Awaken of the force for catheter ablation in right ventricular outflow tract?

This editorial refers to ‘Prospective use of ablation index guidance for right ventricle outflow tract premature ventricular contractions ablation – a proof of concept study’, by A. Gasperetti et al., on pages 91–98. More and more evidence has accumulated demonstrating that catheter-tip to tissue contact force- (CF) guided ablation in human atria leads to appropriate outcomes and safety. Despite the lack of data showing improvement for hard endpoints (such as rhythm stability) in randomized trials, the majority of operators nowadays use this technology in their daily routine. In this context, recent studies reported data on atrial fibrillation (AF) ablation approaches performing point-by-point radiofrequency (RF) ablation based on indirect evaluation of lesion depth and delivery of contiguous RF lesions like the CLOSE approach.1,2 We reported data about CF- and force-time integral (FTI)-target values resulting in ablation-induced atrial scar tissue,3 but this valuable information lacks for ablation or lesion indices until today. This is also true for histological validation of the ablation effect utilizing target indices. Focusing on pulmonary vein isolation (PVI), it has been shown that acute and late pulmonary vein (PV) reconnection resulted from either an insufficient ablation index (AI) and/or from too much interlesion distance.1 However, the criteria for optimal AI and interlesion distance have not yet been adequately addressed to guide ablation of premature ventricular contractions (PVC) or substrate modifications in ventricular tachycardias. In addition, catheter ablation for ventricular arrhythmias are performed in many different ways and no uniformity in techniques has been established.4 This fact emphasizes the urgent need to define endpoints for an effective lesion formation leading to transmurality as well as scar tissue irrespective of the operator or ablation approach used. In this issue of Europace, Gasperetti et al.5 report prospective data from AI-guided catheter ablation of PVCs originating from the right ventricular outflow tract (RVOT) giving insights into procedural success, safety issues, and anatomical considerations. Therefore, the authors aimed to compare AI-guided with non-AI-guided (standard) PVC ablation procedures within the RVOT (See Figure 1). A total number of 60 patients were prospectively enrolled and underwent catheter ablation following predefined per-protocol target values for the AI in the RVOT (RVOT free wall: AI 590; septal RVOT: AI 610). A propensity matched control group consisting of patients from multiple sites who underwent PVC ablation without AI was also analysed and considered as the comparator. In the AI-guided cohort, 34/60 patients (57%) were ablated at the septal RVOT and 26/60 (43%) at the RVOT free wall area. Acute procedural success and procedure-related complications were comparable between AI-guided and non-AI-guided ablation. The use of AI-guidance resulted in a significant decrease of radiofrequency applications (P = 0.02) and radiation exposure (P = 0.004). Interestingly, Gasperetti et al. describe that arrhythmia recurrence was found to be increased after 6-months in patients without AI-guidance (P = 0.003). In addition, AI-guidance was associated with improved overall freedom from PVC recurrence (P = 0.001). Despite the great achievements of this work, some limitations have to be addressed in terms of conceptual and technical issues taking into account that all AI-guided ablation procedures were performed at a single centre whereas non-AI-guided patients were matched from other centres. The main issue is the lack of any validation of the specific and individual lesion formation which would have been feasible using magnetic resonance imaging (MRI), as demonstrated previously.3,6 Focusing on the mid-term outcome, continuous rhythm monitoring might have potentially resulted in different outcomes. Before we are finally ready to decide between the ‘light’ and the ‘dark’ side of the force in terms of catheter ablation for ventricular arrhythmias, some facts need to be discussed. Contact force technology used in PVC ablation in a left ventricle below aortic cusp. PVC, premature ventricular contractions. Despite extensive data on AI and CF sensing in AF ablation, less work has been performed on ventricular arrhythmias. Hendriks et al.7 reported the relationship between CF and clinical outcomes in ventricular arrhythmia ablation in a retrospective analysis and they found no differences in acute success, complications, or arrhythmia recurrence in follow-up with CF sensing compared to non-CF-guided ablation. Casella et al.8 assessed AI values during the successful ablation of PVCs originating in the outflow tract area in a post-procedural manner. Based on their calculation, the authors aimed to achieve an AI of 590 for ablation at the free wall of the RVOT and 610 for ablation in the septal RVOT segments. We know that CF critically influences the identification of ventricular substrates for arrhythmias in humans9 and that reduced contact can lead to inappropriate labelling of otherwise normal tissue. Focusing on these AI-target values it remains questionable why comparable acute ablation effects between AI-guidance and a conventional approach did not result in comparable mid- and long-term freedom from PVC recurrence. Williams et al. reported animal data from MRI demonstrating that a higher catheter-tip to tissue CF resulted in more acute tissue oedema than lower CF. However, chronically there was no difference in lesion size, quality, or transmurality from LGE-MRI.10 Taking all these facts into consideration, MRI could be very valuable to allow for lesion guided as well as reproducible AI-target values to guide catheter ablation of ventricular arrhythmias. In summary, Gasperetti et al. should be truly congratulated for their paper in this issue of Europace. The authors demonstrated that AI-guided PVC ablation was safe and effective in the RVOT and that the prospective use of AI-target values led to improved freedom from arrhythmia recurrence during mid-term follow-up. The study emphasizes the need for the awaken of the catheter-tip to tissue CF as a cornerstone of the AI for catheter ablation of PVCs originating from the RVOT and approaches for ventricular substrate modification. Moreover, and due to this study and others, this manuscript should promote the use of novel force-sensing technologies as part of ablation indices. Hence, presenting and suggesting personal paths in arrhythmia management advanced imaging using MRI might help to define individual anatomical AI-target values to avoid index-guided ‘one size fits all’ concepts. May the force be with us. Conflict of interest: P.S. is member of the advisory board of Abbott, Biosense Webster, Medtronic and Boston Scientific. C.S. has nothing to declare. The opinions expressed in this article are not necessarily those of the Editors of Europace or of the European Society of Cardiology.