Catheter ablation is a recognized treatment of symptomatic atrial fibrillation (AF). Various ablation strategies have been suggested, but pulmonary vein isolation (PVI) remains the cornerstone of radiofrequency ablation (RFA) in both paroxysmal AF (PAF) and persistent AF (PeAF).[¹], [²] New catheter technologies providing real-time measurement of Contact Force (CF) sensing between the catheter tip and endocardium[³] and automated ablation lesion tagging technology based on catheter stability have been introduced to optimize the ablation lesions and thereby achieve durable isolation of the pulmonary veins (PV).[⁴], [⁵] Recently, the Ablation Index (AI) algorithm that incorporates CF, time and power has been developed as a marker of adequate ablation lesion.[²], [⁶]

AI accurately predicts lesion depth in animal models[⁷] and has shown improved clinical success rates when used in PVI ablation.[⁶], [⁸] A new concept using an automated ablation tagging module which combine AI values and a maximum distance of 6 mm between lesions to ensure contiguity has been investigated, and recent data show that this ablation strategy improves PVI durability and clinical outcome in patients with both PAF and PeAF.[⁹], [¹⁰]

The purpose of this study is to evaluate the efficacy and feasibility of this ablation concept in a population of PAF and PeAF patients compared to a conventional CF-guided PVI strategy.

Continuous variables are presented as mean ±SD if they were normally distributed or median and [25th;75th] percentiles if the data are not normally distributed. For comparison we used Students t-test for normally distributed data. For comparison of non-normally distributed data we used Mann Whitney U-test or logistic transformation. Categorical data are presented as frequency and percentage and compared with chi-square test.

Logistic and multivariate logistic regression analyses were used to identify predictors of recurrence. Results are presented as relative risk ratio (95% confidence interval).

A P-value of < 0.05 was considered statistical significant.

All analysis was performed in Stata/IC (Version 15.1, StataCorp LLC, College Drive, USA)

This study compared an ablation strategy combining AI and lesion contiguity to CF alone in AF patients scheduled for first-time PVI ablation. The main finding was a significant lower recurrence of AF/AT at 12 months follow-up in the AI-group. There was no difference regarding complication rate between the two ablation methods.

The primary goal in AF ablation is a durable PVI. The CF sensing catheters were introduced to optimize force feedback and produce more effective lesion sets to achieve the goal. A meta-analysis on CF-guided ablation found a success-rate of 80.1% in PAF patients and only 48.9% in PeAF patients.[¹¹] In our subgroup analysis we found a success-rate in PAF and PeAF after CF-guided ablation of 67.8% and 50.0% respectively, indicating that our data are representative. In the STAR-AF2 trial, a similar outcome was found after PVI in patients with PeAF, and there were no clinical effect of additional linear ablation or ablation of complex fractionated electrograms.[¹²] The importance of a durable PVI has pushed the technology further in developing algorithms which incorporate various information such as CF, time and power into each lesion set during RFA. The TOCCASTAR and EFFICAS I/II studies have shown that CF technology combined with force-time integral improve the rate of isolated PV after 3 months of follow-up and long-term clinical outcome compared to non-CF ablations.[³], [⁵] The AI algorithm which incorporates CF, time and power into each lesion set was developed as a marker of ablation outcome. AI was evaluated in animal and human studies and has shown a rate above 90% of isolated PV in both PAF and PeAF patients at scheduled re-interventions 3 months after index ablation.[⁸], [¹⁰] The recent PRAISE trial reported 93% isolated PV at re-evaluation after 3 months in 40 patients with PeAF scheduled for PVI only.[¹⁰] Freedom from AT after 12 months of follow-up was 80%, which is higher than our results. This may be explained by a difference in our sedation protocol and PV isolation control maneuvers. We used minimal sedation, but patients undergoing AF ablation in general anaesthesia have a higher success rate.[¹³] Furthermore, we did not check for dormant reconduction with adenosine which in some studies have shown a better clinical outcome.[¹⁴] Nevertheless, our data supports that PVI only in patients with AF undergoing first time ablation is a reasonable strategy, and AI is effective, probably due to durable PVI. Furthermore, focus on lesion contiguity by checking the lesion sets around the PV for gaps above 6 mm may also explain the improvement in clinical outcome. Studies have shown that non-contiguity between point-by-point lesions along the ablation lines results in PV reconduction even with effective lesion sets.[³], [¹⁵] Ablation- and total procedural time were longer in the AI group. This indicates that operators use more time creating and placing the lesions which might lead to more sustainable lesions leading to higher success rates.[¹⁶] This finding is consistent with other studies.[⁸]

Our overall improvement in clinical outcome in the AI group is mainly driven by the improvement for patients with PeAF and not PAF. Previous studies have found that the PV often are reconducting even in patients without AF recurrences, and maybe a strategy using CF only is sufficient to achieve reasonable clinical freedom from AF/AT in PAF patients[¹⁷]. It is uncertain if the AI strategy in our population increased the PVI durability compared to the CF-group since we did not re-evaluate this during follow-up. Notably, the PRAISE trial found that only 1 of 8 patients with recurrent AF had PV re-conduction.[¹⁰] This emphasizes the need for other strategies to treat patients with recurrent AF after PVI such as targeting extrapulmonary triggers, low-voltage areas or rotors.

There are several limitations to this study. Although the study reflects real life outcome in consecutive patients undergoing PVI procedure in a high volume center, the two interventions are compared in a retrospective design. We characterized the AF type according to the definition in guidelines, but some misclassification cannot be ruled out. We only used ECG to evaluate the patients at follow-up, and more frequent ECG monitoring could probably have documented episodes of asymptomatic AF/AT during follow-up. Furthermore, follow-up was limited to 12 months thus long-term success rates are not available. Patients did not follow a strict protocol of AAD withdrawal after the procedure. We considered the use of AAD at the 12 months clinical control as a recurrence of AF/AT, however theoretically a patient could have stopped AAD the day before 12 months clinical control.

This retrospective study shows that an ablation strategy combining AI and lesion contiguity improves the clinical outcome after first-time PVI in patients with paroxysmal or persistent AF.