The quotient of mean arterial pressure and heart rate predicts hypoperfusion of collateral-dependent myocardium.

This study tested the hypothesis that the quotient of mean arterial pressure (MAP) and heart rate (HR) (pressure divided by rate = PRQ) effectively predicts myocardial hypoperfusion in regions of myocardium supplied with blood via collateral vessels. Regression analysis of data gathered in a study of the effects of halothane and atrial pacing on the distribution of myocardial blood flow has discovered a strong relationship between the PRQ and the inner-to-outer flow ratio in the collateral-dependent zone (R = 0.78). A significant relationship was also found between PRQ and the ratio of subendocardial blood flow in the ischemic zone to subendocardial flow in the normally perfused zone (R = 0.61). These ratios demonstrate that hypoperfusion of the inner layers of the collateral-dependent zone occurred during the condition of hypotension combined with tachycardia; while normal flow distribution was present if MAP exceeded HR. Halothane (1% end-tidal) did not alter the distribution of coronary flow, indicating that halothane does not cause a coronary steal in this model. The results of this study support the concept that the PRQ is an effective predictor of myocardial hypoperfusion when flow to ischemic zones is delivered by collateral vessels in nonfailing, canine hearts.