Improving results for hypoplastic left heart syndrome
The goals of initial palliation for HLHS, often termed a "Norwood operation" or "Stage I" are threefold:
- Unobstructed blood flow from the right ventricle to the systemic arterial tree
- Unobstructed pulmonary venous return from the left atrium to the tricuspid valve
- A stable, controlled source of pulmonary blood flow
Goal 1: Since the heart has only one good outflow valve -- the pulmonary valve -- systemic outflow is reconstructed by anastomosing the main pulmonary artery to the reconstructed aortic arch, thus forming a "neo-Aorta," so the right ventricle can function as the systemic ventricle.
Goal 2: Because the mitral valve is also too small or completely atretic, an atrial septectomy ensures that pulmonary venous blood has a free pathway from the left atrium to the tricuspid valve and into the systemic ventricle.
Goal 3: Until recently, pulmonary blood flow was derived from a Blalock-Taussig shunt, a small synthetic graft from the innominate artery to the right pulmonary artery. This shunt supplies pulmonary blood flow for several months.
After recovery from the Norwood operation, two more operations are required. The infant's second surgery will divide the shunt and anastomose the superior vena cava directly to the right pulmonary artery. This is known as a bidirectional cavopulmonary anastomosis (BDCPA) or Glenn anastomosis and is performed at 4-6 months of age. A third procedure, the Fontan operation is typically performed at 2-3 years of age. Here, the inferior vena cava is similarly connected directly to the pulmonary artery.
National centers of excellence report Norwood (first stage) mortality of approximately 10-15%. The vast majority of deaths occur at the time of first stage palliation or prior to the performance of the BDCPA. Indeed, the out-of-hospital mortality for Norwood survivors approximated 25% prior to their second stage surgery in a recent multicenter report. Aggressive follow-up of these infants prior to the BDCPA has been shown to reduce this interstage mortality.
Largely because of these unsatisfactory early results with the classical Norwood operation utilizing a Blalock-Taussig shunt, surgeons are currently exploring alternative strategies. The most popular of these is Sano's modification of the Norwood. In this operation, rather than a Blalock-Taussig shunt, a pressure-restrictive synthetic tube graft, usually 5-6mm in diameter, is placed as a direct connection between the right ventricle and the pulmonary arteries. Several retrospective reports have described improved early and interstage mortality with this approach. Intermediate and long-term outcomes are, of course, unknown. There are worries about the presence of an incision in the single ventricle for the proximal conduit insertion as a cause of long-term ventricular dysfunction or arrhythmias. An NIH-funded prospective randomized multi-center trial to compare the classical Norwood to Sano's modification is getting under way in North America in which Children's Medical Center Dallas will participate.
At Children's Medical Center Dallas in 2004, 19 Norwood operations were performed with a mortality rate of 5.2%. There was one interstage mortality in the 18 Norwood survivors prior to BDCPA (5.6%) during that time period. The overall mortality for open heart surgery at Children's in 2004 was 1.7%.