Canadian researchers have discovered that a silent ailment may be to blame for a significant number of the unexplained strokes that affect Canadians every year.

Undiagnosed atrial fibrillation, or an irregular heart rhythm, could be behind as many as one in six unexplained strokes or “mini-strokes” – technically called transient ischemic attacks (TIA), the researchers found.

The findings were presented Thursday at the International Stroke Conference by lead researcher Dr. David Gladstone, an assistant professor of neurology at the University of Toronto’s Department of Medicine.

Atrial fibrillation, or AF, is a risk factor for stroke because it can lead to blood clots in the heart that can then travel to the brain. It’s often not known what causes the heart rhythm disturbance, but the condition is linked to abnormal heart structure, heart infections, or congenital heart diseases.

The problem, the Canadian team has found, is that many cases go undiagnosed.

That’s because the irregular heartbeat may last for just a few minutes at a time, after which the heart reverts back to its normal rhythm. Unless an individual is wearing a heart monitor at the time that occurs, the diagnosis is usually missed.

Typically, stroke patients undergo short-term heart monitoring over 24 over 48 hours to check for atrial fibrillation. However, Gladstone’s team used new heart monitoring technology to screen patients at home for much longer periods.

Over three years, they recruited 570 patients who had recently had a stroke or mini-stroke and who didn’t appear to have AF based on 24 hours of heart monitoring. The participants were broken into two groups:

  • the first received an additional 24 hours of monitoring,
  • the second received continuous monitoring for 30 days at home using a chest electrode belt that automatically detects episodes of atrial fibrillation.

The prolonged monitoring picked up atrial fibrillation in 16 per cent of the patients, compared to three per cent of those who only received an additional 24 hours of monitoring.

The researchers say all those cases of AF that would have otherwise been missed likely account for many of the unexplained strokes.

Moching Hwo-Chan was one of the patients who took part in the study. In July 2011, a stroke caused her to go blind on one side and for her left face, arm, hand, leg and foot to become suddenly paralyzed.

Gladstone, the director of the stroke prevention clinic at Sunnybrook Health Sciences Centre, treated her that day by giving her the clot-busting drug, tPA. Moching started regaining feeling and movement in her limbs during the infusion and by the next day, she had fully recovered.

“She was very lucky; it was really a miraculous save,” says Gladstone.

To understand why Moching, a previously healthy woman, had suffered a stroke in the first place, he enrolled her in his study.

The additional cardiac monitoring showed that she did in fact have undiagnosed intermittent atrial fibrillation. She is now being prescribed anticoagulant therapy to lower her risk of having a second stroke.

Dr. Antoine Hakim, the CEO and Scientific Director of the Canadian Stroke Network, which partly funded the study, says the findings are significant given that about 25 per cent of strokes cannot be explained by high blood pressure, smoking, or any of the other typical risk factors of stroke.

The findings are also significant because the risk of a stroke in someone with atrial fibrillation is 13 times higher than the general population.

“And it is a perfectly preventable situation by anti-coagulating the patient,” he says.

“The one thing that is very important is that once you recognize that a patient has atrial fibrillation, it is a treatable condition. It is avoidable.”

With a report from CTV’s medical specialist Avis Favaro and producer Elizabeth St. Philip