Radionuclide angiographic assessment of global and segmental left ventricular function at rest and during exercise after coronary artery bypass graft surgery

Abstract

Left ventricular ejection fraction (LVEF) was measured by radionuclide angiography at rest and during supine bicycle exercise before and 3 months after coronary artery bypass graft surgery (CABG) in 20 patients with chronic stable angina. The right anterior oblique gated first-pass technique was used to assess LVEF response to maximal exercise (Wmax), while the left anterior oblique equilibrium-gated technique was used to assess LVEF and relative LV volume changes during graded submaximal exercise. Mean LVEF was unchanged at rest after CABG by both the first-pass (60 ± 12% vs 60 ± 12%) and equilibrium-gated (61 ± 13% vs 62 ± 13%) measurements. At Wmax, mean first-pass LVEF was significantly higher postoperatively than preoperatively (63 ± 17% vs 53 ± 17%; p<0.01), with a higher Wmax (750 ± 182 vs 590 ± 202 kpm/min; p<0.001) and higher rate-pressure product (302 ± 59 vs 222 ± 57 units; p<0.001). Similarly, equilibrium-gated LVEF levels during graded exercise, using stepwise regression analysis, were significantly higher postoperatively than preoperatively (p<0.001); at the highest graded work load, they averaged 63 ≠ 19% postoperatively and 53 ≠ 17% preoperatively, with higher work loads (500 ± 190 vs 417 ± 155; p<0.05) and higher rate-pressure products (271 ± 55 vs 207 ± 53; p<0.001). The increase in exercise LVEF after surgery was due to a marked decrease in the ratio, relative to resting values, of counts-based end-systolic volumes during submaximal exercise (preoperative 1.91 ± 1.04; postoperative 1.14 ± 0.46; p<0.01). The five subjects in whom LVEF decreased significantly during exercise postoperatively all had one or more blocked or stenosed grafts. This study documents, by two independent radionuclide techniques, an improved LVEF during exercise at an increased maximal work capacity and rate-pressure product 3 months after successful CABG.