By Michael H. Crawford, MD, Editor
SOURCE: Zhang H, et al. Efficacy of long-term ß-blocker therapy for secondary prevention of long-term outcomes after coronary artery bypass grafting surgery. Circulation 2015;131:2194-2201.
Pre-operative beta-blocker therapy is a performance measure for patients undergoing coronary artery bypass graft surgery (CABG). However, the value of continuing beta-blocker prophylactically post-CABG is unclear. Thus, investigators from Beijing analyzed the use of beta-blockers after isolated CABG and long-term adverse events at one hospital. Patients who had contraindications to beta-blockers were excluded. The 5926 patients who had isolated CABG between 2004 and 2008 were divided into those with and without prior myocardial infarction (MI). Also, they were categorized after at least two follow-up visits in the first year as: always on beta-blockers, never taking, and inconsistent users. The primary endpoint was all-cause mortality, and the secondary outcome was major adverse cardiac and cerebrovascular events (MACCEs). A prior MI was present in 42% and they had a higher risk clinical profile. Consistent beta-blocker use was noted in 49%, and 22% were never users. The always users had a higher clinical risk profile. After a median follow-up of 3 years, 5% of the patients had died, the majority from cardiac causes. The primary and secondary outcomes were not different between the prior MI and no prior MI groups. However, both endpoints were significantly lower in the always users vs the never or inconsistent beta-blocker users. As compared to always users, the risk of mortality in inconsistent users was significantly higher (hazard ratio [HR], 1.96; 98% confidence interval [CI], 1.5-2.57). In never users, mortality (HR 1.42; CI, 1.01-2.00) and MACCE (1.29; CI, 1.1-1.5) were significantly higher. After adjustment for baseline differences, the results were similar. Also, the results persisted across all pre-specified subgroups. In 1636 propensity-matched pairs, the results were the same. Finally, excluding patients with left ventricular ejection fraction < 35% did not affect the results. The authors concluded that in post-CABG patients, long-term beta-blocker use was associated with lower rates of death and MACCEs.
The use of beta-blockers in patients with ischemic heart disease has been challenged by recent studies in the era of percutaneous reperfusion, statins, and more potent antiplatelet drugs. Holding steady are their use in systolic heart failure and early post-MI. Perioperative use in CABG is still recommended to prevent atrial fibrillation and slow the rate if it occurs, but longer term use has been questioned by recent data. Thus, this analysis of a large observational study in post-isolated CABG patients is of interest.
Despite the fact that those who consistently took beta-blockers had higher risk clinical characteristics, they had lower rates of death and MACCEs than those who didn’t take beta-blockers or took them inconsistently. Also, whether or not they had a prior MI or an EF < 35% did not change the results. In addition, statistical adjustment for baseline differences and propensity matching failed to alter the results. Despite this being an observational study, the data are relatively robust and suggest that all patients post-CABG without contraindications should take beta-blockers indefinitely.
There are limitations to the study. Unmeasured confounders could have affected the results. For example, those who consistently took beta-blockers may have been in a higher socioeconomic class and may have had better health behaviors in general. Also, we don’t know the physiologic response to the beta-blockers. In addition, there are no data on why patients discontinued beta-blockers. In addition, medication use was self-reported.
In this study, 69% of the patients received a beta-blocker prescription, far less than what is reported in post-MI studies, which usually show rates in the 90% range. Also, of those who got a beta-blocker prescription, 29% discontinued it. Thus, the authors believe that at least in their setting, there is a great deal of room for improvement.