Cyanotic Congenital Heart Disease

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44 Cyanotic Congenital Heart Disease

Michael L. O’Byrne, Anitha S. John

Cyanotic heart disease refers to cardiac lesions that result in a characteristic blue discoloration of the skin. Typically, patients with cyanotic heart disease present in infancy. These defects may be detected through prenatal screening echocardiography or by screening pulse oximetry in the newborn period. However, patients with untreated acyanotic lesions can present later in life with cyanosis caused by either progressive subpulmonary stenosis in patients with complex heart disease including a ventricular septal defect (VSD, e.g., tetralogy of Fallot) or development of Eisenmenger physiology.

Pathophysiology Of Cyanosis

Cyanosis results from deoxygenated blood entering the arterial circulation. This can result from either abnormal alignment of anatomic segments, resulting in venous drainage being directed to the systemic arterial circulation with limited systemic–pulmonary mixing (e.g., D-transposition) or abundant systemic–pulmonary mixing (e.g., tetralogy of Fallot, single ventricle, total anomalous pulmonary venous connection). The concentration of deoxygenated hemoglobin must exceed 5 g/dL in systemic arterial blood for cyanosis to be manifest, so patients who are anemic may have low oxygen saturations but may not appear cyanotic. Furthermore, clinical cyanosis is often not recognized by parents and even by clinicians, especially in patients who have deeply pigmented skin.

The magnitude of cyanosis depends on which of the two physiologic types mentioned above is present. In the first, the transposition type, cyanosis is independent of the amount of pulmonary blood flow but instead is related to the amount of mixing between the systemic and pulmonary circulations—with more mixing, there is less cyanosis, and with less mixing, there is more cyanosis. In normal physiology, the aorta is fully saturated, and the aortic saturation is higher than the pulmonary saturation. The pulmonary and systemic circulations are in series, and oxygenated blood returns from the lungs and exits to the body via the aorta. In transposition physiology, the pulmonary artery saturation is higher than the aortic saturation. There are two parallel circulations where the oxygenated blood returns mostly to the lungs and deoxygenated blood mostly to the body. The presence of an atrial septal defect (ASD) (or creating one with a balloon atrial septostomy) allows for some mixing between the two circulations, which results in improved systemic saturation (although still lower than pulmonary saturation). Most of these patients have high pulmonary blood flow.

In the second type of cyanotic heart disease, tetralogy physiology, cyanosis depends on the amount of pulmonary blood flow. With much systemic–pulmonary mixing at some level, the greater the amount of pulmonary blood flow, the lesser the degree of cyanosis; the less pulmonary flow, the more cyanosis.

In differential cyanosis, the preductal oxygen saturation (right arm) is higher than the postductal (lower extremity). This occurs when one ventricle delivers the blood to the upper half of the body, and the other ventricle provides some of the blood to the lower half of the body via a patent ductus arteriosus in the absence of complete systemic–pulmonary mixing. This occurs in coarctation of the aorta and interrupted aortic arch and with persistent pulmonary hypertension of the newborn. Reverse differential cyanosis (postductal saturation > preductal saturation) occurs with transposition of the great arteries in addition to the above conditions.

Other factors affecting the oxygen content in both the pulmonary venous and systemic venous blood can worsen cyanosis in these lesions. Pulmonary edema, pulmonary parenchymal disease, or increased metabolic demands can result in a greater than expected degree of cyanosis.

Clinical Presentation And Evaluation

Cyanosis is the most common presenting sign in these newborns when cyanosis is severe. In lesions with abundant mixing and with pulmonary overcirculation, such as truncus arteriosus, total anomalous pulmonary venous connection, and single ventricle without pulmonary stenosis, the cyanosis is less obvious, but tachypnea and respiratory distress may bring the patient to medical attention. Some lesions such as tetralogy of Fallot have a variable presentation depending on the severity of the obstruction to right ventricular outflow. Despite their variability of presentation, these lesions are discussed together because they present at the same age and should all be considered in the differential of a neonate with suspected severe congenital heart disease. It should also be noted that cyanotic congenital heart disease is increasingly diagnosed prenatally via echocardiography, allowing for delivery of infants with the most severe cases in tertiary care hospitals equipped to care for cyanotic heart disease, reducing end-organ damage and complications, and potentially improving overall survival rates.

The differential diagnosis of cyanosis in an infant or young child includes the congenital cardiac lesions described below but also includes acrocyanosis (blue discoloration of extremities caused by peripheral vasoconstriction), pulmonary disease, and methemoglobinemia.

Evaluation of these patients includes a thorough physical examination and pre- and postductal saturations, chest radiography, electrocardiography, and hyperoxia test. Transthoracic echocardiography confirms the anatomy of the lesions and may provide important information regarding cardiac physiology.

The hyperoxia test can be a useful tool for differentiating cardiac and noncardiac cyanosis. It relies on the principle that hypoxemia caused by cardiac abnormalities is not corrected by increasing the inspired fraction of inspired oxygen (FiO2). Therefore, in a child with FiO2 of 100%, a right radial (i.e., preductal) arterial pAO2 less than 150 mm Hg suggests cyanotic congenital heart disease. Higher pAO2s suggest pulmonary disease with rare exceptions. Furthermore, pulmonary disease usually permits a much larger increase in pAO2 than does structural heart disease.

Transposition of the Great Arteries

Transposition of the great arteries means that the pulmonary artery arises above the left ventricle and the aorta above the right ventricle (Figure 44-1). It is the most common cardiac cause of cyanosis in the neonatal period (0.2-0.4 in 1000 live births), accounting for 7% of congenital heart defects. Its incidence is increased in infants of diabetic mothers. It is not seen in patients with DiGeorge syndrome. Cyanosis results because the pulmonary and systemic circulations flow parallel to one another with minimal mixing: deoxygenated systemic venous blood returns to the right atrium and right ventricle and out the aorta, and oxygenated pulmonary venous blood returns to the left atrium and left ventricle and exits into the pulmonary arteries. These two parallel circuits are compatible with survival only because there is some point of mixing, usually at the foramen ovale.

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Figure 44-1 Transposition of the great arteries.

Immediate intervention is usually necessary to augment the interatrial shunt. This is accomplished through a Rashkind balloon atrial septostomy (see Figure 44-1). This procedure allows for increased mixing, resulting in tolerable aortic saturations. Surgery remains the definitive therapy. Historically, this was accomplished through an atrial switch operation—Mustard (see Figure 44-1) or Senning procedures—redirecting inflow from the pulmonary veins to the right ventricle and from the venae cavae to the left ventricle. Perioperative mortality was low, but concerns regarding arrhythmia and the durability of the right ventricle (which remains the systemic ventricle) led to a different surgical approach, with a higher degree of technical difficulty but improved physiology. Currently, the preferred method is the arterial switch operation in which (1) the aorta is bisected and the distal aorta is brought beneath the bifurcation of the pulmonary trunk while the pulmonary trunk is displaced anteriorly (the Lecompte maneuver) where the aorta is anastomosed to the former pulmonary trunk and the main pulmonary artery is anastomosed to the former aortic trunk, (2) the coronary arteries are detached from the former aortic trunk and reimplanted on the pulmonary trunk (the new aortic root) with pericardial patches placed on the sites where the coronary arteries were harvested, and (3) the ASD is repaired (see Figure 44-1).

Tetralogy of Fallot

Tetralogy of Fallot is characterized by an abnormally small subpulmonary conus or outflow tract, resulting in anterior and cephalad displacement of the infundibular (outflow tract) septum. This produces the four characteristic findings: (1) subvalvular pulmonic stenosis, (2) VSD caused by malalignment of the infundibular septum relative to the rest of the ventricular septum, (3) “overriding aorta” (i.e., the aortic valve sits above both ventricles), and (4) right ventricular hypertrophy caused by pressure overload from the large VSD (Figure 44-2). It occurs in 0.19 to 0.26 in 1000 live births and represents 8% of congenital cardiac lesions. Tetralogy of Fallot is found in more than 25% of patients with DiGeorge syndrome and chromosome 22q11.2 microdeletion. The incidence of tetralogy of Fallot is higher than the general population in children of mothers with phenylketonuria and occurs more frequently in children with thrombocytopenia absent radii syndrome. Associated cardiac defects include right aortic arch (25% of patients) and ASD (10% of patients).

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Figure 44-2 Tetralogy of Fallot.

Cyanosis in tetralogy of Fallot is variable, resulting from extensive systemic–pulmonary mixing and decreased pulmonary blood flow caused by the combination of subpulmonic stenosis and a large VSD.

The earliest surgical treatment was palliative, aimed at increasing pulmonary blood flow without addressing the subpulmonary stenosis or the VSD. The Blalock-Taussig shunt, an end-to-side anastomosis of the subclavian artery to the ipsilateral branch pulmonary artery, was the first operation for cyanotic heart disease. Subsequently, other shunts connecting the aorta to a pulmonary artery branch were devised. Nowadays most shunts for cyanotic heart disease are constructed from polytetrafluoroethylene tube grafts connecting the aorta or an arch vessel to the main pulmonary artery or one of its branches. Currently, surgical therapy is directed at complete repair with (1) effective closure of the VSD by baffling the left ventricle by way of the VSD to the overriding aorta; (2) augmentation of the right ventricular infundibulum; (3) valvotomy of the pulmonary valve, if necessary; and (4) placement of a transannular patch, a continuation of the infundibular incision across the pulmonary valve annulus, if there is significant annular hypoplasia.

Double Outlet Right Ventricle with Pulmonic Stenosis

Double outlet right ventricle with pulmonic stenosis has similar physiology to tetralogy of Fallot. The presentation can be similar, with differentiation provided by echocardiography. The surgical approach is similar as well, baffling the left ventricle by way of the VSD to the nearby aorta and either pulmonary outflow augmentation as in tetralogy or placement of an extracardiac right ventricle to pulmonary artery conduit. Because the VSD, the effective left ventricular outflow, is surrounded by muscle, it may be necessary to enlarge it before baffling to the aorta to avoid subaortic stenosis.

Tricuspid Atresia

Tricuspid atresia is absence of communication between the right atrium and either ventricle. All blood returning to the right atrium flows across a patent foramen ovale or ASD to the left atrium, left ventricle, and usually through a VSD to the remnant of the right ventricle. In cases with normally aligned great arteries, the size of the VSD affects the amount of pulmonary blood flow and therefore the degree of cyanosis (Figure 44-3). Because many patients have muscular VSDs, it may be large early in life with relatively high pulmonary blood flow and mild cyanosis. Over time, the VSD may become smaller, resulting in decreasing pulmonary blood flow and increasing cyanosis. Rarely, there is no VSD, and pulmonary blood flow is exclusively from a ductus arteriosus. In cases with transposition of the great arteries, the aorta arises from the small remnant of the right ventricle. These patients usually have high pulmonary blood flow and therefore mild cyanosis. When the VSD is relatively small, there may be additional coarctation of the aorta. These VSDs are rarely muscular and therefore tend to stay about the same relative size over time. High pulmonary blood flow often results in heart failure and, if not surgically addressed, can eventually cause pulmonary vascular disease. In patients with transposition and a restrictive VSD, a Damus-Kaye-Stansel or a Norwood operation is required to effectively bypass the subaortic obstruction by using the pulmonary valve (arising unobstructed from the left ventricle) as an additional (or only) systemic outlet. These operations involve transection of the pulmonary artery above the valve and amalgamation of the pulmonary stump with the ascending aorta and aortic arch, either with (Norwood) (see Figure 44-3) or without (Damus-Kaye-Stansel) supplementary graft material depending on the size difference between the two vessels. The distal pulmonary arteries are then supplied by a systemic-to-pulmonary shunt.

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Figure 44-3 Tricuspid atresia.

Because all patients with tricuspid atresia, regardless of associated abnormalities, have a functional single ventricle, the ultimate treatment is a Fontan operation, in which all systemic venous return goes directly to the pulmonary arteries (without passing through a ventricle) and pulmonary venous return goes to the left atrium and left ventricle and out the aorta (normally aligned great arteries) or through the VSD to the right ventricular remnant to the aorta (transposition). Because the Fontan operation depends on low pulmonary resistance to allow systemic venous blood to flow without a pump into the pulmonary arteries, it cannot be carried out until the high pulmonary resistance of the normal newborn has resolved. An intermediary operation, superior cavopulmonary anastomosis (bidirectional Glenn [see Figure 44-3] or hemi-Fontan), is typically performed at 4 to 6 months of age. In this operation, the superior vena cava is connected to the right pulmonary artery so that all venous drainage from the upper body goes to the lungs but inferior vena caval blood mixes with pulmonary venous return and goes to the body. One or 2 years later, the inferior vena cava is connected to the pulmonary arteries by way of an intraatrial baffle or extracardiac conduit, completing the Fontan circuit (see Figure 44-3).

Critical Pulmonic Stenosis

Infants with extreme narrowing of the pulmonic valve orifice (critical pulmonic stenosis) (Figure 44-4) can present with hepatomegaly and cyanosis from right-to-left shunting across the foramen ovale because of right ventricular failure or low right ventricular compliance.

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Figure 44-4 Critical pulmonic stenosis.

Treatment is aimed at relieving obstruction at the pulmonary valve. This is usually accomplished through balloon valvuloplasty in the interventional catheterization laboratory (see Figure 44-4). Before this, patients are often palliated with prostaglandin E1 infusion to maintain ductal patency to increase pulmonary blood flow and reduce cyanosis. If the right ventricular compliance is sufficiently low because of severe hypertrophy or hypoplasia, valvotomy may not be sufficient to provide adequate pulmonary blood flow, and a temporary systemic–pulmonary shunt may be necessary until compliance improves.

Pulmonary Atresia

Pulmonary atresia with intact ventricular septum is a more severe form of critical pulmonary stenosis. This occurs in 0.07 in 1000 live births. Because the severe obstruction occurs during fetal development, the right ventricular hypertrophy causes poor compliance so that the right ventricle stops growing. Thus, patients have a small right ventricle. In many cases, they also have right ventricle-to-coronary artery fistulae. These may lead to perfusion defects of the left ventricle as coronary blood flow is forced retrograde into the aorta from a suprasystemic right ventricle.

The physiology is similar to that of critical pulmonic stenosis, but because the right ventricular size tends to be smaller than that of critical pulmonic stenosis, it is more likely that a systemic-to-pulmonary shunt will be required even when the atretic valve can be perforated and balloon dilated in the catheterization laboratory or when an outflow tract reconstruction can be performed surgically. Many of these patients never achieve significant right ventricular growth and must be treated as functional single ventricles with a Fontan operation (described above with tricuspid atresia).

Ebstein’s Anomaly of the Tricuspid Valve

Ebstein’s anomaly is a rare anatomic abnormality characterized by displacement of the attachment of the septal and posterior leaflets of the tricuspid valve toward the apex of the right ventricle. The lesion constitutes fewer than 1% of congenital cardiac lesions, representing 0.05 in 10,000 live births. Children of mothers taking lithium have a higher incidence of Ebstein’s anomaly. No extracardiac syndromes are associated with it, but it is commonly associated with other cardiac lesions, including interatrial communication (ASD or patent foramen ovale) as well as VSDs, pulmonic stenosis or atresia, and L-transposition of the great arteries.

Downward displacement of the tricuspid valve partitions the right ventricle into an apical right ventricular portion and a proximal atrialized right ventricle (Figure 44-5). The tricuspid valve anterior leaflet becomes large redundant and “sail-like” with variable tricuspid regurgitation. These patients have a high incidence (20%-30%) of preexcitation with accessory pathway.

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Figure 44-5 Ebstein anomaly of the tricuspid valve.

Hemodynamically, Ebstein’s anomaly has a wide range of possible physiologies, depending on the degree of regurgitation or stenosis of the tricuspid valve, the presence of atrial communication, and the degree of right ventricular dysfunction as a result of the dysplastic valve. Thus, patients can present with symptoms of cyanosis, heart failure, or atrial arrhythmias depending on the balance of the aforementioned factors.

Treatment choices depend on the degree of tricuspid regurgitation and presenting symptoms. Patients with mild symptoms do not require intervention and may have a benign natural history. At the other extreme, patients with severe tricuspid regurgitation have high mortality partly related to pulmonary hypoplasia caused by intrauterine cardiomegaly. Survivors past infancy may develop right heart failure in adolescence with cyanosis if an atrial-level communication exists or may have supraventricular tachycardia.

Early surgical intervention has had poor results, but tricuspid annuloplasty and valvuloplasty have had good results in recent years.

Total Anomalous Pulmonary Venous Connection

Total anomalous pulmonary venous connection means connection of all pulmonary veins to somewhere other than the left atrium. Connections to the innominate vein, the portal system of the liver, and the coronary sinus are representative of the main categories noted below (Figure 44-6). This defect comprises 1% to 3% of congenital cardiac lesions. Anatomically, patients are divided among those whose pulmonary veins connect above the diaphragm (70%), below the diaphragm (25%), or in mixed fashion (i.e., to more than one connection; 5%). Those connecting above the diaphragm are further divided into those connecting to a vein, most often the innominate vein, and those connecting to the heart, either the coronary sinus or the right atrium. The majority of these are unobstructed. Connection below the diaphragm is almost always to the portal vein or one of its branches or to the ductus venosus; hence, they become obstructed when the ductus venosus closes in the first few days of life.

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Figure 44-6 Total anomalous pulmonary venous connection.

The degree of cyanosis depends on the amount of pulmonary venous obstruction. Patients with significant obstruction present with marked cyanosis from decreased pulmonary blood flow accentuated by pulmonary edema and pulmonary arterial hypertension; they also show tachypnea and respiratory distress. Patients without obstruction have high pulmonary blood flow and initially have minimal cyanosis, but they progress to congestive heart failure because of pulmonary overcirculation.

Therapy is surgical with anastomosis of the pulmonary vein confluence to the left atrium in those with extracardiac anomalous connection, unroofing of the coronary sinus in the coronary sinus type, and repositioning of the atrial septum in the right atrial type. With pulmonary vein obstruction, therapy is urgent. With unobstructed veins, there is no technical surgical advantage in waiting, but increasing evidence suggests that delaying surgery until 1 month of age will improve neurocognitive outcomes. Perioperative mortality remains much higher in patients with pulmonary vein obstruction (20%) versus those without obstruction (<5%).

Truncus Arteriosus Communis

Truncus arteriosus communis denotes a single arterial trunk that serves as the common origin of the aorta, pulmonary artery, and coronary arteries (Figure 44-7). It comprises 2% to 2.8% of congenital cardiac lesions. This condition is almost always associated with a VSD. The truncus is fed by a single truncal valve, most commonly with three cusps, but may have two to five cusps, often myxomatous and asymmetric. This truncal valve typically sits over the VSD but in rare cases arises predominantly above the right ventricle. Associated cardiac defects include right aortic arch (33%) and anomalous coronary artery origins. Extracardiac anomalies associated with truncus include 22q11 microdeletion. The physiology of truncus is usually that of high pulmonary blood flow with minimal cyanosis but commonly tachypnea and respiratory distress. Congestive heart failure is exaggerated by poor coronary perfusion secondary to low diastolic pressures from runoff into the pulmonary arteries.

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Figure 44-7 Truncus arteriosus communis.

Treatment is surgical separation of aorta and pulmonary artery, placement of an extracardiac right ventricle to pulmonary artery conduit, and closing the VSD by baffling the left ventricle to the aorta (see Figure 44-7).

Future Directions

Progress in the management of patients with cyanotic heart disease is ongoing and reflects the wide range of clinical disciplines involved in the care of these patients. Noninvasive imaging technologies such as magnetic resonance imaging and computed tomography provide increasingly detailed anatomic and physiologic information, directing medical and surgical care without the risk of more invasive modalities. Treatment continues to improve survival after surgical therapy. These include improvements in surgical technique, intensive care unit management, and long-term medical management. Additionally, hybrid procedures combining conventional surgical and percutaneous catheterization techniques (both pre- and postnatally) are being attempted as part of experimental protocols. These interventions appear to hold much promise, but it remains an empiric question whether these procedures will represent an improvement over conventional surgical techniques or have applicability in wider practice. Finally, with dramatically improved postsurgical survival, research has expanded beyond actuarial survival to define characteristics of patients that differentiate the success or failure of therapy far beyond the immediate postsurgical period such as objective measures of quality of life and neurodevelopmental outcomes.

Suggested Readings

Ballweg JA, Wernovsky G, Gaynor JW. Neurodevelopmental outcomes following congenital heart surgery. Pediatr Cardiol. 2007;28(2):126-133.

Beghetti M, Galie N. Eisenmenger syndrome a clinical perspective in a new therapeutic era of pulmonary arterial hypertension. J Am Coll Cardiol. 2009;53(9):733-740.

Cohen MS, Frommelt MA. Does fetal diagnosis make a difference? Clin Perinatol. 2005;32(4):877-890.

Crean A. Cardiovascular MR and CT in congenital heart disease. Heart. 2007;93(12):1637-1647.

Dorfman AT, Marino BS, Wernovsky G, et al. Critical heart disease in the neonate: presentation and outcome at a tertiary care center. Pediatr Crit Care Med. 2008;9(2):193-202.

Marino BS, Tomlinson RS, Drotar D, et al. Quality-of-life concerns differ among patients, parents, and medical providers in children and adolescents with congenital and acquired heart disease. Pediatrics. 2009;123(4):e708-e715.

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