Over the course of a year, insertable cardiac monitors (ICMs) detected atrial fibrillation in seven times as many stroke patients as those monitored by electrocardiograpy (ECG) and clinician visits, according to a study published June 26 in the New England Journal of Medicine.

While guidelines recommend 24-hour monitoring for atrial fibrillation post-stroke, according to the study researchers, the most effective monitoring duration has not yet been determined. Patients with atrial fibrillation have a greater risk of secondary stroke and other complications. Finding atrial fibrillation as cause of or extant in the patient post-stroke precipitates different treatments for patients, such as the use of anticoagulants vs. antiplatelet regimens.

The Cryptogenic Stroke and Underlying Atrial Fibrillation (CRYSTAL AF) study, headed by Tommaso Sanna, MD, of Catholic University of the Sacred Heart Institute of Cardiology in Rome, tried to determine a more precise length of time for monitoring risk for atrial fibrillation in patients presenting with cryptogenic stroke.

The study spanned 55 sites in Europe, the U.S. and Canada. Of 441 ischemic stroke patients, 221 were implanted with ICMs (REVEAL XT, Medtronic). At six months, atrial fibrillation had been detected in 8.9 percent of patients using ICMs, as opposed to 1.4 percent of patients in the control group receiving standard care. At 12 months, ICMs detected atrial fibrillation in 12.4 percent of patients vs. 2 percent.

Atrial fibrillation was asymptomatic in 74 percent of episodes in the ICM group at six months and 79 percent at 12 months. This constituted 14 of 19 episodes recorded at six months and 23 of 29 episodes recorded at 12 months. Asymptomatic atrial fibrillation was detected in only 33 percent of episodes (one out of three) in the control group and 50 percent at the six-month mark (two of four).

As more occurrences of atrial fibrillation were detected in the ICM group, they also presented with atrial fibrillation over a longer detection time. In the six-month span, the median length of detection from stroke to onset of atrial fibrillation was 41 days in the ICM group and 32 days in the control.

Constant monitoring offered the benefit of catching atrial fibrillation occurring even at short durations. This is part of why the ICM group logged more atrial fibrillation events. Due in part to short durations of atrial fibrillation and its occasionally asymptomatic nature, in order for clinicians to detect episodes, they largely would need to occur during a follow-up visit to be recorded.

Sanna et al suggested further research to determine which populations of patients would benefit most from this monitoring strategy, particularly as they saw some crossover between groups. They also recommended reviewing the cost effectiveness of this strategy over a longer term.

This study was funded by Medtronic.