Despite increasing detection of atrial fibrillation and rates of anticoagulation, continuous electrocardiographic monitoring with an implantable loop recorder did not significantly reduce risk of stroke in the LOOP study.
Results of the LOOP study suggest continuous electrocardiographic monitoring using an implantable loop recorder was associated with a 3-fold increase in detection of atrial fibrillation, but no significant reduction in risk of stroke or systemic arterial embolism.
Presented at the European Society of Cardiology (ESC) Congress 2021, investigators purport results of the study call into question the cost-effectiveness of screening strategies atrial fibrillation screening and initiation of anticoagulation for all atrial fibrillation.
“In a population of high-risk patients, atrial fibrillation was detected and treated much more often in those undergoing ECG monitoring. We found a non-significant 20% reduction in risk of stroke which was not accompanied by a similar reduction in cardiovascular mortality. More studies are needed but our findings may suggest that not all atrial fibrillation is worth screening for, and not all screen-detected atrial fibrillation merits anticoagulation,” said principal investigator Jesper Hastrup Svendsen, MD, DMSc, professor and senior consultant in the Department of Cardiology of Copenhagen University Hospital, in a statement.
While previous studies have assessed use of implantable loop recorders for detection of atrial fibrillation and initiation of oral anticoagulation, the LOOP study was among the most anticipated studies to be presented at ESC Congress 2021 for its potential to demonstrate whether continuous ECG with an implantable loop recorder could reduce stroke risk. The LOOP study was an investigator-initiated, unblinded, randomized controlled trial conducted at 4 centers in Denmark enrolling patients 70-90 years of age without a history of atrial fibrillation and at least 1 additional stroke risk.
Between January 31, 2014, and May 17, 2016, a cohort of 6004 patients was identified for inclusion and underwent randomization in a 1:3 ratio to continuous monitoring with an implantable loop recording or standard care. After randomization, 1501 were assigned to monitoring and 4503 to standard care. The overall study cohort had a mean age of 74.7±4.1 years, 47.3% were women, and the median follow-up was 64.5 (IQR, 59.3-69.8) months. Investigators noted the median duration of monitoring was 39.3 months and no patients included in the study were lost to follow-up.
Per study protocol, patients receiving an implantable loop recorder were recommended anticoagulation if atrial fibrillation episodes were detected and lasted 6 minutes or longer. Patients included in the standard care group had a telephone consultation with a nurse once a year.
The primary outcome was a composite end point of stroke or systemic arterial embolism. Secondary outcomes of interest included a combined endpoint of ischemic stroke, transient ischemic attack, or systemic arterial embolism, a combined endpoint of stroke, systemic arterial embolism, or cardiovascular death, cardiovascular death, and all-cause death.
During the follow-up period, atrial fibrillation was diagnosed among 31.8% (n=477) of patients randomized to continuous monitoring and 12.2% n=550) of those randomized to standard care (HR, 3.17 [95% CI, 2.81-3.59]; P <.0001). Oral anticoagulation was initiated among 29.7% (n=445) of those in the continuous monitoring area and 13.1% (n=591) of those in the standard care arm (HR, 2.72 [95% CI, 2.41-3.08]; P <.001).
Results indicated a primary outcome event occurred 318 participants, with events occurring in 4.5% (n=67) of the continuous monitoring group and 5.6% (n=251) of the standard care group (HR, 0.80 [95% CI, 0.61-1.05]; P=.11). Further analysis revealed cardiovascular death occurred in 2.9% (n=43) of the monitoring group compared to 3.5% (n=157) of the standard care group (HR, 0.83 [95% CI, 0.59-1.16]; P=.27). Additionally, death from any cause occurred among 11.2% (n=168) of patients in the monitoring group and 11.3% (n=507) of patients in the standard care group (HR, 1.00 [95% CI, 0.84-1.19]; P=1.00). A safety analysis indicated major bleeding occurred in 4.3% of patients in the monitoring group and 3.5% of patients in the standard care group (HR, 1.26 [95% CI, 0.95-1.69]; P=.11).
This study was presented as “LOOP Study: screening for AF with an implantable loop recorder to prevent stroke,“ at ESC Congress 2021 and simultaneously published as “Implantable loop recorder detection of atrial fibrillation to prevent stroke (The LOOP Study): a randomized controlled trial,” in The Lancet.