Intraoperative Hemodynamic Changes Are Not Good Indicators of Myocardial Ischemia

Intraoperative myocardial ischemia is associated with an increased risk of a perioperative myocardial infarction (PMI) in patients undergoing coronary artery bypass graft surgery. If reversible physiologic variables could be identified that are indicators of myocardial ischemia, treatment might be instituted early to prevent cardiac morbidity. In patients undergoing elective coronary artery bypass graft surgery, we evaluated the relationship between several premorbid patient characteristics, selected hemodynamic variables, intraoperative myocardial ischemia, and a PMI. In addition we evaluated these selected hemodynamic variables as intraoperative indicators of myocardial ischemia. The following variables were evaluated: heart rate, >80 beats/min; systolic arterial blood pressure, >160 mm Hg; systolic arterial blood pressure, 18 mm Hg; a 5 mm Hg increase in pulmonary artery diastolic pressure; rate pressure product, >12,000 beats/min·mm Hg; and a pressure rate quotient, <1.0 mm Hg/beats/min. The premorbid patient characteristics selected were previous myocardial infarction, recent myocardial infarction (within 1 wk of surgery), type and number of coronary lesions, β-blocker therapy, and calcium blocker therapy. One hundred consecutive (n = 100) patients for elective coronary artery bypass graft surgery were studied prospectively before the initiation of cardiopulmonary bypass (CPB). Patients were monitored with a Hewlett Packard computer ST segment analyzer using leads II and V5. Ischemia was defined as the new onset of ST segment deviation of ≥ mm from the baseline electrocardiogram (ECG) (preinduction) for at least 2 min. ECG and hemodynamic data were monitored continuously and the data were stored at 2-min intervals for subsequent computer analysis. Serial creatine phosphokinase-MB determinations and 12-lead ECG were collected for the initial 3 postoperative days. Sixteen patients (16/100) sustained preCPB myocardial ischemia, and nine patients (9/100) sustained a PMI. Four (4/16) of the patients with preCPB myocardial ischemia detected by ECG sustained a PMI. Using univariate analysis we were able to demonstrate a significant association between preCPB ischemia and a PMI. However, none of the hemodynamic variables demonstrated a high positive predictive value for prebypass myocardial ischemia. In addition, neither the selected hemodynamic variables nor the premorbid patient characteristics were significantly associated with a PMI. In conclusion, we were unable to identify a sensitive, clinically available hemodynamic indicator of intraoperative myocardial ischemia.