Is prolonged monitoring for atrial fibrillation indicated after a cryptogenic stroke?

by Joseph Esherick, M.D., FAAFP, FHM

Two recent trials published in the NEJM suggest that 12-16% of patients with cryptogenic strokes have at least transient episodes of atrial fibrillation lasting at least 30 seconds.  The EMBRACE and the CRYSTAL AF trials used prolonged cardiac monitoring for 3-12 months in patients aged 40 years or older with a cryptogenic stroke and identified that up to 16% of these patients had at least transient atrial fibrillation.

In the EMBRACE study, researchers randomized 572 patients aged 55 or older with cryptogenic stroke to either 30-day electrocardiogram (ECG) monitoring with a portable event monitor or to a standard 24-hour ECG recording. The primary outcome was newly detected AF lasting 30 seconds or more within 90 days of study entry. This endpoint was detected in 16.1% of the prolonged monitoring group, compared with 3.2% in the control group (P<0.001). By 90 days, significantly more patients in the prolonged monitoring group than in the control group were placed on anticoagulants (19% vs. 11%).1

The CRYSTAL AF investigators randomized 441 patients aged 40 or older with cryptogenic stroke to receive an insertable cardiac monitor (ICM) or undergo conventional follow-up. AF lasting more than 30 seconds was detected in 8.9% of the ICM patients versus 1.4% of the control group by 6 months (the primary endpoint; P<0.001). At 12 months, the rates were 12.4% vs. 2.0% (P<0.001). The median time from randomization to the first detection of AF was 84 days with ICM and 53 days with conventional follow-up.2

The big question is whether this represents causality or association?  How long does atrial fibrillation have to last before an atrial clot develops, which would be a potential cause of a cardioembolic stroke?  How frequent does it have to occur to be significant?  In other words, just because we identify that a person had a 30 second episode of Afib during 12 months of continuous cardiac monitoring, does this automatically mean that Afib is what caused his cryptogenic stroke?

Ultimately, the question becomes which of these patients should be on chronic anticoagulation with either warfarin or a newer oral anticoagulant?  

Let me know your thoughts?

MRI of ischemic stroke

References:

1. Gladstone DJ et al. Atrial fibrillation in patients with cryptogenic stroke. N Engl J Med 2014; 370: 2467. 

2. Sanna T et al. Cryptogenic stroke and underlying atrial fibrillation. N Engl J Med 2014; 370: 2478.