Can Intensive AF Screening Prevent Stroke? LOOP Study Results

Atrial fibrillation (AF) portends an increased risk of stroke,1 which can be reduced by 60-65% via treatment with oral anticoagulants.2 However, not all patients with AF are symptomatic – a clinical challenge which can lead to underdiagnoses and potentially insufficient stroke prophylaxis. The objective of the multicenter, randomized controlled LOOP Study trial was to investigate whether systematic, intensive AF screening can prevent stroke in high-risk individuals.3

A total of 6,004 patients aged 70-90 years without AF and the presence of at least one of four conditions – hypertension, diabetes, previous stroke, or heart failure – were randomized (1:3) to either placement of an implantable loop recorder (ILR) or standard care. If AF lasting ≥6 minutes was detected, then initiation of anticoagulation was recommended. Over a median follow-up period of 64.5 months, AF was diagnosed in 32% of participants in the ILR group versus 12% in the control group. Despite widespread acceptance and initiation of anticoagulation in patients with a diagnosis of AF, there was no statistically significant difference in the primary outcome, a composite endpoint of stroke or systemic arterial embolism, between the two arms: 4.5% versus 5.6%.

Intensive screening led to a three-fold increase in rates of AF diagnosis and treatment, but failed to show clinical benefit with regards to stroke prevention or mortality when compared to standard care. These findings suggest that not all potential AF is worth screening and not all screening-detected AF merits anticoagulation. It is believed that more frequent and longer-lasting episodes of AF are associated with a higher stroke risk, compared to the less frequent and shorter ones that are likely to be subclinical in nature and detected via continuous monitoring. New evidence is needed to better understand the complex relationships between AF episode duration, overall burden, symptoms, and medical outcomes.


  1. Virani SS, Alonso A, Benjamin EJ, et al. Heart disease and stroke statistics—2020 update: a report from the American Heart Association. Circulation 2020:141:e139-e596.
  2. Brieger D, Amerena J, Attia J, et al. National Heart Foundation of Australia and the Cardiac Society of Australia and New Zealand: Australian clinical guidelines for the diagnosis and management of atrial fibrillation 2018. Heart Lung Circ 2018;27:1209-66.
  3. Svendsen JH, Diederichsen SZ, Højberg S, et al. Implantable loop recorder detection of atrial fibrillation to prevent stroke (The LOOP Study): a randomised controlled trial. Lancet 2021;Aug 27:[Epub ahead of print].

Clinical Topics: Anticoagulation Management, Arrhythmias and Clinical EP, Cardiovascular Care Team, Heart Failure and Cardiomyopathies, Prevention, Anticoagulation Management and Atrial Fibrillation, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure, Hypertension

Keywords: ESC Congress, ESC21, Heart Failure, Atrial Fibrillation, Control Groups, Follow-Up Studies, Anticoagulants, Stroke, Hypertension, Diabetes Mellitus, Embolism, Reference Standards

< Back to Listings