Peak frequency and local conduction velocity dynamics within ventricular scar: mechanistic insights and substrate homogenisation after ablation

Background and Purpose Peak frequency (PF) annotation has been used to characterise near-field electrograms (EGMs), and quantitative PF analysis has shown that EGMs with the highest PF co-localise with critical parts of the ventricular tachycardia (VT) circuit. Areas of slow or heterogeneous conduction velocity (CV) are key components of re-entry circuits. However, the relationship between PF and local CV within ventricular scar, as well as their behaviour during programmed stimulation and following ablation, remains incompletely understood. Methods A total of 73122 EGMs from 37 VT ablation procedures using an S3 pacing protocol were analysed. PF (derived using wavelet transformation) and local CV (calculated from omnipolar wave speed) were quantified during S1 and S3 pacing within deceleration zones (DZs; defined by ILAM), conduction channels (CCs; defined by ADAS 3D), and surrounding scar. Post-ablation analyses compared matched EGMs within ablated and non-ablated regions. Electrogram heterogeneity was assessed by the coefficient of variation (CoV) of PF and CV. Associations between PF and CV were evaluated using beta regression. Results During baseline S3 mapping, PF was significantly higher in DZs than in surrounding scar (225 ± 6.1 Hz vs. 205 ± 5.9 Hz; P < 0.001), while no difference was observed between CCs and the remainder of the scar. Local CV was lower in DZs compared with surrounding tissue (1.23 ± 0.018 m/s vs. 1.29 ± 0.020 m/s; P < 0.001). Across all EGMs, PF and CV were inversely correlated (P < 0.001). During S3 pacing, PF decreased compared with S1 pacing both within DZs (237 ± 6.3 Hz vs 225 ± 6.1 Hz; P < 0.005) and in non-DZ scar (230 ± 5.9 Hz vs 205 ± 5.9 Hz; P < 0.001), accompanied by a reduction in CV (1.32 → 1.23 m/s in DZs; P < 0.001). After ablation, PF fell markedly in ablated DZs (225 ± 6.1 Hz to 165 ± 6.9 Hz; P < 0.001), while CV increased (1.23 → 1.41 m/s; P < 0.001). Similar but less pronounced changes were observed in non-ablated scar (all P < 0.001). Overall, PF heterogeneity (CoV) decreased from 0.492 to 0.440, and CV heterogeneity from 0.320 to 0.254, indicating post-ablation substrate homogenisation. Conclusion Within ventricular scar, electrograms with higher peak frequencies correspond to regions of slower local conduction velocity. During S3 mapping, both PF and CV decrease, with the highest PF and lowest CV remaining confined to ablation target regions. Following ablation of S3-defined deceleration zones, marked reductions in PF and increases in CV were observed throughout the entire scar, accompanied by a decrease in local heterogeneity, suggesting global substrate homogenisation. Further studies are warranted to determine whether PF changes after ablation could serve as an additional procedural endpoint in VT ablation.