Beta-blockers in heart failure. The 'new wave' of clinical trials

Abstract

There is now considerable clinical trial data to support the use of beta-blockers in patients with congestive heart failure (CHF) due to systolic left ventricular dysfunction. A substantial database has accumulated over the last 20 years supporting the benefits of these agents on ventricular function and clinical status. In addition, morbidity and mortality benefits have been suggested, specifically with the non-selective vasodilating agent, carvedilol. More recently, a "new wave" of clinical trials have been conducted to definitively determine the mortality benefits of beta-blockers in patients with mild to moderate CHF as well as addressing other important clinical questions. These questions include whether the beneficial effects of carvedilol on survival can be reproduced by other agents in prospective, adequately powered studies; whether the benefits of carvedilol in systolic heart failure are due to its beta-blocking properties alone or to a combination of the beta-blocking and ancillary effects of the drug; whether beta-blockers are of benefit in patients with severe New York Heart Association (NYHA) Class IIIB-IV CHF; and, whether beta-blockers are of benefit (additional to ACE inhibitors) in patients with evidence of systolic ventricular dysfunction when commenced in the immediate post-myocardial infarction period. Major studies are currently being undertaken to address the above questions. Most are still underway but 3 studies have recently reported their results: the second Cardiac Insufficiency Bisoprolol Study (CIBIS II), the Research in Left Ventricular Dysfunction Study (RESOLVD), and the Metoprolol CR/XL Randomised Intervention Trial in Heart Failure (MERIT-HF) study. These studies have demonstrated that blockade with beta1-selective, non-vasodilating agents (i.e. bisoprolol and metoprolol) improve survival in patients with CHE Comparison of relative risk reduction in these recent studies with the earlier carvedilol studies raises mechanistic questions, specifically whether non-selectivity, vasodilation and other ancillary properties of carvedilol are critical to its benefit in CHF patients. This question is currently being addressed in the Carvedilol and Metoprolol European Trial (COMET), comparing metoprolol with carvedilol. The beneficial effects of beta-blockers on mortality in patients with mild to moderate CHF have also had major implications in ongoing studies of other agents in this condition. Open-label prescribing of beta-blockers is increasing in these studies and this is having an impact on event rates and thus required duration of administration of study drug. Furthermore, it would now appear unethical to deprive suitable NYHA Class II-III CHF patients of beta-blockers as part of the design of such studies. In conclusion, beta-blockers have now become the most extensively studied class of agents in the treatment of CHF, with a database of over 6000 patients in placebo-controlled studies, and ongoing clinical and mechanistic studies. Despite this, further questions remain regarding the use of these agents in CHF, including their role in the extreme elderly, in patients with diabetes mellitus and in patients with renal impairment.