Pathologic Anatomy of Subaortic Stenosis and Atresia in the First Year of Life

Abstract

Ninety-nine of 1,362 congenitally malformed hearts (7.3 percent) obtained from patients 1 year of age or younger in the Cardiovascular Registry of The Hospital for Sick Children, Toronto, Canada were identified as having subaortic stenosis or atresia. The median age at death of these patients was 23 days (range less than 1 day to 1 year). Although multiple pathologic mechanisms were identified as potentially responsible for subaortic stenosis in this age group, those observed most frequently were (1) conoventricular malalignment, (2) adherent mitral valve, (3) accessory endocardial cushion tissue, (4) restrictive bulboventricular foramen, (5) poorly expanded subaortic conus, or combinations of these. The relatively discrete forms of subaortic stenosis including the fibrous membrane, fibromuscular, hypertrophic obstructive or tunnel forms were noted in only three patients. The remaining 96 patients with subaortic obstruction manifested a wide-spectrum of complex cardiac malformations including interruption or atresia of the aortic arch (29 patients); primitive ventricle with outlet chamber and transposition of the great arteries (12 patients); endocardial cushion defect (12 patients); aortic atresia with normal left ventricle (7 patients); tricuspid atresia with D-transposition of the great arteries (6 patients); and coarctation syndrome (7 patients). The remaining 23 patients had a variety of cardiovascular malformations. Frequently, more than one pathologic mechanism could be identified as causing subaortic obstruction in a single patient; and among any group of patients with a specific congenital defect (interruption of the aortic arch, for example), more than one mechanism could usually be identified. Sixty-eight of these 99 patients had some anomaly of the aortic arch, indicating reduced aortic flow. It is concluded that subaortic obstruction can result from a variety of mechanisms, but that significant intracardtac obstruction to systemic blood flow is usually just part of severely distorted cardiac anatomy.