IS THE PRESSURE RATE QUOTIENT A PREDICTOR OR INDICATOR OF MYOCARDIAL-ISCHEMIA AS MEASURED BY ST-SEGMENT CHANGES IN PATIENTS UNDERGOING CORONARY-ARTERY BYPASS-SURGERY

Perioperative myocardial ischemia is associated with an increased risk of perioperative myocardial infarction (PMI). Several attempts have been made to define intraoperative hemodynamic predictors of myocardial ischemia. In a canine preparation with coronary stenosis, a pressure rate quotient (PRQ = mean arterial pressure/heart rate) less than one (PRQ < 1) indicated subendocardial myocardial ischemia. The authors tested this hypothesis in patients undergoing elective coronary artery bypass graft operation (CABG), using electrocardiogram (ECG) ST-segment changes (leads II/V5) to diagnose myocardial ischemia. Sixty (n = 60) patients having CABG surgery were prospectively studied before initiation of cardiopulmonary bypass. Calibrated ECG leads II and V5 (diagnostic mode) were monitored continuously and recorded with the use of a Hewlett-Packard computer ST-segment analyzer. In addition, arterial and pulmonary artery pressures were monitored. Ischemia was defined as new-onset ST deviation (greater-than-or-equal-to 1 mm from the baseline ECG). ECG and hemodynamic data were stored at 2-min intervals for subsequent computer analysis. Serial creatinine phosphokinase (CPK) X MB (%) determinations and 12-lead ECGs were collected for the initial 3 post-operative days. Of the 3,463 intervals (2 min) available for study, 3,322 (96%) were satisfactorily recorded for 60 patients. Ischemia occurred during 65 intervals in 9 patients (9 of 60), of which only 34% (22 of 65) were associated with a PRQ < 1 (P < 0.01). In contrast, there were 466 intervals during which PRQ was less than 1, but without ECG evidence of ischemia. Four (4 of 60) patients had PMIs, but in only 1 (1 of 4) was pre-CPB ischemia associated with a PRQ < 1. The authors conclude that PRQ < 1 is an insensitive indicator and predictor of myocardial ischemia in patients undergoing elective CABG.