Morbid anatomy in neonates with Ebstein's anomaly of the tricuspid valve: pathophysiologic and clinical implications.

The hearts of six neonates with Ebstein's anomaly of the tricuspid valve who died in the 1st month of life were compared with hearts of six age- and size-matched control neonates. All six hearts had morphologically severe disease with gross right atrial dilation and marked apical displacement of the tricuspid valve. All had a secundum atrial septal defect and four had additional cardiac lesions (pulmonary atresia in two, ventricular septal defect in two). There was significant thinning of the right ventricular free wall distal to the tricuspid valve (3 +/- 0.2 mm vs. control 4.2 +/- 0.2, p less than 0.01) and right ventricular fiber diameter was reduced (7.2 +/- 0.3 microns vs. control 11.4 +/- 0.6, p less than 0.001). The fibrous tissue content of both right and left ventricular free walls was increased (right, 29.3 +/- 2.6% vs. control 8.7 +/- 1.1, p less than 0.001; left, 23.2 +/- 1.5% vs. control 8.5 +/- 0.7%, p less than 0.001). Although the right ventricular abnormalities might be explained by hemodynamic stress in utero, abnormalities of the left ventricular free wall suggest that either genetic or nonhemodynamic environmental factors are involved in the morphogenesis of this condition. Increased right and left ventricular fibrosis may contribute to the poor early outcome in this group and may predispose to late complications, such as subnormal exercise performance, hemodynamic deterioration or late sudden death that may occur in patients with Ebstein's anomaly who survive the neonatal period.