Evidence for muscle fiber hyperplasia in the septum of patients with hypertrophic obstructive cardiomyopathy (HOCM). Quantitative examination of endomyocardial biopsies (EMCB) and myectomy specimens.

Asymmetric thickening of the septum is one of the hallmarks of hypertrophic obstructive cardiomyopathy (HOCM). Endomyocardial biopsies (EMCB) from the right side of the septum and myectomy specimens from its left part were morphometrically investigated to determine the size of septal myocytes, as well as the volume density of the interstitium and fibrous tissue, and to estimate the number of transseptal muscle fiber layers. EMCBs of seven patients with normally shaped hearts, taken as controls (N), EMCBs of seven consecutively examined patients with HOCM (HOCM 1), and of seven HOCM patients with additionally available myectomy specimens (HOCM 2) were evaluated. In myectomy specimens muscle fiber thickness and volume density of the interstitium and fibrous tissue were significantly increased, as compared with the findings in the EMCBs. The echocardiographically determined septal thickness was increased by 93% in HOCM 1 and by 150% in HOCM 2 compared with controls; however, the increase in muscle fiber thickness and volume density of the interstitium did not give a sufficient explanation for the increased septal thickness in both groups of HOCM. Based on EMCB data, the estimated number of septal muscle fiber layers was 715 +/- 93 in group N, 1242 +/- 149 in HOCM 1, and 1119 +/- 177 in HOCM 2, while 810 +/- 232 layers were estimated according to the findings from myectomy specimens. Taking into account that EMBC represent only 1 mm of septal thickness, and myectomy specimens up to 15 mm, an increase in the septal muscle cell layers of about 30% can be estimated in HOCM hearts.(ABSTRACT TRUNCATED AT 250 WORDS)