Asymmetric Septal Hypertrophy (ASH) in Infancy

Clinical and pathologic observations were made in four infants who died with asymmetric septal hypertrophy in the first five months of life. One of these infants was stillborn and the other three were aged 1½ months, 4½ months, and 5 months at the time of their deaths. The three live-born infants demonstrated severe congestive heart failure and cardiac enlargement. The clinical features present in these three infants during life suggested a variety of other congenital cardiac malformations, including congenital mitral regurgitation, pulmonary stenosis, and endocardial fibroelastosis. In each of the four infants the ventricular septum was markedly hypertrophied and was thicker than the postero-basal left ventricular wall; septal to postero-basal free wall thickness ratios ranged from 1.8 to 2.6. Moreover, the septum of each infant contained a disordered arrangement of hypertrophied cardiac muscle cells. In three of the infants the myocardial cellular abnormalities were less marked in the left ventricular free walls than in the ventricular septum. In the fourth infant disorganized cardiac muscle cells were distributed widely in both the ventricular septum and left ventricular free wall; the clinical findings suggested the absence of left ventricular outflow obstruction in this infant. Asymmetric septal hypertrophy was documented in one first degree relative of each infant. It is concluded that asymmetric septal hypertrophy is a genetically transmitted disease that may present clinically in infancy and lead to infant death. Furthermore, the characteristic pathologic feature of asymmetric septal hypertrophy in adults, a disproportionately thickened ventricular septum containing numerous hypertrophied and disorganized cardiac muscle cells, can be present at birth.