Polygenic risk scores offer precision phenotyping for atrial fibrillation susceptibility, potentially optimizing screening strategies in primary stroke prevention among high-risk older adults. 
The LOOP randomized trial evaluated implantable loop recorder screening versus usual care in 6,004 individuals aged 70 years or older with stroke risk factors but no prior atrial fibrillation diagnosis. 
This prespecified post-hoc analysis published in the Journal of American College of Cardiology leveraged genetic data from 5,656 participants, stratifying them by atrial fibrillation polygenic risk score (PRS_AF) at median threshold. Primary outcome comprised stroke and systemic embolism composite. Investigators employed cause-specific 
PRS_AF Predicts Screening-Detected Atrial Fibrillation Burden
Polygenic risk score associated robustly with incident atrial fibrillation (HR 1.20 per standard deviation increase, 95% CI 1.13-1.28, P<0.001). Among implantable loop recorder recipients, higher PRS_AF conferred odds ratio 1.35 (95% CI 1.02-1.78, P=0.037) for prolonged atrial fibrillation episodes exceeding 24 hours, establishing genetic predisposition as determinant of clinically actionable arrhythmia substrate.
Gene-Screening Interaction Drives Stroke Benefit Heterogeneity
Significant interaction emerged between screening allocation and PRS_AF for stroke/systemic embolism prevention (P_interaction=0.006). Implantable loop recorder screening reduced event rates among PRS_AF≥median individuals (HR 0.65, 95% CI 0.43-0.97, P=0.036) but conferred no benefit and potential numeric harm in lower-risk stratum (HR 1.06, 95% CI 0.72-1.57, P=0.75). Continuous prediction grid confirmed risk-stratified screening efficacy across polygenic spectrum.
Bleeding Risk Profile Mirrors Efficacy Pattern
Screening-by-PRS interaction extended to major bleeding (P_interaction=0.036), with increased hazard among low PRS_AF individuals (HR 1.71, 95% CI 1.12-2.64, P=0.011), potentially reflecting anticoagulation initiation following incidental findings. Higher genetic risk mitigated bleeding excess while maximizing stroke prevention.
Precision Screening Through Genetic Profiling
Cardiologists and stroke neurologists gain actionable evidence supporting polygenic risk score integration into atrial fibrillation screening paradigms. High PRS_AF older adults represent optimal implantable loop recorder candidates maximizing net clinical benefit through enriched event rates and favorable safety profile. Cost-effectiveness analyses should incorporate genotyping accessibility as screening decisions increasingly leverage pharmacogenomic infrastructure. Routine polygenic risk score reporting from cardiovascular genetic panels facilitates patient-specific shared decision-making.
Implementation Through Risk-Stratified Protocols
Health systems should pilot PRS_AF-guided screening registries targeting 70+ individuals with CHA2DS2-VASc ≥2, prioritizing high genetic risk phenotypes. Electronic health record integration streamlines risk calculator deployment while guideline updates incorporate gene-environment interactions optimizing resource allocation across heterogeneous atrial fibrillation risk continuum.