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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.
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October 2003
Blood-Thinning
Therapy Cuts Stroke Risk
Study
Confirms Measured Approach
Physicians
Strive for Balance
What
Is an Arrhythmia?
What
Is Atrial Fibrillation?
Online
Resources
What
Is an Arrhythmia?
Arrhythmias (or dysrhythmias)
are abnormal rhythms of the heart which cause the heart to pump
less effectively.
Normally, as the electrical
impulse moves through the heart, the heart contracts - about
60 to 100 times a minute. Each contraction represents one heartbeat.
The atria contract
a fraction of a second before the ventricles so their blood
empties into the ventricles before the ventricles contract.
Under some conditions
almost all heart tissue is capable of starting a heartbeat,
or becoming the pacemaker. An arrhythmia occurs when:
-
the heart's natural pacemaker
develops an abnormal rate or rhythm
-
the normal conduction pathway
is interrupted
-
another part of the heart
takes over as pacemaker
What
Is Atrial Fibrillation?
Atrial fibrillation
is a type of arrhythmia.
With atrial fibrillation,
the electrical signals in the atria (the two small chambers
of the heart) are fired in a very fast and uncontrolled manner.
The atria quiver instead
of contract. The electrical signals then arrive in the ventricles
in an irregular fashion. When the heart does not beat effectively,
the blood may pool and/or clot.
If a blood clot becomes
lodged in an artery in the brain, a stroke (brain attack) may
occur.
About 15 percent of
strokes occur in persons with atrial fibrillation.
Aspirin, warfarin,
and cardiac medications may be used to treat atrial fibrillation.
Always consult your
physician for more information.
Online
Resources
(Our Organization
is not responsible for the content of Internet sites.)
American
Heart Association
Centers
for Disease Control and Prevention (CDC)
HealthierUS.Gov
National
Heart, Lung, and Blood Institute (NHLBI)
National
Institutes of Health (NIH)
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