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| AFFIRM trial reveals gender differences in warfarin response |
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14 March 2006
A 3.5-year follow-up of patients with atrial fibrillation (AF) suggests that warfarin may not protect women against ischemic stroke as effectively as men.
Presenting the results at the 55th American College of Cardiology Annual Scientific Sessions in Atlanta, Georgia, USA, Dr Brian Olshansky, from the University of Iowa in Iowa City, USA, suggested that women may need a higher International Normalized Ratio (INR) for effective anticoagulation, or may need combination antiplatelet therapy."
In a subanalysis of the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) trial, 2466 men and 1594 women with AF were randomly assigned to receive treatment by rhythm control or rate control. During follow-up, more women than men suffered an ischaemic stroke, at 5% versus 3%, respectively. This gave women an unadjusted 1.65-fold increase in stroke risk compared with men. When the investigators examined possible reasons for this gender discrepancy, they found significant differences in the baseline characteristics of the male and female study participants.
The average age of the women was 71 years, significantly older than their male counterparts who were an average of 68 years old. Women had a higher body mass index, at 29 compared with 27 in men, but just 8% smoked compared with 16% of men. The prevalence of other important stroke risk factors, including diabetes and history of stroke did not differ between men and women. Gender-specific patterns of cardiovascular disease were identified, with women having a greater prevalence of hypertension and valvular heart disease but a lower prevalence of coronary artery disease and pulmonary disease. In addition, women had a shorter duration of AF, on average, but were more likely to be hospitalised with the condition than men, and were also found to have a higher maximum ventricular rate. Overall, women were as likely as men to be prescribed warfarin and to have a therapeutic INR at the last assessment. Even after adjustment for stroke risk factors and INR, women still had a 1.59-fold increase in stroke risk compared with men.
Dr Olshansky speculated: "One possible explanation for these findings is that once their patients achieved normal sinus rhythm, physicians were more likely to discontinue warfarin therapy in women than in men, increasing stroke risk in women."
Reference:
ACC 2006
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