Comparison of percentage area of myocardial fibrosis and disarray in patients with classical form and dilated phase of hypertrophic cardiomyopathy.

This study compared the percentage area of myocardial fibrosis and disarray between hypertrophic cardiomyopathy (HCM) and DHCM (progression to dilatation of the left ventricle in patients with HCM, i.e., dilated phase HCM), and investigated whether DHCM is included in the natural course of HCM. Twenty-six autopsied hearts were studied, 14 from patients with HCM, and 12 from patients with DHCM, classified by age/decade group. The section at the level of the binding site of papillary muscle was used for the morphometrical examination. In the overall evaluation of both ventricles, all 4 HCM age groups showed percentage area of myocardial fibrosis < 10%, and the value gradually increased with age. In contrast, the percentage area of the DHCM cases was over 20%, and these cases showed diffuse massive fibrosis that did not increase with age. The percentage area of myocardial disarray was over 90% in 3 cases with DHCM. The percentage areas of myocardial fibrosis and disarray of the DHCM hearts were extremely high compared with the HCM hearts, indicating that DHCM is not included in natural course of HCM. Other abnormalities including contractile proteins may be important role in the widespread myocardial disarray leading to massive fibrosis in the pathogenesis of DHCM.