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).

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