Microvascular involvement in cardiac pathology.

Abnormalities of the microvasculature are centrally involved in the pathogenesis of some forms of heart disease, but in others are consequences of it. Microvascular abnormalities may contribute to the progression of viral myocarditis and Chagas' disease. Focal abnormalities may occur early in some cardiomyopathies and do occur later in most types of myocarditis. The thickening of arteriolar walls in chronic hypertension is likely to contribute significantly to the impairment of coronary haemodynamics associated with adaptive ventricular hypertrophy and the consequent diminution of coronary reserve, increasing diffusion distances and failure of angiogenesis to compensate. However, the resulting myocyte necrosis stimulates inflammatory angiogenesis. When ischemic myocyte injury becomes irreversible there is a concomitant loss of capacity for reperfusion, the no-reflow phenomenon. Less severe temporary ischemia reduces the proportion of functional capillaries. Multiple mechanisms are involved in this microvascular stunning, including: reperfusion injury; leukocyte activation; adhesion and accumulation; and impaired endothelium-dependent vasodilation. Many of the microvascular changes are those of the inflammatory response to cell death and form part of a final common pathway in myocarditis, cardiomyopathy, cardiac hypertrophy and failure, and ischemic heart disease. Stimulation of angiogenesis prior to myocyte necrosis in hypertrophy and control of leukocyte activity in ischemic heart disease could minimize myocyte loss.