Effect of Bypass Surgery on LV Performance
Abstract & Commentary
Synopsis: Successful myocardial revascularization may improve LV performance under stress.
Source: Elhendy A, et al. Am J Cardiol 2000;86:490-494.
Previous studies of the effect of coronary artery bypass graft (CABG) surgery have used resting left ventricular ejection fraction (LVEF) as the gold standard for determining myocardial viability, yet little is known about LV perfusion and contractile reserve after CABG. Thus, Elhendy and colleagues studied 57 patients with EF less than 40% referred for CABG, by dobutamine thallium stress testing before and three months after the CABG. Patients who suffered perioperative myocardial infarction (MI) or had incomplete revascularization were excluded. All patients had a previous MI and underwent CABG for angina. There was no change in EF overall post-CABG. In 12 patients, resting EF increased post-CABG (group A), whereas no change was observed in the remaining 45 (group B). A significant increase in rest to low-dose dobutamine EF occurred in patients in both groups after CABG (13% after vs 7% before; P < 0.001). Both groups showed a reduction in myocardial ischemia perfusion scores after CABG, but was greater in group A (60%) vs. group B (30%; P < 0.01). Elhendy et al concluded that CABG produces significant improvements in resting myocardial perfusion and the EF response to low-dose dobutamine in the absence of an overall increase in the resting EF. These results suggest that successful myocardial revascularization may improve LV performance under stress.
Comment by Michael H. Crawford, MD
Studies of the results of CABG surgery in patients with reduced EF have shown modest improvements in postoperative EF. This study is consistent with these findings in that about 20% of their patients showed an increase in resting EF postoperatively, despite increases in myocardial perfusion in all patients. The magnitude of increase in perfusion was roughly related to return of LV function since the 12 patients with EF increases more than 5% did have the largest increase in perfusion. This suggests that it may take very large increases in perfusion to increase resting EF. Other studies have also shown that improvements in segmented wall motion may not always translate to increases in global EF. This could be because the improved areas are relatively small or that compensatory hyperfunction of normal walls may decrease as regional wall motion abnormalities improve.
Previous studies have demonstrated that mortality is reduced after CABG in patients with symptoms, three-vessel disease, and low EF. Several reasons have been suggested: First, EF may increase—a powerful marker of survival; Second, long-term remodeling may be reduced (unfortunately, there is no echo data to analyze LV structure in this study); Third, ventricular arrhythmia may be reduced; Fourth, myocardial ischemia is probably reduced and LV contractile reserve improved as shown in this study. This study was not designed to evaluate mortality and the follow-up was rather short. A larger, longer study would be necessary to assess the prognostic significance of improved LV contractile reserve. Regardless, this study suggests that revascularization of patients with ischemic cardiomyopathy may be beneficial even if resting EF is unchanged.