A commonly used erectile dysfunction drug, sildenafil, doesn’t help patients who have heart failure with preserved ejection fraction, a condition in which the heart’s lower chambers are stiff and cannot relax and fill fully between beats. That is the finding of the RELAX study, presented today at the American College of Cardiology’s 62nd Annual Scientific Session and simultaneously published in The Journal of the American Medical Association. The study’s lead author called the results disappointing.

Sildenafil, a phosphodiesterase-5 inhibitor, had shown encouraging results in smaller studies and in animal models.

In this study, researchers looked at the drug’s effect on maximum exercise ability as assessed by peak oxygen consumption and on how far people could walk in six minutes, their clinical status and their heart structure and function. They found no benefit, says lead author Margaret Redfield, M.D., heart failure specialist and researcher at Mayo Clinic in Rochester, Minn.

“It was surprising and a disappointment, and it was contradictory to our hypothesis,” says Dr. Redfield. “There are few options for help for these patients, and we hoped we would find something.”

When the heart does not pump blood well, heart failure symptoms such as shortness of breath, fatigue and weakness can result.

The RELAX study is the first multicenter trial to look at the effect of therapy with sildenafil on this condition, also known as diastolic heart failure. The study was a double-blinded, placebo-controlled, randomized trial of 216 stable outpatients with heart failure (with an ejection fraction of greater than 50 percent) with reduced exercise capacity; the median age was 69. Participants were enrolled during a 3.5-year period from the nine U.S. centers including Mayo Clinic that make up the Heart Failure Clinical Research Network and 17 other centers in the United States and Canada.

“This was a very complex study and criteria for study participants were very strict,” Dr. Redfield says. “But it’s most likely that we didn’t see the results we hoped for because this type of heart failure just does not respond to this drug.”

The RELAX study was funded by National Heart, Lung, and Blood Institute grant HL84907 (original) and grant HL110262 (this grant cycle). The institute also funds the Heart Failure Clinical Research Network.

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Traci Klein
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