Myocardial capillaries and coronary flow reserve.

he general assumption among cardiologists is that myoardial ischemia occurs only in the presence of obstructive oronary artery disease. This is based on the misconception hat abnormal coronary flow reserve (CFR) is associated nly with coronary stenosis and results from the increased esistance offered by the stenosis. We showed some time ago hat when the normal coronary vasculature is maximally ilated with adenosine, the capillaries (which do not have mooth muscle and hence do not vasodilate) are the bottleeck to hyperemic flow (1). Thus, although the capillaries rovide only one-quarter of the total microvascular resisance (MVR) at rest, they offer three-quarters of the total VR during hyperemia, despite the total MVR decreasing y one-half during hyperemia from arteriolar and venous asodilation.