Heterogeneity in the coronary circulation.

The blood flow to the subendocardial layers of the left ventricle is approximately 10% higher than that to the outer layers. The larger subendocardial blood flow reserve results from a higher vascular density within that layer. The systolic coronary inflow is the result of the net forward flow and a concealed backflow. The blood flow at the microcirculatory level is not homogeneous, as certain interventions can recruit "dormant" capillaries. When coronary artery occlusion occurs, the resistance of the collateral channels, which is high, becomes the major determinant of the blood flow to the ischemic tissues. The blood flow in such ischemic tissues is heterogeneous, as the extravascular forces on these collateral channels vary. Reperfusion after occlusion is characterized by marked heterogeneity. If reflow is reinstituted late after cell death, the sudden rush of blood under normal pressure ruptures the microvessels, resulting in hemorrhagic infarction and the no-reflow phenomenon.