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An estimated quarter of a million Canadians have a type of irregular heartbeat that dramatically increases their risk of having a potentially fatal stroke — but many are not getting the treatment they need, says the Heart and Stroke Foundation.

The foundation says people with atrial fibrillation are five times more likely to have a stroke and twice as likely to die from it.

Yet many of these patients are unaware of their risk and are not receiving blood-thinning medications that significantly reduce the risk of stroke, says Dr. Marco Di Buono, director of research for Heart and Stroke Ontario.

“This is particularly worrisome because living with the effects of stroke for someone with atrial fibrillation is more severe than living with the effects of stroke for someone who doesn’t have underlying atrial fibrillation,” Dr. Di Buono said.

Patients with the heart rhythm disorder are in hospital longer after a stroke and are often left with more severe physical and cognitive disabilities, he explained. “So their ability to reintegrate into their families, into their communities, into the work force is much more hampered than an individual who doesn’t have A fib.”

“And they’re likely to have recurrent strokes. So that’s a very important piece to highlight because with every recurrent stroke, the chance of mortality increases significantly.”

While rare in people under 40, the risk of developing atrial fibrillation increases with age. After 55, its incidence doubles with each decade of life and with such risk factors as high blood pressure, diabetes and underlying heart disease.

“Up to 15 per cent of strokes are caused by AF,” said cardiologist Dr. Paul Dorian, a foundation spokesman. “In people over the age of 60, that number increases to about one-third of strokes.”

Atrial fibrillation is the most common form of heart rhythm disturbance and is linked to abnormal changes in electrical signals controlling the heart’s pumping action. The condition, which is marked by irregular and/or rapid heart beat, causes blood to pool in the heart — allowing clots to form that can travel to the brain and cause a stroke.

“The clots are fairly large in these circumstances and that’s why the outcomes of atrial fibrillation-related stroke are (believed to be) much more severe,” said Dr. Di Buono, explaining one hypothesis.

He said most people with atrial fibrillation notice symptoms — a flutter of the heart or irregular heartbeat — but only 44 per cent “actually go to their doctor specifically to address those symptoms.”

“The vast majority only get diagnosed with A fib by chance through a routine medical exam or because they’re being screened for something else.”

Candace Allman of Toronto discovered she had the heart arrhythmia after suffering a stroke at work four years ago.

She was on the phone with a friend, who noticed she had begun slurring her words.

“And he hung up and phoned back and told my co-workers that I was having a stroke and to call 911,” said Ms. Allman, 56. “He knew right away. I was very lucky.”

Within half an hour, she was in a hospital emergency room and treated with a clot-busting drug to prevent extensive brain damage.

Other than a slight weakness on her left side, “I had a complete recovery and I don’t show any signs of having had a stroke,” said Ms. Allman, who admits she had not gone to her doctor for a checkup for five years.

“And I think maybe if I had gone, they would have detected the atrial fibrillation and possibly I could have avoided the stroke.”

The Heart and Stroke Foundation wants Canadians to be aware of the risk of stroke posed by atrial fibrillation and physicians to be on the lookout for the condition and to make sure it is treated appropriately.

That may mean prescribing a blood-thinning drug such as warfarin, which helps prevent clots from forming in the heart and “dramatically reduces the risk of stroke,” Dr. Di Buono said.