Hypoplastic left heart syndrome: the importance of phenotypic diagnosis

Pathologic Characteristics of 119 Archived Specimens Showing the Phenotypic Features of Hypoplastic Left Heart Syndrome

To assess the phenotypic variations found among hearts diagnosed at autopsy with hypoplastic left heart syndrome, with attention to implications related to this syndrome as an acquired disease of fetal life, rather than being the consequence of abnormal embryogenesis. We assessed 119 specimens, from 2 archives, diagnosed initially as representing hypoplastic left heart syndrome. Among the 119 specimens, the majority of which had been entered into the archives prior to the availability of surgical treatment for the syndrome, 36 (30%) had the combination of mitral and aortic atresia, 26 (22%) had mitral and aortic stenosis, and 57 (48%) had mitral stenosis combined with aortic atresia. Of the hearts with combined atresia, 92% (33 specimens) had slit-like left ventricles, compared to 12% (3 specimens) of hearts with stenosis of both aortic and mitral valves, and 2 hearts (4%) with mitral stenosis and aortic atresia (P < 0.001). Hypoplasia of the left atrial appendage was present in half (18 specimens, 51%) of those with combined atresia, as opposed to just 18% (10 specimens) of mitral stenosis combined with aortic atresia (P = 0.001). Small left ventricles with valves deemed proportional in size were found in 11 (42%) of those with combined mitral and aortic stenosis. Fibroelastosis was significantly more common in the hearts with mitral stenosis compared to those with mitral atresia (76% vs 11%, P < 0.001). The ascending aorta was significantly smaller in the hearts with aortic atresia. The variability in the morphologic findings support the notion that the lesions seen represent acquired disease occurring subsequent to closure of the embryonic interventricular communication, rather than representing abnormal embryogenesis.