According to the World Health Organization, 1 in every 200 people has nonvalvular atrial fibrillation (NVAF), a condition that causes the heart to beat erratically and increases stroke risk. Because NVAF is often a disease of aging, the percentage of people with NVAF is set to rise dramatically as the world's population ages, experts say.
Recently, the American Academy of Neurology (AAN) convened a guideline author panel to investigate how best to detect NVAF and to recommend therapies that reduce the risk of ischemic stroke with the least chance of bleeding. (Ischemic stroke is caused by lack of blood flow to the brain, often as the result of a clot or embolism that stops flow in a blood vessel.) According to lead author Antonio Culebras, MD, Fellow of the American Academy of Neurology (FAAN), vice president of the AAN, and professor of neurology, SUNY Upstate Medical University, Syracuse, NY, the field of neurology has an “urgent need to develop treatment modalities to address, treat, and manage NVAF.”
WHAT IS NVAF?
When the human heart functions correctly, each beat begins with an electrical pulse from the top of the right atrium, one of the heart's two upper chambers. The pulse then spreads down the heart evenly, stimulating the heart muscle to contract. When the pulse arrives between the upper and lower chambers (called ventricles), it slows slightly to allow blood to be squeezed into the ventricles before being pumped out into the rest of the body.
In NVAF, however, this electrical pulse doesn't travel evenly or smoothly down the heart. As a result, the upper chambers beat erratically, out of sync with the lower chambers. Not all of the blood is squeezed out of the upper chambers, and the ventricles are not filled before they contract. This deprives the body of sufficient blood, leading to stress on the heart, and results in a small amount of blood pooling in the chambers between heartbeats. Pooled blood can clot, and the clot can then travel to the brain, where it may cause a blockage in a blood vessel, known as ischemic stroke. With all other risk factors for stroke being equal, people with NVAF are 5 times as likely to have an ischemic stroke as people without it. In fact, 15 to 20 percent of all strokes are attributable to NVAF, according to Ralph Sacco, MD, MS, FAAN, professor and chair of neurology, University of Miami Health System.
MOST PATIENTS WITH NVAF SHOULD TAKE NOACS
In the last three years several new drugs, called novel oral anticoagulants (NOACs), have been approved by the U.S. Food and Drug Administration (FDA) for the treatment of NVAF. Anticoagulants, also known as blood thinners, prevent blood from clotting. The anticoagulant warfarin (brand name Coumadin) has been used successfully for the past 30 years to reduce stroke risk. However, the major concern with warfarin (as with all blood thinners), is the increased risk of internal bleeding. Another drawback is that its dosage has to be tailored specifically to every patient, and its level in the blood can be affected by the level of vitamin K in the diet and other drugs that the patient might be taking. This means it requires constant monitoring: patients typically have blood drawn and analyzed every two weeks and their drug dosage adjusted accordingly.
The NOACs—dabigatran, rivaroxaban, and apixaban—have been found to be at least as effective as warfarin for preventing blood clotting. Some studies suggest they are better. Studies also show that these newer drugs cause less bleeding in the brain. And because NOACs don't need regular monitoring, patients don't need to have blood drawn every two weeks.
However, unlike warfarin, NOACs don't have an antidote. If a patient is admitted to a hospital with bleeding, doctors can administer an antidote to stop warfarin's anticoagulant properties. With the newer drugs, doctors have to wait for the anticoagulant effects to wear off; luckily, they do so quickly.
“Antidotes are in development—they just haven't reached the stage of FDA approval yet,” says Dr. Sacco.
Warfarin remains the drug of choice for people with mechanical heart valve replacements, according to Drs. Culebras and Sacco. (While nonvalvular atrial fibrillation is caused by irregularities in the electrical signals responsible for contraction of heart muscle, the valvular type is caused by defects—congenital or caused by disease—in the heart valves.) And both neurologists agree that if a patient is already successfully being treated with warfarin, they should stay on this regimen.
“If a patient is doing well on warfarin, we don't want to ‘rock the boat,’” Dr. Sacco says. “But for new patients, the NOACs are good first choices. They are easier to use, require less monitoring, have reasonable safety profiles, and improve the quality of life for patients who have to be on anticoagulants,” Dr. Sacco says.
The AAN guideline states that doctors should—not must—seriously consider prescribing NOACs to patients with NVAF. “We think it's very important for the primary care physician, the person who is going to be following the patient for many years to come, to participate in [deciding]—with the patient—whether or which anticoagulants to use,” says Dr. Culebras.
RECOMMENDATIONS FOR HIGH-RISK GROUPS
According to the AAN guideline, a history of very frequent falling and moderate to severe dementia are factors of concern when it comes to prescribing blood thinners. Patients with these factors should discuss the risk and benefit of blood thinners with his or her neurologist.
The AAN guideline recommends that, wherever feasible, patients in these high-risk groups should be prescribed NOACs. Doctors should determine stroke risk versus bleeding risk in all patients who are candidates for NOACs and make a judgment based on that.
FOR MORE INFORMATION
* For a summary of the guideline, go to AAN.com/guidelines
* For more Neurology Now coverage of stroke, go to bit.ly/NN_StrokeCollection
* For coverage of atrial fibrillation in Neurology Today, go to bit.ly/NT_AtrialFibrillation