Right ventricular endomyocardial biopsy findings in 25 patients with sick sinus syndrome.

A variety of myocardial lesions have been demonstrated in atrial muscle in patients with sick sinus syndrome (SSS), but the right ventricular myocardium has not been studied in detail in a large series. Therefore, we performed right ventricular endomyocardial biopsies in 25 patients with SSS (SSS group), and the presence or absence of ventricular myocardial lesions was determined histologically. As a control, biopsies of corresponding sites in 12 normal autopsied hearts were obtained (N group). The mean cardiac myocyte transverse diameter was 14.2 +/- 3.6 microm in the SSS group and 11.7 +/- 3.1 microm in the N group (P < 0.01). In the SSS group, cardiac myocyte hypertrophy was observed in 20 of 25 subjects (80%), and myocyte size variation was more frequent. Although the difference was not significant, myocyte disorganization, myocytolysis, nuclear deformity, interstitial large mononuclear cell proliferation, and endocardial lesions, which were not seen in the N group, were observed in the SSS group. A variety of myocardial lesions, including cardiac myocyte hypertrophy, are present not only in atrial, but also in ventricular muscle in SSS.