Comparison of Regional Myocardial Perfusion Determined by Ionic Potassium‐43 to That Determined by Microspheres

The ability of ionic potassium-43 (43K) to reflect alterations in regional myocardial perfusion was determined by comparing the distribution of this tracer to that of labeled microspheres and flowmeter measurements under several conditions of coronary blood flow. When flow was normal, the regional distribution of ionic 43K and labeled microspheres were similar. In ischemia induced by partial occlusion and pacing, both 43K and microspheres showed the same decrease in activity (0.7 of control). When a coronary artery was completely occluded, both tracers were decreased to 0.3 of control. In other experiments, resting coronary blood flow was decreased by 25%, 50% and 75% as determined by flowmeter measurements. When this was done, regional distribution of ionic 43K and microspheres both decreased in parallel but to a lesser degree than flowmeter data suggesting a contribution from collateral vessels. The endocardial/epicardial activity in the ischemic region also decreased proportionally. However, under conditions of increased flow during myocardial reactive hyperemia, 43K activity (1.02 of control) did not increase to the same degree as microsphere activity (1.5 of control).