TAPVR occurs when the left atrium fails to form connection with the pulmonary venous plexus in embryogenesis, but instead retains its primitive vascular connections. There are several variants, which depend upon the connections retained. In all variants of TAPVR, the pulmonary veins have no connection with the left atrium, and instead empty into the systemic venous system.
Due to these aberrant connections, oxygenated blood from the lungs is returned to the right atrium and mixes with the deoxygenated blood returning from the systemic circulation. Because the right atrium is receiving blood from both the systemic and pulmonary circulations, both the right atrium and right ventricle become dilated due to fluid overload.
Without a shunt between the right and left sides of the heart, there is no way for oxygenated blood to be circulated to the body, and TAPVR is incompatible with life. Blood is most commonly shunted right-to-left at the atrial level through an atrial septal defect (ASD). It may also be shunted through a ventricular septal defect (VSD) or a patent ductus arteriosus (PDA).
Obstruction can be caused by the pulmonary vein coursing between other vessels, or connecting to the systemic system at an acute angle, causing a pressure backup. If the vein courses inferiorly to the heart, it can be compressed at the level of the diaphragm or at their connections to the portal vascular system.
Patients with severe obstruction present within the first 12 hours of life with severe cyanosis, respiratory failure, and shock. They are tachypneic with respiratory distress, and diminished cardiac output causes hypotension and diminished pulses.
Elevated pulmonary vascular pressure in obstructed patients causes the accumulation of fluid in the lungs, which will show up on chest x-ray as pulmonary edema.
Unobstructed forms of TAPVR present later in life, in children 1-2 years old. They present with similar (although less severe) findings of hypoxia, tachypnea, poor feeding, and failure to thrive.
High volume of blood returning to the right heart combined with high pulmonary vascular pressures leads to dilation and hypertrophy, and eventually signs of right heart failure. A fixed, split S2 and systolic ejection murmur often present due to right ventricular overload.
Chest x-ray in children with unobstructed TAPVR will show normal lung parenchyma with prominence of the pulmonary arteries, innominate vein, and/or SVC leading to the classic “Snowman” or “Figure of 8” sign.
Echocardiogram is used to identify the abnormal pulmonary venous connections in infants with suspected TAPVR. It may be able to directly identify abnormal vascular connection points, estimate the pressures in the pulmonary arteries, view the dilation of the right heart, and assess the degree of intracardiac shunting. When echo is equivocal, X-ray, CT or MRA can be used to further define the anatomy.
Initial treatment of infants with severe TAPVR is aimed at stabilization for surgery. Patients are given oxygen, and mechanically ventilated if necessary. Inotropic medications are used to increase the contractility of the heart, and prostaglandins may be beneficial in keeping the ductus arteriosus open to increase the systemic cardiac output. A PDA may also worsen cyanosis, so prostaglandins should be used with caution. Surgical management of TAPVR is recommended regardless of the presence or absence of obstruction, and should be performed as soon as the patient is stable. The goal of surgery is to create a direct pathway between the pulmonary veins and the left atrium.
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