Staying Within Therapeutic Range Benefits Afib Patients

Huge studies shows benefits of consistent anticoagulation treatment

ORLANDO -- In a large population-based study that encompassed more than 50,000 people in Finland, researchers said that maintaining anticoagulation goals resulted in improved outcomes for patients with atrial fibrillation being treated to prevent strokes.

In the cohort that included 55,072 individuals diagnosed with atrial fibrillation and treated with warfarin, patients who were in the therapeutic anticoagulation range (measured via INR) more than 80% of the time experienced 3.1 strokes per 100 patient-years, compared with 4.7 strokes per 100 patient-years (P<0.05) in a reference group whose time within the target range was 60%-70%, reported Mika Lehto, MD, of Helsinki University Hospital.

In his oral presentation here at the annual scientific sessions of the American Heart Association, Lehto also said that patients who were in the therapeutic range for less than 40% of the time had a substantially increased risk of stroke compared with the reference group -- 9.3 strokes per 100 person-years (P<0.05).

In the so-called FinWAF study, the researchers illustrated consistently that the more time within the therapeutic range, the less morbidity occurred when compared to the median group, and the less time in therapeutic range was associated with greater morbidity:

• Bleeding events in the reference group occurred at a rate of 4.5 per 100 patient-years. Patients who were within the therapeutic range more than 80% of the time experienced bleeding events at 2.6 per 100 patient-years (P<0.05). Patients whose anticoagulation time was in therapeutic range for less than 40% of the time experienced bleeds at 7.5 per 100 patient-years (P<0.05)
• Cardiovascular mortality occurred at the rate of 5.5 events per 100 patient-years in the reference group, compared with 2.2 events per 100 patient-years in the patients who were in therapeutic range more than 80% of the time a(P<0.05), and in those who were in therapeutic range less than 40% of the time the cardiovascular mortality was 11.7 events per 100 patient-years (P<0.05)
• All-cause mortality per 100 patient-years was 20.7 events among patients with INR in the therapeutic range less than 40% of the time, compared with 8.5 events in the reference group and 3.1 event in the patients who were in therapeutic range more than 80% of the time (P<0.05)

"We documented in this unselected nationwide cohort a strong and direct relationship with time in therapeutic range and incidence of stroke, bleeding events and mortality," Lehto said.

The FinWAF study linked patient data from several nationwide registries in Finland through the individual civil registration number. Inclusion in the study required a diagnosis of atrial fibrillation, the purchase of warfarin as treatment for the condition, and at least one INR measurement during the study period. A total of 55,072 individuals had complete inclusion criteria.

The study included patients diagnosed with atrial fibrillation from 2005 to 2009; follow-up continued through 2011.

Mean time in therapeutic ranges was 61.1%; the median time in therapeutic range was 67%. Patients included in the study were in their 70s; about half were men; about a quarter of the patients had vascular disorders in addition to atrial fibrillation; about 25% had hypertension; 17% had congestive heart failure; about 10% were diabetic; about 10% had a history of stroke.

"This is consistent with what we would have expected among patients who have their INR within the therapeutic range," said William Borden, MD, associate professor of medicine at the George Washington University, Washington.

"In this dataset, we see a sort of dose response with the amount of time in therapeutic range," he told MedPage Today. Borden, a co-moderator of the session, said that for doctors, the finding in the large Finnish study could represent a good teaching moment for patients.

"Warfarin treatment can be frustrating for patients and frustrating for [providers] but treatment with warfarin in this patient population has tremendous benefit. This kind of data can be very useful in illustrating for patients the importance of taking their medication and following up with their provider to assure appropriate levels of their warfarin."