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Targeted drugs prevent stroke in atrial fibrillation

ramo12-25-11ALBUQUERQUE, N.M. — Atrial fibrillation (AF) is a heart rhythm disturbance that causes at least 15 percent of strokes. The disease affects more than 6 million people in the U.S.

Strokes result from blood clots that form in the atrium or upper heart chamber. The clots can travel to the brain, cutting blood supply and causing a stroke, as well as to other parts of the body. A stroke can be the first time a patient learns he or she has it because AF may be silent.

AF can result from disease of the heart valves but much more frequently from disease of the atria. In this article, I will address the stroke prevention treatment of the latter, called non valvular atrial fibrillation

Stroke risk is estimated using a score called CHA2DS2 VASC (see chart). The April 2014 guidelines for management of AF outline the risks and benefits of using anticoagulants to prevent stroke. The guidelines recommend anticoagulant therapy for a score of 2 or more and no therapy or aspirin for a 0 score. With a score of 1, no therapy, aspirin or an anticoagulant may be chosen. Aspirin may provide little if any protection and poses a bleeding risk.

The 2014 guidelines recommend warfarin (Coumadin), an anticoagulant used since the 1950s, as the first choice for anticoagulation for non valvular atrial fibrillation. Warfarin use requires at least monthly blood test monitoring to check adequacy of anticoagulation. Warfarin’s effect can be made stronger or weaker with medication or diet, so patients have to be vigilant about what they eat.

A major breakthrough came more than three years ago, when the first of four new anticoagulant drugs that target a specific clotting factor were approved by the FDA. The oral agents are referred to as target-specific because they attack a single part of the coagulation system.

The new target-specific drugs need no monitoring and are not affected by diet, but because they have a short life in the body, missing a dose can leave the patient unprotected.

Unlike warfarin, where we test the level of anticoagulation, there is no way to measure the level with the target-specific drugs. They are prescribed in a one- or two-size-fits-all (meaning the same dosage is given to a 140-pound woman and a 250-pound man). Patients with impaired kidney function need reduced dosage.

Clinical trials found that each of the four FDA approved agents — dabigatran, rivaroxaban, apixaban and in May 2014 edoxaban — are as effective or in some cases superior to warfarin in protecting against stroke, but except for apixaban, patients do not live any longer than if they are on warfarin. There are currently no drugs to reverse their effects if bleeding occurs.

When superior, the difference is not as dramatic as the drug company ads imply. A recent meta-anlysis found that the relative risk of stroke dropped by 25 percent with the target-specific agents when compared to warfarin. Pretty impressive but that means a fall in stroke rate from 3.7 percent a year on warfarin to 3.1 percent a year on the target-specific agents. That means we have to treat about 140 patients for a year to prevent one stroke as compared to warfarin.

The new agents caused 50 percent fewer brain hemorrhages than warfarin, dropping risk from a yearly stroke incidence from 0.5 percent per year with warfarin to anywhere from 0.1 percent to 0.2 percent a year.

So given the advantages, with lower brain hemorrhage numbers, the same or better stroke reduction rates and the better convenience, why haven’t doctors switched everyone to one of the new target-specific agents? I believe there are three major reasons.

First is the concern that lack of monitoring means it is difficult to know the effectiveness of the drugs, and you cannot know who is taking the medication. Second, the lack of a way to effectively reverse the drugs if bleeding occurs, and third, the cost, which can be $300-$350 a month and often not covered by insurance, are impediments to it being embraced by the medical community.

Warfarin requires at least monthly blood tests that can cost up to $150 and in the very best of settings, patients are in the proper anticoagulation range less than 65 percent of the time. Once we can overcome those impediments, a lot more patients with AF will be given those drugs.

If you take warfarin or any of these new drugs, you must have a medical alert bracelet. Most health-care providers are not familiar with these drugs and the fact that they are anticoagulants may be overlooked.

So how do we handle the issue with patients at the New Mexico Heart Institute? We individualize our approach to every patient. We follow the very first statement in Class I recommendations that states, “In patients with AF, anticoagulant therapy should be individualized based on shared decision-making after discussion of the absolute and relative risk of stroke and bleeding, and the patient’s values and preference.”

Dr. Barry Ramo is a cardiologist with the New Mexico Heart Institute and medical editor for KOAT-TV. Send questions for him to Albuquerque Journal Live Well, P.O. Drawer J, Albuquerque, NM 87103, or email them to htaylor@abqjournal.com.

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