Pulmonary Atresia and Ventricular Septal Defect

Pulmonary Atresia and Ventricular Septal Defect (PA/VSD) represents the most severe form of Tetralogy of Fallot. PA/VSD presents a difficult management plan, since variations in blood supply to the pulmonary arterial tree may be complex and create significant variations in the development of the pulmonary arteries. 

Pulmonary atresia is strictly defined as loss of continuity between the right ventricle and the pulmonary artery. Most commonly the pulmonary valve and the proximal pulmonary trunk are involved. The relationship of right and left pulmonary arteries is of surgical importance. The pulmonary arteries are considered 'confluent' when they maintain free communication with each other. However, when the atretic process extends past the bifurcation of the main pulmonary artery (MPA) into the branches, interrupting the continuity between the LPA and RPA, 'non-confluence' is said to exist. 



Clinical considerations... 


NOTES on PA-VSD:




PA-VSD generally presents early in the neonatal period with hypoxemia and cyanosis. Symptoms become evident or progress as the ductus arteriosus begins to close. If the amount of pulmonary blood flow from bronchial and systemic collaterals is insignificant, the loss of ductal flow will be incompatible with life. Treatment with prostaglandins to maintain ductal patency until a surgical shunt can be created is then necessary. Patients with significant systemic collateral flow to the pulmonary arterial tree, may not be hypoxemic in infancy. This shunt is fixed, and the child will likely eventually outgrow the pulmonary blood flow and become more hypoxemic. Rarely, when flow through the collaterals is actually excessive, signs and symptoms of congestive heart failure ensue. 

Physical exam will be noteworthy for some degree of cyanosis. The second heart sound will be single. Additional cardiac sounds may arise from the source(s) of pulmonary blood flow. For example, continuous murmurs from the PDA or systemic-pulmonary artery collaterals may be heard. ECG findings are similar to TOF (Tetralogy of Fallot) with right axis deviation and right ventricular hypertrophy. Without the VSD, right ventricular hypoplasia would be expected and right ventricular forces would be diminished. Chest Xray (CXR) may show the ÒbootÓ shape consistent with a TOF variant. A right sided aortic arch is much more common with PA-VSD than with classic TOF (approximately 50% vs. 20%). Pulmonary vascular markings and the degree of central pulmonary hypoplasia that is evident on CXR is variable depending on the pulmonary arterial connection and the amount of pulmonary blood flow. 

Echocardiography is reliable for confirming the diagnosis and delineating the intracardiac and central pulmonary artery anatomy, and can be used to determine the coronary artery distribution. The distal pulmonary arterial connections and very hypoplastic connections may not be well seen and may require angiography or CT/MRI imaging for more exact delineation. Angiography can also help define the coronary artery anatomy, as anomalies of the coronary arteries that overlie the anterior surface of the right ventricle will impact the childÕs surgical repair. 

Treatment is surgical to establish reliable and adequate pulmonary blood flow. The complexity of the surgical repair is dependent on the source(s) of pulmonary blood flow (patent ductus arteriosus, bronchial collaterals, or other systemic to pulmonary collaterals) and the degree of main, and branch, pulmonary artery hypoplasia. The degree of hypoplasia is directly proportional to the amount of flow the artery received during development. Confluent pulmonary arteries with blood supply from a proximal ductus or systemic collateral may be only mildly hypoplastic or even normal in size. If the pulmonary arteries are nonconfluent and pulmonary blood flow depends on distal or multiple separate collateral connections, hypoplasia may result, as the flow is diminished and unequal. 

Confluent pulmonary arteries of sufficient size can undergo complete repair without palliation. This includes VSD closure and creation of continuity between the RV and the MPA, typically with a valved conduit (Rastelli procedure). If the pulmonary artery hypoplasia is significant, palliation with a systemic to pulmonary shunt will be required. This will stabilize the pulmonary flow and allow for growth. With adequate growth, complete repair can be attempted later. The modified Blalock-Taussig shunt is associated with less pulmonary over-circulation than the older direct aorto-pulmonary connections (Waterston and Potts) and results in less distortion of the pulmonary anatomy that could complicate later repair.