Classification and distribution of myocardial fascicle and fiber disarray in 14 hearts with hypertrophic cardiomyopathy in 25.MU. thick sections.

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Abstract
In the usual thin sections (4-7 .mu.m), myocardial fiber disarray in cases of hypertrophic cardiomyopathy (HCM) usually takes the form of marked cellular disarray. Its diffuse extent is specific for HCM, but its presence alone is not pathognomonic for HCM. Previously thick sections (20-35 .mu.m) were found to be quite adequate for the study of structures of disorganized myocardial fibers. Here, classification and an assessment of the distribution of myocardial fiber disarray were studied in hearts with HCM in 14 Japanese patients and in 45 hearts (25 normal hearts, 10 hearts with hypertension and 9 hearts with myocardial infarction) as the controls. Abnormal myocardial fiber disarray in HCM was classified into poorly-differentiated and well-differentiated fascicular patterns. Abnormal myocardial fiber disarray in most hearts with HCM comprised the former pattern, and its extent was > 30% in all septums of hearts with HCM in comparison with < 10% in the controls. The diffuse disarray was mostly noted in the middle 3/5 in the septum and in the outer and middle thirds in the free wall, where disarray was rare in the control hearts. These findings support the idea that diffuse disarray in the specific portions in HCM may be congenital and specific for HCM. The major focus of the disarray in HCM was the septum with asymmetric hypertrophy. The disarray comprising 2 fascicular patterns involved a large number of fibers running in a vectorially perpendicular direction to the left ventricular cavity. Theoretically, shortening of such fibers would make the wall thinner and the cavity larger, and lengthening would make the wall thick and the cavity small. Thus, a wall with a considerable number of such fibers would be hypofunctional. Apparently, diffuse disarray in the middle 3/5 of the ventricular septum and in the middle and outer thirds of the ventricular free wall is fascicular, and it is congenital, specific and one of the pathogenic factors for HCM.