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Total CK levels were analyzed from all samples. CK-MB was analyzed in samples having a total CK above normal limits (235 U/l). All adverse cardiac outcomes (cardiac death, myocardial infarction, unstable angina, congestive heart failure, and life-threatening dysrhythmia) were recorded. Myocardial infarction was defined by the presence of new Q waves on the standard 12-lead ECG and/or positive myocardial enzymes. Positive myocardial enzymes required total CK-MB > 100 ng/ml for the first 12 postoperative hours and CK-MB > 70 ng/ml thereafter. All intraoperative and postoperative medications, intravenous fluids, urinary output, and blood loss were recorded. All adverse events were recorded. Holter ECG Monitoring ECG (Holter) recordings were obtained continuously for at least 8 h preoperatively, during the 1-h drug infusion preceding induction of anesthesia, intraoperatively, and for 96 h postoperatively using a three-channel AM Holter ECG recorder (Marquette, series 8500). Three bipolar leads, CM5, CC5, and ML, were used. Before study, ECG tracings were obtained with the patient in the supine, upright, and left and right lateral decubitus positions. All recordings were analyzed by a technician and verified by a study physician blinded to patient treatment group. After exclusion of all abnormal QRS complexes, the ST segment was trended continuously for the three leads. The baseline ST-segment level was defined as the average ST segment during a stable period (usually 15–60 min) preceding each ischemic episode. An ischemic episode was defined as: (1) horizontal or down-sloping ST-segment depression from baseline greater or equal to 1 mm lasting at least 1 min or (2) ST-segment elevation from baseline greater or equal to 2 mm measured at the J point. ST-segment depression was measured 60 ms after the J point unless that point fell within the T wave, in which case the point of ST-segment depression measurement was shortened to a minimum of J plus 40 ms. If T-wave changes occurred with ST depression. J-point depression from baseline of at least 1 mm also was required. For each episode, the maximum ST-segment change from baseline and duration of ischemic episode were measured. Because the varying amount of time intraoperatively that a given patient is monitored can result in differences in the absolute amount of ischemia detected, an ischemic burden (total ischemic min/total h monitored) was computed for each patient. Continuous 12-Lead ECG The ECG was continuously monitored during the 1-h preinduction drug infusion using a microcomputer-augmented continuous 12-lead system (MAC II/ST exercise stress system, Marquette). After entry into the operative holding area but before entry into the operating room, patients were fitted with 10 silver/silver chloride ECG electrodes. A modified Mason-Likar lead configuration was used, with the leg electrodes placed midway between the anterior and posterior iliac spines. The six precordial leads were carefully placed in the standard positions in all patients. The frequency response, operating characteristics, and method of analysis of this system have been reported previously. Transesophageal Echocardiography After tracheal intubation, a 5.0-MHz 64-element miniaturized phased-array transesophageal echocardiography (TEE) transducer probe (GE RT6800, Milwaukee, WI) was inserted. The left ventricular short-axis view, at the level of the midpapillary muscles, was continuously recorded on half-inch VHS videotape. A study technician was present throughout surgery to maintain the optimal image and position. The probe was removed as close to completion of skin closure as possible Tapes were edited to obtain samples for analysis of 65-s duration every 15 min and at the following predetermined times: 5 min before and at skin incision; 5 min before, at onset of, and 5 min after clamping and unclamping of major blood vessels; and 5 min before, at onset of, offset of, and 5 min after an increase in systolic blood pressure > 150 mmHg or a decrease in heart rate < 50 beats/min. Edited tapes were analyzed by a blinded investigator: The short-axis cross-sectional image was divided into four segments using the papillary muscles as the guide.
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