Warfarin Treatment, Time in Therapeutic Range, Bleeding and Stroke Risk Among Elderly Patients with Non-Valvular Atrial Fibrillation

Background:
The risk of stroke in atrial fibrillation (AF) increases with age. Despite that, and the known efficacy of warfarin treatment in stroke prevention, there is under treatment in elderly.

Aim:
To estimate the incidence of stroke, mortality and bleeding, in elderly patients with non-valvular AF.

Methods:
A prospective cohort study using the Clalit Health Services (CHS) database between 2004 and 2011. We examined two groups: patients aged 75-84 and ≥85 years. Incidences of stroke, bleeding (gastrointestinal and intracranial) and mortality were estimated per 100 person years in both age subgroups. We compared stroke risk between patients who were or were not treated with warfarin, in both age groups. The benefit of warfarin in stroke prevention was estimated in relation to Time in Therapeutic Range (TTR <40%, 40-60%, >60%) in each age group using time-dependent multivariate analysis.

Results: We identified 17,574 AF patients aged ≥ 85, and 31,866 patients aged 75-84. Patients with AF had high burden of comorbidities, and a high thrombotic and bleeding risk. Only 25 % of patients aged 75-84 and 13 % of patients aged ≥85 received warfarin treatment regularly.

The incidence of ischemic stroke, bleeding and mortality was lower in higher TTR`s (Table 1).

The risk of stroke was lower in warfarin treated patients vs. those that were not treated in all TTR subgroups, more prominently in high TTR (Table 2).

Conclusion:
Despite higher stroke risk in elderly patients, a large proportion of these patients are not treated with warfarin. The incidence of bleeding and mortality is decreasing as the TTR increases. Furthermore, Stroke risk is significantly decreased in patients treated with warfarin, specifically when being with higher TTR.