DrSamGirgis.com has the pleasure of hosting the following post by guest blogger, Dr. Richard Andraws MD, who is a Board Certified Cardiologist
A patient diagnosed with heart failure today will most likely be placed on a class of medications known as beta blockers. These drugs work by inhibiting the effects of adrenaline on the heart: they reduce blood pressure and slow the heart rate, which reduces the heart’s workload; they prevent arrhythmias; essentially, they prevent the toxicity of adrenaline on an injured and weakened muscle.
Evidence for the benefits of beta blockers dates back to the 1970s, although they only became a mainstay of heart failure therapy in the late 1990s with the publication of several landmark trials. On average, beta blockers appeared to reduce death from progressive heart failure by 30% compared with placebo. Based on these trials, three agents are currently approved in the U.S.: long-acting metoprolol, bisoprolol, and carvedilol.
However, an intriguing reexamination of the evidence calls into question whether American patients benefit from beta blockers as much as patients from other countries. O’Connor and colleagues, in the most recent issue of the Journal of the American College of Cardiology, performed a meta-analysis of the landmark beta blocker trials. This is essentially a pooling of the data to obtain a more accurate estimate of overall effect and also to analyze other outcomes. Specifically, they looked at effects on patients enrolled in the U.S. versus patients enrolled overseas.
What they found was that while beta blockers significantly reduced death by 23% overall, this was driven by foreign patients. U.S. patients appeared to derive no benefit. The reasons for this are unclear, but the phenomenon has been observed in trials of other medications. The authors hypothesize that certain genetic factors (particularly a gene that makes some Americans less sensitive to beta blockers) may be more common than in overseas populations. It’s also possible (but less likely) that American patients were “sicker” at baseline, or that American healthcare is better, so the benefits of beta blockers are diluted. Finally, the finding could be due to chance.
All this must be taken with a grain of salt. Looking back at data and pooling it often leads to misleading results. The authors rightly say their results are more hypothesis-generating than definitive. They call for future trials to be designed so as to better assess regional differences in outcomes (which these trials were not designed to do). For now, the preponderance of evidence supports the use of beta blockers in all heart failure patients.
O’Connor CM, Fiuzat M, Swedberg K, et al. Influence of global region on outcomes in heart failure beta blocker trials. J Am Coll Cardio 2011, 58: 915-922.