|
Study clarifies impact of age on safety
of warfarin treatment for atrial fibrillation
Appropriate anticoagulation target
seen as most important for avoiding hemorrhage
BOSTON - November 15, 2004 - A study conducted at Massachusetts
General Hospital (MGH) has clarified the risk of intracranial hemorrhage
in older patients with atrial fibrillation who take the drug warfarin
to prevent ischemic stroke. The report in the November 16 Annals
of Internal Medicine showed that treatment at moderate levels
of intensity has no greater risk of hemorrhage than does lower intensity
treatment. Although the risk of hemorrhage did significantly increase
in patients over 85, that risk often can be minimized by tight control
of warfarin intensity.
"Studying how warfarin therapy is associated with intracranial
hemorrhages is challenging because these events are rare, albeit
devastating," says Margaret Fang, MD, MPH, who led the study
as an MGH research fellow and is now at the University
of California at San Francisco (UCSF). "Because lower level
warfarin therapy can lead to a much higher risk of ischemic stroke,
we also wanted to examine whether less intensive treatment, which
recent guidelines have suggested for older patients, actually results
in a lower risk of hemorrhage."
Atrial fibrillation, a type of irregular heartbeat, is a common
and strong risk factor for stroke. By leading to the formation of
blood clots that travel to the brain, the condition is believed
to account for about 80,000 ischemic strokes a year and can increase
a patient's overall stroke risk fivefold. Many patients with atrial
fibrillation are treated with blood-thinning medications like warfarin,
and previous studies by members of this research team and others
have confirmed that achieving appropriate levels of anticoagulation
- reflected by levels of 2.0 or more on a blood test called the
INR - can significantly reduce the risk that a stroke will occur.
However, elevated anticoagulation levels can increase the risk of
brain hemorrhage, a rare but dangerous complication of warfarin
therapy. Concern about the risk of hemorrhage, especially among
older people, has led some patients to avoid anticoagulation therapy.
The current study was designed to determine at what age and INR
level the risk for intracranial hemorrhage becomes significant.
The research team compiled information on 170 adult atrial fibrillation
patients who had developed intracranial hemorrhage while being treated
with warfarin and compared that data to information from 744 randomly
selected patients from the MGH anticoagulation clinic who had not
developed hemorrhage during the same time period. The study groups
included only patients taking warfarin for atrial fibrillation.
Although the risk of hemorrhage did increase with patients' age,
the most significant increase in risk occurred after age 85. The
risk of bleeding increased in patients with INR levels over 3.5
and sharply rose after 4.0. But even among older patients, achieving
an of INR of less than 2.0 did not reduce risk below that seen at
an anticoagulation level of 2.0 to 3.0.
"Our study emphasizes that physicians should aim for an INR
range of 2.0 to 3.0 when prescribing warfarin for atrial fibrillation,
even for older patients," says Fang. "Although we found
that people aged 85 and older had a higher risk for intracranial
hemorrhage, these are also the patients that gain the greatest benefit
from warfarin for stroke protection. Therefore, the net benefits
of warfarin generally outweigh the potential risks in older patients
with atrial fibrillation." Fang is an assistant adjunct professor
of Medicine in the UCSF Division of General Internal Medicine Hospitalist
Group.
The study authors are also participating in a continuing study of
more than 13,000 atrial fibrillation patients to assess the long-term
risk for hemorrhage both with and without warfarin therapy. That
study is being led by Daniel Singer, MD, of MGH, senior author of
the current study, and Alan Go, MD, of UCSF and Kaiser Permanente
of Northern California, also a co-author of the current study. Additional
co-authors are Yuchiao Chang, PhD, Elaine Hylek, MD, MPH, Jonathan
Rosand, MD, and Steven Greenberg, MD, PhD, all of MGH. This study
was supported by a National Research Service Award, the National
Institute on Aging, and the Eliot B. Shoolman Fund of MGH.
Massachusetts General Hospital, established in 1811, is the original
and largest teaching hospital of Harvard Medical School. The MGH
conducts the largest hospital-based research program in the United
States, with an annual research budget of more than $400 million
and major research centers in AIDS, cardiovascular research, cancer,
cutaneous biology, medical imaging, neurodegenerative disorders,
transplantation biology and photomedicine. In 1994, MGH and Brigham
and Women's Hospital joined to form Partners HealthCare System,
an integrated health care delivery system comprising the two academic
medical centers, specialty and community hospitals, a network of
physician groups, and nonacute and home health services.
Media Contacts: Sue
McGreevey, MGH Public Affairs
Carol Hyman, UCSF
Public Affairs
Physician Referral Service: 1-800-388-4644
Information about Clinical Trials
|
|
 |
