Occasional erratic heartbeats seem to trigger about a fifth of unexplained strokes, while a third of the survivors leave hospital with the cause of their stroke still undetermined.
"Identifying and treating these patients for irregular rhythm could reduce the recurrence of stroke by 40 percent compared to reducing the risk by treating them with aspirin," said Daniel J. Miller, study co-author and senior staff neurologist at Henry Ford Hospital, Detroit.
"The cause doesn't make a difference if there isn't a treatment, and recently two new medications - dabigatran and rivaroxaban - have been approved by the FDA to treat this problem," said Miller, according to a Henry Ford statement.
The study confirmed a 2008 report that found 13 of 56 patients (23 percent) whose heart rhythms were measured by automated monitors for 21 days had intermittent, or paroxysmal atrial fibrillation (PAF). Such episodes can last for a few seconds up to several days.
The study suggested that erratic beats of less than 30 seconds might indicate more prolonged episodes of PAF that lead to small blood clot formation in hearts of patients with otherwise unidentified causes for their strokes.
Miller and colleagues examined the medical records of 156 patients (half women) who had undergone monitoring no more than six months after a stroke, most of them for 21 days. Ninety-seven percent were not taking prescription anticoagulation drugs.
Patients identified at study entry with premature atrial contractions - the most common type of erratic heartbeats - were 13.7 times more likely to have PAF than those without the rhythm problems. "That's a very high risk," Miller said.
These findings were presented at the American Stroke Association's International Stroke Conference 2012.