Cardiology Secrets

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Chapter 6

Cardiology Secrets

History of Pediatric Cardiology

The first successful ligation of a PDA was by Gross and Hubbard in 1938.

Dr. Alfred Blalock (Professor of Surgery at Johns Hopkins), Dr. Helen Taussig (Director of the Pediatric Cardiology Clinic at Johns Hopkins), and Mr. Vivien Thomas (Research Assistant for Dr. Blalock at Johns Hopkins). Their tireless work contributed to the successful research and techniques behind the Blalock–Taussig shunt. The first successful operation occurred in November 1944.

Christiaan Barnard performed the first cardiac transplantation in South Africa in 1967. Infant heart transplantation was attempted unsuccessfully 3 days later by Adrian Kantrowitz in New York City. Neonatal heart transplantation would not be achieved, however, until November 15, 1985, by Leonard Bailey at Loma Linda Medical Center. ∗†

Fetal Echocardiography and Prenatal Conditions that Can Contribute to Neonatal Heart Disease

Maternal indications:

Fetal indications:

The incidence of congenital heart disease is 0.8%. The recurrence risk with a prior sibling with a cardiovascular anomaly is between 1% and 4%.

Table 6-1 lists common genetic and chromosomal syndromes associated with congenital heart disease.

TABLE 6-1

COMMON GENETIC OR CHROMOSOMAL SYNDROMES ASSOCIATED WITH CONGENITAL HEART DISEASE

GENETIC OR CHROMOSOMAL SYNDROME COMMON CARDIAC ANATOMIC LESION
Apert syndrome Ventricular septal defect, coarctation of the aorta, tetralogy of Fallot
Beckwith–Wiedemann syndrome Atrial septal defect, ventricular septal defect, hypertrophic cardiomyopathy
CHARGE syndrome Endocardial cushion defect, ventricular septal defect, double outlet right ventricle, tetralogy of Fallot
DiGeorge syndrome Interrupted aortic arch, truncus arteriosus, tetralogy of Fallot, right aortic arch, ventricular septal defect, aberrant right subclavian artery
Ellis–van Creveld syndrome Atrial septal defect, single/common atrium
Holt–Oram syndrome Atrial septal defect, ventricular septal defect
Kartagener syndrome Mirror image dextrocardia
Marfan syndrome Dilated aortic root, mitral valve prolapse, tricuspid valve prolapse
Neurofibromatosis Atrial septal defect, coarctation of the aorta, interrupted aortic arch, pulmonic stenosis, ventricular septal defect, complete heart block, hypertrophic cardiomyopathy
Noonan syndrome Pulmonary stenosis, hypertrophic cardiomyopathy, tetralogy of Fallot
Pentalogy of Cantrell Atrial septal defect, ventricular septal defect, total anomalous pulmonary venous drainage, tetralogy of Fallot, ectopia cordis
Pierre Robin syndrome Pulmonary stenosis, atrial septal defect
Thrombocytopenia absent radius (TAR) syndrome Atrial septal defect, tetralogy of Fallot
Treacher Collins syndrome Ventricular septal defect, atrial septal defect
Tuberous sclerosis Rhabdomyoma, angioma, coarctation of the aorta, interrupted aortic arch
Trisomy 13 Ventricular septal defect, atrial septal defect, endocardial cushion defect, tetralogy of Fallot
Trisomy 18 Bicuspid aortic valve, pulmonic stenosis, ventricular septal defect, atrial septal defect, endocardial cushion defect, polyvalvular thickening
Trisomy 21 Endocardial cushion defect, ventricular septal defect, atrial septal defect, tetralogy of Fallot, coarctation of the aorta
Turner syndrome Bicuspid aortic valve, coarctation of the aorta, aortic stenosis, ventricular septal defect, atrial septal defect
VACTERL syndrome Ventricular septal defect, atrial septal defect, tetralogy of Fallot
Williams syndrome Supravalvular aortic or pulmonic stenosis
Wolf–Hirschhorn syndrome Atrial septal defect, ventricular septal defect

Adapted from Drose J. Fetal echocardiography. 1st ed. Philadelphia: Saunders; 1988.

Table 6-2 lists teratogens known to cause congenital heart disease. ∗†‡

TABLE 6-2

TERATOGENS THAT CAUSE CONGENITAL HEART DISEASE

TERATOGEN COMMON CARDIAC ANATOMIC LESION
Fetal alcohol syndrome Ventricular septal defect, atrial septal defect, tetralogy of Fallot, coarctation of the aorta
Fetal hydantoin (Dilantin) syndrome Ventricular septal defect, tetralogy of Fallot, pulmonic stenosis, patent ductus arteriosus, atrial septal defect, coarctation of the aorta
Fetal trimethadione syndrome Ventricular septal defect, d-transposition of the great vessels, tetralogy of Fallot, hypoplastic left heart syndrome, double outlet right ventricle, pulmonary atresia, atrial septal defect, aortic stenosis, pulmonic stenosis
Fetal carbamazepine syndrome Ventricular septal defect, tetralogy of Fallot
Valproic acid Ventricular septal defect, coarctation of the aorta, interrupted aortic arch, tetralogy of Fallot, hypoplastic left heart syndrome, aortic stenosis, atrial septal defect, pulmonary atresia
Retinoic acid embryopathy Conotruncal malformations
Thalidomide embyropathy Conotruncal malformations
Maternal phenylketonuria (PKU) (fetal effects) Tetralogy of Fallot, ventricular septal defect, coarctation of the aorta
Maternal systemic lupus erythematosus/Sjögren syndrome (fetal effects) Complete congenital heart block, dilated cardiomyopathy
Fetal rubella syndrome Patent ductus arteriosus, peripheral pulmonary artery stenosis
Maternal diabetes Hypertrophic cardiomyopathy, conotruncal abnormalities

Table adapted from Drose J. Fetal echocardiography. 1st ed. Philadelphia: Saunders; 1988.

image KEY POINTS: PHYSIOLOGIC VARIABLES IN FETAL AND PERINATAL LIFE

The fossa ovalis is composed of the septum primum overlying the septum secundum in the left atrium. In fetal life the right atrial pressure is greater than the left atrial pressure, causing the fossa ovalis to remain patent. After birth, with the increase in pulmonary blood flow and pulmonary venous return to the left atrium, the left atrial pressure increases and causes the septum primum to close against the septum secundum, thereby closing the fossa ovalis. This functional closure of the fossa ovalis occurs within the first few days after birth. This change is followed by complete obliteration of the fossa ovalis shunt at approximately 4 months after birth.

Pulmonary vascular resistance = pulmonary artery pressure/pulmonary blood flow

The very high PVR in the fetus results in low pulmonary blood flow, with diversion of the right ventricular blood away from the pulmonary vascular bed and towards the systemic vascular bed through the ductus arteriosus. This dynamic results in increased thickness of the muscular medial layer of the pulmonary arteries. As a newborn’s lungs expand, they inspire oxygen, which is a potent vasodilator that causes the pulmonary vascular resistance to fall. The rise in the PaO2 causes the smooth muscle in the pulmonary circulation to relax, and vasodilation occurs. The PVR falls dramatically during the first week of life. As the smooth muscle of the pulmonary arteries continues to thin, the PVR continues to fall, reaching a nadir at 6 to 8 weeks after delivery. ∗

image KEY POINTS: ECHOCARDIOGRAPHIC ASSESSMENT OF VENTRICULAR FUNCTION AND PULMONARY HYPERTENSION

It is a noninvasive method that qualitatively and quantitatively assesses right and left ventricular systolic and diastolic function.

It can be used for noninvasive assessment of right ventricular/pulmonary artery pressure by evaluating the tricuspid regurgitation velocity and the ventricular septal contour.

14. Name three scenarios in which a right-to-left shunt is seen in the infant with a PDA.

image A healthy newborn can have right-to-left shunting through the ductus arteriosus during the first 24 hours after delivery with the transitional circulation. If this flow occurs, the right-to-left shunting usually occurs in early systole and is brief in duration.

image A newborn with left-sided obstructive lesions (such as coarctation of the aorta, interrupted aortic arch, severe aortic stenosis, or hypoplastic left heart syndrome [HLHS]) will have right-to-left shunting through the ductus arteriosus in systole and left-to-right shunting in late systole and in diastole. The right-to-left shunting bypasses the level of flow obstruction and provides systemic blood flow.

image Infants with high PVR (e.g., persistent pulmonary hypertension of the newborn or congenital heart disease complicated by marked elevation of PVR) may have right-to-left shunting through the ductus arteriosus.

The modified Bernoulli equation enables one to calculate the pressure difference across an area of stenosis or between two cardiac chambers using the velocity of blood flow across the areas of interest. Pressure 1− Pressure 2 = 4 (V2 − V12). The pressure gradient is measured in mmHg, and the velocity is measured in meters/sec. Because V1 is assumed to be of low velocity (< 1 m/sec), it can be ignored and the formula can be approximated as Pressure 1− Pressure 2 = 4 (Vmax2).

This formula allows the pulmonary artery pressure to be estimated. Two examples are as follows:

image If the velocity across a tricuspid regurgitant jet is 4 m/sec, the calculated right ventricular pressure will be 64 mmHg [P = 4 × (V max2) which is 4 × (42)= 64 mmHg]. By adding an estimation of right atrial pressure (usually use 5 mmHg), the estimated right ventricular pressure (as well as a pulmonary artery pressure in the absence of pulmonary stenosis) would be 69 mmHg. Therefore this patient has pulmonary hypertension.

image If the jet velocity across a ventricular septal defect (VSD) is 4 m/sec, the calculated pressure difference between the right and left ventricles would be 64 mmHg [P = 4 x (42)= 64 mmHg). In a patient with a systolic blood pressure of 80 mmHg, the right ventricular pressure can be estimated by subtracting the calculated pressure difference between the ventricles from the systolic blood pressure (systolic arm blood pressure 80 mmHg − 64 mmHg = 16 mmHg (right ventricular pressure). In this patient the right ventricular pressure and the pulmonary artery pressure would be normal.

17. What is the definition of the echocardiographic term shortening fraction?

Shortening fraction is the percentage change in the internal diameter of the left ventricle dimension from end-diastole to end-systole. It is a measure of cardiac function. Preload, contractility, and afterload all influence the shortening fraction.

The formula to measure shortening fraction is as follows:

image

image

Shortening fraction is typically measured by M-mode assessment of the left ventricular dimension in the parasternal short-axis or long-axis views. Shortening fraction less than 28% is consistent with reduced left ventricular systolic function. Shortening fraction greater than 38% is consistent with hyperdynamic left ventricular systolic function. The normal range for shortening fraction is 28% to 38%.

Ejection fraction is the percentage change in the left ventricular volume from end-diastole to end-systole.

Left ventricular ejection fraction can be calculated by M-mode measurements. However, the method recommended by the American Society of Echocardiography to measure ejection fraction is Simpson’s biplane method, which measures end-diastolic and end-systolic volumes in two orthogonal views. The formula is as follows:

image

EF = Ejection fraction. LV = Left ventricular. The normal range for left ventricular ejection fraction is 55% to 70%.

Shortening fraction will be inaccurate when there are regional wall motion abnormalities or septal wall flattening in the presence of right ventricular volume or pressure overload. Ejection fraction, when measured by Simpson’s biplane method, accounts for wall motion abnormalities, although it can be more time consuming to measure.

With a large-pressure nonrestrictive VSD, the right ventricular and pulmonary artery pressures remain high. The right and left ventricular pressures remain equal with a nonrestrictive VSD. As the pressure across the pulmonary vascular bed will not change and the PVR falls, the pulmonary blood flow (PBF) will increase because there is an inverse relationship between PBF and PVR. PBF = Δ Pressure across the pulmonary vascular bed/PVR. Therefore the magnitude of the left-to-right shunt will increase. ∗†

image KEY POINTS: INNOCENT MURMURS

Two theories exist regarding the origin of a PPS murmur. First, the branch pulmonary arteries are relatively small in diameter shortly after birth. Second, the branch pulmonary arteries bifurcate at an acute angle from the main pulmonary artery, creating mild flow turbulence. As the neonate grows, this angle becomes less acute.

image KEY POINTS: PHYSIOLOGY OF THE CYANOTIC NEONATE

Central cyanosis occurs when deoxygenated blood enters the systemic circulation, creating the appearance of cyanosis of the oral mucosa, lips, tongue, and trunk. Cyanotic heart disease with right-to-left cardiac shunting, inadequate ventilation (central nervous system depression or airway obstruction), ventilation/perfusion problems (V/Q mismatch), and pulmonary arteriovenous fistulae are causes of central cyanosis.

Cyanosis may be perceived when there is 5 g of reduced (deoxygenated) hemoglobin in the capillaries. In a neonate cyanosis is observed when the oxygen saturation is below 70%. Neonates have a higher hematocrit level than infants that results in a lower oxygen saturation needed to detect clinical central cyanosis. An experienced observer can sometimes detect cyanosis when the saturation falls between 80% and 85%.

Peripheral cyanosis can occur in states of low cardiac output, even when the arterial saturation is normal. When the cardiac output is low, the arteriovenous oxygen difference widens, leading to an increased amount of reduced hemoglobin in the capillaries. Low output cyanosis is commonly referred to as acrocyanosis. Polycythemia can also cause cyanosis because of the increased levels of reduced hemoglobin in the circulation.

Measuring oxygen saturation at both preductal and postductal sites is part of the initial evaluation in a patient with suspected heart disease. If the preductal oxygen saturation is higher than the postductal oxygen saturation, there is differential cyanosis. This sign occurs when the great arteries are normally related and deoxygenated blood from the pulmonary circulation enters the descending aorta through a PDA (right-to-left shunting). This pattern of cyanosis is seen with persistent pulmonary hypertension of the newborn (PPHN) and with left ventricular outflow obstruction (aortic arch hypoplasia, interrupted aortic arch, critical coarctation, and critical aortic stenosis).

Reversed differential cyanosis occurs when the postductal saturation is higher than the preductal saturation. The classic clinical scenario for reversed differential cyanosis occurs with transposition of the great arteries with preductal aortic arch obstruction or pulmonary hypertension when oxygenated blood from the pulmonary artery enters the descending aorta by right-to-left shunting through the ductus arteriosus. Reversed differential cyanosis also occurs with total anomalous pulmonary venous connection above the diaphragm. It is seen less frequently when there is an anomalous right subclavian artery connected by the ductus to the right pulmonary artery.

Oxygen capacity refers to the maximal amount of oxygen that can be bound to each gram of hemoglobin in blood. (i.e., oxygen capacity = 1.36 mL × hemoglobin level; as each gram of hemoglobin takes up 1.36 mL of oxygen). The total oxygen-carrying capacity is specific to each patient. Oxygen saturation is the amount of oxygen actually bound to hemoglobin compared with the oxygen capacity. It is expressed as a percentage. Oxygen saturation can tell how much oxygen is being carried only if the amount of hemoglobin is known.

The oxygen dissociation curve shows the relationship between oxygen saturation (%) and the partial pressure of oxygen, PO2, in mmHg. This relationship is a sigmoid-shaped curve, with it being fairly flat in the upper range of oxygen saturation (above 85%). Blood pH, temperature, PCO2, 2,3-diphosphoblycerate, and the type of hemoglobin influence the relationship between oxygen saturation and the partial pressure of oxygen ( Fig. 6-2).

A hyperoxia test attempts to differentiate between pulmonary disease with V/Q mismatch and cyanotic congenital heart disease. Initially, one measures the oxygen saturation in room air. If the oxygen saturation is low, the patient should be placed in 100% FiO2. The patient with pulmonary disease will show an increase in PO2 (to a variable degree). In the patient with a fixed intracardiac mixing lesion, the PO2 does not change significantly. A preductal and postductal arterial blood gas result should be obtained. A preductal arterial blood gas result can be obtained from the right radial artery. A postductal arterial blood gas can be obtained either from an umbilical artery or from a lower extremity artery. In pulmonary disease the preductal arterial PO2 in 100% FiO2 usually exceeds 150 mmHg. If the ductus arteriosus is patent and a right-to-left ductal shunt occurs because of high PVR, the postductal PO2 will be lower than the preductal PO2. In addition, the arterial PCO2 is elevated relative to the patient’s respiratory effort.

In cyanotic congenital heart disease (CHD), the PO2 in room air is below 70 mmHg (usually <50 mmHg) and does not change significantly in 100% oxygen. Typically, the arterial PCO2 is normal or low. This finding is the result of hyperventilation that occurs as a response to the hypoxia. Acidosis is typically of a metabolic nature because of abnormal systemic perfusion, tissue hypoxia, or both. In some cases the hyperoxia test must be done with the administration of positive pressure ventilation to expand atelectatic lung adequately to exchange gas.

Common mixing lesions may not be excluded. Examples are total anomalous pulmonary venous return, tetralogy of Fallot with a predominant left-to-right shunt, and HLHS.

As published in Pediatrics in 2011, pulse oximetry assessment of the right hand and a foot is recommended before discharge of all newborns from the hospital. If the oxygen saturation is less than 90% in the right hand or foot, the test is positive and further evaluation is needed. If the oxygen saturation is 95% or greater in the right hand or foot and the difference is 3% or less between the two sites, then the test is negative. If the oxygen saturation is 90% to 95% or greater than 3% difference between the two sites is found, then the test should be repeated in 1 hour up to two times. It is considered a positive screen if these findings are reproduced twice. ∗†‡

image KEY POINTS: CONGESTIVE HEART FAILURE

Severe anemia, bradyarrhythmia, tachyarrhythmia, infection, large systemic arteriovenous (AV) fistula (e.g., vein of Galen AV malformation), and severe atrioventricular valve insufficiency.

Heart failure in infants manifests as signs and symptoms of increased pulmonary blood flow (PBF) or inadequate systemic blood flow. Signs of excessive PBF include tachypnea, sweating, poor feeding, failure to thrive, gallop rhythm, and hepatomegaly. Congenital heart disease may present as shock or catastrophic heart failure in an infant with obstructive left-sided lesions and decreased systemic blood flow. Symptoms may include a loud S2 and decreased peripheral pulses. Assessment of preductal and postductal saturations should be sought.

Ductal-dependent abnormalities:

Non–ductal-dependent abnormalities:

Obstruction to systemic blood flow:

Left-to-right shunt:

Mixing lesions:

Myocardial dysfunction/pericardial disease:

The newborn heart has fewer myofilaments with which to generate the force of contraction. The newborn ventricle has decreased compliance compared with an adult ventricle. Therefore the newborn heart generates less augmentation in stroke volume for a given increase in diastolic volume. The oxygen consumption and cardiac output/m2 are much higher in the newborn, and there is very little systolic reserve. Tachycardia is therefore the usual neonatal response to stress, because any increase in stroke volume is limited.

The goals of treating the neonate depend on the etiology of the CHF. Is the CHF a result of an arrhythmia, myopathic process, decreased systemic blood flow, or increased PBF? The main drugs used to treat CHF in the newborn are inotropic agents, diuretics, and afterload reduction agents. PGE is indicated when ductal-dependent cardiac lesions are diagnosed. Supraventricular arrhythmias with significant heart failure require prompt pharmacologic or electrical cardioversion. CHF secondary to a myopathy should be treated with inotropic agents, diuretics, afterload reduction agents, or a combination thereof.

Compensatory mechanisms include increased heart rate, enhanced stroke volume (Frank–Starling mechanism), sympathetic nerve activation (increased sympathetic tone, renin-angiotensin system activation), increased 2,3-diphosphoglycerate, increased atrial natriuretic peptides, and myocardial hypertrophy. ∗†

image KEY POINTS: TREATMENT OF HYPOTENSION ON THE NEONATE

In the preterm infant the immature cardiovascular system is poorly equipped to handle the transitional circulation from a low vascular resistance circulation, when the placenta is removed, to the sudden presence of a high systemic circulation. The immature myocardium, residual fetal circulatory shunts, cytokine release mediated hypotension, and the impact of positive pressure ventilation on venous return and cardiac output all contribute to inadequate systemic perfusion. However, the primary mechanism of hypotension in a preterm infant is inadequate peripheral vasomotor regulation. Although hypovolemia is a common cause of hypotension in the pediatric population, hypovolemia in sick preterm infants is infrequently the cause of hypotension during the immediate postnatal period.

Preterm neonates have a relative inability to regulate cerebral blood flow compared with those born at term. Hypotension is associated with decreased cerebral blood flow. Hypotension and rapid wide swings in blood pressure have been shown to be predictive of both germinal matrix-intraventricular hemorrhage and periventricular leukomalacia.

In preterm neonates dopamine increases blood pressure primarily through vasoconstriction (increased afterload) as the immature cardiovascular system has an enhanced alpha-adrenergic sensitivity. Dopamine also increases preload by decreasing the venous capacitance, which may also contribute to the beneficial cardiovascular effects of dopamine. Low-dose dopamine (2 to 5 μg/kg/min) has this primary alpha-adrenergic effect. Higher-dose dopamine will have a beta1-adrenergic effect on the myocardium. Dopamine has a renal but not mesenteric or cerebral vascular effect in preterm infants.

Dopamine may be the preferred inotrope in the treatment of hypotension secondary to neonatal sepsis because it increases peripheral vascular contractility. However, dobutamine may be preferred in treatment of hypotension secondary to cardiomyopathy, which frequently occurs with perinatal asphyxia. Whereas dopamine has a greater increase in arterial blood pressure than dobutamine, dobutamine has been shown to increase superior vena cava blood flow and may improve end-organ perfusion to a great extent. ∗†‡

image KEY POINTS: CYANOTIC CONGENITAL HEART DISEASE

D-transposition of the great arteries is the most common form of cyanotic congenital heart disease in the neonate, and accounts for between 6% and 10% of infants with congenital heart disease. In children “outside” the newborn period, tetralogy of Fallot is the most common, representing 7% to 9% of cardiac cases of cyanosis.

The five Ts

The Non-Ts

The screening is performed for the following reasons:

In d-transposition of the great arteries, the aorta arises from the morphologic right ventricle and the pulmonary artery arises from the morphologic left ventricle. Variation in the origin and course of the right and left coronary arteries may occur and can generally be determined by echocardiography before surgery.

The circulation is in parallel instead of a normal in-series circulation. (right atrium→right ventricle→aorta)(pulmonary vein→left atrium→pulmonary artery). The systemic venous blood does not get oxygenated. Survival depends on intercirculatory shunts (atrial septal defect [ASD], VSD, PDA).

Patients with d-transposition of the great arteries may have an intact ventricular septum and exhibit cyanosis in the first hours to days of life. They will develop tachypnea, respiratory distress, and acidosis and die if not treated. Patients with d-transposition of the great arteries with a reasonable VSD may have minimal cyanosis and present with CHF in the first 4 to 8 weeks of life. A smaller group of patients may have transposition of the great arteries, VSD, and pulmonary stenosis and have a more variable presentation.

Prostaglandins keep the ductus arteriosus patent and help assist with the mixing of the circulations, thereby improving oxygenation.

Progressive hypoxemia from poor intercirculatory mixing is a medical emergency. An atrial septostomy may be necessary to improve hypoxemia even after Prostaglandin E1 (PGE) has maintained ductal patency. The balloon atrial septostomy permits unrestricted bidirectional mixing of fully saturated blood in the left atrium with desaturated blood in the right atrium to achieve a higher net saturation of blood in the systemic circulation. After this procedure, patency of the ductus is generally no longer essential. Variations in oxygen saturation can be expected, although mixing is usually excellent.

Tetralogy of Fallot is the most common CHD-related cause of cyanosis beyond 1 year of age. The constellation of anatomic features consists of a VSD, pulmonary stenosis, right ventricular hypertrophy, and overriding of the aorta over the ventricular septum. A right-sided aortic arch may be present in 25% of cases.

The most common clinical manifestation is a murmur secondary to obstruction across the right ventricular outflow tract. The murmur is not caused by the VSD (large defect, equal pressures in both ventricles). Cyanosis depends on the severity of the right ventricular outflow tract obstruction along with the presence or absence of a PDA.

In TAPVR all the pulmonary veins drain into the systemic veins. TAPVR is rare, occurring in 2% to 3% of all cases of congenital heart disease. The different types of total anomalous pulmonary venous return depend on their drainage sites. There is a marked predominance of males for the infracardiac type.

57. What are the different types of TAPVR?

image Supracardiac: represents 50% of all total anomalous pulmonary venous return. The pulmonary veins usually drain into the right superior vena cava via a left vertical vein. Although generally nonobstructive, they can be obstructed in some cases (the vertical vein is “pinched” between the left pulmonary artery and the left bronchus, or at superior vena cava insertion).

image Cardiac: represents 20% of all total anomalous pulmonary venous return. The pulmonary veins drain into the coronary sinus or directly into the right atrium. They can be obstructed (obstruction can occur at the site of the obligate right-to-left atrial shunt) or non-obstructed.

image Infra cardiac: represents 20% of all total anomalous pulmonary venous return. The common pulmonary vein drains below the diaphragm into the portal venous system, ductus venosus, inferior vena cava, or hepatic veins. These veins are almost always obstructed.

image Mixed: represents 10% of all total anomalous pulmonary venous return. It represents a combination of the other types of TAPVR ( Fig. 6-3).

The different presentations of TAPVR depend on whether or not the pulmonary veins are obstructed. Neonates with obstructed TAPVR present within the first few hours of life with severe pulmonary venous congestion, tachypnea, tachycardia, and cyanosis. The clinical picture of obstructed TAPVR may be indistinguishable from that of severe respiratory distress syndrome (RDS). In infants with nonobstructed total anomalous pulmonary veins, tachypnea develops gradually, with a typical presentation occurring in approximately 4 to 6 weeks.

In the absence of an atrial communication in TAPVR, blood cannot get to the left atrium or left ventricle and out the aorta to provide any cardiac output. An ASD is necessary for survival with this lesion. An echocardiogram should demonstrate right ventricular hypertrophy and a right-to-left shunt via a patent foramen ovale (PFO).

In patients with obstructed TAPVR, cardiac surgery is an emergency and involves anastamosis of the common pulmonary vein to the left atrium. Nonobstructive TAPVR can be managed semi-electively, with the key factor being initial control of CHF.

Scimitar syndrome has the following components: right lung hypoplasia, anomalous connection of the right pulmonary veins to the inferior vena cava, right pulmonary artery hypoplasia, anomalous systemic arterial supply to the right lung, bronchial anomalies, and dextroposition of the heart, reflecting the hypoplastic right lung. The term scimitar syndrome derives from a feature on the chest x-ray: the right pulmonary veins cast a shadow resembling the handle of a scimitar in the right lower zone as they drain anomalously into the inferior vena cava.

In truncus arteriosus one large vessel arises from the heart. The coronary arteries, pulmonary arteries, and systemic arteries arise from a single common trunk. A VSD is always present. The truncal valve may be stenotic or regurgitant.

Cyanosis may or may not be seen immediately after birth. Signs of CHF develop days to several weeks after birth as the PVR falls, increasing PBF. Cyanosis may be minimal secondary to high PBF. Tachypnea or difficulty feeding can be a sign of CHF. With truncal stenosis there can be a systolic ejection murmur. There is a single second heart sound. The pulses are bounding, and significant truncal regurgitation will generally produce a widened pulse pressure with a prominent diastolic murmur.

DiGeorge syndrome with hypocalcemia is present in approximately one third of cases with truncus arteriosus. Attention to the presence of a thymic shadow should be sought on the chest radiograph.

Infants with HLHS can present within the first few hours to days of life. Clinical symptoms depend on the status of the inter-atrial communication, patency of the ductus, PVR, and potentially the degree of AV valve competency. Common clinical signs are tachypnea, hepatomegaly, pulmonary rales, and a single second heart sound (S2). Cyanosis may be minimal. Closure of the ductus will result in decreased peripheral pulses and a “shock-like” picture ( Fig. 6-4).

Management of HLHS requires correction of acidosis; prostaglandins; avoidance of hyperventilation; and most important, maintenance of adequate systemic perfusion. Generally, supplemental oxygen is unnecessary. Echocardiography should assess the ventricular function, patency of the ductus, and adequacy of the inter-atrial communication.

The key is an abnormal frontal plane axis. A leftward axis for a newborn (i.e., left superior axis −90 to 0 [see Fig. 6-5]) strongly implies a structural anomaly of the heart. Dominant left ventricular forces often accompany this anomaly. The differential diagnosis includes tricuspid atresia, pulmonary valve atresia with intact ventricular septum, critical pulmonary stenosis, or complex single left ventricle.

A rightward superior/northwest axis (i.e. −90 to −180 degrees) suggests an AV canal defect. Note: A normal electrocardiographic reading does not rule out CHD.

68. What are some common chest x-ray findings in infants with cyanotic congenital heart lesions?

image d-transposition of the great arteries with an intact ventricular septum: Cardiomegaly with increased pulmonary vascular markings. Egg-shaped cardiac silhouette, with a narrow, superior mediastinum.

image Tetralogy of Fallot : Normal heart size or smaller than normal. Decreased pulmonary vascular markings, concave main pulmonary artery segment with an upturned apex (boot-shaped heart). This can have a right-sided aortic arch.

image Total anomalous pulmonary venous return: Cardiomegaly with right atrial and ventricular enlargement. Increased pulmonary vascular markings. “Snowman” heart can be seen with supracardiac, unobstructed veins (usually seen after several months). With pulmonary venous obstruction there is radiographic evidence of pulmonary edema (diffuse reticular pattern).

image Tricuspid atresia: Normal size, or mild cardiomegaly. Straight right heart border. Decreased pulmonary vascular markings.

image Pulmonary atresia: Normal size, or mild cardiomegaly. Right atrial enlargement. Decreased pulmonary vascular markings.

image Ebstein anomaly of the tricuspid valve: In severe cases the heart is enormous, balloon shaped, and occupies almost the entire cardiothoracic area ( Figs. 6-6 and 6-7).

image Truncus arteriosus: Cardiomegaly, with increased pulmonary vascular markings. Right-sided aortic arch may be seen (30% of cases).

image Single ventricle: Depends on presence or absence of pulmonary stenosis. Can have cardiomegaly with increased pulmonary vascular markings, or a relatively normal-sized heart with decreased pulmonary vascular markings.

image KEY POINTS: ACYANOTIC AND OBSTRUCTIVE CONGENITAL HEART LESIONS

AV septal defects (also commonly called endocardial cushion defects or AV canal defects) are common in children with Down syndrome. Endocardial cushion defects can be complete with large ventricular and atrial components or incomplete with just a defect in the septum primum and a smaller VSD. AV canal defects of any variety have a cleft in the mitral valve. Competency of the AV valve should be assessed by echocardiography.

Infants with a VSD are usually identified after they leave the hospital because both the heart murmur of a VSD and the symptoms of heart failure do not appear during the first few days of life. In the immediate postnatal period, the PVR is still elevated, thereby limiting the shunting of blood from the left ventricle into the right ventricle and across the pulmonary bed. As the PVR falls (PVR↓), an increased volume of blood flows through the defect, which increases the intensity of the murmur and the amount of PBF (↑PBF).

Pulmonary stenosis in a neonate that is sufficiently severe to cause cyanosis and acidosis (rare) with signs of right-sided heart failure (rare) is defined as critical pulmonary stenosis. Ductal patency is essential for maintaining PBF. The degree of pulmonary stenosis can be measured by echocardiography. Pulmonary balloon valvuloplasty, in the cardiac catheterization laboratory, is undertaken to relieve the stenosis after stabilization of the infant.

Aortic stenosis in a neonate that results in CHF with circulatory shock (acidosis and poor peripheral pulses) is termed critical aortic stenosis. In affected infants the systemic circulation depends on the patency of the ductus arteriosus with flow from the pulmonary artery into the descending aorta. These infants are ductal dependent to provide cardiac output. In some infants inotropic support, ventilation, and correction of acidosis may be required. The aortic valve can be tricuspid, bicuspid, or unicuspid. Aortic stenosis may be a component of other left-sided anomalies. Echocardiography should assess not only the architecture of the aortic valve but also the mitral valve architecture and the degree, if any, of left ventricular hypoplasia. Most infants are palliated by an aortic balloon valvuloplasty; however, long-term follow-up is mandatory.

Neonatal coarctation of the aorta is obstruction in the thoracic aorta or the transverse aortic arch and requires patency of the ductus arteriosus to maintain cardiac output. Typically, these infants become symptomatic when the ductus arteriosus closes. A murmur may be present. Four-extremity blood pressure measurements should be obtained, with careful attention to the right arm and lower extremities. In extreme cases affected infants have signs and symptoms of acute circulatory shock, with decreased or absent femoral pulses. Neonates with circulatory collapse should be fully resuscitated before surgery with correction of acidosis. Prostaglandins should be administered to reestablish ductal patency, because there is an obligate right-to-left ductal shunt. In neonates with critical coarctation (ductal dependent), surgery is required and can generally be performed by a left thoracotomy.

The likelihood of congenital heart disease is between 90% and 95%. This condition is referred to as dextrocardia.

VSD and PDA are commonly present.

DiGeorge syndrome (22q11 Deletion Syndrome) is a constellation of clinical symptoms that includes a lack of thymus gland and a lack of parathyroid (hypocalcemia), with certain common conotruncal heart defects. A similar syndrome (velocardiofacial syndrome) may have associated midline facial defects (i.e., cleft palate) with a lower proclivity for thymic deficiency. ∗†‡

image KEY POINTS: VASCULAR RINGS

A complete vascular ring is formed by abnormal vascular structures completely encircling the trachea and esophagus (e.g., double aortic arch and a right aortic arch with a left-sided ligamentum arteriosum). An incomplete vascular ring occurs when there is vascular compression of the trachea and esophagus without completely encircling these structures (e.g., innominate artery compression and pulmonary sling).

Most infants with vascular rings present with symptoms within the first several weeks to months of life, with a double aortic arch and pulmonary sling being symptomatic earlier than the other rings. Infants may hold their heads hyperextended to alleviate the symptoms of airway obstruction. Symptoms of respiratory distress, stridor, “seal bark” cough, apnea, dysphagia, and recurrent respiratory infections may occur. Dysphagia may first be detected when infants transition from liquid formula to solid food ( Fig. 6-8).

Double aortic arch is the most common vascular ring (40%). A right-sided aortic arch with a left ligamentum is the second most common vascular ring (30%).

Surgical intervention is indicated in all symptomatic patients with vascular rings. Symptoms include respiratory distress, recurrent respiratory infections, dysphagia, and apneic spells.

Initial evaluation for a vascular ring should be a chest x-ray. Additional imaging, including a barium swallow and echocardiogram, is helpful in this diagnosis of a vascular ring. However, computed tomography angiography, which can now be done rapidly and therefore does not require general anesthesia, is considered by most institutions to be the single best diagnostic test when a vascular ring is suspected. Magnetic resonance imaging is the preferred diagnostic test at other centers. Bronchoscopy is extremely helpful in assessing the airway compromise.

87. How does a surgeon repair some of the more common forms of vascular rings?

image Double aortic arch: A thoracotomy is performed on the side opposite the dominant aortic arch (typically a left thoracotomy). The lesser arch is clamped, divided, and oversewn. The ligamentum arteriosum is always ligated and divided. Dissection around the esophagus and trachea to lyse any residual adhesive bands is performed.

image Right aortic arch and left ligamentum arteriosum: A left thoracotomy is performed with dissection and lysis of any residual adhesive bands around the esophagus and trachea.

image Pulmonary artery sling: Transection of the left pulmonary artery with translocation of the left pulmonary artery anterior to the trachea to its normal position arising from the main pulmonary artery. A barium swallow will reveal an anterior indentation of the esophagous on the lateral projection. ∗†‡

image KEY POINTS: SEGMENTAL CARDIAC AND CARDIAC MALPOSITION ANALYSIS

The segmental approach to the classification of congenital heart disease was originally proposed by Dr. Richard Van Praagh and colleagues in the 1960s and early 1970s. The three main cardiac segments are (1) atria, (2) ventricles, and (3) great arteries. Therefore congenital heart disease is expressed in these three segments.

Normal cardiac segmental anatomy is {S, D, S}.

Because depolarization occurs in the left ventricle before the right ventricle, the presence/location of the Q waves over the precordium can assist in the anatomic location of the left ventricle and right ventricle. If Q waves are seen in V5 and V6, and lead 1, the left ventricle is D-looped and on the left side. If Q waves are seen in V4R, V1 and V2, but not seen in V5 and V6, it is likely that the ventricles are L-looped (Figs. 6-9 and 6-10).

The chest x-ray, electrocardiography, and echocardiogram are three modalities that can help locate the position of the atria.

The atrial sidedness follows the visceral organ arrangement.

The word heterotaxy means “different arrangement.” There is abnormal relationship and arrangement of the cardiac atria and the thoracoabdominal organs, including the spleen, lungs and intestines. Polysplenia (associated with left atrial isomerism) or asplenia (right atrial isomerism) is present. These patients are at high risk for malrotation of the intestines, which should be investigated with ultrasound or barium study. The cardiac malformations are complex typically, with abnormal venoatrial connections ( Fig. 6-11).

The sinoatrial node (the pacemaker of the heart) is located in the right atrium. The p wave axis on the electrocardiogram will determine from where the sinoatrial node pulse is originating and therefore where the sinoatrial node and right atrium are located.

The coronary sinus and the suprahepatic portion of the inferior vena cava drain to the right atrium. In atrial situs solitus the systemic veins (superior and inferior vena cavae) drain to the right atrium, and the pulmonary veins drain to the left atrium. However, the most reliable echocardiographic marker of the right atrium is the drainage of the coronary sinus and the suprahepatic inferior vena cava.

Dextrocardia is a condition in which the heart lies in the right side of the chest. It may occur with dextroposition, when the heart is pushed into the right side of the chest (e.g., left-sided diaphragmatic hernia or hypoplastic right lung). It also may occur when the cardiac apex is directed to the right side of the patient. This term does not define the segmental atrioventricular or ventriculoarterial relationships.

Mesocardia occurs when the heart occupies the midline of the thorax. ∗†‡

image KEY POINTS: FEEDING NEONATES WITH CHD

There are noticeable variations in strategies for preoperative feeding management between providers. Approximately 56% of clinicians will provide enteral feedings to neonates with ductal-dependent CHD. Clinicians practicing outside the United States are eight times more likely to enterally feed ductal-dependent neonates than clinicians practicing in the United States. Clinical assessment, arterial blood gas assessment, blood lactate level, diastolic blood pressure, echocardiogram, abdominal x-ray, and abdominal near-infrared spectroscopy may be helpful in making this decision.

The most commonly reported reason for exercising caution when feeding neonates with ductal-dependent CHD is the theoretical risk of intestinal hypoperfusion, which may lead to necrotizing enterocolitis. The two most common findings seen in neonates with CHD and necrotizing enterocolits are widened pulse pressure and low diastolic blood pressure, which are seen in patients with retrograde diastolic flow in the descending aorta. ∗†‡

Cardiac Surgery

The modified Blalock–Taussig shunt is a Gore-Tex interposition shunt placed between the subclavian artery (right or left) and the right or left pulmonary artery. It is used for congenital heart lesions that require increased PBF in the neonatal and infancy periods. Examples include lesions with a hypoplastic pulmonary annulus, atretic pulmonary valve annulus, or severely hypoplastic main and branch pulmonary arteries. The cardiac malformations in such instances would include severe tetralogy of Fallot, tetralogy of Fallot with pulmonary atresia, tricuspid atresia, pulmonary atresia with VSD, and pulmonary atresia with intact ventricular septum. A modified Blalock–Taussig shunt is used in the first stage of HLHS repair (modified Norwood operation) ( Fig. 6-12).

The modified Blalock–Taussig, the bidirectional Glenn procedure, and the Sano modification of the Norwood operation are the most common types of shunts used today. The Waterston shunt (anastomosis from the ascending aorta to the right pulmonary artery) and the Potts shunt (anastomosis from the descending aorta to the left pulmonary artery) shunts are no longer used.

A bidirectional Glenn anastomosis is a connection from the right superior vena cava to the right pulmonary artery, or the left superior vena cava to the left pulmonary artery, or both (bicaval bidirectional Glenn anastomosis). The pulmonary arteries are in continuity, so a right bidirectional Glenn anastomosis connection will send blood flow into the right and the left pulmonary arteries. This anastomosis is usually the intermediate step to a Fontan procedure. Lesions for which a bidirectional Glenn procedure is used include those with single ventricle anatomy (HLHS, hypoplastic right heart syndrome, tricuspid atresia, and pulmonary atresia).

In neonates coarctation of the aorta is generally approached through a left thoracotomy. In older children a primary catheter balloon intervention may be considered. The three standard surgical approaches involve resection and end-to-end anastamosis (most common), subclavian flap repair (ligation of distal subclavian artery to use the proximal portion to overlay patch the coarctation segment), or patching with foreign material (Dacron).

The Jatene procedure (arterial switch) is performed for d-transposition of the great arteries. The coronary arteries are removed from the aorta and re-implanted into the pulmonary artery, which becomes the new aorta.

Left ventricular dysfunction, supraventricular arrhythmias, and supravalvar aortic and pulmonary stenosis are all potential complications. Both left ventricular dysfunction and arrhythmias may be a sign of coronary insufficiency. In patients with transposition of the great arteries and a VSD, a residual VSD should be ruled out by echocardiography. The presence of ventricular arrhythmias should also elicit questions regarding the adequacy of the ventricular function and coronary re-implantation.

The modified Norwood procedure is performed as follows:

image A. Stage 1: Anastomosis of the proximal main pulmonary artery to the aorta, with aortic arch reconstruction and trans-section and patch closure of the distal main pulmonary artery; a modified right Blalock–Taussig shunt (right subclavian artery to right pulmonary artery) to provide PBF, and lastly, atrial septectomy to allow for adequate left-to-right atrial communication.

image A. Stage 1 (alternate approach): In some centers a Norwood–Sano operation is performed as a first stage. In this operation the modified Blalock–Taussig shunt is replaced with a right ventricle to main pulmonary artery connection (Sano modification) to provide PBF.

image B. Stage 2: Bidirectional Glenn anastomosis (approximately 4 to 6 months)

image C. Stage 3: Completion of a Fontan operation (approximately 1 to 2 years)

Tachycardia, decrease in oxygen saturation, increase in cardiac filling pressures, abrupt decrease in chest tube drainage, increasing cardiac size on chest x-ray, and poor perfusion are all warning signs of postoperative cardiac tamponade. Abrupt resolution of postoperative bleeding should prompt consideration for development of a pericardial effusion. Pulsus paradoxus may not be evident in mechanically ventilated patients unless they are spontaneously breathing.

The infant should be kept deeply sedated and generally paralyzed. The wound should be covered. Lung tidal volume should be adjusted appropriately so that the lung does not herniate. Monitored cardiac pressures are usually low. These patients require broad-spectrum antibiotic coverage. Before the chest is closed, vigorous diuresis is usually required. When the chest is eventually closed, all of the intravascular pressures will increase, airway compliance will increase, and tidal volume should be adjusted downward.

Junctional ectopic tachycardia (JET) is a common arrhythmia after surgery. The rhythm generally occurs in the first 24 to 48 hours following surgery. Typical electrocardiographic findings include AV dissociation and narrow QRS morphology with a rapid QRS rate (170 to 210 bpm). Treatment for JET involves slowing the ectopic rate to allow restoration of AV synchrony. Core temperature cooling (i.e., 35 to 36° C) has been effective. Amiodarone has also been used to slow the junctional rate so as to allow temporary pacing to restore AV synchrony. Typically, as the infant recovers from surgery with less need for intravenous inotropic support, the JET resolves.

Extracorporeal membrane organization (ECMO) can provide a means to assist the heart and lungs (or both) temporarily. Venoarterial ECMO is used in neonatal patients with either life-threatening pulmonary disease (congenital diaphragmatic hernia, or persistent fetal circulation) or neonates with postoperative ventricular failure. ∗†‡§

image KEY POINTS: PREOPERATIVE STABILIZATION

In critical congenital heart lesions the ultimate outcome depends on timely and accurate assessment of the structural anomaly and on evaluation and resuscitation of secondary organ damage. The principles of preoperative management are as follows:

The starting dose of PGE1 is 0.05 to 0.1 μg/kg/min. This drug should be administered using a continuous intravenous drip, preferentially through an umbilical venous line, or a well-functioning intravenous line. Once the effects of PGE1 are seen (improved oxygen saturations, decreased acidemia), the dose can be slowly reduced to 0.01 μg/kg/min.

113. What are the neonatal presentations of CHD?

114. In which patients should PGE1 be used?

115. What are some of the side effects of PGE1?

Side effects of PGE1 include the following:

Side effects may be more complex in infants weighing less than 2 kg.

In lesions with right ventricular outflow obstruction, the ductus arteriosus helps improve PBF by shunting blood into the pulmonary arteries, (e.g., tetralogy of Fallot with severe pulmonary valvar or subvalvar obstruction, tricuspid atresia, pulmonary atresia). In lesions with left ventricular outflow obstruction (e.g., HLHS, critical aortic stenosis, neonatal coarctation of the aorta), the ductus arteriosus maintains cardiac output to the systemic bed, optimizing myocardial perfusion.

Patients with PPHN may fail to demonstrate a significant rise in PaO2 secondary to right→left shunting. Patients with PPHN have oligemic lung fields on chest radiograph. Approximately 10% of neonates on venoarterial ECMO for respiratory distress and PPHN will have unsuspected CHD.

Genetic testing with fluorescence in situ hybridization (FISH) analysis should be considered, especially if a conotruncal abnormality is present. Abdominal ultrasound should be considered if there is any association of known renal, splenic, or situs concerns. Laboratory studies including renal and hepatic function should be evaluated to look for end-organ dysfunction. A head ultrasound or other central nervous system imaging modality may be considered, especially if there were any in utero concerns.

Neonates with sepsis will demonstrate similar clinical findings to those of neonates with ductal-dependent systemic CHD. Antibiotic delivery will have little impact in this cohort. Patency of the ductus is critical in the group with CHD to maintain coronary perfusion and prevent myocardial ischemia. ∗†

image KEY POINTS: POSTOPERATIVE MANAGEMENT

120. What information is needed to care for the neonate with congenital heart disease after cardiothoracic surgery?

121. What is the purpose of the postoperative echocardiogram?

The postoperative echocardiogram, most commonly transesophageal, should assess for the following:

See Table 6-3.

TABLE 6-3

NONCARDIAC CAUSES OF RESPIRATORY COMPROMISE AFTER CARDIOTHORACIC SURGERY 2

Central nervous system Neuromuscular
1. General anesthesia 1. Residual neuromuscular blockade
2. Administration of analgesics or sedative/hypnotics 2. Respiratory muscle weakness—from disuse and/or malnutrition
3. Hypoxic-ischemic encephalopathy Alveolar disease
4. Apnea of prematurity 1. Acute lung injury from cardiopulmonary bypass
Isolated neuropathies
1. Hemidiaphragmatic paresis or paralysis – phrenic nerve injury		 2. Increased lung fluid from left-to-right shunt lesions
3. Atelectasis
2. Vocal cord paralysis – recurrent 4. Pneumonia
Airway abnormalities proximal to the alveoli 5. Pulmonary hemorrhage
1. Tracheostomy or endotracheal tube obstruction 6. Pulmonary hypoplasia
2. Post-extubation subglottic edema Extrinsic lung compression
3. Laryngotracheomalacia 1. Pleural effusion (transudate vs. exudate)
4. Left mainstem bronchomalacia from long-standing left atrial or left pulmonary artery enlargement 2. Pneumothorax, hemothorax, chylothorax
Chest Wall
1. Midsternal
  2. Thoracotomy
  3. Clam-shell incisions

(Adapted from Newth CJL, Hammer J. Pulmonary issues. In: Chang AC, Hanley FL, Wernovsky G, Wessel DL, editors. Pediatric cardiac intensive care. Baltimore: Williams & Wilkins; 1998. p 352.)

Procedures associated with phrenic nerve injury:

Chylothorax is a rare complication of cardiac surgery with an incidence of approximately 0.85% to 3.8%. Chylothorax may occur as a direct injury to the thoracic duct in surgeries such as coarctation of the aorta repair or PDA ligation. Second, it may occur with thrombosis of the superior vena cava, leading to increased hydrostatic pressure in the superior vena cava and thoracic duct. Third, high central venous pressures after a surgery such as a Glenn palliation for HLHS may cause chylothorax. Most common surgeries that are complicated by chylothoraces are tetralogy of Fallot, Glenn and Fontan palliation, and orthotopic heart transplantation.

Placement of a chest tube with the initiation of a medium-chain triglyceride diet is the initial management. Total parenteral nutrition with enteric rest (nothing by mouth) may be needed if conservative management fails. Adjuvant therapy includes diuretics, albumin infusions, immunoglobulin replacement, electrolyte replacement, and fresh frozen plasma and antithrombin replacement. Anticoagulation with heparin or enoxaparin should be considered. Corticosteroids have been shown to have some benefit after the Fontan operation. Octreotide infusion followed by thoracic duct ligation may be needed in cases not amenable to other measures. Caution should be used with octreotide, and it is generally recommended that the patient receive nothing by mouth during octreotide infusion.

Increased risk adjusted congenital heart surgery score, prolonged intubation time, low birth weight, and neurological co-morbidities.

NIRS is a noninvasive method that is used to monitor hemoglobin oxygen saturation using nonpulsatile oximetry. A fair correlation exists between superior vena cava venous oxygen saturation and cerebral NIRS. Somatic NIRS (renal) may be helpful to show regional perfusion. NIRS in conjunction with pulse oximetry may yield an estimate of cardiac output.

Although there is no correct answer, the clinician should consider whether the infant was fed before surgery, length of bypass and circulatory arrest times, adequacy of the cardiac output, presence of bowel sounds, minimization of vasoconstrictive agents, and the absence of lactic acidosis. Local systemic monitoring with NIRS may be helpful. ∗†‡§

Cardiac Transplantation

Most rejection episodes in the era of cyclosporine immunosuppression are relatively asymptomatic, especially in the older child. The neonatal recipient, however, can often have the nonspecific findings of fever, irritability, tachycardia, loss of appetite, and an S3 gallop on physical examination.

Rejection, infection, coronary artery disease, hypertension, renal dysfunction, and tumors may occur.

Yes.

During cardiac transplantation all nerves to the heart are severed so that there is no direct sympathetic or parasympathetic control of heart rate. Concomitantly, during the first few postoperative days the stroke volume of the transplanted heart is relatively fixed, and the contractility of the heart is diminished secondary to the ischemia that occurred during harvest and implantation. Cardiac output is directly proportional to changes in the heart rate in the early postoperative period. Therefore many surgeons try to maintain cardiac output by pacing the heart with temporary pacing wires.

Some evidence suggests that infants who receive transplants when younger than 6 months of age have improved survival 10 years after the transplant compared with older children. Newborn infants do not have a mature complement system and do not produce a typical isohemagglutinin response to blood groups. As such, it is possible to perform ABO-incompatible heart transplantation during infancy. ∗†‡§

image KEY POINTS: INTERVENTIONAL CARDIOLOGY

p3140See Table 6-4.

An interrupted inferior vena cava prevents access to the right side of the heart from the femoral veins. This interruption, however, is usually below the level of the hepatic veins. Therefore the umbilical vein remains an alternative way to gain access to the right side of the heart.

Although originally developed using fluoroscopy, a balloon atrial septostomy may be performed at the bedside using transthoracic echocardiography guidance. ∗†

image KEY POINTS: INTERPRETING NORMAL AND ABNORMAL ELECTROCARDIOGRAMS IN THE NEWBORN PERIOD

Compared with the electrocardiographic reading of an older infant or child, the newborn electrocardiographic reading is remarkable for the following reasons:

The normal electrocardiogram in a newborn shows a preponderance of right ventricular forces because the right and left ventricles are of equal mass at birth. The mean QRS axis for a newborn is 110 degrees. Left axis deviation (<30 degrees) is always abnormal. Downward forces in the QRS in lead AVF and upward forces in lead 1 indicate a left axis deviation. This appearance is typically associated with tricuspid atresia. Patients with AV septal defects typically have a superiorly oriented frontal QRS loop manifested by dominant S waves in the inferior leads (III and aVF) and a prominent R wave in aVR. This finding is in contradistinction to tricuspid atresia in which the RV precordial leads lack RV dominance.

The upper limit of normal for a quiet awake newborn in 166 bpm. Healthy newborn infants may transiently reach 230 bpm. The differential diagnoses should include fever, infection, anemia, pain, hypovolemia, hyperthyroidsim, myocarditis, and drug interaction.

Sinus bracycardia is defined as sinus rhythm with a heart rate (awake) below the lower normal limit (91 bpm first week of life and 107 bpm first month of life). Symptoms of severe bradycardia may include poor growth, feeding intolerance, and dyspnea. The differential diagnoses include central nervous system abnormalities, hypothermia, hypopituitarism, increased intracranial pressure, maternal drugs, hypothyroidism, long QTc, and a transient form related to maternal anti Ro/SSA+ mothers. Blocked premature atrial beats are common, often having a pause that may average out the heart rate on the monitor to a lower than clinically relevant number, but rarely cause symptoms.

SVT is the most common tachycardia in the term newborn and premature infant and manifests as a narrow complex tachycardia at rates of 250 to 300 bpm. The mechanism is usually a re-entrant type of tachycardia. It can be treated with adenosine (100 to 250 μg/kg) given as a rapid push. Adenosine blocks conduction through the AV node, resulting in a transient bradycardia and interruption of the re-entrant circuit. Once the heart rate has been converted to normal sinus rhythm, the infant should have a 12-lead electrocardiogram to rule out a delta wave and the presence of a Wolff–Parkinson–White type of SVT.

Ventricular tachycardia typically has a broad QRS complex (>120 msec). Ventricular-atrial dissociation may be present. A 12-lead electrocardiogram may reveal a QRS axis different than the sinus QRS axis. Fusion (sinus capture beats and a tachycardia beat) affirms the diagnosis.

Hypomagnesemia may mimic hypokalemia.

Prolongation of the QT interval may be evident.

A delta wave is a slurring in the upstroke of the QRS complex; it generally occurs in association with a short PR interval. The delta wave signifies that some or all of the atrial depolarization to the ventricle is by way of a bypass tract rather than solely antegrade through the AV node. This finding is associated with a Wolff–Parkinson–White pattern on the electrocardiogram. Patients with a Wolff–Parkinson–White pattern may develop SVT (also called Wolff–Parkinson–White syndrome) ( Fig. 6-14).

Anatomic substrate results in a direct electrical communication between the atria and the ventricles rather than through the AV node. Conduction becomes a fusion between AV nodal conduction and antegrade conduction via the bypass tract. Patients with an electrocardiogram having a Wolff–Parkinson–White pattern may have SVT and be considered as having Wolff–Parkinson–White syndrome.

All patients with a Wolff–Parkinson–White pattern on their electrocardiograms should have an echocardiogram to rule out structural heart disease. Digoxin should not be used in patients with Wolff–Parkinson–White syndrome because of its effect on increasing conduction through the accessory pathway rather than through the normal AV node. Associated lesions include the following:

The upper limit of normal (2SD) is 440 msec on the fourth day of life (2.5% of normal neonates will have a prolonged QTc). Newborns with a prolonged QTc on the first day of life should have a repeat electrocardiogram performed in 1 or 2 days. Prolonged QTc has been associated with an increased risk of sudden infant death syndrome. Newborns with a QTc greater than 440 msec should have a very detailed family history obtained for early sudden cardiac death, seizures, syncope, and unexplained car accidents.

image KEY POINTS: ARRHYTHMIAS

Congenital complete heart block in the fetus can occur as a result of structural congenital heart disease (L-TGA, left atrial isomerism, or maternal collagen vascular disease). Heart block occurs in women with a variety of connective tissue diseases (e.g., systemic lupus erythematosus, Sjögren syndrome). The incidence is 1/15,000 to 1/20,000 infants. Anti-RO (SSA) and La (SSB) antibodies are found in many of these women, but only a minority of fetuses are affected. Most cases are identified between 18 and 24 weeks’ gestation ( Fig. 6-16).

The most common benign arrhythmia in the fetus is a premature atrial contraction. This benign dysrhythmia is commonly detected during fetal monitoring. Blocked premature atrial contractions often cause what appears to be a pause on the monitoring strips, and they occur when the ventricle is refractory and not conducted ( Fig. 6-17).

All types of tachyarrhythmias and bradyarrhythmias can be detected. Premature beats account for 80% to 90% of fetal arrhythmias but are generally benign. Re-entrant supraventricular tachyarrhythmias account for 5% of fetal arrhythmias, complete heart block 2.5%, and atrial flutter 1% to 2%. Ventricular arrhythmias are rare ( Fig. 6-18).

The most common SVT in a neonate relates to an accessory pathway. In this form of SVT conduction tends to proceed antegrade via the AV node and retrograde through the bypass tract. The electrocardiogram tends to have a narrow QRS complex with a short repolarization interval and rates greater than 220 bpm. A rare form of SVT (permanent junctional reciprocating tachycardia) may have a long repolarization with a more incessant course and slower rates (180 to 200 bpm).

Spontaneous resolution of SVT will occur in the first year of life in nearly 50% of patients. Most (60% to 90%) of infants with Wolff–Parkinson–White syndrome undergo spontaneous resolution by 1 year of age.

Antiarrhythmic preference is often based on the severity of the symptoms. For straightforward SVT that terminated with intravenous adenosine, beta blockers tend to be relatively safe and effective. In infants with beta-blocker refractory SVT, alternative drugs to consider are flecainide, sotalol, and amiodarone. All three of these drugs have potential pro-arrhythmic side effects and institution of such antiarrhythmics should occur in a hospital (monitor/telemetry) setting. In general flecainide should not be administered to patients with significant structural heart disease. The QTc should be closely followed in patients on either sotalol or amiodarone ( Fig. 6-19).

Atrial flutter is a relatively uncommon arrhythmia in newborns and infants. Presenting symptoms typically occur within the first 2 days of life, and there does not tend to be an association with structural heart defects. The ventricular rate depends on the degree of AV nodal conduction. Spontaneous termination is rare. Direct cardioversion or overdrive esophageal atrial pacing therapies are effective in more than half of the cases. Symptoms of CHF relate to the duration of the tachycardia. Approximately 20% of infants may have a second supraventricular arrhythmia, which will typically manifest within 48 hours.

LQT syndrome is a genetic mutation of several genes encoding ionic (Na+/K+) currents responsible for ventricular repolarization. The incidence is 1 in 3000 to 1 in 5000. A detailed family history is critical and should assess for early sudden death, fainting, seizures, and unexplained car accidents. There is a low penetrance, and gene carriers may not always show the phenotype at a young age. Beta blockers are the first choice of therapy and should be instituted in patients with the diagnosis regardless of symptoms.

Cor Pulmonale

Cor pulmonale is a severe abnormality in right ventricular function that occurs as a result of lung pathology. The common denominator in all cases is a significantly elevated PVR and right ventricular hypertension. The right ventricular dysfunction is manifested as a combination of right ventricular hypertrophy with decreased right ventricular compliance, and right ventricular dilation with decreased systolic function. By definition, cor pulmonale excludes all cases of right ventricular pathology caused by congenital heart disease.

Cor pulmonale may result from any chronic pathology that causes PVR to remain elevated after birth.

The chronic management of cor pulmonale depends on the underlying etiology. Factors that worsen PVR, such as hypoxia and acidosis, should be avoided. Intralipid administration as part of hyperalimentation may also increase pulmonary artery pressure and should be used only with great caution. Diuretics are commonly used in infants with BPD, although the evidence for their long-term benefit is not well established. A variety of pulmonary vasodilators are available with different actions and side effect profiles. ∗

image KEY POINTS: ENDOCARDITIS

Staphylococcus spp., Group B Streptococcus, Escherichia coli, Listeria monocytogenes, Candida spp., and gram-negative organisms such as Acinetobacter spp., Serratia spp., Enterobacter spp., and Klebsiella spp.

Infants with underlying congenital heart disease, infants with normal cardiac anatomy and a PDA, and infants with an indwelling central venous catheter are at risk for developing endocarditis.

Early signs of endocarditis in neonates may be very subtle; heart murmurs, skin abscesses, and hepatomegaly are the most common signs found in neonatal patients. The findings that one sees in children with subacute bacterial endocarditis—splenomegaly, petechiae, and splinter hemorrhages—are not usually seen in the newborn infant. ∗

image KEY POINTS: CARDIOMYOPATHY IN THE NEONATE

Table 6-5 lists these three types of cardiomyopathy.

TABLE 6-5

ECHOCARDIOGRAPHIC FINDINGS IN THE THREE TYPES OF NEONATAL CARDIOMYOPATHY

TYPE OF CARDIOMYOPATHY FUNCTION SEEN ON ECHO OTHER ECHO FINDINGS
Dilated cardiomyopathy Globular left ventricle
Globular and poorly contracting right ventricular size, and contractility possibly normal or similarly depressed		 Endocardial fibroelastosis
Hypertrophic cardiomyopathy Marked left or biventricular hypertrophy with normal/hyperdynamic systolic function +/− Presence of asymmetric septal hypertrophy (left ventricle)
The left ventricular cavity smaller than normal
Ventricular filling impaired by diastolic relaxation abnormalities
Restrictive cardiomyopathy Normal ventricular size and contractility Abnormal diastolic filling
Markedly decreased ventricular compliance

Pompe disease (glycogen storage disease type II or acid maltase deficiency).

CHF, feeding intolerance, tachypnea, tachycardia, arrhythmias, and sudden cardiac death.

Noonan syndrome (10%).

The annual incidence of DCM (<1 year of age) is 4.4 in 100,000 children. The most common causes are myocarditis and neuromuscular disorders. Forms of DCM may be familial, autosomal dominant, autosomal recessive, or X-linked. Inborn errors of metabolism, including Barth syndrome, carnitine deficiency, and mitochondrial disorders, should be sought. Genetic and metabolic consultation should be considered early in the diagnosis of neonatal DCM.

The natural history of DCM in infants and children relates to the diverse nature of the disorder and the age at presentation. For all children the median age at diagnosis is 1.5 years with a 1-year and 5-year survival rate at 87% and 77%, respectively. Transplantation is generally not offered for patients with neuromuscular disorders or inborn errors of metabolism.∗†‡§

Cardiac Tumors

Rhabdomyoma is the most common cardiac tumor seen in newborns and infants (approximately 50%). Rhabdomyomas are considered hamartomas, overgrowth of normal tissue at the site of origin, rather than true neoplasms. Rhabdomyomas seldom cause obstruction and usually regress. Symptoms in neonates are variable but if present relate to intracardiac obstruction, myocardial involvement, or arrhythmias.

Fibroma is the second most common primary cardiac tumor in infants and young children, accounting for approximately 25% of such tumors. These are benign connective tissue tumors arising from fibroblasts and myofibroblasts. They are usually single and intramural; they may involve the left ventricular posterior wall and septum. Fibromas are often located in the left ventricle and may cause left ventricular outflow tract obstruction and CHF. Surgical excision is required for cure insofar as spontaneous regression is rare.

Approximately 50% to 75% of patients with cardiac rhabdomyomas have tuberous sclerosis. Multiple rhabdomyomas are more consistent with the diagnosis of tuberous sclerosis than a solitary tumor. Classically, tuberous sclerosis is associated with the triad of epilepsy, mental retardation, and facial angiofibromas.

Bradycardia, SVT, Wolff–Parkinson–White syndrome, and ventricular tachycardia.

Depending on size and location, cardiac tumors have been demonstrated to cause death from the following:

∗Neill CA, Clark EB. The developing heart: a history of pediatric cardiology. London: Kluwer Academic Associates; 1995.

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