Time in Therapeutic Range Affects Risk of Stroke, Bleeding in Patients With AF on Warfarin: Presented at AHA

By Alex Morrisson

ORLANDO, Fla -- November 12, 2015 -- The longer the time a patient with atrial fibrillation (AF) remains in therapeutic range, the less likely that individual is going to have a stroke or other cardiovascular event, according to a study presented here at the 2015 Annual Meeting of the American Heart Association (AHA).

In a cohort that included 55,072 patients from Finland diagnosed with AF and treated with warfarin, those individuals who spent greater than 80% of the time within therapeutic range experienced 3.1 strokes per 100 patients years, compared with the reference group who experienced 4.7 strokes per 100 patient years (P < .05).

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 < .05).

In the FinWAF study, the researchers found consistently that the more time within the therapeutic range, the less morbidity occurred.

In analysing bleeding rates, they found that there were 4.5 events per 100 patient-years in the reference group. The reference group was defined as patients whose INR fell within the therapeutic range 60% to 70% of the time. By comparison, patients who were within the therapeutic range more than 80% of the time experienced 2.6 per bleeding events per 100 patient years (P < .05). Patients whose anticoagulation time was in therapeutic range for less than 40% of the time experienced 7.5 bleeds per 100 patient years (P < .05).

Cardiovascular mortality occurred at the rate of 5.5 events per 100 person-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 (P < .05), and in those who were in therapeutic range less than 40% of the time experienced 11.7 events per 100 patient-years (P < .05).

All-cause mortality 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 events in patients who were in the therapeutic range more than 80% of the time.

“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,” said Mika Lehto, MD, Helsinki University Hospital, Helsinki, Finland.

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 1 INR measurement during the study period. A total of 55,072 individuals me complete inclusion criteria.

[Presentation title: Risk of Stroke, Bleeding and Mortality Is Strongly Associated With the Quality of Warfarin Therapy. Results From the FinWAF Registry With 54568 Patients. Abstract 376]

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