INTRAOPERATIVE HEMODYNAMIC-CHANGES ARE NOT GOOD INDICATORS OF MYOCARDIAL-ISCHEMIA

Intraoperative myocardial ischemia is associated with an increased ris k of a perioperative myocardial infarction (PMI) in patients undergoin g coronary artery bypass graft surgery. If reversible physiologic vari ables could be identified that are indicators of myocardial ischemia, treatment might be instituted early to prevent cardiac morbidity. In p atients undergoing elective coronary artery bypass graft surgery, we e valuated the relationship between several premorbid patient characteri stics, selected hemodynamic variables, intraoperative myocardial ische mia, and a PMI. In addition we evaluated these selected hemodynamic va riables as intraoperative indicators of myocardial ischemia. The follo wing variables were evaluated: heart rate, >80 beats/min; systolic art erial blood pressure, >160 mm Hg; systolic arterial blood pressure, <8 0 mm Hg; mean arterial blood pressure, <60 mm Hg; pulmonary artery dia stolic pressure, >18 mm Hg; a 5 mm Hg increase in pulmonary artery dia stolic pressure; rate pressure product, >12,000 beats/min.mm Hg; and a pressure rate quotient, <1.0 mm Hg/beats/min. The premorbid patient c haracteristics selected were previous myocardial infarction, recent my ocardial infarction (within 1 wk of surgery), type and number of coron ary lesions, beta-blocker therapy, and calcium blocker therapy. One hu ndred consecutive (n = 100) patients for elective coronary artery bypa ss graft surgery were studied prospectively before the initiation of c ardiopulmonary bypass (CPB). Patients were monitored with a Hewlett Pa ckard computer ST segment analyzer using leads II and V5. Ischemia was defined as the new onset of ST segment deviation of greater-than-or-e qual-to 1 mm from the baseline electrocardiogram (ECG) (preinduction) for at least 2 min. ECG and hemodynamic data were monitored continuous ly 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 pati ents (16/100) sustained preCPB myocardial ischemia, and nine patients (9/100) sustained a PMI. Four (4/16) of the patients with preCPB myoca rdial ischemia detected by ECG sustained a PMI. Using univariate analy sis we were able to demonstrate a significant association between preC PB ischemia and a PMI. However, none of the hemodynamic variables demo nstrated a high positive predictive value for prebypass myocardial isc hemia. 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, clinical ly available hemodynamic indicator of intraoperative myocardial ischem ia.