A common practice of prescribing anticoagulants to people who have had unexplained strokes should stop, according to a study that shows it is not beneficial to prevent the risk.

Anticoagulants were thought to prevent additional strokes in people whose initial stroke has an unknown cause but who have a heart condition, atrial cardiopathy, that resembles atrial fibrillation, a common cause of stroke.

"We know these drugs work for people with atrial fibrillation, so we thought that they would probably work for people with atrial cardiopathy as well," said Mitchell Elkind, Professor of Neurology at the Vagelos College of Physicians and Surgeons.

However, the trial of 1,015 people, published in JAMA, found that patients with atrial cardiopathy who were given the anticoagulant apixaban had the same stroke rate, 4.4 per cent as patients who were given aspirin, the current standard of care.

"It's disappointing as a physician-scientist to not have your hypothesis proven, but this study is still providing really useful information. It tells neurologists that patients with this type of heart condition, atrial cardiopathy, should not get anticoagulants, which are riskier than aspirin and should be reserved for people with definitive evidence of atrial fibrillation," Elkind said.

One-third of strokes have unknown causes, a challenge for neurologists trying to help their patients avoid subsequent strokes.

The team found that the unexplained strokes occur due to changes in the heart that resemble changes seen in AFib.

They said there are several possible reasons why the trial did not support their hypothesis, including that they tested the right treatment in the wrong patients.