Blood Thinners for Atrial Fibrillation Patients?

September 2, 2013

A New Tool Shows Who Benefits...and Who Doesn’t

There’s a common heart condition that can quadruple or even quintuple your risk of having an ischemic stroke, the type caused by a blood clot or other blockage. Called atrial fibrillation (AF), it’s a disorder that affects the heart’s rhythm. Blood can be left behind in the upper chambers of the heart during abnormal contractions…and that blood is prone to form a clot that might travel to the brain. To prevent strokes in AF patients, doctors often prescribe anticoagulant medication (blood thinners).

Anticoagulants are very effective at preventing blood clots, but they bring dangers of their own—namely, a greatly increased risk for major bleeding. For instance, users may develop gastrointestinal bleeding…or may experience a cerebral hemorrhage. That’s why blood-thinning drugs should be used only when their benefits clearly outweigh their risks.

Problem: It’s not easy to tell which AF patients are likely to have a stroke and thus do need anticoagulants…and which are unlikely to have a stroke and therefore should stay off the blood thinners.

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Various sets of guidelines have been developed to help doctors and AF patients make the important yes-or-no decision about blood thinners—but these guidelines do only a mediocre job. As a result, many patients are misclassified as low risk, don’t get the blood thinners and wind up having strokes…while others are misclassified as high risk, take the blood thinners and end up with serious side effects from the drugs.

Good news: Researchers from Harvard, Kaiser Permanente Research in California and elsewhere have devised a new scoring system that more accurately predicts which AF patients should be on blood thinners—and which should not.

SETTLING ON A SCORE

An advantage the researchers had in devising the new risk assessment tool was their access to the database of one of the nation’s largest health-care plans, Kaiser Permanente. They found more than 13,500 patients with known AF, then tracked their medical records to look for use of the common anticoagulant warfarin (Coumadin)…and also for ischemic stroke or other thromboembolic events (conditions caused by blood clots), such as blockages to arteries in the legs.

The patients were followed for up to seven years or until they had a stroke or other thromboembolic event, left the health plan or died. Only their time off warfarin was considered, because this analysis wanted to determine the risk for stroke, which would potentially be avoided by the warfarin.

The researchers looked at conditions that affect stroke risk, then determined the individual amount of risk that each factor contributed. Based on the real-life data—meaning what really happened to actual patients who had the various risk factors—the researchers devised a scoring system called the ATRIAstroke score that doctors can use with their AF patients to gauge blood thinners’ benefits versus risks.

Scoring system: Risk factors that contribute one point each to the ATRIA score include having diabetes…high blood pressure…congestive heart failure…protein in the urine…poor kidney function…or being female (since female AF patients are at higher risk). In addition, up to nine more points are added based on the interplay between age and previous history of stroke. The points for different age groups ranged from zero to six for people without a previous stroke…and from seven to nine for people who have had a stroke. The math gets a little tricky, but here are two examples: A male younger than 65 with no other risk factors would get the minimum score of zero…a female of 85 who had suffered a previous stroke and had all the other risk factors would get the maximum ATRIA score of 15.

USING THE SYSTEM

Here’s how the scores are categorized in terms of risk for stroke or other thromboembolic event…

• Zero to five—low risk of 0.9% or less per year. AF patients in this category are unlikely to benefit from taking blood thinners.
• Six—moderate risk of 1% to 1.9% per year. Even though this category comprises just a single score, a goodly number of study participants did fall into this category. For AF patients with a score of six, the researchers tended to favor the use of blood thinners, though the benefits were less clear than for patients at higher risk. Here, patients’ preferences regarding the risk for stroke versus the risk and inconvenience of taking blood thinners need to be carefully weighed, the researchers noted.
• Seven to 15—high risk of 2% or more per year. Anticoagulation therapy appears to provide a clear net benefit for AF patients in this category. Now, a 2% risk may not seem that much higher than the 0.9% or less risk that is deemed low—but since the risk is cumulative over time, that difference becomes more and more significant as the years pass. For instance, the five-year cumulative risk would be around 10% or more for people in this category.

Validating the results: After developing the ATRIA scoring system, the researchers tested its validity against another large database of AF patients (again from Kaiser Permanente, but this time drawing on data from different years and different regions). Then they compared the predictive powers of the ATRIA system against the older predictive systems—and found that the ATRIA scores did indeed more accurately reflect the odds that any given patient would experience a stroke when not taking a blood thinner.

If you have AF: Whether or not you are currently taking a blood thinner and whether or not you have ever had a stroke, ask your doctor to assess your stroke risk based on the ATRIA scoring system. If your score is low but your doctor still wants you to take a blood thinner—or if your score is high but your doctor has not prescribed a blood thinner—ask for an explanation. If you are not satisfied with that explanation, consider seeking a second opinion on whether anticoagulation therapy is a sensible choice for you. The scoring system is not meant to lock anyone into a decision, the researchers said, but rather to provide an informed way for AF patients and doctors to discuss the risks and benefits of anticoagulation therapy. Important: You and your doctor should review your decision periodically—because as you get older or as your medical condition changes, your ATRIA score changes, too.

Source: Daniel Singer, MD, professor of medicine, Harvard Medical School, and professor, Harvard School of Public Health, Boston. His study was published in Journal of the American Heart Association.

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