Preventing Stroke With Atrial Fibrillation

Most patients with AF feel fine once their heart rate is controlled. But their well-being is deceptive, since they are still at risk for stroke. The risk is particularly high in older patients, in patients with hypertension, and especially in patients with previous strokes or heart valve disease, particularly an artificial valve or narrowing of the mitral valve (mitral stenosis).

Fortunately, anticoagulants ("blood thinners") can help protect AF patients from stroke. Three choices are currently available.

Aspirin is the simplest, safest, and least expensive, but it is also the least effective, reducing the risk of stroke by about 20%.

Warfarin (Coumadin) reduces the risk of stroke by about 60%. It has been the mainstay of therapy for decades, but it requires careful attention to medications and dietary factors that affect therapy as well as frequent adjustments in dose, based on the results of blood tests performed every two or three weeks.

Dabigatran (Pradaxa) , a major new option, was approved for use in the U.S. in October 2010. Dabigatran is at least as effective and safe as warfarin, and it does not require the dietary restrictions and frequent blood tests that make warfarin therapy tricky and inconvenient. On the downside, dabigatran therapy requires two pills a day, and because it is new, long-term results are not known. Dabigatran is also much more expensive than warfarin and, unlike warfarin (which can be reversed by vitamin K), there is no way to rapidly counter its anticoagulant effect. Patients with severe liver or kidney disease, recent strokes, or artificial or severely diseased heart valves should not use dabigatran.

Rivaroxaban (Xarelto) is similar to dabigatran; it has already been approved in the U.S. to prevent blood clots after hip and knee surgery, and, based on successful trials, is up for FDA approval to prevent strokes due to AF. Apixaban (Eliquis) is an even newer member of the same drug class. It has been approved in Europe, and a major 2011 American trial reported that it was safer and better than warfarin for preventing strokes in patients with AF.

Which program is best for a patient with AF? The so-called CHADS2 score can help estimate the risk of stroke and guide the choice (see chart).

Patients with a CHADS2 score of 0 do not need anticoagulants; those with a score of 1 may take aspirin, warfarin, or dabigatran (or rivaroxaban or apixaban once approved); and those with a score of 2 or higher should take warfarin or dabigatran (or rivaroxaban or apixaban), as should patients with AF and mitral stenosis or artificial heart valves.

The best aspirin dose has not been determined, but most doctors recommend 81 to 325 milligrams (mg) a day. The dose of warfarin should be adjusted to maintain an INR (international normalized ratio) result of 2.0 to 3.0. The standard dose of dabigatran is 150 mg twice a day.

Researchers are working hard to improve the management of AF. But for now, the tried and true will serve most patients well: slow the racing heart, consider restoring normal rhythm if symptoms persist, and reduce the risk of stroke by preventing clots.

Atrial fibrillation is an old problem, but it can be treated effectively, whether by standard therapy or new innovations.