If patients with a heartbeat irregularity stop taking their blood thinner, their risk of suffering a stroke soars.

Atrial fibrillation (AF) is a common heartbeat irregularity that can raise the risk of stroke by 50 percent. To reduce this risk, doctors commonly prescribe a blood thinner called Coumadin (warfarin). But if patients stop taking the medication, they face an 89 percent increased risk of stroke during the six months that follow, and a stroke risk of more than double for the six months after that.

Researchers from the University of Sydney also found they had a stroke risk of twice that in patients up to three years after they had discontinued taking the drug, the study said.

They reviewed the records of 68,288 people with atrial fibrillation. The average age of the patients was 78 and just over 50 percent were women.

AF is a condition that requires people to take blood thinners. In the past, Coumadin (warfarin) was the usual agent of choice. 

However, many people are switching over to newer blood thinners, which require less monitoring but are also shorter acting.

The researchers are concerned that if people miss doses on these newer medications they are more likely to suffer a stroke as a consequence.

The study was presented at the European Society of Cardiology in London.