Inadequate systemic perfusion is the second most common manifestation of symptomatic heart disease in newborn infants. Affected infants present with moderate to severe respiratory distress in addition to signs of decreased systemic perfusion. Respiratory distress is caused by increased pulmonary venous pressure causing pulmonary edema. Pulmonary venous pressures are increased because (1) there is obstruction to the egress of blood from the lungs or from the left atrium into the left ventricle or (2) the left ventricle cannot adequately eject blood. In some infants, the decrease in systemic perfusion is profound, with decreased to absent peripheral pulses, cool extremities, hypotension, and severe metabolic acidosis. In these cases, the compromise of systemic blood flow is life threatening and requires urgent diagnosis and therapy. In other infants, respiratory distress is the most impressive finding, and the signs of decreased systemic perfusion are subtle, often leading to the erroneous conclusion that the infant has primary pulmonary disease rather than heart disease. This is particularly true when the infant does not have a heart murmur, which may occur in this group of cardiac defects. Signs of decreased systemic perfusion, which may be indicated solely by mildly decreased pulses or by a mild metabolic acidosis, should be carefully sought and considered in all infants with significant respiratory distress.

The two hemodynamic categories of cardiovascular pathophysiology that cause decreased systemic perfusion are left heart obstruction and cardiomyopathy. This chapter will review the various anatomic defects that cause left heart obstruction. Cardiomyopathies in newborn infants are reviewed in Chapter 9.

The primary pathophysiologic abnormality in the infant with inadequate systemic perfusion is the inability of the heart to supply an adequate amount of oxygen to the tissues to meet metabolic needs. In this context, the onset is more acute and severe as compared with the chronic heart failure syndrome discussed in Chapter 11. Furthermore, in contrast to cyanotic infants (Chapter 6), oxygen saturation is usually normal or only mildly decreased in infants with decreased systemic perfusion. Instead, the overriding problem is inadequate systemic blood flow.

Fetal Physiology and the Transition at Birth

In the normal fetus, different ventricles perfuse the upper and lower portions of the body. The right ventricle supplies the lower body, and the left ventricle supplies the upper body. During fetal life, obstruction to one ventricle, or a myopathic process isolated to that ventricle, does not lead to decreased systemic perfusion. Inflow can be diverted to the healthy unobstructed ventricle via the foramen ovale, and a portion of the outflow of the healthy ventricle can be diverted to the other vascular bed via the ductus arteriosus (Chapter 3, Figure 3-5). Left-sided obstruction causes decompensation after birth because the postnatal changes in the circulation prevent the right ventricle from performing the work of the left ventricle. At birth, pulmonary blood flow increases greatly, causing the flap of the foramen ovale to close the atrial communication. In newborn infants in whom blood flow into or out of the left ventricle is critically obstructed, closure of the foramen ovale causes decreased systemic perfusion almost immediately after birth. Blood flow may cross the foramen ovale in a left-to-right direction, but this occurs at the cost of increased left atrial pressures. Thus, an early and important finding in these infants is pulmonary edema, resulting in severe respiratory distress.

Some infants have either an open incompetent foramen ovale or a more distal obstruction (eg, coarctation of the aorta) that is not dependent on decompression through the foramen ovale. Adequate systemic perfusion in these infants depends on patency of the ductus arteriosus. In the infant with hypoplastic left heart syndrome or interruption of the aortic arch, adequate systemic blood flow depends on a widely patent ductus arteriosus. Thus, these infants typically develop symptoms within the first 72 hours of life as the ductus arteriosus begins to constrict. In contrast, infants with coarctation of the aorta do not require full patency of the ductus arteriosus but merely a large ductal ampulla to maintain flow around the coarctation site into the descending aorta. The ampulla, which is located at the aortic end of the ductus arteriosus, provides a pathway for blood to flow from the aortic arch past the site of coarctation to the descending aorta (Figure 8-1). The ductus arteriosus constricts initially at the pulmonary end, and only days later does the constriction progress to the aortic end. Thus, aortic obstruction and associated symptoms may be delayed for several days or weeks after birth in infants with significant coarctation of the aorta.

Left heart obstruction may occur either at the inflow of blood to the left atrium or ventricle or at the outflow of blood from the left ventricle. The defects can be considered according to the anatomical site of obstruction, starting at the pulmonary veins and progressing through the left heart to the ascending and descending aorta (Table 8-1).

Total Anomalous Pulmonary Venous Connection With Obstruction

Anatomic and Physiologic Considerations

The most proximal obstruction to filling of the left heart occurs at the level of the pulmonary veins. The embryonic pulmonary venous confluence is not part of the true left atrium but is a coalescence of the pulmonary veins from the five lobes of the lungs that eventually connects to the left atrium. In total anomalous pulmonary venous connection, the confluence does not connect to the left atrium; instead, it connects to various venous structures above or below the diaphragm. Pulmonary veins draining above the diaphragm usually have only modest pressure gradients associated with high flow through the venous channels. As discussed in Chapter 7, infants with supradiaphragmatic total anomalous pulmonary venous connection usually present with tachypnea secondary to high pulmonary blood flow rather than decreased systemic perfusion. An uncommon exception occurs when the superior course of a left vertical vein passes between the left pulmonary artery and bronchus rather than in front of both. This is termed a hemodynamic vise. As the left pulmonary artery and pulmonary veins fill with blood after birth, the vertical vein becomes compressed, and the predominant signs are due to decreased systemic perfusion.

The most common anomalous pulmonary venous connection that is associated with postnatal pulmonary venous obstruction occurs when the pulmonary venous confluence coalesces below the diaphragm with the umbilicovitelline system. In this situation, the pulmonary venous confluence descends anterior to the esophagus and connects near the liver to the portal system or the ductus venosus (Figure 8-2). Because the ductus venosus is large in utero and pulmonary blood flow is small, the connection is unobstructed during fetal life. Immediately after birth, pulmonary blood flow increases greatly, and the loss of placental blood flow is associated with constriction of the ductus venosus. These changes at birth result in increased flow through the anomalous venous channel, which is inadequate to provide unimpeded flow. The result is obstruction to egress of blood from the lungs, marked increase in pulmonary venous pressure, and pulmonary edema.

Determining the location of the abnormal connection in a newborn infant with total anomalous pulmonary venous connection with obstruction may be possible at the bedside if the ductus arteriosus is patent. When pulmonary venous outflow is obstructed, pulmonary vascular resistance is high, and right-to-left shunting occurs across the ductus arteriosus. If the veins drain superiorly, the pulmonary venous return preferentially descends with the superior vena caval flow toward the tricuspid valve, then into the right ventricle, main pulmonary artery, ductus arteriosus, and descending aorta. Consequently, oxygen saturation in the lower portion of the body is higher than that in the upper body. Conversely, if the veins drain below the diaphragm, pulmonary venous blood preferentially crosses the foramen ovale to the left atrium and ventricle and ascending aorta (Figure 8-2). In this situation, oxygen saturation in the lower portion of the body is lower than that in the upper body.

Clinical Presentation

The clinical presentation of the infant with obstructed total anomalous venous connection is dramatic and occurs shortly after birth. Moderate to severe respiratory distress with tachypnea, intercostal and subcostal retractions, nasal flaring, and grunting develop soon after birth. Oxygen saturation measured by pulse oximetry is usually modestly decreased, often in the mid-80s, but it may be much lower if obstruction is severe. As discussed above, a small difference in oxygen saturation may be present between the upper and lower extremities if the ductus arteriosus is patent. The pulses are often mildly to moderately decreased in all extremities, and perfusion may be similarly decreased. The blood pressure may show a narrow pulse pressure. The precordium is hyperactive with a prominent parasternal impulse because the right ventricle is ejecting much more blood than normal and is doing so at suprasystemic pressures. The first heart sound is normal, and splitting of the second heart sound often is easy to hear because of the markedly increased pulmonary blood flow in patients who do not have obstructed pulmonary venous return. A split second heart sound in the newborn infant with decreased systemic oxygen saturation is very unusual and strongly supports the diagnosis of total anomalous pulmonary venous connection. A nonspecific murmur associated with increased flow across the right ventricular outflow tract may be present, although this may not be present when severe pulmonary venous obstruction is present.

This presentation is easily confused with persistent pulmonary hypertension of the newborn infant, another life-threatening condition with a similar early course of severe decompensation. Moreover, pulmonary arterial pressure is often suprasystemic in infants with total anomalous pulmonary venous connection with obstruction, which further complicates differentiating between these two conditions.

It is critically important to differentiate the two as soon as possible because emergency surgery can be lifesaving in the infant with total anomalous pulmonary venous connection. To do so, it is valuable to consider the perinatal period. The prenatal course and delivery are usually benign in the infant with obstructed total anomalous pulmonary venous connection. In contrast, the infant with pulmonary hypertension frequently has a history of perinatal complications such as premature rupture of membranes, meconium in the amniotic fluid if not frank aspiration, low Apgar score, in utero growth retardation, or other findings consistent with perinatal distress.

Despite the potential differences in the perinatal course, a high index of suspicion is critical if the correct diagnosis is to be made quickly. Because of the difficulty in differentiating the two conditions, every infant who is thought to have persistent pulmonary hypertension of the newborn should undergo echocardiography urgently to evaluate the possibility that the pulmonary hypertension is caused by total anomalous pulmonary venous connection with obstruction.

Ancillary Tests

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  The chest radiograph in infants with anomalous pulmonary venous connection shows a small to normal-size heart and diffusely increased vascularity, with alveolar and interstitial edema (Figure 8-3). The markings are less coarse than those of meconium aspiration seen in the infant with persistent pulmonary hypertension, but this is a subtle difference.

  
  
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  The electrocardiogram may be helpful in differentiating total anomalous pulmonary venous connection from pulmonary hypertension of the newborn. A “qR” pattern in the right precordial leads, which reflects severe right ventricular hypertrophy because of the markedly increased pulmonary arterial pressures, is frequently present in infants with anomalous pulmonary venous connection (Figure 8-4). Although persistent pulmonary hypertension of the newborn also may cause right ventricular hypertrophy, it is usually manifested as failure of inversion of the T waves in the first 2 weeks of life and not as a “qR” pattern in the right precordium.

  
  
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  Echocardiography is diagnostic of total anomalous pulmonary venous connection and should be performed on all infants suspected of having pulmonary hypertension of the newborn. Furthermore, echocardiography is indicated for all infants being considered for extracorporeal membrane oxygenation and in whom a definitive diagnosis has not been made. However, making the correct diagnosis and defining the precise pulmonary venous anatomy requires a skilled and experienced echocardiographer. Exclusive right-to-left shunting across the foramen ovale is always found in patients with anomalous pulmonary venous connection. Color Doppler echocardiography has facilitated definition of venous anatomy (Figure 8-5). Color flow patterns can demonstrate the location of the obstruction, and pulsed wave Doppler can estimate its severity.

Therapeutic Considerations

Endotracheal intubation, positive pressure ventilation, and stabilization of the metabolic status of infants with obstructed anomalous pulmonary venous connection should be instituted immediately. Positive end-expiratory pressures may decrease alveolar edema and dramatically improve the ventilatory and cardiovascular status of the infant acutely. Prostaglandin E₁ should be administered to infants in whom obstructed total anomalous venous connection is suspected, without waiting for echocardiography to be performed. Prostaglandin E₁ may be helpful in dilating the ductus venosus and may be lifesaving in other causes of left-sided obstruction, so administration of this medication should be initiated even before a definitive diagnosis is obtained. Once the diagnosis is made, prostaglandin E₁ may be discontinued if no longer indicated. After stabilization and definitive diagnosis, the infant with total anomalous pulmonary venous connection with obstruction should be taken urgently to the operating room for repair.

Cor Triatriatum

Anatomic and Physiologic Considerations

Pulmonary venous return to the heart may be obstructed at the entrance to the left atrium. Congenital stenosis of one or more pulmonary veins occurs rarely. This is usually a progressive disease that presents later than the newborn period. Results of interventional and surgical approaches are generally disappointing. Recently, acquired pulmonary vein stenosis involving one or more pulmonary veins has been noted in premature infants with bronchopulmonary dysplasia, which also appears to have a poor prognosis.

More commonly, obstruction occurs between the pulmonary venous confluence and the primitive left atrium during formation of the heart. The left atrium is effectively separated into two chambers, and the condition is therefore called cor triatriatum, meaning “heart with three atria.” It is possible that the developmental mechanisms that result in anomalous pulmonary venous connection and cor triatriatum are similar, but in cor triatriatum, the confluence comes in close enough contact with the atrium to create a single chamber but with incomplete coalescence. The pulmonary veins usually enter the accessory chamber that is connected to the left atrium by an opening of variable size (Figure 8-6). Although the anatomy may be variable, the more distal true left atrium usually communicates with the left atrial appendage and the foramen ovale.