What Is the Appropriate Level of Blood-Thinning Medication for Elderly People with Atrial Fibrillation?

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The summary below is from the full report titled "Advanced Age, Anticoagulation Intensity, and Risk for Intracranial Hemorrhage among Patients Taking Warfarin for Atrial Fibrillation." It is in the 16 November 2004 issue of Annals of Internal Medicine (volume 141, pages 745-752). The authors are M.C. Fang, Y. Chang, E.M. Hylek, J. Rosand, S.M. Greenberg, A.S. Go, and D.E. Singer.

What is the problem and what is known about it so far?

The heart usually beats with a regular rhythm controlled by electrical signals. These signals move like a wave from the top chambers of the heart (the atria) to the bottom chambers (the ventricles). In some people, however, the electrical signals become disorganized and make the muscles of the atria quiver rather than beat in an organized fashion. This condition, called atrial fibrillation, produces an irregular heart rhythm that increases the risk for forming blood clots inside the chambers of the heart. These blood clots can be pumped out into the vessels that send blood to the brain, causing a stroke. For this reason, doctors usually treat patients who have atrial fibrillation with blood thinners. Unfortunately, people receiving blood thinners are at risk for bleeding inside the skull (intracranial hemorrhage, or ICH). Elderly people are thought to be more susceptible to ICH when they are being treated with blood thinners. Recently, guidelines have been issued for doctors who treat patients with atrial fibrillation, suggesting that to avoid ICH, patients older than age 75 years who have never had a stroke be treated with lower doses of blood thinners than younger patients.

Why did the researchers do this particular study?

To find out if there was a relationship between patient age, level of blood thinning, and occurrence of ICH.

Who was studied?

One hundred seventy patients with atrial fibrillation who were being treated with blood thinners and had developed ICH were compared with 1020 similar patients who had not had ICH.

How was the study done?

This was a "case–control" study in which patients with a particular disease (cases) were compared with those without the disease (controls). The researchers identified all patients who were treated at the Massachusetts General Hospital for ICH and had been given blood thinners for management of atrial fibrillation (cases). They also identified similar patients being cared for in the blood-thinning clinic who had not had ICH (controls). Data were collected on characteristics of all patients, including age, sex, intensity of blood thinning (the international normalized ratio [INR]), and other medical conditions.

What did the researchers find?

Although the risk for ICH increased with age (particularly at age 85 years or older), a very low INR did not protect patients older than age 75 years from this complication. On the other hand, INRs above the recommended target range were associated with an increased incidence of ICH.

What were the limitations of the study?

The risk for ICH may have been affected by the duration of blood thinner treatment as well as INRs, but data were not available to test this possibility.

What are the implications of the study?

Using a very low dose of blood thinner in elderly patients with atrial fibrillation does not reduce the risk for ICH and may expose patients to unnecessarily high risk for stroke.