Extensive myocardial fiber disarray in aortic and pulmonary atresia. Relevance to hypertrophic cardiomyopathy.

Myocardial fiber disarray is a distinctive histopathologic finding seen in asymmetric hypertrophic cardiomyopathy. We studied 14 hearts with aortic atresia and intact interventricular septum, six hearts with pulmonic atresia and intact interventricular septum, eight normal infant hearts matched for age of the study hearts, and one nonadult heart with hypertrophic cardiomyopathy and asymmetric hypertrophy and quantitatively analyzed tissue sections through both ventricles and the septum. Normal hearts had an average overall fiber disarray of 8.7% (range 3.8-17%) of the left ventricle including septum. Hearts with pulmonary atresia had an overall disarray of 70.4% (range 13-97%) of the entire right ventricle, and those with aortic atresia 62.1% (range 26-97%) of the left ventricle. The one infant heart with hypertrophic cardiomyopathy showed 15.5% disorder of the left ventricular free wall, 75% disorder of the septum and 47% overall myocardial fiber disarray. Thus, while quantitative criterion distinguished normal from abnormal hearts, they did not distinguish among the various pathologic states. Although extensive myocardial fiber disarray is not exclusive to, or pathognomonic of, hypertrophic cardiomyopathy, it is a useful finding taken in the context of the overall disease. The sensitivity and specificity of this isolated morphologic observation as an indication of hypertrophic cardiomyopathy may be misleading.