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Introduction Ablation Index (AI) is a novel catheter-based parameter developed to improve and increase efficacy and safety of Pulmonary Vein Isolations (PVI) in the treatment of Atrial Fibrillation (AF). This method involves the incorporation of contact force, time and power in deliverance of ablation lines. The aim of this study is to evaluate the impact of AI on the AF free burden over one-year post redo ablation for persistent AF. The study evaluates a secondary endpoint in medical management escalations post procedure. Methods A retrospective single centre study of 39 patients (Mater Private Hospital, Dublin) who had redo ablations for persistent AF between the period of Jan 2016 till December 2019. We evaluated and analysed the efficacy of AI on redo PVIs in comparison to conventional established ablation techniques. Both groups were matched for age, gender, and duration of PeAF. Group 1 (17 patients) was the AI group with ablation index intervention and group 2 was the contact force (CF) -guided group with 22 patients. Each cardiologist carried out a minimum of 100 ablations per year to confirm the uniformity of performance. Patient follow-up data was analysed at staged intervals for one-year post procedure. Inclusion criteria are: Patients must have had one prior PVI procedure for PeAF, complete follow up data available and all procedures completed using the Carto 3D Mapping System. Statistical analysis was carried out using SPSS (IBM SPSS Statistic Version 26). A Kaplan Meier graph was generated to evaluate the AF free interval. All continuous variables were expressed as the mean ± SD and Students T Test to was applied to give the significant differences for continuous variables. Results Patient characteristics are demonstrated in Table 1. There were no significant differences in age, sex, weight, height, CHADVASC or anti-arrythmia agents, which indicated similar patient profile in each cohort. Pulmonary vein reconnections at redo PVI procedure were comparable at 100% in the AI group and 86% in the CF group (p = 0.1). Freedom from AF burden was (mean 8.72 ± 4.33 months) in CF group Versus (mean 9.35 ± 4.1 months) in AI guided ablation (p=0.71) (figure 1). The AI group demonstrated greater numbers of patients in whom antiarrhythmic therapy could be deescalated over one year (AI, n=11/17, 65% Vs. CF, n=2/22, 9% with p=0.01) while fewer patients underwent escalation of their antiarrhythmic therapy (AI n=2/17, 12% vs CF n=6/22, 27% p= 0.03) (table 1). Conclusion This is the first study to analyse the outcomes of ablation index on repeat PVI procedures. Despite no significant difference in AF recurrence outcomes demonstrated in this study, there was a significant difference in the medical de-escalation in favour of the use of the AI over the short term follow up period. This may reflect effective ablation lesions. A longer-term analysis would be recommended to determine the efficacy of AI use in PeAF redo procedures.

Background Patients with atrial fibrillation (AF) frequently have atrial scarring characterised by discrete regions of low voltage. Pre-existing left atrial scarring is an independent predictor of pulmonary vein isolation (PVI) failure. Novel mapping algorithms have also been developed to assess the degree of atrial fibrosis. This may be expressed as a percentage of the total left atrial (LA) volume mapped. In addition to the electrical remodelling seen, structural remodelling occurs, with dilatation and reduced function. The most accurate determinant of LA function is debated, but the most frequently used method is transmitral A Wave velocity on pulsed-wave Doppler. The relationship between LA function and electrical changes seen in AF has not been defined. Methods This was a single centre observational study. Left atrial voltage maps were created in patients undergoing PVI for the first time in the Mater Private Hospital between August 2016 and April 2017. LA voltage maps were initially created with a Lasso catheter with some further points taken with a Smarttouch ablation catheter (both Biosense Webster, Diamond Bar, California). Voltage greater than 0.5 mV was accepted as normal tissue and voltages Results Out of 96 patients who had undergone PVI, only 24 were found to have had sinus rhythm on pre-procedural echo. The mean age was 63.5 (standard deviation or SD 10.6) years. 66% of the group were men. 58% had paroxysmal AF. The mean amplitude of the A-wave in the study was 0.61 (SD 0.16) ms-1. An average of 1269.7 (SD 857.0) mapping points were taken. The mean LA percentage scar was 25.1 (SD 20.3) %. Using linear regression, adjusted for age at time of procedure, there was a significant negative association between a wave (in ms-1) and % LA scar (Beta coefficient -72.44, 95% CI -122.99 to -21.88, p=0.007). Using pairwise correlation, the correlation coefficient between LA scar and A wave was -0.38, p=0.06. Conclusion Our study found an inverse correlation between transmitral A wave and degree of left atrial scarring when LA function was adjusted for patient age, indicating that LA electrical remodelling as measure by percentage scar is associated with decreased LA function in patients with AF. However, there were only 24 patients in this study and ongoing research with more patients is warranted to further substantiate this.