Study population
Of the 451 patients who underwent RFCA for AF using the CARTO (Biosense Webster, Irvine, CA) three-dimensional mapping system between November 2013 and March 2016 at Asan Medical Center in Seoul, South Korea, we included PAF patients who underwent first PV isolation. We excluded patients who had any of the following: (1) persistent AF (n = 173); (2) previous RFCA (n = 37); or (3) previous maze operation (n = 2), additional left atrial line or complex fractionated atrial electrogram ablation (n = 63), incomplete PV isolation (n = 4), and incomplete data (n = 15). The main study population was comprised of 157 patients with or without cavotricuspid isthmus ablations (Fig. 1). The patients were divided into two groups according to the use of the VISITAG™ module during the procedure (with VISITAG, n = 62; without VISITAG, n = 95). This study conformed to the ethical guidelines of the 1975 Declaration of Helsinki and was approved by the Institutional Review Board of Asan Medical Center (2017-0357). The need for informed consent was waived due to the retrospective nature of the study.
Ablation procedure and follow-up
The demographic, electrocardiographic, and echocardiographic characteristics of the patients were obtained by independent research personnel at the time of admission for the RFCA procedure. A duodecapolar catheter was initially placed in the coronary sinus and right atrium. Double transseptal catheterization was performed under hemodynamic monitoring and fluoroscopic guidance, one for mapping and one for the ablation catheter. A 7 Fr Lasso catheter or Pentaray catheter (Biosense Webster, Irvine, CA) was placed for mapping. Analgesia was maintained with remifentanil throughout the procedure. Electroanatomical mapping and ablation procedures were performed using the CARTO® system (Biosense Webster, Irvine, CA). Mapping and ablation were completed using a 7.5 Fr NaviStar SmartTouch SF irrigation catheter with a 3.5 mm tip (Biosense Webster). We performed PVI using a target contact force of 10–30 grams and delivered energy of 30–35 watts (power control mode) for the anterior wall and 25–30 watts for the posterior wall. In the VISITAG group, the ablation lesions were tagged automatically based on predefined criteria on the VISITAG module (Fig. 2). Ablation lines were made sequential point-by-point fashion to avoid gaps in the line with VISITAG™ setting of our center (minimum time of 5 s, maximum range of 2.5 mm, force over time of 50%, minimum force of 5 g, and non-projected tags). Manual or projected tags were not used in VISITAG group. In the control group, we delivered a point-by-point RF application in a power-controlled mode with same energy setting as VISITAG group. We tagged the ablation lesions manually according to the physician’s discretion, based on the reduction in bipolar electrogram during ablation as well as drop of the local impedance.
The procedural endpoint was the complete entrance block of all 4 PVs, defined as elimination of all ostial PV potentials during sinus or paced rhythm in both groups. Additional ablation between gaps along the intended ablation line was not done after the electrical isolation of the PV from the left atrium. A 30-minute waiting period was observed to monitor for early reconnection. Uninterrupted anticoagulation, either using warfarin or non-vitamin K antagonist oral anticoagulants, was maintained before and after the procedure. Activated clotting time was adjusted for 300–350 s during the procedure. Patient follow-up was conducted at 1, 3, 6, and 12 months after the index procedure with 12-lead electrocardiogram and 24-hour Holter monitoring. Additional rhythm monitoring was performed if the patient had symptoms suggestive of arrhythmic recurrence.
Gap analysis
The gaps in the ablation line were assessed according to three predefined criteria for VISITAG™ tagging. Criterion 1 followed the VISITAG™ settings of our center which described above (minimum time of 5 s, maximum range of 2.5 mm, force over time of 50%, minimum force of 5 g). For Criterion 2, the tagging was repeatedly assessed using the criteria established by Lin et al. [6], which consisted of a minimum time of 15 s, a maximum range of 4 mm, 60% force over time, and 6 g minimum force. For Criterion 3, we reassessed the gaps by applying the criteria reported by Okumura et al. [7], which consisted of a minimum time of 5 s, a maximum range of 3 mm, 25% force over time, and 8 g minimum force. Gaps in the VISITAG line were defined as a margin-to-margin distance of 5 mm between two adjacent VISITAG™ tags (Fig. 2). The gaps in the line were assessed by two independent research personnel who were blinded to the study outcomes. The electroanatomical maps were rotated three-dimensionally to avoid inadequate measurement by angle. Interobserver variability was assessed by gap analysis of 20 randomly selected samples and demonstrated excellent consistency (kappa value, 0.88). Conflicted cases were resolved by the consensus.
Study outcome
The primary study outcome was rate of recurrence of AF or atrial tachycardia (AT) after a blanking period of 3 months. The recurrence of AF or AT was diagnosed when a sustained episode lasting > 30 s was documented on the electrocardiogram or Holter monitoring, either routine or symptom driven. The secondary outcome was the location and prevalence of VISITAG gap by each of the three criteria. In addition, the rate of recurrent AF and AT was reassessed according to the presence or absence of VISITAG gap on the PVI line to assess the clinical impact of such gaps. Total procedure time, ablation time, fluoroscopic time, and procedure-related complications after PVI were also evaluated in the current study. All clinical outcomes were verified and adjudicated by an independent researcher.
Statistical analysis
All statistical analyses were performed using R software (version 3.3.1; R Foundation for Statistical Computing, Vienna, Austria; www.r-project.org). All P values were two-sided, and P values < 0.05 were considered statistically significant. Continuous variables were presented as either means with standard deviation or median values with interquartile ranges. Categorical variables were presented as frequency and percentage. Continuous variables were compared using Student’s t test or the Wilcoxon rank-sum test. Categorical variables were compared using the χ2 test or Fisher’s exact test, as appropriate. The cumulative rates of recurrent AF and AT were demonstrated using Kaplan–Meyer analysis with differences assessed using the Log-rank test. Cox’s proportional hazard model was used to demonstrate the association between gap and recurrence of AF and AT during follow-up.