Right ventricular-pulmonary artery connection in stage 1 palliation of hypoplastic left heart syndrome.

See related article on page 1378. T he Norwood procedure has undergone numerous modifications since its original description. The term “modified” Norwood now applies to several variations both in the reconstructive techniques and in the conduct of bypass. Surgeons now have available technical modifications that can be applied to the variable anatomy encountered within the complex spectrum of hypoplastic left heart syndrome. Of equal importance to the technical advances, better understanding of the Norwood physiology and improved postoperative management have resulted in improved outcomes. In fact, it is difficult to separate the technical aspects from the physiologic as, more than in any other lesion, the two are interdependent. Perhaps one of the most critical observations made regarding post-Norwood physiology was the concept of pulmonary over-circulation and balancing the systemic/pulmonary flow (Qp/Qs) ratio. Initial surgical response to increased understanding of this phenomenon included the use of smaller shunts, with a 3.5-mm shunt being used for most infants and even a 3.0-mm shunt for those weighing less than 3.0 kg. Despite a more favorable Qp/Qs ratio with the use of smaller shunts, the fact that the shunt in a typical Norwood procedure comes off a systemic vessel unavoidably results in diastolic runoff and lower diastolic pressure. In addition, using a “one size fits all” approach can result in significant variation in saturations and hemodynamics because of other variables such as size of the patient, size of the feeding vessel, overall cardiac output, and pulmonary vascular resistance. Hence, inadequate systemic perfusion as a result of increased Qp/Qs and significant cyanosis related to a decreased Qp/Qs are not uncommon in the early postoperative period. The management of these patients can be quite complex and unfortunately not always successful. In addition, concern has been raised regarding the effect of the diastolic runoff in terms of both short-term and long-term coronary blood flow, although no evidence exists that myocardial perfusion is significantly affected by the classic shunt physiology. Nonetheless, the not infrequent progressive myocardial failure seen in some patients after palliation for hypoplastic left heart syndrome raises concern about coronary perfusion as a potential cause. The importance of balancing shunt flow is so critical that placement of an adjustable snare around the shunt or placement of hemaclips has been tried. However, the potential risks of shunt thrombosis when snares are used, as well as potential infectious issues from repeated mediastinal exploration for snare adjustment, must be considered. Pulmonary blood flow can be limited by the use of a 3.0-mm polytetrafluoroethylene shunt (Gore-Tex; W. L. Gore & Associates, Inc, Flagstaff, Ariz); however, it is generally believed that such shunts are at increased risk of thrombosis and may require early reintervention as a result of worsening cyanosis. Hence, management of Qp/Qs, and particularly over-circulation, has been medical, with ventilator adjustment, use of systemic vasodilators, and support of overall cardiac output being the mainstays of therapy. Although the using a right ventricular–pulmonary artery (RV-PA) conduit rather than a typical systemic–pulmonary artery shunt is one of the more recent and intriguing modifications to the Norwood procedure, RV-PA conduits have been described in place of classic systemic shunts in other congenital defects such as pulmonary atresia with ventricular septal defect and pulmonary atresia with intact ventricular septum. Although the first application of this technique to the Norwood From the Department of Cardiothoracic Surgery, Children’s Hospital Medical Center, Cincinnati, Ohio.