A registry analysis found that patients who only had short episodes of atrial tachycardia and/or atrial fibrillation (AT/AF) did not have an increased risk of clinical events.

The researchers defined short episodes of AT/AF as episodes in which the onset and offset of the condition were present within a single electrogram recording. They defined clinical events as hospitalizations for heart failure, atrial or ventricular arrhythmias, stroke or transient ischemic attack, syncope and death.

Lead researcher Steven Swiryn, MD, of the Feinberg School of Medicine at Northwestern University, and colleagues published their results online Oct. 17 in Circulation.

“We knew that people with atrial fibrillation are at higher risk of stroke, but the next question was, how much atrial fibrillation?” Swiryn said in a news release. “Other studies have shown that prolonged episodes of atrial fibrillation pose a risk, but what about short ones? The answer until this study was ‘no one knows.’ Now we have good, solid data that if all you have is short episodes of atrial fibrillation, the risk is so low that it doesn’t warrant anticoagulants.”

The researchers evaluated 5,379 patients who enrolled in the prospective RATE (Registry of Atrial Tachycardia 
and Atrial Fibrillation Episodes) registry between 2006 and 2012 at 225 U.S. sites. Patients were at least 18 years old and had a St. Jude Medical pacemaker or implantable cardioverter defibrillator (ICD) implanted within 45 days. St. Jude Medical funded the RATE registry.

Patients were excluded if they had permanent atrial fibrillation or atrial fibrillation within three months of enrollment. They were followed for up to 24 months.

Of the patients, 3,141 had pacemakers and 2,238 had ICDs. Patients with pacemakers were seven years older on average compared with those with ICDs.

After a median follow-up of 22.9 months, during which the researchers analyzed 37,531 electrograms, there were 359 deaths, 837 clinical events and 2,232 total hospitalizations, including 94 hospitalizations for AF, 265 hospitalizations for heart failure and 47 hospitalizations for stroke. From a random sample of 300 pacemaker and 300 ICD patients, half of the patients had at least one episode of AT/AF, including 48 percent of pacemaker patients and 52 percent of ICD patients.

The incidence of AT/AF was 0.283 cases per patient-year in pacemaker patients and 0.233 cases per patient-year in ICD patients.

Patients with clinical events were more likely to have long AT/AF compared with those without clinical events. The researchers defined long episodes of AT/AF as episodes in which the onset and/or offset of the condition was not present within a single electrogram recording.

In addition, 9 percent of pacemaker patients and 16 percent of ICD patients had only short episodes of AT/AF. Patients with clinical events had similar rates of AT/AF compared with those without clinical events.

The researchers cited a few limitations of the study, including that they could not examine the full duration of all AT/AF episodes due to device memory and detection limitations. They also noted that they might have overestimated the number of long AT/AF episodes. In addition, they did not account for other risk factors such as older age, diabetes and hypertension.

“Our unique finding that patients with only short episodes of AT/AF were not at increased risk of clinical events is reassuring and should help clinicians to further resolve the anticoagulation recommendations published in society guidelines and avoid overreaction to such findings,” the researchers wrote. “The results of our study suggest that immediate anticoagulation in patients with only short episodes of AT/AF is unlikely to result in reduction of the risk of stroke, at least during a 2-year follow-up. Scrutiny of such patients for the appearance of longer episodes is important because many will progress over time.”