People with a common type of abnormal heart rhythm were more likely to die within several years if they had been prescribed digoxin, a drug used to help control abnormal heart rates, in a new analysis.
The research involved 4,060 people with atrial fibrillation, in which the heart's upper chambers quiver chaotically instead of contracting normally. More than two-thirds of the participants were treated with digoxin at some point either shortly before or during the 3.5-year study.
Dr. Samy Claude Elayi, from the University of Kentucky in Lexington, said digoxin - which is widely available in generic form - may benefit some people who have heart failure in addition to a heart arrhythmia.
"But in patients that have no heart failure and (have) atrial fibrillation, I think there is no reason to use this drug as a first line," added Elayi, who worked on the study.
Another cardiology researcher, however, said the new study isn't robust enough to warrant changing treatment strategies, and that earlier studies have shown digoxin is safe.
Elayi and his colleagues re-analyzed data from a past trial of people with atrial fibrillation and a high risk of stroke that were treated with a variety of drug combinations, including beta blockers and calcium channel blockers.
Over the study period, 666 people died, according to results published in the European Heart Journal.
People who had taken digoxin in the previous six months, the study team found, were 41 percent more likely to die of any cause and 61 percent more likely to die from a heart rhythm problem, in particular.
That increased risk of death was seen in people with and without heart failure, and in both men and women.
Digoxin works by helping to stabilize the upper heart chambers affected by atrial fibrillation, Elayi said - but it can also cause problems by creating a bad rhythm in the heart's lower chambers. That can lead to dizziness, fainting and heart palpitations.
The researchers noted that they didn't have data on what dose of digoxin people were prescribed - or how closely they stuck to those prescriptions.
Because the trial wasn't originally intended to measure the negative effects of digoxin, and people weren't assigned randomly to one arm or the other, the analysis also can't prove that digoxin caused the extra deaths.
Dr. Ali Ahmed, who has studied digoxin at the University of Alabama at Birmingham, called that a major limitation of the new study.
He said an earlier randomized controlled trial - considered the gold standard of medical research - did not find more deaths among people with heart failure taking digoxin. Other research, Ahmed added, has suggested that low doses of the drug can actually lower the risk of death among some patients.
An analysis like this one can't fully account for the likelihood that sicker patients are prescribed certain drugs more often, he said.
"When you do non-randomized studies, you always wonder, was it really digoxin or was it the other confounders" such as patients' chronic diseases, that led to more deaths.
"This should be taken with extreme caution, because of the potential for confounding and bias from a variety of sources," Ahmed, who wasn't involved in the new research, told Reuters Health.
"The fundamental thing is you cannot overrule the findings of a randomized controlled trial with non-randomized data."
'Not a killer'
Digoxin can be bought for about $10 for a month's supply. It's been used worldwide for decades to help control heart rate, the researchers said.
Elayi said the findings don't mean that people with heart failure and atrial fibrillation shouldn't be taking the drug.
But based on his team's study, he said he would recommend other heart medications before digoxin for people without heart failure. However, if an atrial fibrillation patient also has very low blood pressure - which makes drugs such as beta blockers and calcium blockers unsafe - digoxin might be a reasonable second choice, he added.
In that case, doctors should prescribe digoxin at low doses and keep a close watch on the amount of the drug in patients' blood, Elayi told Reuters Health.
In addition, he said, "From the patient perspective, if doctors put them on the drug they should check their rationale for that."
But according to Ahmed, patients and doctors shouldn't worry about taking or prescribing the drug because of this study. Digoxin, he said, "is not a killer."