| disease | Total Anomalous Pulmonary Venous Return |
Total anomalous pulmonary venous return (TAPVR) refers to a condition where all pulmonary veins do not enter the left atrium but instead directly connect to the right atrium or the systemic venous system. It is often associated with an atrial septal defect. The incidence rate accounts for 1.5% to 2% of congenital heart diseases.
bubble_chart Etiology
The lung primordium develops from the foregut, and the pulmonary vascular plexus originates from the visceral venous plexus, draining into the cardinal veins, umbilical vein, and egg yolk veins. Before the atria are separated, the common pulmonary vein protrudes from the mid-posterior wall of the atrium and divides into two branches, each of which further splits into two, connecting to the left and right lungs, respectively. Later, the dilated common pulmonary vein is absorbed into the enlarging left atrium, causing all four pulmonary veins to open into the left atrium and disconnect from the systemic venous channels. If the connection between the common pulmonary vein and the left atrium fails to develop while maintaining connections with the cardinal veins, umbilical vein, or egg yolk veins, various types of anomalous pulmonary venous connections occur. The most common scenario is drainage into the innominate vein or coronary sinus.
**Pathology:** Darling classified total anomalous pulmonary venous connection (TAPVC) into four types based on the site of anomalous connection: (1) **Supracardiac type (55%)**: The pulmonary veins converge posterior to the left atrium and drain via a vertical vein into the left innominate vein, sometimes into the superior vena cava or azygos vein. The vertical vein passes anterior to the left pulmonary artery and left main bronchus before entering the innominate vein, where compression may cause venous obstruction. (2) **Cardiac type (30%)**: All pulmonary veins drain directly into the right atrium or via a common pulmonary vein into the coronary sinus. Obstruction may occur between the common pulmonary vein and the coronary sinus. (3) **Infracardiac type (12%)**: All pulmonary veins converge posterior to the heart and descend via a vertical vein through the diaphragmatic esophageal hiatus into the portal vein, inferior vena cava, or ductus venosus. The return blood must pass through the high-resistance hepatic vascular bed to reach the right atrium, or the descending vertical vein may be compressed, leading to pulmonary venous obstruction. (4) **Mixed type (~3%)**: All pulmonary veins enter the right atrium through multiple channels. Most patients with infracardiac or mixed types die in infancy. Approximately 75% of TAPVC patients have a patent foramen ovale, and 25% have an atrial septal defect. The right atrium and ventricle are often dilated and hypertrophied, the pulmonary artery is enlarged with increased pressure, and the left atrium is small. Pulmonary venous obstruction is most common in the infracardiac type, followed by the supracardiac type, with an incidence as high as 50%. Other associated cardiovascular anomalies include patent ductus arteriosus, aortic coarctation, persistent truncus arteriosus, transposition of the great arteries, single ventricle, pulmonary atresia, tetralogy of Fallot, and double-outlet right ventricle.
**Pathophysiology:** In TAPVC, all pulmonary venous blood enters the right atrium. Some of this blood must then pass through a patent foramen ovale or atrial septal defect into the left atrium; otherwise, death occurs shortly after birth. The right atrium receives all systemic and pulmonary venous return, leading to a massive increase in blood flow. In patients with a patent foramen ovale, the interatrial communication is small, allowing only a small amount of mixed caval and pulmonary venous blood to enter the left atrium and be pumped by the left ventricle into the systemic circulation, resulting in **grade I cyanosis**. However, due to the excessive blood flow in the right heart and pulmonary circulation, pulmonary artery pressure rises, and most patients die of **right heart failure** within months after birth. If the atrial septal defect is large, more blood flows from the right atrium into the left atrium, causing **marked cyanosis**, while pulmonary hypertension develops later, allowing survival beyond one year. Patients with pulmonary venous obstruction exhibit **severe cyanosis**, pulmonary congestion, and **pulmonary edema**, with most dying within weeks after birth.In TAPVC, due to significantly elevated pulmonary pressure, all patients, regardless of age, exhibit **obstructive pulmonary vascular disease** in the small pulmonary arteries.
bubble_chart Clinical Manifestations
The patient's symptoms depend on the presence or absence of pulmonary venous obstruction, the size of the interatrial communication, and other coexisting cardiac anomalies. In cases with a small interatrial communication, pulmonary hypertension and right heart failure develop early after birth, with rapid progression and severe symptoms. In cases without pulmonary obstruction and with a large interatrial communication, pulmonary hypertension appears later, but cyanosis is pronounced, and the disease progresses more slowly. Infants exhibit slow growth, rapid breathing, increased heart rate, and grade I cyanosis, often leading to misdiagnosis as pneumonia or respiratory distress syndrome. Physical examination may reveal no specific murmurs, although sometimes a systolic blowing ejection murmur can be heard at the second left intercostal space near the sternum, along with a split and accentuated second heart sound at the pulmonary valve area. A diastolic rumbling murmur may be audible at the lower left sternal border. Cardiac dullness is enlarged, and a heaving precordial impulse may be present. Clubbing of the fingers and toes is generally mild.
(1) Chest X-ray shows increased pulmonary vascular markings, prominence of the pulmonary artery trunk, enlargement of the right ventricle and right atrium. In patients with anomalous drainage into the left superior vena cava, the upper mediastinal shadow is widened, and the entire cardiac silhouette appears as a "figure 8".
(2) Electrocardiogram reveals right axis deviation, hypertrophy of the right ventricle and right atrium, and sometimes incomplete right bundle branch block.
(3) Right heart catheterization and selective pulmonary angiography demonstrate elevated oxygen saturation at the site where pulmonary venous blood drains into systemic veins, decreased peripheral arterial oxygen saturation, and elevated or normal right atrial pressure. In cases with a small interatrial communication, the right atrial pressure gradient is higher than that of the left atrium. In patients with pulmonary venous obstruction, right ventricular and pulmonary arterial pressures are significantly elevated, and pulmonary capillary wedge pressure exceeds the mean left atrial pressure. Selective pulmonary angiography can reveal the course of the anomalous pulmonary venous trunk, the site of abnormal drainage, the presence of pulmonary venous obstruction, and associated cardiovascular anomalies.
(4) Two-dimensional echocardiography and Doppler examination may fail to visualize the pulmonary venous orifices in the left atrium. Right ventricular diastolic volume overload and interruption of the atrial septal echo can also be observed, along with visualization of the anomalous pulmonary venous trunk and associated cardiovascular anomalies. Doppler examination can detect abnormal flow connections and right-to-left atrial shunting.
Treatment measures:
The efficacy of total anomalous pulmonary venous connection repair depends on factors such as age, the site of anomalous connection, the presence of pulmonary venous obstruction, and the size of the atrial septal defect. Infants with pulmonary venous obstruction and a small atrial septal defect who develop early heart failure have an extremely high mortality rate. The Texas Heart Institute reported 125 surgical cases, with a mortality rate of 52% for patients under 1 year old, 20% for those aged 1-2 years, and 15% for those over 2 years. No surgical deaths occurred in children over 10 years old. Radical surgery is recommended when pulmonary blood flow is more than twice the systemic blood flow and pulmonary vascular resistance is below 6 Wood units/m² of body surface area. For infants under 1 year old, aggressive medical treatment should be prioritized to improve symptoms. If the atrial septal defect is small, a balloon catheter can be used to enlarge it, improving hemodynamics and clinical symptoms to delay surgery.
Surgical methods: Under cardiopulmonary bypass, the anomalously connected pulmonary veins are redirected to the left atrium, the atrial septal defect is patched, and the vertical vein is ligated. Specific techniques: (1) Supracardiac type: A longitudinal incision is made in the right atrium to expose the right atrial cavity. The atrial septal defect is enlarged by cutting along its right edge. A corresponding transverse incision is made in the posterior left atrial wall opposite the common pulmonary vein trunk, extending to the interatrial groove to create an elliptical opening about 2.5-3 cm long. A matching incision is made in the common pulmonary vein trunk. The anastomosis begins at the left apex with continuous suturing of the left atrial and common pulmonary vein incisions. The atrial septal defect is patched with a Dacron or autologous pericardial patch to enlarge the left atrial cavity. The right atrial incision is closed, and the vertical vein is ligated. (2) Intracardiac type: The right atrium is opened, and the tissue between the patent foramen ovale or atrial septal defect and the enlarged coronary sinus ostium is excised to create a large opening. If necessary, the pulmonary venous drainage is extended leftward by incising along the coronary sinus ostium. A large Dacron patch is then used to cover the defect and coronary sinus ostium. For cases where all pulmonary veins drain directly into the right atrium, the atrial septal defect is enlarged, and a Dacron patch is used to redirect the anomalous pulmonary venous openings along with the enlarged defect to the left atrium. (3) Infracardiac type: Two methods are available. The first is similar to the supracardiac approach, with anastomosis of the left atrium and common pulmonary vein trunk followed by atrial septal defect repair and ligation of the anomalous draining vein to the abdomen. The second method, Clarke's technique, involves tilting the cardiac apex to access the posterior heart. The common pulmonary vein trunk is divided and ligated. A longitudinal incision is made near the cardiac end, which can be extended to the distal end of the common pulmonary vein trunk. After excising the left atrial appendage, an oblique incision is made in the posterior left atrial wall, and the edges of the left atrial and pulmonary vein incisions are sutured to form an anastomosis. After repositioning the heart, the left atrium is opened to repair the atrial septal defect. The anastomosis should match the size of the mitral valve orifice to ensure unobstructed pulmonary venous return. The left atrial cavity must be enlarged to accommodate pulmonary venous return, preventing postoperative pulmonary edema. Successful surgical intervention can alleviate symptoms and significantly improve cardiac function.
More than 90% of patients with total anomalous pulmonary venous connection die within 1 year after birth. Patients with pulmonary venous obstruction require immediate surgical treatment once diagnosed. For those without pulmonary venous obstruction, medical treatment and balloon catheter dilation of the atrial septal defect to control congestive heart failure may allow a temporary delay in definitive surgery for a short period.
