Impact of left atrial posterior wall isolation on the p wave characteristics in patients referred for catheter ablation of atrial fibrillation

Background Left atrial (LA) fibrosis, often manifesting as low-voltage areas (LVA), is an important driver and substrate of atrial fibrillation (AF). The posterior wall (PW) is a frequent site of LVA and a considered a target for ablation. Purpose Our aim was to investigate the impact of PW isolation (PWI) on the P-wave characteristics of surface electrograms (ECGs). Methods Consecutive AF patients referred for catheter ablation with PWI using a pentaspline PFA catheter were included. Standard 12-lead ECGs were acquired immediately before and after PWI. Baseline correction by zero-referencing at P-wave onset and linear detrending was performed. A clinically interpretable panel of P-wave parameters, including P-wave duration, amplitude and area, morphology class and terminal force, fragmentation/complexity indices, entropy-based measures, and aggregate measures such as dispersion and frontal P-wave axis were automatically extracted. Parameters before and after PWI were calculated for the entire cohort as well as for sub-groups stratified by AF type, sex, and LA dilatation. High density 3D EAM was performed before and after PWI to quantify the area of ablated PW > 0.5mV. Features were considered relevant with a p value <0.05 (two-sided paired Wilcoxon signed-rank) and Cohens d > 0.5 reflecting at least moderate effect size. Results Seventy-one patients (age 69±9 years, 39% paroxysmal, 39% female, LAVI 41±13 ml/m2) with stable sinus rhythm of at least 10 beats before and after ablation were analyzed. The ablated area at the PW ≥ 0.5mV was 10±6cm2. For the entire cohort, relevant effect sizes were mainly observed for the inferior leads II, III, aVR, and aVF, with Shannon entropy and fractionation being the most relevant one (between 0.51 and 0.62) (Figure). This observation was confirmed for all subgroups. Patients with healthy (>0.5mV) posterior wall area >9 cm2 showed mainly changes in lead I features with PWI. The established P-wave duration did not changewith PWI in any lead or sub-group (Figure). Conclusion Changes of surface ECG P-wave parameters reflect the electrical contribution of the LA posterior wall. Whether these features may serve as a tool to predict PW-LVA and finally tailor ablation strategies prior to invasive mapping as well as to monitor PWI during follow-up needs further investigation.