Cryptogenic stroke due to undetected atrial fibrillation – longer ECG monitoring may be the key

Up to 40% of ischemic strokes remain unexplained after routine evaluation and thus are considered cryptogenic. However, a number of these strokes may be due to an undetected episode of paroxysmal atrial fibrillation (AF) where anticoagulation can reduce the risk of subsequent ischemic stokes. Although a minimum of 24 hours of ECG monitoring is guideline recommended in the evaluation of ischemic stroke to identify AF, the optimal duration of monitoring remains undetermined. Among patients with cryptogenic stroke, two concurrent publications evaluated the AF diagnostic yield of extended ECG monitoring.

In the first study, 572 patients with a history of cryptogenic stroke or transient ischemic attack in the prior 6 months were randomized to 30-day event triggered ECG monitoring or 24-hour ECG monitoring. Among patients with 30-day monitoring, an episode of AF lasting at least 30 seconds was identified in 16.1% of patients compared with 3.2% in 24-hour monitoring (absolute difference, 12.9 percentage points; 95% confidence interval [CI], 8.0 to 17.6; P<0.001; number needed to screen, 8). In the second study, 441 patients with cryptogenic stroke and 24 hours of ECG monitoring as part of the initial work-up were randomized to additional monitoring with an implantable loop recorder device with an AF detection algorithm or conventional follow-up during which any further monitoring was decided by local policy. The trial’s primary end-point was the time to first detection of AF (at least 30 seconds in duration).   At 6 months there was a marked difference in AF detection between groups with AF detected in 8.9% of patients monitored with an implantable loop recorder versus 1.4% of the control group (HR, 6.4; 95% CI, 1.9 to 21.7; P<0.001). By 12 months this difference in AF detection had increased to 12.4% in monitored patients versus 2.0% in controls (HR 7.3, 95% CI 2.6 to 20.8; P<0.001). The preponderance of detected AF episodes were asymptomatic in this trial.


In the evaluation of patients with cryptogenic stroke, prolonged ECG monitoring resulted in markedly increased rates of AF detection. Future studies are needed to both identify patient populations most likely to benefit from prolonged ECG monitoring and the outcome implications of improved AF detection in cryptogenic stroke.

Summarized by Steven M. Bradley and Hussain Contractor

  • Gladstone DJ, Spring M, Dorian P, Panzov V, Thorpe KE, Hall J, Vaid H, O’Donnell M, Laupacis A, Côté R, Sharma M, Blakely JA, Shuaib A, Hachinski V, Coutts SB, Sahlas DJ, Teal P, Yip S, Spence JD, Buck B, Verreault S, Casaubon LK, Penn A, Selchen D, Jin A, Howse D, Mehdiratta M, Boyle K, Aviv R, Kapral MK, Mamdani M; EMBRACE Investigators and Coordinators. Atrial fibrillation in patients with cryptogenic stroke. N Engl J Med. 2014 Jun 26;370(26):2467-77