Total anomalous pulmonary venous return
In TAPVR, there is no direct pulmonary venous drainage into the left atrium, as in a normal heart. The pulmonary veins may drain into various structures above or below the diaphragm. The recipient chambers above the diaphragm may include the right atrium, the coronary sinus, or the superior vena cava via a vertical vein. Alternatively, when the pulmonary veins drain below the diaphragm, they may join into a descending vein that enters the inferior vena cava or one of its larger tributaries, often via the ductus venosus. As the ductus venosus closes soon after birth, obstruction to the pulmonary venous return may develop early. Rarely, the drainage may be mixed, with some veins draining above the diaphragm and others below it.
In TAPVR, mixing of oxygenated and deoxygenated blood occurs before or at the level of the right atrium. Right atrial blood subsequently may pass into the right ventricle and pulmonary artery. It may also travel through an atrial septal defect (ASD) or patent foramen ovale (PFO) into the left atrium. The right atrium, right ventricle, and the pulmonary artery are generally enlarged, while the left atrium and ventricle may remain normal or diminish in size. The clinical presentation of TAPVR depends on the presence or absence of obstruction of the pulmonary venous channels.
If the pulmonary venous return is obstructed, severe pulmonary congestion and pulmonary hypertension occur, requiring urgent surgical intervention. Obstructed TAPVR is a pediatric cardiac surgical emergency, as prostaglandin therapy alone may not be sufficient.
Partial anomalous pulmonary venous return
In PAPVR, not all pulmonary veins drain abnormally. One or more pulmonary veins abnormally return to the superior or inferior vena cava, the right atrium, or the coronary sinus. Such drainage produces a left-to-right shunt of oxygenated blood. PAPVR frequently involves one or both of the veins from one lung, more often the right one. Often, an associated ASD is found and it is usually of the sinus venosus type. Conversely, when a sinus venosus ASD is found during echocardiography, a careful search for associated PAPVR should be made.
The history, physical signs, and electrocardiographic and radiographic findings of PAPVR and TAPVR are similar to those seen in patients with an isolated ostium secundum ASD. In some cases, an anomalous vein draining into the inferior vena cava is visible on chest radiography as a crescentic shadow of vascular opacity (like a scimitar) along the right border of the cardiac silhouette (scimitar syndrome). In these patients, an associated ASD is not seen; rather, pulmonary sequestration and anomalous arterial supply to the affected lobe of lung are encountered.
Frequency:
- In the US: In the general population, the incidence of congenital heart disease (CHD) is approximately 0.8%. TAPVR is estimated to account for 1-3% of all cases of CHD. It also accounts for 2% of all deaths from heart disease during infancy. PAPVR occurs in approximately 1 in every 160 individuals, or 0.6% of the population. Most PAPVR cases are found in association with atrial septal defects (ASD). In fact, nearly 15% of all ASD patients exhibit this coexisting anomaly. Particularly, in the patients with sinus venosus type ASD, the incidence of PAPVR may be as high as 85%.
Mortality/Morbidity: The majority of patients with TAPVR develop symptoms of cyanosis and congestion within the first year of life and, if left untreated, about 80% of patients would die. In contrast, PAPVR is frequently not discovered until adulthood, and is generally not fatal.
Race: There is no particular racial predilection.
Sex: Infracardiac TAPVR is seen more frequently in males. There is no sex predilection for PAPVR.
Age: TAPVR usually presents in infancy. PAPVR may be discovered at any age.
Anatomy: TAPVR results from abnormal embryogenesis where the initial communication between pulmonary portion of the foregut plexus and the cardinal and umbilico-vitelline venous system persists. This results in all the pulmonary veins draining into the right atrium, or the systemic veins directly.
Anatomical types
- Supracardiac
- Pulmonary veins drain via the vertical vein into the anomalous vein
- Direct drainage into superior vena cava (SVC)
- Drainage into right atrium
- Drainage into the coronary sinus
- Infracardiac (13% of patients)
- Draining into portal vein
- Drainage into the inferior vena cava (IVC)
Clinical Details: Three major clinical patterns of TAPVR are seen: (1) severe pulmonary venous obstruction, (2) early heart failure, and (3) mildly symptomatic or asymptomatic TAPVR.
- Severe pulmonary venous obstruction: Some patients with severe pulmonary venous obstruction present in the neonatal period with severe findings, most commonly those with infracardiac TAPVR. Cyanosis and severe tachypnea are prominent. Murmurs may be absent. Infants are severely ill and fail to respond to mechanical ventilation. Rapid diagnosis and urgent surgical correction are necessary for survival.
- Early heart failure: This group of patients presents with congestive heart failure in early life, but the overall pulmonary venous return is only mildly obstructed. They usually have a large left-to-right shunt. Due to the presence of pulmonary arterial hypertension, such infants become severely ill. Systolic murmurs are audible along the left sternal border, and there may be a gallop rhythm. A continuous murmur is occasionally heard along the upper left sternal border over the pulmonary area. Cyanosis is usually mild in intensity.
- Asymptomatic TAPVR: Minimally symptomatic or asymptomatic patients with TAPVR have no significant pulmonary venous obstruction. There is total mixing of systemic venous and pulmonary venous blood and a large left-to-right shunt exists. Pulmonary hypertension is, however, absent. These patients are less likely to be severely symptomatic during infancy. Clinical cyanosis is usually mild or absent.
- PAPVR: An uncomplicated anomalous connection of a single pulmonary vein usually does not produce any symptoms since only 20% of blood is shunted to the right; however, with 2 or more veins draining to the right, and particularly when associated with ASD, the PAPVR patients begins to manifest symptoms as they grow. These symptoms develop often during adulthood and may include easy fatigue, dyspnea, and occasionally heart failure.
In PAPVR, when two or more pulmonary veins drain into the right atrium (shunting >60% of blood to the right), symptoms of dyspnea on exertion, and heart failure occur. In patients with the scimitar syndrome, the respiratory symptoms in part develop due to hypoplasia of the right lung. On physical examination, findings are the same as those encountered in patients with ASD. The important difference, however, is that the two components of the second heart sound, though similarly widely split, move normally with respiration in those where atrial septum is intact.
Preferred Examination: Echocardiography is the preferred examination. The echocardiogram demonstrates an enlarged right ventricle and a small left atrium. It can also show the pattern of abnormal pulmonary venous connections. When Doppler venous flow pattern of the abdominal veins is obtained, the finding of venous flow away from the heart is pathognomonic of TAPVR below the diaphragm. Shunting occurs almost exclusively from right to left at the atrial level.
Electrocardiograms demonstrate right ventricular hypertrophy, usually a qR pattern in V3 R and V1. The P waves are frequently tall and spiked.
TAPVR is a cyanotic lesion. Echocardiographic results usually confirm the diagnosis. MRI and fast CT are also useful for defining pulmonary venous drainage. At cardiac catheterization, the presence of anomalous pulmonary veins may be demonstrated by means of selective pulmonary arteriography.
Limitations of Techniques: Sometimes, echocardiographic views are limited, and MRI may be necessary.
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