Hypoplastic left heart syndrome is the most common lethal cardiac malformation of the newborn. Its treatment, apart from heart transplantation, is the Norwood operation. The initial procedure for this staged repair consists of reconstructing a circulation where a single outlet from the heart provides systemic perfusion and an interpositioning shunt contributes blood flow to the lungs. To better understand this unique physiology, a computational model of the Norwood circulation was constructed on the basis of compartmental analysis. Influences of shunt diameter, systemic and pulmonary vascular resistance, and heart rate on the cardiovascular dynamics and oxygenation were studied. Simulations showed that 1) larger shunts diverted an increased proportion of cardiac output to the lungs, away from systemic perfusion, resulting in poorer O2 delivery, 2) systemic vascular resistance exerted more effect on hemodynamics than pulmonary vascular resistance, 3) systemic arterial oxygenation was minimally influenced by heart rate changes, 4) there was a better correlation between venous O2 saturation and O2 delivery than between arterial O2 saturation and O2 delivery, and 5) a pulmonary-to-systemic blood flow ratio of 1 resulted in optimal O2 delivery in all physiological states and shunt sizes.

Competing risks analysis defines the prevalence of the various outcomes after Norwood operation and predicts improved outcomes with successful modification of controllable risk factors.

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Primary repair for infants with multiple ventricular septal defects is associated with good late outcomes. The right atrial approach is satisfactory for most muscular defects, although limited apical left ventriculotomy was used for apical defects. Pulmonary artery banding should be limited to patients with complex associated defects.

Although improvements in management might have lessened the effect of some of the traditionally reported risk factors related to variations in the cardiovascular anatomy, noncardiac abnormalities and low birth weight remain as a future challenge for the physician caring for the patient with single-ventricle physiology.

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Staged reconstruction has significantly improved the intermediate-term outlook for patients with HLHS. Factors addressing improvements in early (< 1 month) first-stage survival would be expected to add significantly to an overall improved late outcome. Currently employed refinements in operative technique are associated with eliminating or reducing pulmonary artery distortion and dysrhythmia.

Infant development is delayed after the Norwood operation. Pilot data do not suggest that regional cerebral perfusion improves infant development. Further study with a multicenter clinical trial is imperative to address this important question.