Warfarin underused

New research indicates that most patients with atrial fibrillation -- the most common type of heart arrhythmia -- who suffered a stroke and were eligible for anticoagulation treatment, were not taking any warfarin or were not taking enough.

"These are missed opportunities for stroke prevention," lead author David J. Gladstone, from the University of Toronto, said in a statement. "Sadly, we frequently see patients admitted to a hospital with a devastating stroke who are known to have atrial fibrillation, yet were either not taking warfarin or were taking a dose that is not therapeutic."

Warfarin, also known by the trade name Coumadin, can reduce the risk of stroke by preventing the formation of blood clots, which often occur in patients with atrial fibrillation. The clot may detach from the wall of the blood vessel and become lodged in the brain, blocking the flow of blood and causing a stroke. Atrial fibrillation doesn't always cause symptoms, but the condition can be quite dangerous.

As they reported in the current online issue of Stroke, the researchers analyzed data for 597 patients with known atrial fibrillation and potentially preventable strokes who were entered in the Registry of the Canadian Stroke Network from 2003 to 2007.

The strokes were disabling in 60 percent of the patients and fatal in 20 percent.

Overall, just 10 percent of patients had a therapeutic international normalized ratio (INR) at admission. An INR is the commonly used method of determining if blood-thinning drugs are working.

Prior to admission, just 39.9 percent of patients were taking warfarin and 29.0 percent were receiving no other drugs to prevent stroke. Of those taking warfarin, 74.2 percent had an INR level that was less than therapeutic, the report indicates.

Among patients with a history of stroke or transient ischemic attack (TIAs, or "mini-strokes"), just 18 percent had a therapeutic INR with warfarin therapy when they were admitted to the hospital, the researchers note.

"Too often and for too long we have overstated the inconvenience of warfarin and exaggerated its risks, ignoring convincing evidence of its effectiveness in practice," John Worthington, from Liverpool Health Service in New South Wales, UK, and colleagues write in a related editorial. (A side effect of blood-thinning drugs is potentially serious bleeding.)

However, the paper by Gladstone and his colleagues "reminds us of the perils of discounting the benefits of warfarin."