Nearly three million people in the U.S. have atrial fibrillation, and their risk for stroke is five times higher than people without the heart rhythm disorder. That’s because the rapid, irregular heartbeats that define atrial fibrillation can cause blood clots to form, which lead to stroke.
Warfarin (Coumadin), is often prescribed to lower stroke risk in these people because it reduces the blood's tendency to form clots. This is commonly referred to as “thinning” the blood, explained James Daubert, MD, a heart rhythm specialist at Duke. However, frequent blood tests are needed to determine if the drug is making the blood too thin – which can lead to serious bleeding risks including bleeding in the brain – or too thick, which can cause stroke. Diet is a concern too, as vitamin K, found in green leafy vegetables, inhibits the drug’s effectiveness. These issues make some doctors hesitant to prescribe warfarin, and some people unwilling to take it.
“Only about half of patients with atrial fibrillation who should be on an anticoagulant are on such medications to prevent stroke,” said Daubert.