BACKGROUND:

Surgical myocardial revascularization (CABG) is an effective treatment for triple vessel and left main coronary artery disease used for thousands of patients annually in the United States. CABG certainly prolongs life, and data demonstrates that it improves functional status for the majority of patients. The intervention in this trial is based upon the outcomes of the investigators' first trial, which showed a benefit to maintaining mean intra-bypass mean arterial pressure (MAP) at 65 mm Hg in the high MAP group vs. 52 mm Hg in the low MAP group. Intra-bypass MAPs corrected for intervals less than full flow were 81 mm Hg for the high group and 59 mm Hg for the low MAP group. Cardiac and neurologic morbidity and mortality were 4.8 percent in the high MAP group versus 12.9 percent in the low MAP group (p=.026). All adverse outcomes were lower in the high MAP group (16.1 percent) than in the low MAP group (27.4 percent). Data from the previous study also suggests that outcomes may be further improved by maintaining intra-bypass MAP close to the patient's preoperative MAP. This is consistent with the investigators previous work in non-cardiac surgery, which shows that maintaining MAP within patient's usual autoregulatory range is associated with lower cardiac and renal complication rates. This study will determine whether refining the approach to hemodynamic management will further improve patient outcomes after coronary revascularization.

DESIGN NARRATIVE:

The First Clinical Study

During the first three years of grant support, from August, 1991 to November, 1995, clinical research was conducted on a comparison of intraoperative high versus low mean arterial pressure (MAP) on outcomes after coronary artery bypass. In this study, 248 patients undergoing primary, nonemergency coronary bypass were randomized to either low (n = 124) or high (n = 124) mean arterial pressure during cardiopulmonary bypass. The impact of the mean arterial pressure strategies on the following outcomes was assessed: mortality, cardiac morbidity, neurologic morbidity, cognitive deterioration, and changes in quality of life. All patients were observed prospectively to six months after the operation. Results are described under the Results Section.

Second Clinical Study

The second clinical study under grant R01HL44719, began in December, 1995 and was a prospective trial of 412 patients who were evaluated pre-operatively, monitored intra-operatively and followed post-operatively according to a standardized surveillance protocol. Patients were randomized to two forms of hemodynamic management during cardiopulmonary bypass. In one group, the intra-operative mean arterial pressure (MAP) during bypass was maintained at 65 mm Hg (or 81 mm Hg at full flow), thus employing the most effective strategy from the investigators' first trial. In the second group, the intra-operative MAP was maintained at their pre-operative MAP (but below 90 mm Hg), a strategy supported by data from the first trial. The principal outcome was the occurrence of any one of the following: mortality at six months, major cardiopulmonary morbidity (i.e., myocardial infarction, pulmonary edema, cardiogenic shock or low flow state), cognitive complications (defined by a summary definition which included improvement and decline on neuropsychologic tests of memory, psychomotor/attention, and linguistic function), major neurologic complications (i.e., new focal deficits, such as hemiplegia, aphasia, cortical blindness) and significant deterioration in functional status at six months postoperatively. The long term objective was to preserve and further improve the quality of life after CABG.

Although the study was described as a clinical trial, the Behavioral Medicine Study Section defined it as clinical research, not a NIH-defined Phase III trial.