Left ventricular function under stress before and after myocardial revascularization

Abstract

To compare left ventricular responses to stress during exercise-induced myocardial ischemia and after myocardial revascularization, 35 patients (mean age 55 ± 7 years, class III angina) with three-vessel coronary artery disease underwent a rest and exercise initial-transit radionuclide angiocardiography before aortocoronary bypass grafting. Left ventricular ejection fraction decreased during exercise ( p < 0.01), but cardiac output was augmented with an increased heart rate ( p < 0.0001) and left ventricular end-diastolic volume ( p < 0.001). Group A ( n = 15) underwent six serial resting studies at different volume loads during the first 24 hours after operation while heart rate and blood pressure were held constant. These data revealed no significant change in left ventricular ejection fraction, but preload varied in all patients because of bleeding and fluid administration, with a mean end-diastolic volume change of 115 to 176 ml. This range of end-diastolic volume was similar to that defined with rest and exercise testing before operation. Group B ( n = 20) underwent a repeat rest and exercise test 3 months after operation that demonstrated no change in resting function. However, exercise ejection fraction and peak systolic pressure/end-systolic volume ratio increased ( p < 0.001 and p < 0.05, respectively) while end-diastolic volume decreased ( p < 0.05) compared with the values before operation. These data indicate that patients with coronary artery disease have chronically adapted cardiac function that makes use of both rapid heart rate and a wide range in preload to augment cardiac function under stress. This adaptation is present early after revascularization, but by 3 months after operation an increased contractile force replaces preload reserve as the secondary mechanism for augmenting function under stress.