Muscle fiber disarray in patients without hypertrophic cardiomyopathy

Muscle fiber disarray (MFD) has been described as the histologic feature of hypertrophic cardiomyopathy (HC), but it was also found in normal and other abnormal conditions. Its distribution related to the topography of the myocardium has not been described. In this paper, the incidence of MFD in hearts free from HC, the frequency of the histologic disorganization and the affected muscles involved were studied at autopsy. 29 hearts with acute myocardial infarction and 1 with suppurated myocarditis were employed. Macroslides containing the point of maximum septal enlargement were selected for histological examination. The areas of MFD were measured by a polar planimeter and correlated with the involved wall, the total slice area, parietal widths and involved muscles. 27 patients (90%) presented with MFD; hypertrophic ventricular walls were observed in 10, 8 of which had MFD. The remaining 20 patients with nonhypertrophic ventricular walls had MFD in 19 instances. There was septal posterior involvement in 26 cases (p less than 0.0005). 12 patients (44.4%) had only one wall involved. Only 1 patient presented more than 5% of MFD in regard to the total area. The septal wall was the most affected (p less than 0.0005). The most commonly affected muscle was the deep-sinospiral, either alone or combined with other muscles (p less than 0.01). Greater MFD was found (23/30) in patients with septum/posterior wall ratio less than 1.3 cm. It is concluded that MFD may affect up to 10% of the septum in patients free from HC, and that secondary hypertrophy is not a prerequisite for MFD.(ABSTRACT TRUNCATED AT 250 WORDS)