Diagnosis of myocardial ischemia by the pressure-rate quotient and diastolic time interval during coronary artery bypass surgery

Diagnosis of intraoperative myocardial ischemia by the rate-pressure product (RPP), pressure-rate quotient (PRQ), and diastolic time interval (DTI) was studied in 13 patients undergoing coronary artery bypass grafting (CABG) with fentanyl, vecuronium/pancuronium, and enflurane anesthesia. Criteria for ischemia were 1 mm of ST segment elevation or depression or T wave inversion on the ECG. RPP was calculated by multiplying the systolic arterial pressure (SAP) times the heart rate (HR); PRO was determined by dividing the mean arterial pressure (MAP) by the HR; and DTI was defined as the interval from the closure of the aortic valve on M-mode transesophageal echocardiography to the onset of the ORS complex on the ECG. Six of 13 patients experienced episodes of ischemia (a total of 32 episodes out of 134 measurements). RPP of 12,000 was not found to correlate with myocardial ischemia (P 0.05), whereas a PRO of < 1.0 or DTI of < 400 ms was associated with myocardial ischemia (P < 0.005). In this preliminary study, it is concluded that both the PRO and DTI are indicators of myocardial ischemia; it is also suggested that ischemia may be prevented by maintaining (1) DTI over 400 ms (HR < 75 beats per minute), and (2) PRO greater than 1.0 (MAP greater than HR).