Radiofrequency Ablation of the Diseased Human Left Ventricle: Biophysical and Electrogram-Based Analysis.

BACKGROUND: 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. OBJECTIVES: 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. METHODS: 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. RESULTS: 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 ß: 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. CONCLUSIONS: 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).