With its episodes of rapid and irregular heartbeats, the condition — atrial fibrillation — afflicts at least 2.2 million people in the United States, according to government estimates. While some experience no symptoms and most others seem to suffer little more than weakness or shortness of breath, the condition is now recognized as a major source of strokes and a precursor to potentially fatal deterioration of the heart.

Already, Medicare and private insurers are spending billions of dollars annually to cope with atrial fibrillation, mostly on hospitalizations, tests and drugs unapproved for such patients. The number of patients is forecast to soar, and spending could climb even more rapidly if many of them receive what many doctors say is now their best hope for a cure — an expensive procedure known as catheter-based ablation.

Advocates of the procedure say it is less invasive than open-heart surgery — the only proven method for curing many patients — and in the long run more cost-effective than drugs, which generally offer temporary relief. Thousands of patients worldwide are estimated to have had the procedure done since 2000.

Federal regulators, however, have not approved as safe and effective any of the devices used. So hospitals and doctors are finding it difficult to be fully reimbursed for the procedure’s cost, which is generally calculated at $25,000 to $50,000.

With politicians and employers debating ways to tame the explosive growth in health care costs, such treatment stands out as another potentially budget-straining medical commitment.

“This is one of those areas where the practice of medicine has moved faster than the approval process,” said Daniel G. Schultz, head of the Center for Devices and Radiological Health at the Food and Drug Administration. “This is very high on our list of areas that need concerted attention.”

Dr. Schultz said the F.D.A. would soon schedule a public meeting with medical and industry experts to discuss what is known — and still needs to be known — about the welter of drugs and devices now being used without approval to treat atrial fibrillation.

Some of the biggest questions focus on ablation, which involves burning, freezing, or otherwise neutralizing the portions of the heart muscle where abnormal electrical pulses set off the irregular heartbeats. The technique aims to restore the ability of the two atria, situated at the top of the heart, to effectively gather blood and prime the ventricles, the heart’s main pumps.

The original form of atrial ablation, using surgical tools, is still employed, but almost always restricted to cases where the chest is already being cut open for heart valve replacement or other surgery. But most atrial ablations are now minimally invasive procedures using tiny devices mounted at the end of long, flexible plastic catheters that are threaded into the heart through veins.

Full-scale clinical trials have not yet demonstrated the long-term benefits from the catheter-based treatment. But, based on promising results from less rigorous studies, major medical societies have endorsed it. It is not uncommon for off-label drugs and devices to be used where doctors believe they can be more successful than any approved therapies.

Still, any situation where off-label therapies have become as widespread as they are in atrial fibrillation “spotlights where we lack good evidence of which patients can benefit from which therapies,” said Dr. Carolyn M. Clancy, director of the federal Agency for Healthcare Research and Quality.

Gathering such data for atrial fibrillation could be especially challenging, she said, because the severity of the condition varies so much among patients and most have other health problems as well that can affect the risks and benefits of competing therapies.

Lacking regulatory guidelines, doctors currently use either experimental equipment or equipment that the F.D.A. has approved for other purposes, like destroying tumors or fixing other heart arrhythmias. While such off-label use of devices is legal for doctors, insurers are sometimes reluctant to cover it, and health care providers may have less legal protection from lawsuits if something goes wrong.