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

In the usual thin sections (4-7μ), 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. In our previous report, we stated that thick sections (20-35μ) was quite adequate fro the study of structures of disorganized myocardial fibers. In the present paper, 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 control, in the thick sections. In these thick sections, 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 over 30% in all septums of hearts with HCM in comparison with less than 10% in the controls. The diffuse disarray was mostly noted in the middle three fifths 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 symmetric hypertrophy. The disarray comprising two fascicular patterns involved a large number of fibers running in a vectorically perpendicular direction to the left ventricular cavity. Theoretically, shortenning 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. We conclude that diffuse disarray in the middle three fifths of the ventricular septum and in the middle and outer thirds of the ventricular free wall is fascicular, and that it is congenital, specific and one of the pathogenic factors for HCM.