Atrial Tachycardia With Concomitant Prolonged HV Interval With an SCN5A Missense Variant (p.R367H).

Predictors of effective ablation lesion delivery in the human left ventricle are not established, particularly in scar. Impedance drop and electrogram (EGM) attenuation are potential surrogates to assess this.This study sought to establish the relationships between ablation index (AI) and force-time integral (FTI) with impedance drop and EGM attenuation in the human left ventricle.Patients undergoing ventricular tachycardia ablation were recruited. EGMs were collected preablation and postablation, with impedance, AI, and FTI measured during. Based on preablation bipolar voltage, myocardium was adjudged a low-voltage myocardium (LVM) (<0.50 mV), intermediate-voltage myocardium (IVM) (0.51-1.50 mV), and normal-voltage myocardium (NVM) (>1.50 mV). Relationships between these parameters were explored.A total of 402 ablations were analyzed in 15 patients. The percent impedance drop correlated with AI and FTI (P < 0.0005; repeated-measures correlation coefficient: 0.54 and 0.44, respectively), a relationship that became weaker with increased myocardial fibrosis, (repeated-measures correlation coefficient for NVM, IVM, and LVM, AI: 0.67, 0.60, and 0.52, respectively; FTI: 0.59, 0.51, and 0.42, respectively). The curve between AI/FTI and impedance drop plateaued at 763 AI and 713 gram-seconds, an impedance drop of 7.5%. Shallower curves occurred progressively from NVM to LVM (P < 0.0005). Mixed models demonstrated that AI and FTI had a greater effect on impedance drop than myocardial fibrosis, drift, or orientation, (standardized β: 0.54 and 0.48, respectively). EGMs were attenuated with ablation (29.3%; IQR: 4.4%-53.3%; P < 0.0005), but attenuation did not correlate with AI or FTI.On biophysical analysis, ablation beyond an AI of 763 and FTI of 713 gs offers minimal additional efficacy on average. Fibrosis blunts ablation efficacy. AI is a stronger correlate with impedance drop than FTI. EGM attenuation does not correlate with ablation parameters. (Late Potentials and Ablation Index in Ventricular Tachycardia Ablation; NCT03437408)