Truncus arteriosus

Pathophysiology

A persistent truncus arteriosus occurs when conotruncal septation fails to separate the truncal artery into the aorta and pulmonary arteries. A single great vessel straddles a large outlet ventricular septal defect. This single great vessel gives rise to the pulmonary artery and ascending aorta. A spectrum of severity is based on the origin of the pulmonary arteries from the truncal artery. A main pulmonary artery may arise from the truncal artery (type I), the branch pulmonary arteries may arise separately but in close proximity (type II), or the branch pulmonary arteries may arise widely separate from the lateral aspects of the truncal artery (type III). Truncal valve abnormalities are often encountered in patients with this lesion. Truncus arteriosus results in unrestrictive left to right shunting of blood and pulmonary overcirculation. Congestive heart failure and pulmonary artery hypertension is a nearly universal finding. Pulmonary vascular obstructive disease will occur early if no intervention is undertaken. It is important to evaluate truncal valve function preoperatively since significant stenosis or insufficiency of the truncal valve will require intervention at the time of surgery.

Surgical technique

Total repair of truncus arteriosus requires cardiopulmonary bypass and aortic cross-clamping. The pulmonary artery is separated from the truncal root and the truncal vessel is closed directly or with a patch of synthetic material or cryopreserved homograft. A ventriculotomy is then made in the right ventricular outflow tract. The ventricular septal defect is closed, often utilizing a running monofilament suture. Next, a valved homograft conduit is implanted, connecting the right ventricle to the pulmonary arteries. Truncal valve repair, replacement or valvotomy is performed as an initial step when indicated. Transesophageal echocardiography is utilized to evaluate adequacy of repair following weaning from cardiopulmonary bypass. Cardiopulmonary bypass time and aortic cross-clamp time required to complete repair are moderate in length. Delayed sternal closure is often required following repair of truncus arteriosus.

Postoperative considerations

Repair of truncus arteriosus is one of the more extensive cardiac procedures performed on neonates. The postoperative course is consequently more complex. Invasive monitoring catheters utilized following surgery include arterial, central venous, and left atrial lines. An oximetric catheter placed in the pulmonary artery is utilized to assess cardiac output and pulmonary artery pressure. Vasoactive infusions required for hemodynamic management might include dopamine or dobutamine, epinephrine, milrinone, nitroprusside and/or phenoxybenzamine. Sedation and hyperventilation are initiated early following surgery. Infusions of fentanyl and a neuromuscular blocking agent are usually required to minimize pulmonary artery hypertensive episodes. Inhaled nitric oxide has proven useful in the management of postoperative pulmonary artery hypertension.

Bleeding is a potential postoperative complication. Suture lines exposed to systemic pressure, and homograft suture lines under elevated pressure predispose these patients to early postoperative bleeding. Hemodynamic instability can occur following surgery, especially in patients who have truncal valve dysfunction. Atrioventricular conduction disturbances may be encountered since surgical manipulation in the area of the atrioventricular conduction tissue is required for repair. Pacing capability should be readily available. Systemic arterial oxygen saturation following surgery should be normal. Intracardiac pressures should be normal. Length of hospital stay required following repair of truncus arteriosus is variable, but ten days to two weeks is average.