Atrial fibrillation: What you don’t feel can still hurt you

Those little runs of racing heartbeat that you dismiss as nothing -- or don’t even feel -- do boost your risk of suffering a stroke or of dislodging a dangerous blood clot, a new study says.

It’s widely known that a person with atrial fibrillation is at increased risk of stroke. A-fib, as it’s called, is a condition in which there’s misfiring in the electrical system of the heart’s blood-collection chambers, causing these -- the atria -- to quiver and pump erratically. Because the condition is thought to be responsible for 1 in 5 ischemic strokes (in which a blood clot reduces blood flow to the brain), physicians treat patients who have it with blood-thinners such as warfarin or two new anticoagulant medications named dabigatran (marketed as Pradaxa) or rivaroxiban (marketed as Xarelto).

About 2.6 million Americans probably have atrial fibrillation -- many more than are treated for stroke prevention, according to a report released earlier this week. But the latest study suggests that even more may suffer a stroke after episodes of arrhythmia that are less severe or sustained.

Research published Thursday in the New England Journal of Medicine tracked 2,580 patients with high blood pressure who had recently had a pacemaker implanted. The electronic medical devices are designed to shock a heart suffering from ventricular fibrillation into normal rhythm and avert a heart attack. But they’re also able to detect atrial fibrillation.

The international group of researchers looked for instances of “subclinical” atrial fibrillation -- cases in which the heart beats faster than 190 beats per minute for more than six minutes, but not at the rate of 300 to 400 beats per minute that would prompt a physician to diagnose and treat a patient. In many such cases, a patient might be unaware of any change in heart rate.

Those runs of irregular heartbeat were pretty common -- just more than 10% of the study participants had at least one in a three-month monitoring period. And compared with study participants who did not have such episodes, participants who did were 2.5 times more likely to suffer a stroke or a blood clot requiring emergency treatment over the next two and a half years.

Such subjects were also five times more likely to go on to develop atrial fibrillation that met the clinical definition.

The researchers estimated that about 13% of “unexplained” strokes may be the result of such “subclinical atrial fibrillation.”

We all experience occasional irregular heartbeats -- and freaking out won’t help, because stress can be a contributor. But if the ticker does seem to break out in a run for no apparent reason, it’s wise to raise it with your physician.