Warfarin decreases risk of stroke for patients with atrial fibrillation (AF) dependent on percent time in the therapeutic range (TTR) with an international normalized ratio (INR) of 2 to 3. We hypothesized that gender differences in ischemic stroke risk are related to TTR. From the AFFIRM database of 4,060 patients with AF, we determined the incidence of ischemic stroke by gender. We evaluated the INR at time of ischemic stroke and calculated TTR. We determined the relation between gender and ischemic stroke by TTR. Women had CHADS(2) Scores (3.7 ± 1.3 vs 2.5 ± 1.3, p <0.0001) and more ischemic strokes than men (5% vs 3%, odds ratio 1.6, 95% confidence interval 1.19 to 2.26, p = 0.002). Mean INR near time of ischemic stroke was 2 for women and men; median values were subtherapeutic (1.7 and 1.8, respectively). Women spent more time outside the therapeutic range (40 ± 0.7% vs 37 ± 0.5%, p = 0.0001), with more time below the therapeutic range (29 ± 0.7% vs 26 ± 0.5%, p = 0.0002). A higher TTR protected against ischemic stroke for women but not for men. Women who had a comparably high TTR (≥66%) still had more ischemic strokes (p = 0.009). A fitted Cox proportional hazard regression model showed that gender, TTR <46% versus >80%, age, and previous stroke were significantly related to stroke incidence. In conclusion, women in AFFIRM were at greater risk of ischemic stroke than men, in part related to differences in TTR. Women with AF may benefit from more aggressive or novel anticoagulation to decrease their risk of stroke.
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