Underuse of blood thinners places very elderly at risk for stroke, study finds

July 02, 2000

Frail and elderly people with chronic atrial fibrillation -- in which the upper chambers of the heart flutter instead of keeping a steady beat -- are at high risk for stroke. Yet this group is less likely to receive stroke-preventing drugs than younger patients, a new study from researchers at Washington University School of Medicine in St. Louis has found. The researchers also discovered that warfarin, a blood thinner often sold as Coumadin®, lowers the risk of stroke, heart attack or death by one-fourth in this population.

Atrial fibrillation allows blood to pool in the heart, promoting clotting. If a clot breaks off and enters the bloodstream, it can lodge in the brain, causing a stroke. The disorder affects about 2 million Americans and is responsible for nearly 75,000 strokes or transient ischemic attacks (mini-strokes) each year. And it becomes more common with age.

Clinical trials with otherwise healthy subjects between ages 65 and 75 have shown that warfarin reduces the risk of stroke and that aspirin is less effective. The frail elderly could not be included in the trials, although atrial fibrillation causes one-third of strokes in octogenarians. In the current study, researchers in Missouri and Connecticut determined whether such patients are getting blood-thinning drugs, which patients are unlikely to receive them and the medical consequences of underuse.

"We found that warfarin was underprescribed and that the most important predictor of underuse was advanced age. We also found that warfarin can decrease the risk of stroke in a real-world population of frail and very elderly patients," said Brian F. Gage, M.D. "Our findings are the first to show a significant benefit of prescribing antithrombotic therapy in octogenarians with atrial fibrillation."

Gage is an assistant professor of medicine at Washington University School of Medicine in St. Louis and director of the Blood Thinner Clinic at Barnes-Jewish Hospital, which is part of the Washington University Medical Center. He is lead author of a paper in the April 2000 issue of Stroke that describes the research. The Health Care Financing Administration (HCFA) and the American Heart Association supported the study.

Other neglected groups found

Nurses at the Missouri Patient Care Review Foundation, the fiscal intermediary between HCFA and Missouri hospitals, reviewed Medicare Part A claims for admissions to all Missouri hospitals between Oct. 1, 1993, and Dec. 31, 1994. They identified more than 21,000 patients with atrial fibrillation, most of whom had been hospitalized for other disorders. From a random sample of these patients, they identified 597 cases who had chronic atrial fibrillation not associated with heart-valve disease. The median age was 80.

The data showed that 45 percent of the patients in the study group had failed to receive a prescription for an antithrombotic drug when they left the hospital, even though electrocardiograms had confirmed atrial fibrillation. Twenty-one percent were prescribed aspirin; only 34 percent were prescribed warfarin.

Statistical analyses revealed that the patients over 75 were 1.7 times less likely than the younger patients in the study to have received antithrombotic therapy. Other neglected groups were women and people treated in rural facilities. "Patients who live far from a hospital or lab might not have access to monitoring for warfarin therapy," Gage said. "The undertreatment of females is harder to explain because warfarin is just as effective in women as in men."

Consequences of underuse

The researchers analyzed Medicare claims for 463 of the 597 patients to identify subsequent hospital admissions within 500 days of the initial admission. This allowed them to compare outcomes -- stroke, transient ischemic attack, heart attack or death -- of patients who received no antithrombotic therapy, patients taking warfarin and patients taking aspirin. "Having found that these drugs are underprescribed in the elderly, we had the opportunity to examine the consequences," Gage said. "That issue has not been adequately studied."

Patients who received antithrombotic therapy were much less likely to have had one of the adverse outcomes during the subsequent 500 days, the researchers discovered. Warfarin therapy was associated with a 24 percent relative risk reduction (24 percent fewer patients in the warfarin group than in the untreated group had an adverse event). Aspirin was associated with a nonsignificant 5 percent relative risk reduction.

By applying these results to the 20,000 Medicare recipients who have atrial fibrillation and are hospitalized each year in Missouri, the researchers calculated that increasing the use of warfarin therapy by only 5 percent would avoid 91 deaths or hospitalizations in the following 12 months.

"The take-home message is that [elderly people should be checked for atrial fibrillation]," Gage said. "If they have an irregular pulse, an electrocardiogram can be ordered -- no expensive tests are needed. If atrial fibrillation is found, they need antithrombotic therapy -- most commonly warfarin."
Note: For more information, see: Gage BF, Boechler M, Doggette AL, Fortune G, Flaker GC, Rich MW, Radford MJ, "Adverse Outcomes and Predictors of Underuse of Antithrombotic Therapy in Medicare Beneficiaries With Chronic Atrial Fibrillation," Stroke 31(4), 822-827, April 2000. The full text of the paper can be found at: http://stroke.ahajournals.org/cgi/content/full/31/4/822 .

Washington University School of Medicine

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