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Many people with heart failure are advised to avoid coffee because of fears that caffeine might provoke an arrhythmia. Now a rare example of a randomized controlled trial in the field offers some assuring evidence that these patients may be able to safely drink coffee.

The health effects of coffee have been the subject of considerable debate, with wildly disparate views based only on observational studies in the absence of high quality, randomized controlled trials with clinically-relevant endpoints. Much of the debate has centered on the role of caffeine.

In , researchers in Brazil report on the short-term electrocardiographic effect of high-dose caffeine in 51 patients with moderate-to-severe heart failure. They performed a double-blind, randomized crossover trial comparing 500 mg of caffeine or placebo. Participants drank five cups of coffee over 5 hours, during which time they underwent ECG monitoring. At the end of the 5 hour period, a treadmill test was performed.

The researchers found "no association between caffeine ingestion and arrhythmic episodes," either during ECG monitoring or the treadmill test. They also found no evidence of ventricular or supraventricular premature beats or other arrhythmias.

"Our results challenge the intuitive notion that caffeine intake should be limited or prohibited in patients with heart disease and at risk for arrhythmia," the authors wrote. "To date, there is no solid evidence to support the common recommendation to limit moderate caffeine consumption in patients at risk for arrhythmias."

In an accompanying commentary, , and , both of Duke Clinical Research Institute in Durham, N.C., wrote that the study "is a welcome addition to the literature." But they note that "the short term nature of the exposure and the small number of patients... preclude any reliable information on clinical outcomes."

, a cardiologist at the University of Kentucky, has long been interested in the coffee issue. "I think the results add further support to the safety of moderate coffee drinking (two to four cups per day). Unless there is a genetic abnormality, as was documented in a valley in Costa Rica, coffee does not appear to increase coronary artery events and it decreases adult onset diabetes mellitus. The major clinical implication is that we can reassure our patients that moderate coffee (fully caffeinated) intake is fine if enjoyed, unless bothersome arrhythmias or other bothersome symptoms are associated. In addition, hospitals should offer caffeinated coffee to cardiovascular patients able to ingest it, in moderate levels, instead of prohibiting it for cardiovascular patients as in the past. The limitation as evidence-based medicine is that the study was extremely short-term."

One important detail of the trial may limit its application to broader populations. Nearly all the patients in the trial were taking a beta-blocker, which slows down the heart and may have prevented or blunted an arrhythmic response. Although caffeine is known to raise the heart rate, no such elevation was observed in the study. Whayne agreed that "not taking one might have made a difference," though it is important to emphasize that all heart failure patients should be "on a beta blocker unless there is a specific contraindication."

The senior author of the paper, Luis Rohde, MD, ScD, of Brazil’s Federal University of Rio Grande do Sul, agreed that “based on our results, beta-blockade might have attenuated the potential ‘side-effects’ of caffeine. So I would be careful to translate our findings to other populations. But based on the overall body of scientific evidence about the potential cardiovascular risks and benefits of caffeine ingestion, it seems reassuring that modest to moderate ingestion would be safe for almost everybody (including people without cardiovascular disease).”

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