Pulmonary atresia is usually classified into tetralogy of Fallot with pulmonary atresia (TOF-PA) and pulmonary atresia with intact ventricular septum (PA-IVS). It can also be part of more complex cardiac lesions. Our objective was, analyzing fetal and neonatal human heart specimens, to determine the anatomical and pathophysiological mechanisms responsible for the different phenotypes of pulmonary atresia.

We analyzed macroscopically 151 specimens with pulmonary atresia from the anatomic collection of the French Reference Center for Complex Congenital Heart Defects. Measurements included the height and width of the subpulmonary atrium, the diameter of the tricuspid valve, the size and thickness of the subpulmonary ventricle, the location of the outlet septum, the nature of the pulmonary atresia (muscular or valvar), the diameter of the pulmonary arteries.

Hearts were classified in six groups: TOF-PA, 53 (35%); PA-IVS, 43 (28%): tricuspid anomalies, 17 (11%); anomalous ventriculo-arterial connections, 27 (18%); univentricular hearts, 11 (7%). Pulmonary atresia was mostly valvar in tricuspid anomalies and PA-IVS and muscular in the other groups. Pulmonary arteries were larger in PA-IVS. Outlet septum was incorporated to ventricular septum in PA-IVS and tricuspid anomalies, malaligned in TOF-PA, variable in other groups. The right ventricular wall was thicker in PA-IVS and thinner in tricuspid anomalies. The tricuspid valve was, by definition, abnormal in tricuspid anomalies and was also abnormal in most of PA-IVS specimens. The right atrium was larger in tricuspid anomalies.

The anatomical differences between the groups support the hypothesis of mechanisms occurring at different stages of cardiac development. Larger pulmonary arteries in PA-IVS, incorporated outlet septum and valvar atresia in PA-IVS and tricuspid anomalies may indicate a late phenomenon. Increased right ventricle thickness in PA-IVS may impair transpulmonary blood flow, leading to late valvar atresia. A similar phenomenon could induce pulmonary atresia in tricuspid anomalies, secondary to another type of right ventricle myopathy with a thinner myocardium, and to tricuspid regurgitation.