Hidden heart rhythm problem may underlie some strokes

Monitoring stroke patients’ heartbeats after they leave the hospital reveals that some have atrial fibrillation that was previously undetected, two studies find. Atrial fibrillation, a heartbeat that’s occasionally out of rhythm, is itself a risk factor for stroke, but some people don’t know they have it. Researchers now report that electronic monitors attached to or under the skin can spot the irregularity in people who have had strokes with no apparent trigger, suggesting that this kind of tracking might need to become a standard part of such patients’ care.

Most strokes result when a blood clot lodges in the brain. In atrial fibrillation, the upper chambers of the heart, or atria, beat erratically and cause a disruption of blood flow that can contribute to clot formation. People diagnosed with atrial fibrillation are sometimes put on prescription blood thinners to limit clotting. While the cause of atrial fibrillation is poorly understood, people who have it face a risk of stroke around five times as high as those in the general population.

Strokes can arise from blood flow problems in tiny brain arteries, damage to large vessels elsewhere or cardiac problems — all of which can lead to clotting. High blood pressure often plays a role. But about one in four clot-based strokes have no identifiable trigger, leaving questions about how best to treat the patients to avoid a second stroke.

In the new studies, researchers focused on patients with such unexplained strokes to see if atrial fibrillation might be present and detectable.

In one study, small heart rhythm monitors implanted under the skin of the chest in 221 survivors of strokes or ministrokes revealed that after six months, 8.9 percent of the patients had atrial fibrillation that was previously undetected. This number rose to 12.4 percent after a year as more episodes were spotted, says study coauthor Rod Passman, a cardiac electrophysiologist at Northwestern University School of Medicine in Chicago. Longer observation of such patients, he says, suggests that closer to 30 percent of them have “silent” atrial fibrillation.

In the other study, neurologist David Gladstone of the University of Toronto and a largely Canadian team randomly assigned 286 people to wear external heart rhythm monitors for a month. The people in the study had had a stroke or a transient ischemic attack, also known as a ministroke. Atrial fibrillation turned up in 16.1 percent of the patients, who tended to be older than the people in the other study. Both studies appear in the June 26 New England Journal of Medicine.

Passman says the implanted heart monitors in his study — the size of a computer thumb drive — are already obsolete. Smaller ones the size of a matchstick that last up to three years have since been developed by Medtronic, a medical technology company based in Minneapolis, which provided support for the study. These newer implants can send any abnormal heart rhythm signals via cell phone towers to a doctor’s office, Passman says.

Quite often, little attention is paid to the heart rhythm of people who survive an unexplained stroke if they have no history of atrial fibrillation, says Hooman Kamel, a stroke neurologist at Weill Cornell Medical College in New York City who wasn’t involved in the new studies. He says these findings suggest that monitoring such patients can reveal hidden atrial fibrillation, which doctors would then monitor and treat with blood thinners or other medications if deemed necessary for that patient.

But many questions linger. For example, the atrial fibrillation in these patients could have developed after the stroke, says cardiologist Stuart Connolly of McMaster University in Hamilton, Ontario. Because of that, the studies don’t establish that atrial fibrillation caused these strokes or ministrokes.

Passman acknowledges that the data don’t show cause and effect. But he says that if poor heart rhythm generates clots, any stroke that would result from those clots would happen sometime after an atrial fibrillation episode. That suggests a role for real-time monitoring. “The merger of wireless technology and implantation will allow us to monitor patients remotely and potentially intervene before something happens — and that something could be a stroke,” he says.