Background: Although ablation energy (AE) and force-time integral (FTI) are well-known active predictors of lesion characteristics, these parameters do not reflect passive tissue reactions during ablation, which may instead be represented by drops in local impedance (LI). This study aimed to investigate if additional LI-data improves predicting lesion characteristics and steam-pops. Methods: RF applications at a range of powers (30W, 40W, and 50W), contact forces (8g, 15g, 25g, and 35g), and durations (10-180s) using perpendicular/parallel catheter orientations, were performed in excised porcine hearts (N=30). The correlation between AE, FTI and lesion characteristics was examined and the impact of LI (%LI-drop [%LID] defined by the ΔLI/Initial LI) was additionally assessed. Results: 375 lesions without steam-pops were examined. Ablation energy (W*s) and FTI (g*s) showed a positive correlation with lesion depth (ρ=0.824:P<0.0001 and ρ=0.708:P<0.0001), surface area (ρ=0.507:P<0.0001 and ρ=0.562:P<0.0001) and volume (ρ=0.807:P<0.0001 and ρ=0.685:P<0.0001). %LID also showed positive correlation individually with lesion depth (ρ=0.643:P<0.0001), surface area (ρ=0.547:P<0.0001) and volume (ρ=0.733, P<0.0001). However, the combined indices of AE*%LID and FTI*%LID provided significantly stronger correlation with lesion depth (ρ=0.834:P<0.0001 and ρ=0.809P<0.0001), surface area (ρ=0.529:P<0.0001 and ρ=0.656:P<0.0001) and volume (ρ=0.864:P<0.0001 and ρ=0.838:P<0.0001). This tendency was observed regardless of the catheter placement (parallel/perpendicular). AE (P=0.02) and %LID (P=0.002) independently remained as significant predictors to predict steam-pops (N=27). However, the AE*%LID did not increase the predictive power of steam-pops compared to the AE alone. Conclusion: LI, when combined with conventional parameters (AE and FTI), may provide stronger correlation with lesion characteristics.

Objective: To investigate the incidence, risk factors and clinical characteristics of periaortic VTs after AVR. Background: The periaortic region is the origin of some ventricular tachycardias (VTs) after aortic valve replacement (AVR). However, the clinical characteristics of periaortic VTs after AVR are yet to be clarified. Methods: We retrospectively analyzed clinical courses of 109 patients who had undergone surgical AVR (SAVR) without other structural heart diseases between April 2009 and Jun 2019 and evaluated the incidence and characteristics of periaortic VTs after SAVR. Results: Three patients (2.8%) developed periaortic VTs after SAVR. The average duration of onset was 12.3±6.6 years. All VTs arose from the inferior axis; they included both left and right bundle branch block configuration (LBBB and RBBB). Two patients underwent cardiac magnetic resonance imaging; late gadolinium enhancement (LGE) was observed in the mid-layer of the left ventricle basal anteroseptal wall in both cases. Patients with periaortic VTs had significantly wider interventricular septum, lower left ventricular ejection fraction (LVEF), larger LV diameter at systole, and higher positive rates of signal-averaged ECG and non-sustained VTs on Holter. On ablation, local fragmented potentials with low voltage zones were observed in accordance with the distribution of LGE. Multiple VTs originating from the periaortic region were provoked in the sessions. Conclusions: Periaortic VTs long after surgical AVR are not rare, and arrhythmia risk stratification, including that by signal averaged electrocardiogram (SAECG), Holter, and cardiac magnetic resonance imaging (MRI) should be considered.