Electrocardiographic markers of subclinical atrial fibrillation detected by implantable loop recorder

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: Foundation. Main funding source(s): The LOOP Study was funded by Innovation Fund Denmark [grant number 12-1352259], The Research Foundation for the Capital Region of Denmark, The Danish Heart Foundation [grant number 11-04-R83-A3363-22625], Aalborg University Talent Management Program, Arvid Nilssons Fond, Skibsreder Per Henriksen, R og Hustrus Fond, the European Union’s Horizon 2020 program [grant number 847770], Læge Sophus Carl Emil Friis og hustru Olga Doris Friis’ Legat, and an unrestricted grant from Medtronic. BACKGROUND: Atrial fibrillation (AF) is a well-known and treatable risk factor for stroke, which has sparked a substantial interest in AF screening. However, further insights into subclinical AF development are warranted to inform strategies of screening and subsequent clinical management upon AF detection. PURPOSE: This study sought to identify 12-lead electrocardiogram (ECG) parameters associated with the onset, burden and progression of subclinical AF detected by long-term continuous monitoring. METHODS: We included AF-naïve individuals aged 70-90 years with ≥1 additional stroke risk factors (hypertension, diabetes, heart failure, or prior stroke) who underwent implantable loop recorder (ILR) monitoring in the LOOP Study. Using data from daily ILR recordings and computerized analysis of baseline ECG, we studied empirically selected ECG parameters for AF detection (≥6 minutes), cumulative AF burden, long-lasting AF (≥24 hours), and AF progression. RESULTS: Of 1370 individuals included, 419 (30.6%) developed AF during follow-up, with a mean cumulative AF burden of 1.5% [95% confidence interval (CI): 1.2-1.8%]. Several P-wave-related and ventricular ECG parameters were associated with new-onset AF as well as with cumulative AF burden in AF patients. P-wave duration (PWD), P-wave terminal force in lead V1, and interatrial block (IAB) further demonstrated significant associations with the risk of AF episode ≥24 hours. Among AF patients, we observed an overall reduction in cumulative AF burden over time (incidence rate ratio 0.70 [95% CI: 0.51-0.96]), whereas IAB was related to an increased risk of progression to AF episodes ≥24 hours (hazard ratio 1.86 [95% CI: 1.02-3.39]). Further spline analysis revealed longer PWD to also be associated with this progression in AF duration. CONCLUSIONS: We identified several ECG parameters associated with new-onset AF detected by ILR. Especially PWD and IAB were robustly related to the onset and the burden of subclinical AF as well as progression over time. [Figure: see text]