Continuous monitoring for unknown AF and OAC if indicated does not prevent stroke

LOOP Study: screening for AF with an implantable loop recorder to prevent stroke

News - Aug. 29, 2021

Presented at the ESC congress 2021 by: Prof. Jesper Hastrup Svendsen, MD - Copenhagen, Denmark

Introduction and methods

The LOOP study was an investigator initiated study that aimed to investigate whether continuous monitoring for unknown AF using an implantable loop recorder (ILR) and initiation of oral anticoagulation (OAC) if AF was detected, could prevent stroke in high risk patients.

A total of 6004 participants were included in the study. Participants were >70 years old and had at least one risk factor: Hypertension, diabetes, heart failure or previous stroke. Participants were randomized in a 1:3 ratio to receive an ILR (n=1501) or standard of care (n=4503). In the ILR group, participants were advised to start OAC if AF>6 min was recorded. Mean age was 74.7 years, 47.3% were women, 90.7% had hypertension and the median CHA2DS2-VASc score was 4. The primary outcome was time to the combined endpoint of stroke or systemic arterial embolism. Mean follow-up was 65 months.

Main results

  • AF was diagnosed in 1027 participants: 477 (31.8%) in the ILR group and 550 (12.2%) in the control group. AF was significantly more often diagnosed in the ILR group compared to the control group (HR 3.17, 95%CI 2.81-3.59, P<0.001). OAC was initiated in 29.7% in the ILR group and in 13.1% in the control group (HR 2.72, 95%CI 2.41-3.08, P<0.001).
  • There was no significant difference in the primary outcome of time to the combined endpoint of stroke or systemic arterial embolism between the two groups. The primary endpoint occurred in 4.5% in the ILR group vs. 5.6% in the control group (HR 0.80, 95% CI 0.61-1.05, P=0.11).
  • There were also no significant differences in death from any cause and major bleeding between the two groups. Death from any cause occurred in 11.2% in the ILR-group vs. 11.3% in the control group (HR 1.00, 95%CI 0.84-1.19, P=1.00). Major bleeding occurred in 4.3% in the ILR-group vs. 3.5% in the control group (HR 1.26, 95%CI 0.95-1.69, P=0.11).


Continuous heart rhythm monitoring using ILR resulted in a three-times increase in AF detection and initiation of OAC compared to standard care in patients at high risk of stroke. However, ILR screening and initiation of OAC if indicated did not lead to a significant reduction in stroke or systemic arterial embolism. No effect on mortality was observed and rates of bleeding were modest.

-Our reporting is based on the information provided at the ESC Congress–

The results of this study were simultaneously published in The Lancet.

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