In a study that examined use of the
anticoagulant medication warfarin and risk of stroke following a diagnosis of
atrial fibrillation in older patients, women, especially those 75 years or
older, had a higher risk of stroke than men, regardless of their risk profile
and use of warfarin, suggesting that current anticoagulant therapy to prevent
stroke might not be sufficient for older women, according to a study in the May
9 issue of JAMA.
"Atrial fibrillation (AF)
is the most common cardiac arrhythmia, accounting for approximately one-third
of hospitalizations for cardiac rhythm disturbances.
It has
been estimated that 2.2 million people in the United States and 4.5 million in
the European Union have paroxysmal or persistent AF. Patients with AF have a 5-fold
increase in the risk of stroke compared with the general population; therefore,
antithrombotic agents are prescribed to reduce this risk.
Sex-based
differences related to AF have been identified, the most concerning being that
women with AF have an increased risk for cardiovascular
events, including stroke," according to background information in the
article. It has been suggested that underutilization of oral anticoagulation
treatment among women has been a contributing factor to this increased risk.
Meytal
Avgil Tsadok, Ph.D., of the McGill University Health Center, Montreal, and
colleagues compared usage patterns of warfarin and subsequent stroke incidence between
men and women 65 years or older with AF.
The
study included patients admitted to the hospital with recently diagnosed AF in
the province of
Quebec, Canada, from 1998-2007, using administrative data with linkage
between hospital
discharge, physicians, and prescription drug claims databases.
The
cohort comprised 39,398 men (47.2 percent) and 44,115 women (52.8 percent). At
admission, women were older (74.2 percent of women were older than 75 years,
compared with 61.4 percent of men) and had a higher CHADS2 (congestive heart
failure, hypertension, age 75 years or older, diabetes mellitus, prior
stroke or transient ischemic attack) score than men.
Warfarin
prescription rates were slightly higher among women compared with men (60.6
percent in women vs. 58.2 percent in men); women tended to have more
prescriptions filled for warfarin within 30 days postdischarge, compared with
men.
The
proportions of warfarin prescriptions filled were slightly increased to 68
percent in women as well as men when prescription rates were assessed within 1
year after discharge. In general, adherence to anticoagulation therapy was
relatively high and similar in both sexes.
The
researchers found that crude stroke rates were significantly higher in women
compared with men (5.8 percent vs. 4.3 percent). The difference between sexes
was mainly driven by the rates in the older (75 years and older) patients.
"Furthermore, older women had significantly higher rates of stroke than
older men, regardless of warfarin use, and women had higher rates of stroke
compared with men, regardless of adherence level," the authors write.
Analysis indicated that women had a 14 percent higher risk of stroke than men,
after adjusting for various factors.
The
authors note that it is not yet known why women with AF are more susceptible to
stroke. "The increased risk may be attributable to physiology (such as
uncontrolled hypertension), vascular biology, genetic factors, hormonal or
thromboembolic factors, or psychosocial factors that differ between men and
women. We were not able to identify these factors with our database."
"Although
epidemiologic studies have investigated sex differences in stroke occurrence,
little is known about warfarin effectiveness between men and women in the
real-world clinical setting. Our results suggest that elderly women with AF may
need to be targeted for more effective stroke prevention therapy.
Clinicians
should be aware of the elevated stroke risk in older women with AF, and new
strategies should be applied to effectively prevent stroke equally in men and
women."
More
information: JAMA.
2012;307[18]:1952-1958.
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