The Effect of Aortocoronary Bypass Grafts on Myocardial Blood Flow Reserve and Treadmill Exercise Tolerance

Twenty-five patients had myocardial blood flow reserve determinations (percentage increase in myocardial blood flow with stress), treadmill exercise tests and coronary and bypass cineangiography pre- and postaortocoronary bypass surgery. Twenty of the patients had the postoperative studies performed three months after operation, three at two months and two at five and six months, respectively. Eleven of the 25 patients had all significant coronary artery obstructions (75% or greater) bypassed and all grafts were open at the time of restudy. Preoperatively, blood flow reserve had been abnormal in nine and all had positive treadmill tests. Postoperatively, all eleven patients had normal myocardial blood flow response to stress and treadmill tests were negative in ten (one patient was not restudied on the treadmill). In six patients, no patent grafts could be demonstrated. These patients continued to show abnormal blood flow reserve and positive treadmill studies. Eight of the 25 patients had partial revascularization in that some grafts were open, some closed, and some significantly occlusive lesions were not bypassed. Four of these eight patients had normal flow and treadmill studies and the remainder continued to have an abnormal response to one or both of the measurements. The relationship between treadmill exercise response, myocardial blood flow reserve, and graft patency was significant at the 0.005 level for patients with all grafts open or closed. No significant correlation was obtained between any of the measurements in those patients with partial revascularization. The data indicate that successful aortocoronary bypass grafting provides myocardial revascularization as reflected in a return to normal of the myocardial blood flow reserve and response to treadmill stress testing.