Thousands of Canadians who suffer unexplained strokes each year may have an undiagnosed, erratic heart rhythm that puts them at risk of repeat and potentially lethal brain attacks, Canadian doctors are warning in the largest study of its kind.
Researchers in 16 stroke centres nationwide who followed nearly 600 patients found that continuous, 30-day heart monitoring detects five times as many cases of “silent” atrial fibrillation as the standard, 24-hour test.
Presented Thursday at the International Stroke Conference in Honolulu, Hawaii, the three-year study “provides the strongest evidence to date to support intensive heart monitoring in patients with unexplained strokes or mini-strokes,” the American Stroke Association said in a statement.
An estimated 50,000 strokes occur in Canada each year. One in four is a “cryptogenic” stroke, meaning a stroke of unknown cause.
The new study found that one in six people with unexplained strokes or mini-strokes had silent atrial fibrillation that would have otherwise gone undetected, and untreated, using standard heart monitoring.
With atrial fibrillation, or AF, the heart quivers and beats chaotically instead of contracting strongly with each beat. Blood can pool in the upper chambers of the heart, allowing clots to form and travel up to the arteries that feed the brain, causing a stroke.
Strokes caused by AF tend to be more severe and debilitating than other types of strokes, said Dr. David Gladstone, lead author of the new study and director of the stroke prevention clinic at Sunnybrook Health Sciences Centre in Toronto.
“One in four patients who has an atrial fibrillation stroke dies within 30 days of their stroke,” he said. “Fifty per cent are dead at one year.”
AF is a major worldwide cause of stroke-related death, disability and dementia, he said. If detected, patients can be put on anti-clotting drugs that can reduce the risk of stroke by about two-thirds “and even up to 80 per cent,” said Gladstone, an assistant professor of medicine at the University of Toronto.
But if people aren’t experiencing classic symptoms – palpitations or fluttering in the chest, a racing heart, shortness of breath or dizziness – AF can be difficult to detect. As well, the arrhythmia, or irregular heart beat, may be fleeting, coming and going in short bursts that last only minutes.
Unless someone has a heart monitor strapped on at the time, the diagnosis is usually missed, and the patient is prescribed only Aspirin or another mild blood thinner, “which is going to put them at ongoing high risk of recurrent strokes in the future,” Gladstone said.
The new study involved 572 patients with unexplained stroke.
All had undergone standard, 24-hour monitoring using a Holter device – a heart monitor the size of an old Sony Walkman that clips on a belt with wires taped to the patient’s torso – plus an electrocardiogram, or ECG. “All the tests came back unremarkable,” Gladstone said, meaning that “they didn’t reveal any obvious cause.”
The patients were randomized into two groups: One received an additional 24 hours of Holter monitoring, the other was asked to wear a special heart monitor – a soft, elastic electrode belt worn around the chest that picks up electrical signals from the heart – for 30 consecutive days.
Overall, atrial fibrillation was detected in 16 per cent of the patients in the 30-day group versus three per cent in the 24-hour group.
Not only was the AF detection rate higher in the 30-day group, significantly more of these people were put on stronger anti-clotting drugs.
“The harder we look for AF, the more we will find,” Gladstone said. “The implication is that more strokes may be prevented if we look harder for this risk factor in patients with unexplained strokes.”
The study, which included stroke centres in Montreal, Quebec City, Ottawa, Kingston, Toronto, Edmonton, Calgary, Victoria and Vancouver, will likely change medical practice worldwide, said Calgary neurologist Dr. Michael Hill.
“It has substantial implications for what we’re going to do from now on with patients with unexplained strokes. It will have an immediate impact on what people do in stroke prevention clinics around the world,” said Hill, director of the acute stroke unit at Foothills Medical Centre in Calgary.
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