Total Anomalous Pulmonary Venous Connection
- A total anomalous pulmonary connection, is characterized by drainage of the entire pulmonary venous circulation (all pulmonary veins) into systemic venous vessels which connect to the right atrium with no veins connecting to the left atrium.
- Four subtypes have been identified based on the origins of the anomalously draining veins.
- Type I (supracardiac) occurs when all pulmonary veins return to a common vertical vein, which may drain into a left superior vena cava or brachiocephalic vein.
- Type II (cardiac) is characterized by connection of the pulmonary veins to the common pulmonary vein which drains directly into the heart either via the coronary sinus or right atrium.
- Type III (infradiaphragmatic) refers to a defect where all pulmonary veins drain into a venous channel that passes through the diaphragm to the portal vein, ductus venosus, or hepatic vein, which then re-enters the heart via the left inferior vena cava.
- Type IV (mixed) consists of defects that combine two or more of the other types, with any combination of anatomic entry of the pulmonary veins into venous circulation.
- The anomalous pulmonary venous system may have varying level of obstructions, due to compression by adjacent structures, which leads to pulmonary hypertension. Obstruction is typically severe in Type III, as the diaphragm can significantly compress the pulmonary venous structures.
- Drainage of the entire pulmonary venous system into systemic venous circulation causes mixing of blood; resulting in blood of similar oxygen concentration in all heart chambers. Therefore, the patient's arterial oxygen saturation is dependent on the amount of pulmonary blood flow which in turn, is dependent on pulmonary resistance and obstruction of the pulmonary veins. With large pulmonary blood flow, oxygen saturations can reach the high 80s: in contrast, with limited blood flow, saturations can be much lower and even incompatible with life.
- When obstruction of the pulmonary venous return is significant, the infant will be acutely ill within days of birth. Pulmonary edema will lead to tachypnea and gasping, while mixing of blood supplies leads to cyanosis.
- When pulmonary venous return is unrestricted, the infant generally does not appear acutely ill but may show mild tachypnea and/or minimal cyanosis.Although clinical problems in such patients will vary depending on severity of the defects and the presence or absence of pulmonary venous obstruction, it is generally recommended that surgical repair be performed as soon as the diagnosis is made.