The number of people with a dangerous heart arrhythmia is higher than previously estimated and increasing, researchers reported on Monday.

In a study of Minnesota residents, the incidence of atrial fibrillation rose more than 12 percent between 1980 and 2000, the researchers said. At that rate, the number of U.S. residents with the rhythm will rise to 16 million by 2050 - nearly three times previous estimates, they added.

“This is a major problem for our country,” said Dr. Teresa Tsang, senior author of the study to be published in Circulation: Journal of The American Heart Association. “Unless we are able to prevent atrial fibrillation, it will exact a major toll on our healthcare resources in the coming years.”

Atrial fibrillation is a condition in which the heart’s upper chambers quiver instead of beating regularly. This arrhythmia increases the risk of stroke, heart failure, cognitive impairment and death.

Many people do not experience heart palpitations, shortness of breath or other symptoms that would bring the condition to the attention of a health care provider, Tsang explained.

Scientists do not know the cause of the condition, but its risk factors include high blood pressure, diabetes, and valvular heart disease.

Recent data have also indicated that obesity is a risk. The rise in U.S. obesity mirrored the rise in the arrhythmia and might explain 60 percent of the new cases in Tsang’s study, she said.

Researchers identified more than 4,500 adults in Olmsted County, Minnesota whose medical records showed at least one incidence of atrial fibrillation and confirmed its presence with an electrocardiogram.

Based on this data, the study estimated that 5.1 million Americans currently live with the condition. That’s nearly twice as many as estimated by other studies, which have examined patients in health maintenance organizations only.

“Even with this number, we still believe that we’re underestimating the prevalence,” Tsang said.