Prolonged electrocardiographic (ECG) monitoring in patients with cryptogenic stroke improved the detection of atrial fibrillation by a factor of five compared with standard 24-hour monitoring, results published June 26 in the New England Journal of Medicine showed. Detection changed anticoagulation treatment as well.

David J. Gladstone, MD, PhD, of the Sunnybrook Health Sciences Centre in Toronto, and other researchers in the EMBRACE (30-day Cardiac Event Monitor Belt for Recording Atrial Fibrillation after a Cerebral Ischemic Event) trial compared two different monitoring strategies and oral anticoagulant use in patients with strokes or transient ischemic attack (TIA) of unknown origin. These patients often are prescribed antiplatelet therapy to prevent secondary stroke, but if they have paroxysmal atrial fibrillation, anticoagulants likely are a better treatment.

They enrolled 572 patients 55 years or older at 16 centers between 2009 and 2012 and randomized them to either 24-hour ECG Holter monitoring (the control group) or a 30-day event-triggered loop recorder (the intervention group). None of the patients had known atrial fibrillation, and their stroke had to have occurred within six months.

The primary outcome was detection of atrial fibrillation or flutter of at least 30 seconds. Secondary outcomes included the use of anticoagulants at 90 days and detection of atrial fibrillation lasting 2.5 minutes or longer.

Prolonged monitoring detected atrial fibrillation in 16.1 percent of the intervention group. By comparison, the 24-hour monitoring spotted atrial fibrillation in only 3.2 percent of patients in the control group. Prolonged monitoring was superior at detecting continuous atrial fibrillation as well (9.9 percent vs. 2.5 percent).

At 90 days, 18.6 percent of the intervention group was being treated with anticoagulants compared with 11.1 percent of the control group.

The results support the use of prolonged monitoring of patients with a recent cryptogenic stroke or TIA to determine if they have atrial fibrillation, which potentially would change the course of their treatment, Gladstone et al proposed.

“We think that the common practice of relying on 24 to 48 hours of monitoring for atrial fibrillation after a stroke or TIA of undetermined cause is insufficient and consider it an initial screen rather than a final test, especially given our finding that the yield of clinical follow-up alone as a means of detecting atrial fibrillation was negligible,” they wrote.

The burden and prevalence of atrial fibrillation seen in EMBRACE is likely conservative, they added. The protocol allowed patients to stop wearing a monitoring device if atrial fibrillation was detected, so total burden was not captured. They reported a prevalence rate of 16.1 percent in the intervention group, but monitoring started late for some patients and ended at 30 days.

Their results suggest that “a substantial proportion of such patients [those with cryptogenic stroke] have paroxysmal atrial fibrillation that goes undiagnosed and untreated.”