Transmural perfusion gradients distal to various degrees of coronary artery stenosis during resting flow or at maximal vasodilation.

Regional myocardial perfusion (assessed by 15 mu tracer microspheres) was determined at various levels of stenosis of the left circumflex coronary artery in anesthetized dogs. Measurements during control and at three levels of stenosis produced by a micrometer-driven mechanical occluder were made in each heart. No change was found in the transmural distribution of coronary blood flow until 93% stenosis. At levels above 93% stenosis there was a linear decrease in subendocardial perfusion with only minor changes in subepicardial perfusion. During maximal vasodilation produced by reactive hyperemia, the decrease in subendocardial flow was observed at levels greater than 60% stenosis. It is concluded that the subendocardium of the left ventricle has a large vasodilator reserve and severe stenoses are required to disrupt flow when autoregulation is intact. When autoregulation is abolished, reduction in subendocardial flow occurs at lesser degrees of stenosis.