A group of cardiologists from Italy report their study results in the January 2011 issue of the American Journal of Cardiology, available online now.
They caution, however, that they only studied patients undergoing CABG with left ventricular dysfunction and, therefore, their findings are only pertinent to this patient population. The findings “should not be extended to all patients with preserved left ventricular function and/or different cardiac surgeries.”
They note that atrial fibrillation is common after CABG, particularly in patients with heart failure. And while postoperative prophylaxis with a beta-blocker is recommended, it’s not always prescribed, and, until now, no study has specifically compared the relative effectiveness of these two widely used beta-blockers for this purpose.
Dr. Ferdinando Iellamo from University Tor Vergata in Rome and colleagues enrolled 320 patients (mean age, 66 years) with an ejection fraction < 40% who’d been referred to a four-week inpatient cardiac rehab program after recent CABG.
Starting four to five days after surgery, half of the patients were randomly assigned to bisoprolol at a starting dose of 1.25 mg once daily and half to carvedilol at a starting dose of 3.125 mg twice daily. The dose of each drug was subsequently increased, according to standard practice and clinical judgment, until the maximum tolerated dose was achieved. The mean doses of bisoprolol and carvedilol used were 2.5 and 12.5 milligrams per day, respectively. There was no restriction on standard therapies such as furosemide.
The study team performed electrocardiographic monitoring continuously for five days after enrollment and twice daily thereafter until hospital discharge.
During follow-up, atrial fibrillation developed in 23 patients on bisoprolol (14.6%) versus 37 patients on carvedilol (23%), yielding a relative risk with bisoprolol of 0.60 (P = 0.032).
Roughly a quarter of atrial fibrillation episodes were silent (26%). Electrical cardioversion was performed in one patient on bisoprolol and two on carvedilol.
Side effects of beta-blocker therapy were similar in the two groups and their incidence was not significantly different.
A total of 22 patients (7%) withdrew from the study. Fourteen (4.4%, 6 on bisoprolol and 8 on carvedilol) could not tolerate treatment due to orthostatic hypotension or severe asthenia. Five patients (2 on bisoprolol and 3 on carvedilol) developed symptoms of heart failure necessitating an increased dose of furosemide and a temporary decrease of beta-blocker dose.
At the end of follow-up (4 weeks postdischarge), a significant decrease in heart rate from baseline was detected in both groups, without significant effects on systolic and diastolic blood pressure. Patients treated with bisoprolol showed a significantly greater decrease in heart rate (-15.6 beats per minute) than those treated with carvedilol (-15.6 vs -9.4 beats per minute; P = 0.021).
The researchers speculate that the greater effectiveness of bisoprolol could be due to its greater beta-1-receptor selectivity, “imparting a greater degree of protection against increases in sympathetic activity.”
Am J Cardiol 2011.