Why the study?
Subclinical atrial fibrillation poses an increased stroke risk, but whether oral anticoagulation prevents stroke is unclear, prompting investigation into whether cardiac structure and function modify the treatment effect of screening.
Does implantable loop recorder screening for subclinical atrial fibrillation reduce stroke or systemic embolism in older patients at risk of stroke, and is this effect modified by echocardiographic measures of cardiac structure and function?
Does implantable loop recorder screening for subclinical atrial fibrillation reduce stroke or systemic embolism in older patients at risk of stroke, and is this effect modified by echocardiographic measures of cardiac structure and function?
While conventional echocardiographic measures did not modify the effect of SCAF screening, reduced left atrial contraction strain identified a high-risk subgroup of patients who derived significant stroke risk reduction from implantable loop recorder monitoring.
Left atrial strain may identify patients who benefit from ILR screening; this subgroup interaction leaves open the need for prospective validation.
Background Subclinical atrial fibrillation (SCAF) poses an increased stroke risk, but whether oral anticoagulation for SCAF prevents stroke is unclear. We sought to investigate the treatment effect of SCAF screening according to measures of cardiac structure and function. Methods This was an echocardiographic substudy of the LOOP (Atrial Fibrillation Detected by Continuous ECG Monitoring) study, which randomized older people at risk of stroke to usual care or an implantable loop recorder (ILR) with monitoring for SCAF and subsequent oral anticoagulation. A subset (24% of trial population) underwent echocardiography to measure left ventricular size and function, left atrial volume and strain, and valvular pathology. The primary outcome was a composite of stroke or systemic embolism. Results The study included 1422 participants (ILR: n=1001; control: n=421; mean age: 74 years; men: 54%). During follow‐up, 354 (25%) were diagnosed with AF (ILR versus control: 30% versus 12%). During a median follow‐up of 5.5 years (interquartile range, 4.9–5.9 years), 55 (4%) developed the primary outcome (ILR versus control: 3.9% versus 3.8%). No conventional measure of cardiac structure and function modified the treatment effect from randomization. However, left atrial contraction strain significantly modified the treatment effect ( P interaction=0.003), such that a lower risk of the primary outcome was noted from ILR with lower left atrial contraction strain values (hazard ratio [HR], 0.38 [95% CI, 0.16–0.87], for participants with contraction strain<16.5%). Conclusion In a post hoc analysis of the LOOP study, conventional echocardiographic measures did not modify the effect of SCAF screening for stroke prevention. However, a significant stroke risk reduction was observed from ILR randomization among participants with reduced left atrial contraction strain.
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Olsen et al. (2025) studied this question.
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