Cardiac myofibril disorientation and Z band abnormalities in idiopathic cardiomyopathy. An electron microscope study.

Morphological alterations in idiopathic cardiomyopathy were examined and their clinicopathological significance was discussed. Six cases of congestive type and five of hypertrophic type chosen from 22 patients according to our strict criteria were examined by light and electron microscopy. The diameter values of cardiac muscle fibers were broadly distributed with multiple peaks in congestive cases and with 4 peaks in the hypertrophic cases in contrast to the 2 peaks in controls. The chief electron microscopic alterations consisted of myofibril disorientation and Z band abnormalities. The congestive cases were characterized by decreased and disdarrayed myofibrils (loose myofibril disorientation), wheras the hypertrophic cases by abundant myofibrils characteristically entangled with each other (tight myofibril disorientation). The Z band showed 3 types of abnormalities. Type 1 was characterized by widening, bifurcation and overriding of Z bands while the regular sarcomere was retained. The changes were more conspicuous in the hypertrophic cases than in the congestive cases. Type 2 was represented by clumping of Z band substance, and Type 3 by an interwoven form of electron dense fibers. Types 2 and 3 were seen in some of the hypertrophic and congestive cases. The tight myofibril disorientation and Type 1 of Z band abnormalities were considered important cytopathological clues for the diagnosis of the hypertrophic type of idiopathic cardiomyopathy.