Prognostic Value of ECG-derived f-wave Indices from Implantable Loop Recorder: Analysis from the LOOP Study

BACKGROUND: ECG-derived indices of atrial remodeling have demonstrated predictive value in established atrial fibrillation (AF) but remain unexplored in screening-detected or symptomatic AF. OBJECTIVE: We investigated the prognostic value of ILR ECG-derived atrial fibrillatory rate (AFR), average f-wave envelope amplitude (FWA), and the organization index derived from the signal's spectral characteristics (ExpDec). METHODS: We analyzed 1,411 LOOP study participants (758 men, median age 73 years) with implantable loop recorders (ILR) and no prior AF. Baseline AFR, ExpDec, and FWA indices were extracted from AF episodes ≥60 minutes occurring within one year after ILR implantation. Multivariate Cox regression assessed associations with all-cause mortality (primary endpoint) and a composite endpoint of cardiovascular death (CVD) or heart failure hospitalization (secondary endpoint). RESULTS: During the first year of monitoring, AF episodes ≥60 minutes were detected in 96 patients (6.8%). Low AFR (<317 fpm), ExpDec (<1.25), and FWA (<97 μV) were associated with increased risk of all-cause mortality (Hazard ratio [95% CI]: 2.5 [1.3, 4.8], 2.8 [1.4, 5.5], and 2.7 [1.4, 5.4], respectively) and similarly for the composite endpoint of CVD or heart failure hospitalization although with larger uncertainty (Hazard ratio [95% CI]: 4.0 [1.6, 9.9], 3.7 [1.4, 10.1], 2.9 [0.97, 8.6], respectively). FWA demonstrated a significant, yet modest, negatively correlation with left atrial volume. CONCLUSION: In screening-detected AF, indices of a more organized fibrillatory process (low AFR/ExpDec) and advanced structural abnormalities (low FWA) were associated with increased mortality and heart failure events. F-wave analysis identifies high-risk patients in early AF, potentially enabling targeted interventions.