Rehabilitation helps stroke survivors to relearn skills such as raising arms. (Duke University/Associated Press)

People with an irregular heart beat condition should be closely monitored after they start taking a common blood thinner because they are at much higher risk of stroke in the first month, Canadian researchers have discovered.

Warfarin is routinely prescribed for people diagnosed with atrial fibrillation to reduce the long-term risk of an ischemic stroke from a clot that forms in the heart and goes to the brain.

Now researchers at Toronto’s Institute for Clinical Evaluative Sciences have found that patients newly prescribed warfarin are at three times higher risk of ischemic stroke in the first 30 days compared with the rest of the five-year study period.

"Especially in the high-risk period in the first 30 days, there should be closer monitoring," said Jennifer Tung, a pharmacist at Sunnybrook Health Sciences Centre and the study’s lead author. "That means making sure that patients are receiving the blood tests to monitor the warfarin and also making sure that patients are given appropriate education to recognize signs of stroke as well as bleeding."

Tung stressed patients should not stop taking warfarin, as the research also demonstrated its long-term benefits for stroke prevention, which are well established.

The study was published in Thursday’s issue of the journal Stroke.

The research was based on hospital and data from 148,446 patients aged 66-years and older with atrial fibrillation who received warfarin between 1997 and 2010.

Tung called the findings clinically important given that 27 per cent of those who experienced an ischemic stroke in the study (1,639 of 6,006) died in hospital or within a week of discharge.

The Heart and Stroke Foundation’s FAST campaign makes it easier to recognize stroke signs quickly. 

FAST stands for:

  • Face- is it drooping?
  • Arms – can you raise both?
  • Speech – is it slurred or jumbled?
  • Time – call 911 right away.

Strokes that did not result in hospitalization weren't included in the observational study, which points to associations rather than cause and effect.

The study was funded by the Ontario Drug Policy Research Network. One of the study’s authors is a consultant for several pharmaceutical companies.