Can CABG Really Improve Left Ventricular Function?

By Michael Crawford, MD

Professor of Medicine, Chief of Clinical Cardiology, University of California, San Francisco

Dr. Crawford reports no financial relationships relevant to this field of study.

SYNOPSIS: In implantable cardioverter defibrillator (ICD) candidates with an ejection fraction < 35% who underwent coronary artery bypass graft surgery, mean ejection fraction improved significantly, especially in those with baseline ejection fraction between 25-35%, obviating the need for ICD in 58%.

SOURCE: Vakil K, Florea V, Koene R, et al. Effect of coronary artery bypass grafting on left ventricular ejection fraction in men eligible for implantable cardioverter-defibrillator. Am J Cardiol 2016;117:957-960.

Current guidelines specify that patients with ischemic cardiomyopathy with a left ventricular ejection fraction (LVEF) of < 35% who are at least 90 days post-coronary artery bypass graft (CABG) surgery should receive an implantable cardioverter defibrillator (ICD). Although it is reasonable to expect LVEF to improve post-bypass surgery, there is little evidence that it rises to > 35%, obviating the need for a prophylactic ICD. Thus, investigators from the Department of Veterans Affairs evaluated the incidence and predictors of improvement in EF to > 35% after isolated CABG surgery in 375 patients (of almost 3,000 total patients) who underwent a pre- and postoperative echocardiogram. Among these patients, 74 presented with an EF < 35% and were candidates for ICD. All patients were men with a mean age of 65 years. Mean preoperative EF was 28% (range 15-35%). All were on guideline-recommended heart failure therapy preoperatively. Postoperative EF improved to > 35% in 38 patients, with the mean EF rising from 30 to 46% (P < 0.001). In the other 36 patients it remained unchanged at 26%. Improvement in EF postoperatively was more likely if the preoperative EF was 26-35% as compared to the rest (odds ratio [OR], 4.95; 95% confidence interval [CI], 1.73-14.1; P = 0.003). Also, more patients who improved had at least one arterial graft (100% vs. 83%; P = 0.01). In the 44 patients who underwent a myocardial perfusion study, measures of infarct, viability, or ischemia were not predictive of outcomes, nor were any other clinical variables. The authors concluded that about half the patients with ischemic cardiomyopathy and an LVEF < 35% improved their EF to > 35% after CABG surgery and became ineligible for an ICD. However, EF improvement was unlikely in those with an EF < 25%.

COMMENTARY

This study supports the guideline that cardiologists should wait 90 days post-CABG before assessing LVEF to determine if there is an indication for ICD placement for primary prevention of sudden cardiac death (SCD) in patients with ischemic cardiomyopathy and LVEF < 35%. Whether the same results would be obtained with percutaneous revascularization is unknown, but there is no reason to suspect that it wouldn’t, unless the revascularization was incomplete. Those with an EF < 25% were unlikely to improve their EF to > 35% with CABG. It is unclear if cardiologists still should wait to see if EF improves after CABG or place the ICD before surgery in these patients. The demonstration of an increase in EF overall post-CABG is consistent with other studies, but this is the first to examine the 35% cutoff below which a primary prevention ICD is indicated. Of course, an EF > 35% doesn’t guarantee freedom from SCD, and other risk factors should be considered as well in making the decision not to place an ICD.

There are significant limitations to this study. It is a retrospective observational study with no controls, but it is unlikely that a controlled trial will ever be conducted in this area. Also, it suffers from the selection bias of those who underwent a pre- and post-operative echo, but how this would influence the results is not clear. More importantly, it is not revealed when echoes were performed pre- and postoperatively. Thus, if some of the echoes were performed early postoperatively, there may have been further improvements at three months. The study population was all men, so the results may not apply to women.

An interesting subplot in the study was the use of nuclear perfusion imaging in some of the patients. The detection of myocardial scarring, ischemia, and viability did not predict the change in EF. This is consistent with the results of the Surgical Treatment for Ischemic Heart Failure (STICH) trial subgroup with perfusion studies, which also could not demonstrate any predictive value for a viability study. Earlier PET studies showed that the presence of viability only identified about 80% of those who would have a significant improvement in LV function after CABG. If a PET study alone was used to decide in whom to operate, 20% who could have benefited would be denied CABG. Thus, revascularization should be performed in all patients with CAD and low EF, if it could be performed with reasonable survival, and that a viability study was only useful if the surgeons or interventional cardiologists turned the patients down, to bolster one’s argument if it showed viability.