Blood-Thinning
Therapy Cuts Stroke Risk
More
Warfarin Better In Atrial Fibrillation
Intensive
drug therapy to prevent blood clots in people with the heart condition
called atrial fibrillation can reduce deaths and damage caused by strokes
without increasing the risk of dangerous bleeding, according to a study
reported in the New England Journal of Medicine.
It is a finding of life-and-death interest
to the growing numbers of US adults with the condition. Incidence of
atrial fibrillation increases with age.
An estimated 2.3 million US adults now have atrial fibrillation,
and one of every 20 people age 70 or older has the condition.
Atrial fibrillation reduces the heart's ability to pump
blood, and the resulting sluggish flow promotes formation of clots that
can block brain arteries and cause strokes.
Blood-thinning therapy with aspirin or warfarin, a much
more potent anticoagulant, can prevent those clots. But physicians are
concerned that too-intensive treatment can cause bleeding in the brain
that does the same damage as a clot-caused stroke.
Study
Confirms Measured Approach
Atrial fibrillation
is the leading cause of stroke among the oldest US adults.
Clotting is measured by what is called the international
normalized ratio (INR). A higher INR means freer-flowing blood with
a lower risk of clots but a higher risk of dangerous bleeding.
Physicians have known that an INR of 2 or higher can
effectively reduce the risk of stroke, but there have been questions
about the level at which a higher INR becomes dangerous.
The new study of more than 13,500 patients with atrial
fibrillation shows that "the risk of hemorrhage does not increase
until you reach an INR of about 4," says Dr. Elaine M. Hylek, at
Harvard Medical School and lead researcher on the study.
Previous studies have shown that an INR of 2 or higher
can reduce the risk of strokes in patients with atrial fibrillation,
Dr. Hylek says.
"This is the first time it has been shown that
the severity and mortality of strokes are affected by the intensity
of anticoagulation medication," she says.
Physicians
Strive for Balance
Not all atrial
fibrillation patients receive anticoagulant therapy. Those regarded
as having a very low risk of stroke receive no medication at all. Others,
at some risk, are told to take aspirin. Warfarin is reserved for the
highest-risk patients, because it requires careful monitoring to achieve
the desired INR.
A third of the 596 strokes reported in the study occurred
in patients taking warfarin. Among those patients, an INR under 2 nearly
doubled the risk of having a severe stroke and more than tripled the
risk of dying because of the stroke.
Increased risk of bleeding in the brain was found only
in INR readings of 3.9 or higher, Dr. Hylek says.
"The message is that patients with atrial fibrillation
should maintain an INR at a minimum of 2 or higher," she says.
"An INR of about 2.5 should not influence physicians toward a lower
level."
The aging of the US population means that more and more
people will become aware of the INR and what it means, Dr. Hylek says.
The study "reinforces that we do know the optimal
range" of INR readings, says Dr. Robert G. Hart, at the University
of Texas Health Sciences Center at San Antonio and author of the accompanying
editorial.
A reading between 2 and 3 is best, not only for people
with atrial fibrillation but also for those who take warfarin because
they have mechanical heart valves, he says.
"For the very elderly with a high risk of bleeding,
I would aim at the lower part of that range when possible," Dr.
Hart says.
Always consult your
physician for more information.
Online
Resources
American
Heart Association
Centers
for Disease Control and Prevention (CDC)
HealthierUS.Gov
National
Heart, Lung, and Blood Institute (NHLBI)
National
Institutes of Health (NIH) |
