia can occur in structurally normal hearts and in various forms of CHD. Usual complex implies that the QRS morphology in tachycardia is similar to that in normal sinus rhythm (Fig. 14-25). Occasionally, widening of the QRS in SVT may result from bundle branch block or related to the tachycardia mechanism (i.e., SVT with aberrancy). A wide QRS complex may make the distinction between supraventricular and ventricular tachycardia difficult.

FIGURE 14-25 The initial portion of the intraoperative recording demonstrates normal sinus rhythm. A premature atrial beat initiates a narrow complex tachycardia (i.e., QRS morphology the same as in sinus rhythm). The supraventricular tachycardia is associated with hemodynamic changes such as a decrease in the systemic arterial pressure (ART 1, scale of 0 to 100 mm Hg) (arrow) and increase in the central venous pressure (CVP, scale of 0 to 30 mm Hg) (broken arrow). Spo₂, Oxygen saturation.

The two types of SVT are automatic and reentrant. They can be differentiated by evaluating characteristics of the tachycardia, usually assisted by the input from a specialist. The evaluation of a tachyarrhythmia should include a surface 15-lead ECG and continuous rhythm strip to document onset and termination. If a medication such as adenosine has been administered, a recording of the response to the drug or pacing maneuvers should be obtained. The management of SVT depends on the clinical status of the child, type of tachycardia, and precise electrophysiologic mechanism. General management principles include the following:

Hemodynamic stability should be determined. Synchronized direct current cardioversion (0.5 to 1.0 J/kg) should be performed for hemodynamic instability.²³⁷

Antiarrhythmic therapy is based primarily on the clinical condition and suspected tachycardia mechanism. Vagal maneuvers may be considered but should not delay treatment. Adenosine is the drug of choice in the acute setting for diagnosis and termination of most supraventricular tachycardias.²⁴⁰ β-Blockers are most often used for chronic therapy.

Others measures include treatment of fever if present, sedation, correction of electrolyte disturbance, decreasing or withdrawing medications associated with sympathetic stimulation (i.e., inotropic agents) or with vagolytic properties (i.e., pancuronium).

In addition to pharmacologic therapy, atrial pacing or cardioversion may be required.

Ventricular Arrhythmias

Premature Ventricular Contractions or Beats

Premature ventricular contractions (PVCs) are characterized by prematurity of the QRS complex, a QRS morphology that is different from that in sinus rhythm, usually a prolongation of the QRS duration for age, abnormalities of the ST segment and T wave, and premature ventricular activity not preceded by a premature atrial beat. PVCs of a single QRS morphology (i.e., uniform), without associated symptoms, and in children with structurally normal hearts are considered benign. An ECG during sinus rhythm should allow careful measurement of the QT interval. Further investigation and consultation are warranted in the presence of PVCs of multiple morphologies (i.e., multiform), if they occur with moderate frequency or in succession (i.e., couplets or runs) and are associated with symptoms or a structurally abnormal heart.

Ventricular ectopy in the perioperative period may be the result of profound hypoxemia, electrolyte disturbances, or metabolic derangements. Other causes include the use of recreational drugs, myocardial injury, poor hemodynamics, and prior cardiac surgical intervention.

Ventricular Tachycardia

Ventricular tachycardia (VT) is relatively uncommon in children. It is defined as three or more consecutive ventricular beats occurring at a rate greater than 120 beats/min (Fig. 14-26). The QRS morphology in VT is different from that in sinus rhythm, and the QRS duration is typically prolonged for age. ECG features that support this diagnosis include AV dissociation, intermittent fusion (i.e., QRS complex of intermediate morphology between two other distinct QRS morphologies), QRS morphology of VT similar to that of single PVCs, and tachycardia rate in children usually below 250 beats/min.

FIGURE 14-26 The tracing demonstrates frequent, uniform premature ventricular beats and episodes of nonsustained, monomorphic ventricular tachycardia.

Acute onset of VT in pediatric patients may be caused by hypoxia, acidosis, electrolyte imbalance, or metabolic problems. Ventricular tachycardia may also occur in the context of depressed ventricular function, halothane anesthesia with or without hypercarbia, poor hemodynamics, prior surgical interventions, cardiomyopathies, myocardial tumors, acute injury (e.g., inflammation, trauma), and prolonged QT syndromes.^241,242

Long QT Syndrome

Long QT syndrome (LQTS) (Fig. 14-27) is an electrical cardiac disturbance that can predispose children to arrhythmias that include torsades de pointes ventricular tachycardia (Fig. 14-28), ventricular fibrillation, and bradyarrhythmias, and any of these can result in syncope, cardiac arrest, or sudden death.²⁴³ It occurs with an incidence of 1 case per 2500 births; congenital and acquired forms have been described. The congenital varieties are likely the result of genetic defects in the cardiac ion channels responsible for maintaining electrical homeostasis.²⁴⁴ Thirteen genotypes have been described on five chromosomes. The cLQT1-3 (Romano-Ward) cases account for 90% of the children. The Romano-Ward syndrome has an incidence of 1 case per 10,000 births and an autosomal dominant pattern of inheritance. The Jervill Lange-Nielsen syndrome has an incidence of 1 case per 1,000,000 births, an autosomal recessive pattern of inheritance, and an association with deafness. Diagnostic criteria proposed for the long QT syndrome include electrocardiographic findings, clinical history (e.g., deafness, syncope), and family history.²⁴⁵ A frequent feature is prolongation of the QTc on the resting ECG.

FIGURE 14-27 For a patient with long QT syndrome, the electrocardiogram demonstrates prolongation of the QT interval.

FIGURE 14-28 The rhythm strip displays positive and negative oscillation of QRS complexes, which is characteristic of torsades de pointes ventricular tachycardia.

An important consideration in the care of children with cLQTS is ensuring adequate β-adrenergic blockade preoperatively and minimizing adrenergic stimulation.²⁴³ Since the introduction of β-adrenergic blockade in patients with cLQTS in 1975, the mortality rate has decreased more than 10-fold. The risk for developing torsades de pointes from the many drugs known to trigger it is almost unpredictable; these drugs have been divided into several groups that are listed and updated online (www.qtdrugs.org).

In a retrospective study of children with cLQTS, three adverse events were reported during emergence from anesthesia immediately after administration of ondansetron and anticholinesterase medications; one was described as torsades de pointes.²⁴⁴ These arrhythmias resolved quickly with intravenous β-blockers, lidocaine, or the administration of both agents. This report suggests that children with cLQTS are at risk for arrhythmias during periods of enhanced sympathetic activity (i.e., during emergence), particularly in the presence of drugs that prolong the QT interval. Conditions (e.g., hypothermia) and drugs (www.qtdrugs.org) that are known to prolong the QT interval should not be combined if possible. Despite the fact that most intravenous and inhalational medications routinely administered during anesthesia prolong the QT interval, adverse events are rare. This may be attributed in part to the need for a second abnormality beyond a prolonged QT interval to be present to trigger arrhythmias (i.e., increased dispersion of repolarization). Fortunately, most anesthetics do not increase the dispersion of repolarization.

Torsades de pointes is a rare but potentially life-threatening arrhythmia, even in the presence of prolonged QT interval. To trigger torsades de pointes, a second phenomenon must occur (i.e., increased dispersion of repolarization). Dispersion of repolarization refers to the variance in the rate of repolarization; in this case, it is a circumscribed region in the heart muscle (i.e., transmurally from the epicardium to the endocardium). There is much debate over how to quantify an increased dispersion of repolarization from surface ECGs. Some suggest the dispersion is the QTc-max to QTc-min, whereas others recommend measuring the duration of the T wave from its peak to the end; in both instances the upper limit of normal is 65 msec and abnormal values exceed 100 msec.

Prolongation of the QT interval and genesis of torsades de pointes occur more commonly in the presence of several conditions and drugs: electrolyte derangements (e.g., hypokalemia, hypocalcemia, hypomagnesemia), combination drug therapies (e.g., antibiotics, antiarrhythmic agents, class III antiarrhythmics such as amiodarone and procainamide), antipsychotic drugs, cisapride, neurologic or endocrine abnormalities (e.g., hypothyroidism), 5-HT₃ receptor–blocking drugs (except palonosetron), neostigmine, stress (including induction of and emergence from anesthesia and laryngoscopy), female sex, bradycardia, and coronary artery disease. Although many anesthetics prolong the QT interval, few affect the dispersion of repolarization (as in the case of sevoflurane),²⁴⁶ and the risk of torsades de pointes during general anesthesia in children is rare.

Management of torsades de pointes includes the following considerations:

1. Although some atypical forms of supraventricular tachyarrhythmias may mimic VT, a wide QRS tachycardia should always be considered to be of ventricular origin.

2. The initial approach in the setting of an acute ventricular rhythm disturbance consists of prompt evaluation of clinical status and hemodynamic stability. Sustained ventricular arrhythmias are poorly tolerated and require immediate attention. In the unstable child, cardiopulmonary resuscitation should be instituted while preparing for cardioversion. Expert consultation is advisable when advanced drug therapy is contemplated. Potential pharmacologic interventions include lidocaine, amiodarone, and procainamide.²⁴⁷ The latter two should not routinely be administered during torsades de pointes due to QT prolongation.

3. Magnesium sulfate is considered the first-line treatment of torsades de pointes. Procainamide and amiodarone are contraindicated due to prolongation of the QT interval. Isoproterenol and overdrive pacing may be effective for bradycardia. Electrical cardioversion (1 to 2 J/kg) should be performed only if the arrhythmia is refractory to pharmacologic treatment.

4. cLQTS should be treated with β-blockade (not overdrive pacing); some forms of the cLQTS may require the implantation of a cardioverter-defibrillator.

Ventricular Fibrillation

Ventricular fibrillation (VF) is an uncommon arrhythmia in children. It is characterized by chaotic, asynchronous ventricular activity that fails to generate an adequate cardiac output. The ECG during VF demonstrates low-amplitude, irregular deflections without identifiable QRS complexes. A loose ECG electrode may mimic these surface electrocardiographic features, and immediate clinical assessment should be performed and adequate pad contact ensured when VF is suspected.

Management of VF includes the following considerations:

1. This is a lethal arrhythmia if untreated.

2. Immediate defibrillation (initial dose of 2 J/kg) is the definitive therapy. Cardiopulmonary resuscitation, beginning with chest compressions, should be immediately resumed and continued for 2 minutes. If defibrillation is unsuccessful, the energy dose should be doubled (4 J/kg) and repeated. Pediatric paddles (2.2 cm in diameter) are recommended for children weighing less than 10 kg. Adult paddles (8 to 9 mm in diameter) are suggested for children weighing more than 10 kg to reduce impedance and maximize current flow.

3. Adequate airway control and chest compressions should be rapidly instituted while preparing for defibrillation or between shocks if several defibrillation attempts are needed. Resuscitative drugs and amiodarone should be considered without delaying defibrillation.

Pacemaker Nomenclature

Pacemaker nomenclature follows the guidelines of the North American Society of Pacing and Electrophysiology and the British Pacing and Electrophysiology Group²⁴⁸ (Table 14-5):

Permanent Cardiac Pacing

Chest Radiography

The standard posteroanterior and lateral chest radiographs provide clues to a child’s underlying cardiovascular anatomy; however, plain radiographs are an insensitive screening tool for cardiac disease.²⁶⁴ Children with numerous types of significant CHD may have initially normal-appearing radiographs; alternatively, an infant with a poor inspiratory effort and the presence of a large thymus may give the appearance of cardiomegaly and have normal intracardiac anatomy (Fig. 14-29).

FIGURE 14-29 For a neonate with apneic episodes undergoing evaluation for potential cardiac disease, the radiograph demonstrates a poor inspiratory effort resulting in a large cardiothymic silhouette, making interpretation of cardiac size difficult. No evidence of cardiac disease was identified in this child.

Interpretation of a chest radiograph begins with identification of the patient’s name and ensuring that the right-left orientation of the radiograph is correct. All catheters and tubes should be followed to verify their location, course, and likely site of termination. The bones and soft tissues should be inspected for evidence of sternal wires, fractures, vertebral anomalies, or wide intercostal spaces, suggesting a prior thoracotomy. Sidedness, including the location of the gastric bubble, liver, and position and orientation of the cardiac mass, should be observed. The lung parenchyma should be examined for evidence of focal consolidation, such as pneumonia or atelectasis, and for pulmonary vascular markings.

The cardiac silhouette and great vessels should be assessed. In young children, the thymus may obscure the superior portions of the cardiac shadow. Careful inspection of the cardiac silhouette includes an assessment of overall size and evidence of individual chamber or vessel dilation. The size of the main pulmonary artery segment may provide further evidence of the degree of pulmonary overcirculation in children with left-to-right shunt lesions. The tracheal indentation can usually be seen and is useful in determining aortic arch sidedness, although in a young child with a prominent thymus, this can be difficult to assess.

More useful than an individual radiograph as a diagnostic tool are serial chest films obtained to monitor a child’s cardiovascular status over time. In a young child with a volume overload lesion, the physical examination and growth parameters coupled with the degree of cardiomegaly and pulmonary overcirculation are more helpful than more advanced imaging techniques. A plain chest radiograph may also guide initiation and titration of pharmacologic therapy and the timing of a surgical intervention.

Barium Esophagram

The current applications and uses of barium esophagram (swallow) studies in the diagnosis of CHD are limited. This modality has been largely replaced by MRI and chest tomography.^265–267 In some cases, a barium esophagram is used as an initial screening tool when there is concern about the presence of a vascular ring.^268,269 A double aortic arch represents one of the most common types of vascular rings in young children, but other vascular anomalies such as a right aortic arch with an aberrant left subclavian artery and left-sided ligamentum arteriosus may also cause symptoms. The indentation pattern in the barium column is consistent with the specific vascular anomaly (Fig. 14-30).

FIGURE 14-30 Barium swallow in a child with respiratory symptoms demonstrates a filling defect posteriorly in the mid-esophagus, which is consistent with an aberrant subclavian artery.

Echocardiography

Echocardiography is the primary diagnostic modality for the initial evaluation and serial assessment in most types of pediatric heart disease.^270,271 Using a variety of transducers, ultrasound is used to acquire real-time images of cardiovascular structures. Various echocardiographic modalities are available, including transthoracic,²⁷² transesophageal,^273–276 fetal,^277,278 epicardial,²⁷⁹ intracardiac imaging,²⁸⁰ and intravascular ultrasound.²⁸¹ Each plays an important role in the diagnostic evaluation and management of children with suspected or confirmed cardiovascular disease.

Advantages of echocardiography include its noninvasive nature, provision of excellent temporal and spatial resolution, generation of portable real-time images, cost-effectiveness, and ease of use. As with any type of ultrasound, these waves are transmitted well through homogeneous tissues and fluid but poorly through air and bone. Another limitation of echocardiography is related to limited acoustic windows in certain patient groups, such as those who have undergone multiple cardiothoracic procedures, older individuals, or children with a significant amount of soft tissue or body fat. For this reason, cardiovascular MRI is being increasingly used for noninvasive imaging. Additional challenges of echocardiography include the need to obtain serial two-dimensional tomographic images by sweeping the transducer scan in multiple planes to synthesize these images into three-dimensional structures in one’s mind and to achieve expert interpretation. Despite these limitations, echocardiography remains the main diagnostic imaging modality for most children. Many medical and surgical management strategies are primarily based on the findings allowed by this approach.

A standard transthoracic study consists of a two-dimensional examination, M-mode imaging, and Doppler evaluation (i.e., color flow, pulsed-wave, or continuous-wave modalities). Two-dimensional imaging provides structural assessment of the heart and adjacent vasculature. Cross-sectional images are obtained from several windows that allow excellent anatomic detail in multiple planes (Video 14-11). In most cases, this is adequate for a detailed segmental evaluation of the cardiac anatomy as described earlier. M-mode echocardiography allows one-dimensional imaging of the heart with excellent temporal resolution (Fig. 14-31). It is known as an ice pick view of the heart in real time and is primarily used in the assessment of ventricular dimensions and function.

FIGURE 14-31 An M-mode echocardiogram enables determination of left ventricular dimensions and calculation of shortening fraction. IVS, Interventricular septum; LV, left ventricle; LVEDD, left ventricular end-diastolic dimension; LVESD, left ventricular end-systolic dimension; LVPW, left ventricular posterior wall; RV, right ventricle.

Color flow Doppler techniques allow evaluation of directionality and velocity of blood flow. In addition to detecting flow across cardiac valves and great vessels, color flow imaging allows detection of subtle lesions such as small septal defects that can be difficult to identify by standard two-dimensional imaging alone. Traditionally, flow toward the transducer is displayed in red, and flow away is represented as blue. Turbulent blood flow is associated with increased Doppler velocities and can be readily identified as a mosaic of colors; it typically has a greenish tint (Video 14-12).

Pulsed- and continuous-wave Doppler represent spectral modalities that complement the color flow data and provide quantitative information. Pulsed-wave interrogation localizes specific sites of stenosis or turbulence but is limited in the magnitude of velocities it can detect. Continuous-wave Doppler allows quantification of much higher velocities (see Video 14-12). Velocities obtained with pulsed- and continuous-wave Doppler provide estimates of pressures within various cardiac chambers by applying the simplified Bernoulli equation. It states that the difference in pressure between two locations is approximately four times the square of the velocity of the jet of flow between them:

The applications of three-dimensional echocardiography in CHD continue to be investigated.^282–284 This approach can provide clear and useful volumetric assessments when the images are adequate. A significant advantage of this modality is that it is able to display cardiovascular structures and their interrelationships in detail, in many cases facilitating the understanding of pathologic conditions over two-dimensional imaging. Three-dimensional echocardiography may also be useful when interventions are planned.

Magnetic Resonance Imaging

Cardiovascular MRI-angiography has emerged as a complementary technology to other imaging modalities (Videos 14-14 and 14-15). Benefits have been reported in the assessment of complex pathology,^294–300 delineation of systemic and pulmonary vascular anomalies,^299,300 evaluation of global and regional ventricular function,³⁰¹ assessment of myocardial viability,³⁰² and characterization of pulmonary blood supply in children with structural alterations of the pulmonary vascular tree.³⁰³ Additional applications that may further expand the utility of cardiovascular MRI include the quantification of left-to-right shunts^304–306 and measurement of blood oxygen saturation.³⁰⁷ MRI is beneficial for guiding interventions in pediatric heart disease.^308–310

Although the temporal resolution of MRI is inferior to echocardiography, new sequences and techniques allow real-time acquisition similar to that of fluoroscopy. An important aspect in the acquisition of MRI data with high spatial resolution is the use of cardiac and respiratory gating to allow sampling during only specific portions of the cardiac and respiratory cycles. Slow heart rates and low respiratory rates facilitate this process. MRI, in contrast to computed tomography (CT), does not involve radiation exposure, making it preferable for serial examinations that many young children with cardiovascular pathology require. However, this may be associated with the need for multiple episodes of anesthesia and their inherent risks.

Because of the nature of the magnetic fields generated in MRI, the presence of several types of metal, including pacemakers, ICDs, cerebrovascular clips/coils, or recently implanted intracardiac or intravascular coils and devices, are considered contraindications. Titanium hardware may minimize the artifact produced by the foreign material; stainless steel generates significant artifacts within the study.

An additional limitation of MRI is the need for patient immobility during long examinations for optimal image quality. For small children, this requirement usually necessitates the use of deep sedation or general anesthesia.^311–313 For infants with complex and often cyanotic CHD, specialists are often asked to provide care during the procedures. The severity of the cardiovascular disease and the need for breath holding may add to the challenges presented to the anesthesia care provider in a remote location.^314,315 The lengthy nature of the studies and the significant time requirements to perform postprocessing of the images cause MRI to be much more time intensive for the interpreting physician than other noninvasive imaging modalities.

A significant advantage of this technique is avoidance of harmful radiation inherent to traditional catheterization techniques. As MRI technology improves, with faster scans, increasing availability, and decreasing cost, it will continue to play an increasing role in the diagnosis and longitudinal follow-up of congenital and acquired pediatric heart disease.

Computed Tomography

Cardiac CT, with or without electrocardiographic gating, has become an option among the various cardiovascular imaging modalities (Fig. 14-32).^{294,298,316,317} The major advantage of CT over MRI is the very rapid scan times, and for most children, sedation is minimal or unnecessary. A significant drawback of CT is the large radiation burden, although typically estimated to be similar to or slightly greater than a diagnostic cardiac catheterization, and the likely need for iodinated contrast agents with their concomitant risks.

FIGURE 14-32 Computed tomography images show the aortic arch anatomy in an infant with severe aortic arch obstruction (arrows).

Cardiac CT is not as accurate as MRI for delineation of intracardiac anatomy, but it provides excellent spatial resolution and information on extracardiac structures. CT has been beneficial in the evaluation of aortic arch anomalies and vascular rings and for defining systemic and pulmonary venous returns. In adult patients, multislice CT provides excellent information on coronary arteries and the presence of atherosclerotic disease; in infants and children with smaller vessels and more rapid heart rates, these images are more difficult to obtain.

Cardiac Catheterization and Angiography

Cardiac catheterization involves the invasive measurement of intracardiac and vascular pressures and blood oxygen saturation coupled with angiography to assess cardiac anatomy and hemodynamics (Figs. 14-33 and 14-34). Before the era of two-dimensional echocardiography, cardiac catheterization was frequently used for diagnostic purposes. With the advances in noninvasive imaging, diagnostic procedures represent a relatively small proportion of these studies. Current indications for cardiac catheterization at most centers include the assessment of physiologic parameters such as pressure and resistance data, anatomic definition when other diagnostic modalities are inadequate, need for electrophysiologic testing or treatment, and when interventions are anticipated.

FIGURE 14-33 A cardiac catheterization diagram is valuable when caring for patients with structural anomalies, such as this child with complex congenital heart disease. Data routinely obtained at cardiac catheterization are shown, including oxygen saturation determinations (in %), pressure measurements (in mm Hg), and hemodynamic calculations. Catheter courses are indicated by arrows. The atrial pressures are given for the a wave (a), which represents the atrial systole; v wave (v), which represents the end of systole (rise in atrial pressure before atrioventricular valve opening); and mean (m), all in mm Hg. See section on “Interpretation of a Cardiac Catheterization Report,” this page.

FIGURE 14-34 In the hemodynamic tracing obtained during cardiac catheterization, notice that the pulmonary artery systolic pressure (100 mm Hg) is at systemic levels in this child with multiple, left-sided obstructions. ART, Systemic arterial pressure; PA, pulmonary artery pressure.

Most catheterizations are performed for interventions, including endomyocardial biopsies; angioplasties and stenting of stenotic vessels, dilation of valves, and conduits; and occlusion techniques for native defects, fistulous connections, and surgically created defects no longer considered necessary (Fig. 14-35, Video 14-16)  (see Chapter 20). In some cases, such as critically ill neonates with complex heart disease, catheter-based interventions such as balloon atrial septostomy and other procedures can be lifesaving.

FIGURE 14-35 Several types of interventions are performed in a pediatric cardiac catheterization laboratory. A, Balloon atrial septostomy. B, Blade atrial septostomy. C, Double-balloon mitral valvuloplasty. D, Placement of a ductal coil occluder device. E, Transcatheter closure of a secundum atrial septal defect. F, Pulmonary artery dilation with stent placement.

In most children, access to the central circulation is accomplished percutaneously through a femoral approach. Most examinations involve hemodynamic evaluation with recording of pressure data through catheters positioned at various sites of interest. Oxygen saturation data are obtained by reflectance oximetry or blood gas measurement from various cardiac chambers and vessels. In contrast to the oxygen saturation calculations derived from a blood gas analysis, reflectance oximetry provides measured values. This allows determination of oxygen content (i.e., total amount of hemoglobin in the blood) and, when combined with values of oxygen consumption, assessment of blood flows and other calculations (e.g., shunts).³¹⁸ Additional data that may be obtained include pressure gradients, cardiac output, and parameters for deriving vascular resistances and valve areas.

Fluoroscopy and cineangiography are essential components of most cardiac catheterization studies. Of the two, cineangiography accounts for most of the radiation exposure as images are recorded during the injection of contrast material, typically at 15 or 30 frames/sec.³¹⁹ Most angiograms are obtained during biplane imaging by positioning the equipment to obtain optimal views allowing for delineation of the pathology in question (i.e., axial angiography) (Video 14-17, A and B).^320,321

Although cardiac catheterization has evolved over the years, providing an improved margin of safety, it remains an invasive procedure involving several risks. They include excessive blood loss, vascular complications,^322,323 infection, arrhythmias, vascular or cardiac perforation,³²⁴ systemic air embolization, myocardial ischemia, and those associated with the administration of contrast agents. These complications are more likely in infants and small children.³²⁵ Interventional catheterizations, by the nature of the procedures, are associated with a greater rate of complications and greater potential for morbidity and mortality. However, as transcatheter interventions become safer and more effective, an increasing number of children may obviate the need for surgery, often undergoing procedures on an outpatient basis.³²⁶ Evolving approaches in this field include percutaneous implantation of valves,³²⁷ strategies that combine cardiac catheterization and surgical intervention (hybrid procedures),^328–330 and catheter-based interventions during fetal life.³³¹

Interpretation of a Cardiac Catheterization Report

Pressure Data

Atrial pressure tracings are characterized by several waves (a, c, and v waves) and descents (x and y). Reported values correspond to the a and v waves and the mean pressures. The right atrial pressure is typically a wave dominant. The mean right atrial pressure is normally less than 5 mm Hg. In the presence of significant tricuspid valve regurgitation or a junctional rhythm, the v wave becomes the dominant wave. The left atrial pressure tracing, in contrast to the right atrium, displays v wave dominance, which is accentuated during mitral regurgitation. The mean left atrial pressure rarely exceeds 8 mm Hg.

Ventricular pressures are recorded and reported during systole, at end systole, and at end diastole. For the right ventricle the systolic pressure is normally in the 25 to 30 mm Hg range, with end-diastolic pressure of 5 to 7 mm Hg. The systolic pressure in the left ventricle normally increases with age and should equal the systolic arterial pressure; the end-diastolic pressure is typically less than 10 mm Hg.

The pulmonary artery pressure is reported in terms of systolic, diastolic, and mean pressures. The systolic pulmonary artery pressure in a normal child should be equal to the right ventricular systolic pressure, and the mean pulmonary artery pressure should not exceed 20 mm Hg. The pulmonary artery wedge pressure is obtained by advancing a catheter into a distal vessel until it is occluded, reflecting the left atrial pressure.

The aortic pressure and contour of the tracing depends on the site of interrogation. Typically, there is an increase in the systolic pressure as the catheter navigates toward the peripheral circulation. This phenomenon is known as pulse wave amplification.

Pressure gradients, or the pressure differences between two distinct sites, can be measured in several ways (i.e., mean gradient and peak gradient). It is important to consider that several factors may affect their determination. This is significantly influenced by the severity of the obstruction and the ventricular function. Smaller gradients may be seen under sedation or anesthesia.

Shunt Calculations

Shunts are characterized in terms of their direction (e.g., left-to-right, right-to-left, bidirectional) and magnitude. Left-to-right shunts can be quantified based on the pulmonary () to systemic () blood flow ratio. In the equation, S_sysao₂ is the systemic arterial O₂ saturation, is the mixed venous O₂ saturation, S_pulmvo₂ is the pulmonary venous O₂ saturation, and S_pulmao₂ is the pulmonary arterial O₂ saturation.

A ratio that exceeds 3 to 1 is considered a significant shunt, although smaller ratios may be associated with considerable symptoms.

Cardiac Output Determinations

The volume of blood ejected by the heart into the systemic circulation, or cardiac output, can be derived in several ways. Thermodilution measurements use saline as an indicator to measure pulmonary blood flow. In the absence of intracardiac shunts, this is equivalent to cardiac output (expressed as liters per minute). In the Fick method, oxygen is used as an indicator, and cardiac output is obtained by the application of the following formula:

In the equation, is the oxygen consumption (assumed or measured), C_syso₂ is the systemic arterial O₂ content, and is the mixed venous O₂ content. The O₂ content = O₂ saturation × (1.36 × 10 × hemoglobin concentration).

Vascular Resistances

Resistance represents the change in pressure in the systemic or pulmonary circulation with respect to flow. It is expressed in Wood units (mm Hg/L/min) and is usually normalized for body surface area. The systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR) are derived as follows:

General Issues

Anesthesia for children with heart disease³³² is challenged by the following factors:

TABLE 14-6 Surgical Procedures for Congenital Heart Disease

To optimally care for these children, the following objectives should be met:

This combination of daunting challenges and difficult objectives can be intimidating even for the most experienced clinician. When caring for children with cardiovascular disease, an interdisciplinary approach is recommended, allowing for the formulation and execution of optimal individualized management plans. If available, consultation with the child’s cardiologist or primary care physician should include inquiries about the details of the child’s disease, overall clinical status, past and current medical treatment, prior catheterization or surgical interventions, and presence of residual pathology. The interaction between members of the perioperative team should allow an exchange of information, discussion of concerns, and recommendations that may facilitate patient care and the development of comprehensive care plans.³³⁴ This is particularly important in the management of children with complex disease.

A complete medical history and focused examination is essential during the preoperative assessment. In addition to evaluating the child’s disease processes, overall clinical status, and functional reserve, this allows appraisal of issues that may affect anesthesia management (e.g., limited vascular access, difficult airway, gastroesophageal reflux, manipulations to manage pulmonary and systemic blood flow and pressures). Available diagnostic studies (e.g., ECG, chest radiograph, echocardiogram, Holter monitor, cardiac catheterization) should be reviewed. Depending on the nature of the procedure, complexity of the disease, and potential impact on perioperative outcome, additional evaluation and diagnostic studies may be warranted. In many cases, the anesthesiologist plays a major role in determining whether the available information is adequate.

A fundamental goal in the preoperative evaluation is the identification of children who are at increased risk because of cardiac and pulmonary limitations imposed by their cardiovascular disease. After the preoperative visit, the anesthesiologist caring for a child with CHD should have an understanding of the pathophysiology of the cardiac defect and implications of any previous interventions. Abnormal indices that should raise potential concerns include hypoxemia (Spo₂ less than 75%), exceeding 3 to 1, outflow tract gradients greater than 50 mm Hg, pulmonary hypertension (i.e., mean pulmonary artery pressure above 30 mm Hg), increased pulmonary vascular resistance index (more than 2 Woods units/m²), or polycythemia (i.e., hematocrit greater than 60%). Several clinical states may place children at significant risk for severe cardiopulmonary decompensation during anesthesia and surgery: recent congestive heart failure, uncontrolled arrhythmias, severe ventricular dysfunction, unexplained syncope, substantial exercise intolerance, or any condition associated with significant functional cardiac or pulmonary impairment. For some children, a planned admission to the intensive care unit (with or without a tracheal tube) should be discussed with the parents, child, and whole care team.

Clinical Condition and Status of Prior Repair

Children with CHD may present for anesthesia care before or after palliation or for definitive procedures. Corrective procedures are those that result in a normal life expectancy and full cardiovascular reserve.³³⁵ Children undergoing these interventions usually require no further medical or surgical treatment. In the strict sense, only a few procedures fulfill these criteria: ligation, division, or occlusion of a PDA and closure of an isolated secundum ASD. Other interventions or surgical procedures may result in repair or correction but not necessarily in normal hemodynamics or life expectancy. The clinician should assume some limitation in cardiovascular reserve, a need for close follow-up, further medical management, and potential or additional surgical therapies. In other cases, as in children with palliated CHD, the circulation may still be abnormal. These individuals have been reported to be at greater risk for adverse perioperative events.^336–338 Published data from the Pediatric Perioperative Cardiac Arrest (POCA) Registry examined anesthesia-related cardiac arrests in children with congenital and acquired heart disease.³³⁹ Compared with other children, cardiac arrests were found to occur more frequently in children with heart disease. Causes were primarily cardiovascular in nature. These events occurred more frequently in the general operating room, usually during the surgical maintenance phase. The most common anatomic substrate in this setting was that of a single ventricle, particularly those early in the palliation pathway. The overall mortality rate for children with heart disease was greater than those without heart disease, with the greatest mortality rate occurring in children with aortic stenosis and cardiomyopathy.

The effects of previous procedures on the heart and other systems require careful consideration. Problems may remain or develop after surgical intervention include residual shunts, valvar stenoses or outflow tract obstruction, valvar regurgitation, pulmonary hypertension, arrhythmias, and ventricular dysfunction. Children who require a detailed appraisal of perioperative risks include those with residual significant pathology, suspected or known pulmonary hypertension, or single-ventricle physiology and those after conduit placement or cardiac transplantation (see Chapters 15, 16, and 21).

Acknowledgment

We wish to thank Timothy C. Slesnick, MD, for his prior contributions to this chapter.