Atrial fibrillation is more common than suspected

April 09, 2003

Irregular heartbeats that put people at higher risk of stroke are more common than patients and doctors might think, according to a report in a recent issue of Circulation, which is published by the American Heart Association.

A study led by a University of Washington researcher asked patients with previous episodes of atrial fibrillation or flutter to provide electrocardiogram samples for 30 seconds every two weeks for six months, just simply to test equipment in a drug study. The researchers found there was a one in six chance that a patient would record "silent"atrial fibrillation before a symptomatic episode was documented.

Doctors have long suspected that much "atrial fib" goes unreported, but this is the largest group of studies to suggest just how unreported it is. The authors suggest that doctors should assume the worst when treating someone at risk of atrial fibrillation and stroke.

"There's a significant amount of atrial fib going on that people do not know about because they don't feel any symptoms. What this study tells us is that doctors simply don't know how often their patients have atrial fibrillation. When a doctor thinks a patient has a certain amount of atrial fib, the person is probably having significantly more," says the lead author, Dr. Richard L. "Rick" Page, Robert A. Bruce professor and the division head of cardiology in the UW School of Medicine.

Atrial fibrillation is just one of the arrhythmias, or forms of irregular heartbeat, although it is among the most common. Atrial fibrillation usually first shows up in middle age and affects one in 20 people over 65 and one in 10 people over 80. People with atrial fibrillation are at greater risk for stroke than people in the general population.

Page and many other cardiologists believe that since doctors cannot know the full extent of their patients' atrial fibrillation, they should regularly prescribe medicine to thin their patients' blood. Some doctors may be prescribing the blood thinner warfarin (brand name Coumadin) while their patient has symptoms, but then stop the blood thinner when the symptoms disappear. The Circulation paper suggests that a significant percentage of patients still have atrial fib, even though they may go several months without noticing symptoms.

"This is where the real risk is: if you are a doctor and you believe your patient does not have recurrent atrial fibrillation, and you stop prescribing the blood thinner, the patient may still be having the atrial fib - and therefore still be at persistent risk of stroke," Page says. "Nowadays, many of us continue to prescribe the blood thinner even after the heart rhythm appears to have normalized, because the atrial fibrillation may not be gone at all."

Some people take aspirin to thin their blood, but Page stressed that this is no substitute for Coumadin in dealing with patients who have atrial fibrillation and risk factors for stroke. He suggested that people with atrial fibrillation who are at high risk of stroke consult a doctor. The risk factors for stroke include: history of high blood pressure, diabetes, congestive heart failure, prior episodes of stroke or embolisms, and age over 65.

"This study is further proof that they ought to have their blood thinned indefinitely," Page says.

The study pool included 1,380 people with previous cardiac episodes of atrial fibrillation or flutter. They were considered good candidates for testing an investigational antiarrhythmic drug therapy, Azimilide. The reason we know of their asymptomatic episodes is that they used a heart monitor during testing of Azimilide. During the testing for up to six months, patients were asked to report when they felt atrial fibrillation. They were also asked to transmit a 30-second electrocardiogram every two weeks even when they did not feel any symptoms.

The main reason researchers asked patients to send these ECG recordings when the patient felt fine was to make sure patients knew how to operate the heart monitoring equipment. In addition, researchers used these recordings to capture atrial fibrillation. The analysis showed that one out of six patients sent a signal that showed atrial fib was taking place, even though the patient did not realize it. "This sampling represents just a snapshot. This clearly underestimates the frequency of the problem. But because the occurrences were so common, and it was placebo-controlled, it reached the level of importance that we and Circulation agreed it should be published," Page says.

The study showed that 13 percent of the people who took Azimilide had asymptomatic atrial fibrillation, versus 18 percent of the people who took a placebo. Further data are being collected to demonstrate the effect of Azimilide on recurrence of symptomatic atrial fibrillation and flutter.
Other authors of the paper, published March 4, include Drs. Edward L.C. Pritchett and William E. Wilkinson of Duke University Medical Center; Dr. Stuart J. Connolly of McMaster University, Hamilton, Ontario, Canada; and Thomas W. Tilsch and Drs. Daniel J. Schnell and Stephen Marcello of Procter & Gamble Pharmaceuticals.

The UW School of Medicine is part of UW Medicine, which also includes UW Medical Center, Harborview Medical Center, UW Physicians, UW Physicians Neighborhood Clinics, and the UW's membership in the Seattle Cancer Care Alliance and the Children's University Medical Group. UW Medicine has major academic and service affiliations with the Children's Hospital and Regional Medical Center, the Fred Hutchinson Cancer Research Center, and the Veteran's Administration Medical Centers in Seattle and Boise. The School of Medicine is consistently among the top five recipients of federal funding for biomedical research; its 1,600 regular faculty include four Nobel Laureates, 25 members of the National Academy of Sciences, and 26 members of the Institute of Medicine.

University of Washington

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