Rate-pressure product correlates poorly with myocardial oxygen consumption during anaesthesia in coronary patients

In 26 patients having coronary grafts, haemodynamics, coronary sinus blood flow and the arterio-coronary sinus difference of oxygen content were determined, awake and at four intervals during morphine-oxygen or halothane--oxygen anaesthesia. Rate-pressure product (RPP), triple product (TP) and myocardial oxygen consumption (MVO2) were calculated. The correlation of the two indirect indices to MVO2 were tested by repeated measures and regression analyses. No significant correlations were seen at four of five study times, when outlying data points were appropriately excluded. A pitfall of using more than one data point from each patient in the linear regression analysis is pointed out. In addition to the lack of correlation of RPP to MVO2, RPP was an imprecise predictor of myocardial lactate production and of postoperative infarction.