Sustained myocardial hypertrophy seven years or more after heart transplantation: a morphometric study of endomyocardial specimens.

: Myocyte hypertrophy is typical in transplanted hearts at 3 years. Because chronic hypertrophy may, if severe enough, increase the risk of infarction or gradual heart failure, our goal was to document the time course of its development and to look for signs of cellular changes in long-term survivors. We used light microscopic morphometry to estimate myocyte width in right ventricular endomyocardial biopsy specimens taken from 18 patients 1 week, 1 year, and 7 years after transplantation, and we used electron microscopic morphometry to estimate myocyte myofibril volume fractions and myocardial blood vessel length per unit volume in 10 patients at 7 to 12 years. Controls were pretransplant right ventricular biopsy specimens from 10 disease-free donor hearts. Myocyte width at 1 week (mean, 21.4 microns; SD, 2.7) was significantly greater than control (11.8, 2.2, p less than 0.01). By 1 year there was a small but significant regression (19.1, 2.4, p less than 0.05), but there was no significant change between 1 and 7 years (20.2, 2.5). Myocardial blood vessel length per unit volume at 7 to 12 years (1128 mm/mm3; SD, 259) was not significantly different from controls (1355, 298); myofibril volume fraction, however, (0.43, 0.04) was significantly lower than in controls (0.48, 0.03, p less than 0.01) but was not lower than in a different group of transplant patients studied previously at 3 years (41.4, 0.03). Myocyte hypertrophy occurs immediately after transplantation and is maintained indefinitely, with normal myocardial vascularity. There is a small reduction of myofibril content, which appears to be stable in long-term survivors.