Prognostic value of ECG-derived f-wave indices from implantable loop recorder: Analysis from the LOOP study

Electrocardiogram (ECG)-derived indices of atrial remodeling have demonstrated predictive value in established atrial fibrillation (AF) but remain unexplored in screening-detected or symptomatic AF.

We investigated the prognostic value of implantable loop recorders (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).

We analyzed 1411 LOOP study participants (758 men, median age 73 years) with ILR and no prior AF. Baseline AFR, ExpDec, and FWA indices were extracted from AF episodes ≥60 minutes occurring within 1 year after ILR implantation. Multivariate Cox regression assessed associations with all-cause mortality (primary end point) and a composite end point of cardiovascular death (CVD) or heart failure hospitalization (secondary end point).

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 [HR] 95% confidence interval [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 end point of CVD or heart failure hospitalization, although with larger uncertainty (HR [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, negative correlation with left atrial volume.

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.