Total anomalous pulmonary venous connection overview

# Overview
Total anomalous pulmonary venous connection (TAPVC) is a rare cyanotic congenital heart defect (CHD) in which all four pulmonary veins are malpositioned and make anomalous connections to the systemic venous circulation. (Normally, pulmonary venous return carries oxygenated blood to the left atrium and to the rest of the body). A patent foramen ovale or an atrial septal defect must be present in order to allow systemic blood flow.

# Historical Perspective
Total anomalous pulmonary venous connection was first described by Dr. Winslow, in 1739. The first description of the anatomic characteristics of total anomalous pulmonary venous connection was done by Dr. Brody in 1942. Anatomic description was further completed by another article authored by Dr. Darling in 1957. The first antemortem diagnosis was made in 1950. The first successful surgical repair was performed by Dr. Lewis, surgeon, in 1956.

# Classification
Total anomalous venous connection (TAPVC) is classified into four subtypes based on the location of pulmonary venous drainage. These subtypes include, supracardiac, cardiac, infracardiac, and mixed. Supracardiac (type I) is the most common form. Pulmonary venous obstruction is usually seen in infracardiac subtype though. Smith classification is another system that classified this disorder to two categories based on the presence of pulmonary obstruction and the location of anastomosis in relation to diaphragm.

# Pathophysiology
In patients of Total anomalous pulmonary venous connection (TAPVC) there is a mixing of oxygenated pulmonary venous blood with deoxygenated blood from systemic circulation.

# Causes
Like many other congenital heart defects, the exact cause of total anomalous pulmonary venous connection is not known. Few factors like genetics, maternal alcohol syndrome and some drugs have been found to occur with increased frequency.

# Differential Diagnosis
Total anomalous pulmonary venous connection should be differentiated from other cyanotic congenital heart diseases found in the pediatrics population. These disorders include tetralogy of Fallot, persistent truncus arteriosus, transposition of the great vessels, tricuspid atresia, trilogy of Fallot, and pentalogy of Fallot.

# Epidemiology and Demographics
Total anomalous pulmonary venous connection is a rare cyanotic congenital heart disease and occurs in 6 to 12 per 100,000 live births.

# Risk Factors
There are certain factors that increase the risk of congenital heart diseases, including maternal obesity, medication during pregnancy, alcohol and drugs, rubella during pregnancy, diabetes during pregnancy, and genetic factors.

# Screening
There is insufficient evidence to recommend routine screening for total anomalous pulmonary venous connection.

# Natural History, Complications and Prognosis
The natural history of untreated patients of TAPVC is not very favorable. It depends on the type of obstruction and amount of shunting across the atrium.

# Diagnosis

## History and Symptoms
The clinical features in total anomalous pulmonary venous connection depend on the type of anatomic variant present in the patient. This, in turn, determines the amount of mixing between the pulmonary and systemic circulation. In patients with obstructed TAPVC, pulmonary venous circulation drains into the systemic venous circulation. This causes increased returns to the right side of the heart and pulmonary hypertension that can manifest as cyanosis, dyspnea, pulmonary edema, respiratory failure, shock, and hypotension. In patients with unobstructed TAPVC clinical findings are quite similar to conditions with left-to-right shunting like dyspnea, difficulties in feeding, and failure to thrive.

## Physical Examination
The physical findings depend on the degree of obstruction and the degree of left-to-right shunting. Physical examination of patients may be remarkable for a decreased pulse, hypotension, tachypnea, peripheral edema, S3 gallop, diastolic murmur due to tricuspid regurgitation, hepatomegaly, and cyanosis.

## Laboratory Findings
There are no particular laboratory findings associated with the total anomalous pulmonary venous connection, however, hypoxia, acidosis, and hypercarbia may be observed in severe cases.

## Electrocardiogram
Electrocardiography findings are not very specific. However, they can show changes due to the dilatation of the right side of the heart. Possible findings include tall P wave, right axis deviation, and ST changes corresponding to right ventricular hypertrophy.

## X-ray
The findings on chest radiography vary depending on the type of anatomic variant of total anomalous pulmonary venous connection (TAPVC). Snowman sign is considered pathognomonic for the diagnosis of total anomalous pulmonary venous connection.

## MRI
Magnetic resonance imaging can be helpful as a diagnostic tool in conditions where the echocardiographic findings are inconclusive.

## CT
Computed tomography can be helpful as a diagnostic tool in conditions where the echocardiographic findings are inconclusive.

## Echocardiography
2D echocardiography along with doppler ultrasonography is a useful tool to diagnose total anomalous pulmonary venous connection.

## Other Imaging Findings
In patients with total anomalous pulmonary venous connection, cardiac catheterization can be used as a diagnostic and therapeutic modality. However, with the availability of better non-invasive tools the use of these are decreasing.

# Treatment

## Medical Therapy
Medical therapy are primarily used to stabilize the patient of total anomalous pulmonary venous connection.

## Surgery
Surgery is the mainstay of treatment in total anomalous pulmonary venous connection and should be performed as soon as possible. The surgical procedure varies depending upon the anatomy of the TAPVC lesion.