Continuous heart rhythm monitoring—with anticoagulation if atrial fibrillation (AF) is detected—does not prevent strokes in those at risk. That is the finding of the LOOP study, presented during a Hot Line session at the European Society of Cardiology’s 2021 congress (ESC 2021, 27–30 August, virtual) and published in The Lancet.
AF increases the risk of stroke by five-fold, but this risk can be reduced with anticoagulation treatment. The LOOP study was initiated because patients with AF are often asymptomatic and thus remain undiagnosed and untreated.
As part of the study, Danish national registries were used to identify individuals from the general population aged 70 years or older with at least one of the following additional stroke risk factors: hypertension, diabetes, heart failure or previous stroke. The exclusion criteria included any history of AF, currently using oral anticoagulation, a contraindication to oral anticoagulation, or a cardiac implantable electronic device (CIED).
Participants were randomised in a 1:3 ratio to receive continuous ECG monitoring or standard care. Those in the monitoring group had an implantable loop recorder inserted under the skin on the left side of the chest under local anaesthesia. The device continuously (24/7) recorded the heart’s electrical activity. Every night, any ECGs indicating heart rhythm abnormalities (such as AF) were transferred remotely to a server for evaluation by clinicians.
If AF lasting more than six minutes was diagnosed, patients were advised to start oral anticoagulation. The standard care group had a telephone consultation with a nurse once a year. The primary outcome was time to the combined endpoint of stroke or systemic arterial embolism.
A total of 6,004 participants were randomised: 1,501 to monitoring and 4,503 to standard care. The mean age was 74.7 years and 47.3% were women. The median duration of monitoring was 39.3 months, and the median follow-up period was 64.5 months.
Participants in the monitoring group were more likely to have AF detected and to start oral anticoagulation compared to those receiving standard care. AF was diagnosed in 477 participants (31.8%) in the monitoring group and 550 (12.2%) in the control group (hazard ratio [HR] 3.17; 95% confidence interval [CI] 2.81–3.59; p<0.001). Oral anticoagulation was initiated in 445 participants (29.7%) in the monitoring group and 591 (13.1%) in the control group (HR2.72; 95% CI 2.41–3.08; p<0.001).
The primary outcome occurred in 318 participants, including 67 (4.5%) in the monitoring group (0.88 events per 100 person-years; 95% CI 0.68–1.12) and 251 (5.6%) in the control group (1.09 events per 100 person-years; 95% CI 0.96–1.24). There was no significant difference between the two groups (HR 0.80; 95% CI 0.61–1.05; p=0.11).
Cardiovascular death occurred in 43 participants (2.9%) in the monitoring group versus 157 (3.5%) in the control group (HR 0.83; 95% CI0.59–1.16; p=0.27), and death from any cause occurred in 168 participants (11.2%) in the monitoring group versus 507 (11.3%) in the control group (HR1.00; 95% CI0.84–1.19; p=1.00).
Principal investigator Jesper Hastrup Svendsen of Copenhagen University Hospital-Rigshospitalet, Copenhagen, Denmark, said: “In a population of high-risk patients, AF 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 AF is worth screening for, and not all screen-detected AF merits anticoagulation.”