Persistence of subendocardial perfusion after subtotal coronary embolisation.

The effects of acute subtotal embolisation of small coronary arteries on regional coronary flow and vasodilator reserve were investigated in seven open chest dogs. Unlabelled plastic microspheres (26(2) ?m in diameter) were injected as boluses of 200 000-400 000 microspheres into the circumflex artery. Embolisation was repeated until reactive hyperaemia was totally abolished, which occurred after the injection of 62 000(4000) microspheres per gram. Intracoronary adenosine was then infused for 20 min at 1.2 mg·min-1. Regional myocardial blood flow was measured by radioactive microspheres under control conditions, after coronary embolisation, and during adenosine infusion. Coronary blood flow (0.98(0.07) ml·min-1·g-1) was reduced to 0.66(0.08) ml·min-1·g-1 after embolisation (p<0.005) when reactive hyperaemia was practically abolished. Embolisation reduced epicardial flow from 0.93(0.08) to 0.40(0.09) ml·min-1·g-1 (p <0.001), whereas endocardial flow was unchanged (1.03(0.11) vs 0.92(0.14) ml·min-1·g-1; NS); as a consequence, the endocardial to epicardial flow ratio increased from the control value of 1.11 (0.06) to 2.31(0.35) (p<0.005). Adenosine infusion increased coronary blood flow from 0.66(0.08) to 1.66(0.41) ml·min-1·g-1 (p <0.05). Endocardial blood flow increased more than epicardial blood flow, leading to a further increase in the endocardial to epicardial flow ratio (3.79(0.13); p<0.05). Thus it is concluded that (a) embolisation of small arteries abolishes the reactive hyperaemic response to transient coronary occlusion; (b) microembolisation predominantly reduces subepicardial perfusion; and (c) adenosine administration may increase total and regional flow after subtotal occlusion of coronary small arteries.