The relationship between the perfusion deficit, infarct size and time after experimental coronary artery occlusion

It is well known that coronary occlusions of short duration do not produce infarcts in the dog heart, but permanent occlusions always do. The aim of this paper was to investigate with quantitative direct measurements the determinants of infarct size within these two extremes. We measured left ventricular MV2, coronary and collateral blood flow and infarct size after occlusion times varying between 45 minutes and 24 hours. MVO2 was kept low in one group by establishing low heart rates with a synthetic opiate. In another group, MV2 was kept elevated by giving synthetic catecholamines (dobutamine) that stimulated contractility and heart rate. Under the described experimental conditions LV-coronary blood flow reflected the true demand for blood and oxygen. The ratio of collateral blood flow over coronary blood flow (both measured with tracer microspheres) was therefore a good approximation of the supply-demand ratio (SD). Since collateral flow was inhomogeneously distributed across the left ventricular wall, the SD-ratio showed similar variations. As the collateral blood flow increased with elapsed time after coronary occlusion, the SD-ratio improved. Since high LV-O2-demand increased coronary flow but exerted practically no influence on collateral flow, this situation influenced the SD-ratio in a negative way. Decreased O2-demand had the opposite effect. The SD-ratio is thus a valid expression of the relative and absolute blood flow deficit as influenced by the local and general O2-demand. We found significant and characteristic correlations between the SD-ratio and infarct which was only influenced by time. A blood flow deficit of 90% (i.e., collateral flow = 10% of required flow) produced a 50%-infarct (relative to the risk-region) with a 45-min occlusion but a 90%-infarct with occlusion times of 3 hrs and longer. If the perfusion deficit is only 0.5 (collateral flow = 50% of required flow), no infarct is detectable at occlusion times shorter than 3 hrs. Small perfusion deficits of only 20% below required flow caused infarctions at 24 hrs and longer. In the group where the SD-ratio was closer to unity because of a low overall LV-O2-consumption (bradycardia), infarcts at t = 24 hrs were significantly smaller than in the group with a high LV-MVO2.