Ultrastructural Morphometry of Endomyocardial Biopsy Samples

Background. The coronary microvasculature may be abnormal even in the presence of angiographically normal epicardial arteries. Abnormalities of small coronary vessels have been invoked as a cause of angina. Methods and Results. To quantitatively evaluate the morphology of capillaries in patients with idiopathic dilated cardiomyopathy (DCM) or the syndrome of angina and small vessel disease (SVD), we performed electron microscopic morphometry of capillaries in right ventricular biopsy samples taken from 32 patients. Ten had angina, normal epicardial coronary arteries, and evidence for SVD; 12 had DCM; and 10 had normal hearts. In patients with DCM, the ratio of microvessels to myocytes was not different than that of controls (0.49±0.06 versus 0.51±0.05). Mean crosssectional areas of the capillaries (lumen plus wall) and lumen were significantly greater than those of controls (45.3+15.1 versus 22.7±83 inm2, p<0.001; 17.6±6.9 versus 11.6±6.2 jum2, p<0.05, respectively). Fibrous content of the myocardium, as assessed by quantitative light microscopy, was significantly increased (163+3.3% versus 5.0±2.4%,p<0.001). In contrast, in patients with SVD, the capillary-to-myocyte ratio was reduced (0.33±0.08, p<0.001). Although mean cross-sectional areas of the entire capillary (32.4± 19.7 ,um2) and the lumen (8.9+7.8 ,um2) were not statistically different than those of controls, there was an absence of capillaries less than 15 ,um2 in cross-sectional area, and the frequency distribution of the lumen area was skewed to the left. Swollen endothelial cells frequently encroached upon the lumen. There was a mild increase in fibrous content (9.5+3.7%, p <0.05). Conclusions. Enlarged capillaries and a normial ratio of capillaries to myocytes appear to be features of DCM. Of the patients with SVD, there was both a relative lack of capillaries and capillary lumen narrowing from swollen endothelium. These changes may induce ischemia and angina and may result in mild fibrosis. (Circulation 1991;84:203-210)