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Continuous heart rhythm monitoring—with anticoagulation if atrial fibrillation is detected—does not prevent strokes in those at risk. That's the finding of late breaking research presented in a Hot Line session today at ESC Congress 2021 and published in The Lancet.

Atrial is the most common heart rhythm disorder, affecting more than 33 million people worldwide. The disorder increases the risk of stroke by five-fold, but this risk can be reduced with treatment. The LOOP study was initiated because patients with atrial fibrillation are often asymptomatic and thus remain undiagnosed and untreated.

The study investigated whether continuous electrocardiogram (ECG) using an implantable loop recorder, and subsequent anticoagulation if atrial fibrillation was detected, would reduce the risk of stroke or systemic arterial embolism in patients at risk.

Danish national registries were used to identify individuals from the aged 70 years or older with at least one of the following additional stroke risk factors: hypertension, diabetes, or previous stroke. The exclusion criteria included any history of atrial fibrillation, currently using , a contraindication to oral anticoagulation, or a cardiac implantable electronic device (CIED).

Participants were randomized 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 anesthesia. The device continuously (24/7) recorded the heart's electrical activity. Every night, any ECGs indicating heart rhythm abnormalities (such as atrial fibrillation) were transferred remotely to a server for evaluation by clinicians. If atrial fibrillation 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 randomized: 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 atrial fibrillation detected and to start oral anticoagulation compared to those receiving standard care. Atrial fibrillation 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 (HR 2.72; 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% CI 0.59–1.16; p=0.27), and death from any cause occurred in 168 participants (11.2%) in the monitoring group versus 507 (11.3%) in the (HR 1.00; 95% CI 0.84–1.19; p=1.00).

Principal investigator Professor Jesper Hastrup Svendsen of Copenhagen University Hospital—Rigshospitalet, Denmark says that "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 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 merits anticoagulation."

More information: Jesper H Svendsen et al, Implantable loop recorder detection of atrial fibrillation to prevent stroke (The LOOP Study): a randomised controlled trial, The Lancet (2021). DOI: 10.1016/S0140-6736(21)01698-6

Journal information: The Lancet