High‐power, short‐duration ablation during Box isolation for atrial fibrillation

Abstract Background It has been demonstrated that a high‐power, short‐duration (HPSD) ablation during pulmonary vein (PV) isolation is effective and safe. However, studies about the HPSD ablation during the posterior wall isolation, the Box isolation (BOXI), are limited. We evaluated the efficacy, feasibility, and safety of HPSD ablation during BOXI. Methods One‐hundred sixty patients with all types of atrial fibrillation underwent BOXI with HPSD ablation (n = 80) or conventional technique (n = 80). In the HPSD group, ablation was performed with 50 W and a target lesion size index of 5.0 using a contact force (CF) sensing catheter. Ablation near the esophagus was performed with 50 W for 5 seconds and a CF < 10 g. In the conventional group, ablation was performed with 30‐40 W for 30 seconds, but 20 W near the esophagus. Results The BOXI creation (26 ± 8 minutes vs 47 ± 17 minutes, P < .0001) and procedure (65 ± 12 minutes vs 87 ± 23 minutes, P < .0001) times were significantly shorter in the HPSD group than the conventional group. The number of pacing capture sites did not differ between the two groups. No complications including gastrointestinal symptoms occurred. The atrial tachyarrhythmia‐free rate at 12‐months after a single procedure was 86.3% in the HPSD group and 76.3% in the conventional group, respectively (P = .132). The incidence of PV reconnections and gaps in the lines during the second procedure did not differ between the two groups. Conclusion The BOXI with HPSD ablation is effective, feasible, and safe with short BOXI creation and procedure times without reducing the clinical outcomes.


| INTRODUC TI ON
Radiofrequency (RF) catheter ablation of atrial fibrillation (AF) has been widely performed. 1 In persistent AF, the additional benefit of a posterior wall box isolation (BOXI) over the pulmonary vein isolation (PVI) has been reported in previous studies. [2][3][4][5][6][7][8][9][10][11][12] Although a durable lesion formation of the PVI or BOXI is essential for successful outcomes, ablation on the posterior wall has a risk of esophageal injury. A lower-power, long-duration (LPLD) ablation (10-35 W for 10-30 seconds) is commonly used on the posterior wall. [13][14] In contrast, a high-power, short-duration (HPSD) ablation (50 W for 2-15 seconds) during the PVI has been advocated to decrease the procedure time without an increase in complications. [15][16][17][18][19] However, the optimal RF power and duration settings on the posterior wall near the esophagus are not fully elucidated and studies about HPSD ablation during BOXI are limited. Therefore, we evaluated the efficacy, feasibility, and safety of HPSD ablation using contact force (CF) sensing catheters during BOXI as compared to that with the conventional technique.

| ME THODS
One-hundred sixty consecutive patients with AF underwent catheter ablation from June 2018 to May 2019. The patients were divided into two groups: HPSD ablation group (n = 80); and conventional group (n = 80). We performed conventional methods in the first 80 patients, then HPSD methods in the last 80 patients. The clinical characteristics of each group are shown in Table 1 A 20-pole circular mapping catheter (Optima TM ; Abbott) and irrigated-tip ablation catheter (FlexAbility TM or TactiCath TM CF sensing catheter; Abbott) were used for mapping and ablation. The EnSite NavX TM system (Abbott) was used. Esophageal temperature monitoring was performed using a probe (SensiTherm TM ; Abbott).

| BOXI with HPSD ablation
All ablation applications except for those near the esophagus were delivered with 50 W and a target lesion size index (LSI) of 5.0 using the TactiCath TM CF sensing catheter with a target CF of 5-20 g.
Ablation applications near the esophagus were delivered with 50 W for 5 seconds with a CF of <10 g, but the application was stopped when the esophageal temperature increased to 40°C. We used a catheter irrigation rate of 30 mL/min and temperature cutoff of 42°C.
Ablation was started at the anterior antral wall of the left PVs in a point-by-point fashion. When PVs were not isolated by only anterior line, segmental ablation at the breakthrough points of the posterior portions of PVs was performed. Then, a roof line ablation was performed. Continuously, the anterior antral wall of the right PVs was ablated. Finally, a floor line ablation was performed (Figure 1).
The PVs and posterior wall were mapped using a circumferential mapping catheter (Optima TM ). When residual electrograms or gaps were detected within the box lesion using the ablation catheter or a circumferential mapping catheter, applications were added until all electrograms were eliminated.
When AF was still sustained after the BOXI, the AF was internally cardioverted. The BOXI was confirmed by high output (10 V) pacing along the ablation lines using the ablation catheter during sinus rhythm (loss of pacing capture). 3 Additional ablation was performed at the pacing capture sites. The exit block was also confirmed by pacing within the box lesion.
Finally, the AF inducibility was evaluated by rapid pacing from the coronary sinus for 20 beats, while shortening the cycle length by 10 ms from 250 to 180 ms after isoproterenol (10 µg) injection.
When non-PV foci, atrial flutter, and atrial tachycardia were induced, they were ablated. Other extensive ablation of complex fractionated atrial electrogram or low-voltage areas was not performed.

| BOXI with conventional technique
All ablation applications except for those near the esophagus were delivered with 30-40 W for 30 seconds at each site using a non-CF sensing catheter (FlexAbility TM ). We used a catheter irrigation rate of 8-15 mL/min and temperature cutoff of 42°C. Ablation applications near the esophagus were delivered with 20 W and the application was stopped when the esophageal temperature increased to 40°C.
The BOXI was performed in the same manner.

| Periprocedural care and follow-up
Anticoagulation therapy was continued before and after the ablation for 3 months in all patients. We performed transesophageal echocardiography in patients with sustained AF 1 day before the procedure.
All antiarrhythmic agents were interrupted at least five half-lives before the procedure. Amiodarone was not used in any patients. In patients with persistent and longstanding persistent AF, those antiarrhythmic drugs were re-administered after the procedure and discontinued by 3 months (blanking period). An oral proton pump inhibitor was continued after the ablation for 1 month in all patients.
We asked a family doctor to follow-up with the patients every month and record an electrocardiogram (ECG) every month and 24-

| Statistical analysis
Statistical analysis was performed using the JMP Pro software (SAS Institute Inc.). Data are given as mean ± SD and as number and percent. Continuous variables were compared using an unpaired t test or Wilcoxon rank-sum test between the two groups. Categorical variables were compared between groups by a Chi-square analysis or Fisher's exact test. Atrial tachyarrhythmia-free survival curve was estimated using the Kaplan-Meier method, and a log-rank test was used for comparisons between the two groups. Tests were twosided and P < .05 was considered significant.

| RE SULTS
The baseline patient characteristics are listed in Table 1. There were no significant differences between the two groups. In both groups, BOXI was completely achieved in all patients.

| Procedural data
In the HPSD group, the mean CF was 10.  Table 2 shows the procedure characteristics. The total RF energy in the HPSD group was significantly lower than that in the conventional group. The mean RF time for each lesion, and BOXI creation, procedure, and fluoroscopic times were significantly shorter in the HPSD group than the conventional group. The number of 10 V pacing capture sites did not differ between the two groups. The number of additional applications for residual electrograms within the box lesion was significantly smaller in the HPSD group than the conventional group.
The inducibility of atrial tachyarrhythmias and the incidence of an SVC isolation and CTI ablation did not differ between the two groups. The number of RF point with esophageal temperature rise to 40°C was significantly smaller and the maximum esophageal temperature was significantly lower in the HPSD group than the conventional group.

| Complications
There were no instances of esophageal injury (gastrointestinal symptoms, gastric hypomotility, or atrioesophageal fistula), pericardial tamponade, strokes or transient ischemic attacks, PV stenosis, or death in either group.

| Clinical outcomes
In the HPSD group, 11 (13.8%) patients had a recurrence of an atrial tachyarrhythmia, including AF in eight patients, atrial flutter in 1,

| PV reconnections and line gaps during the second procedure
A second procedure was performed in seven patients in the HPSD group and 14 in the conventional group (Table 3 Table 3). The incidence and distribution of PV reconnections and gaps in the roof or floor lines did not differ between the two groups (Table 3).

| Main findings
The present study demonstrated that (a) BOXI with HPSD ablation is effective, feasible, and safe with short BOXI creation, procedure, and fluoroscopic times and small amount of the total RF energy deliveries; and (b) the number of pacing capture sites, atrial tachyarrhythmia-free rate, and incidence of PV reconnections and line gaps were similar between the HPSD and conventional groups.

| Beneficial effects of the BOXI in persistent AF
Previous studies have shown that BOXI in addition to the PVI results in a better outcome than a PVI alone or PVI plus a roof line ablation in patients with persistent AF. [4][5][6][7][8][9][10][11][12] The BOXI can capture the triggers, rotors, and low-voltage areas in the posterior LA, 5 facilitate AF termination and its noninducibility, 5 and decrease the rotors and multiple wavelets on the anterior wall, inferior wall, and LA appendage. 20

| Safety of the HPSD ablation on the posterior wall
An animal study has suggested that HPSD (50 W for 5 seconds) ablation has lower complication rates than LPLD ablation (40 W for 30 seconds). 21 Winkle et al 16

| Advantages of the LSI-guided HPSD ablation
The LSI is multiparametric index that incorporates RF time, CF, and power, therefore, a high-power application can reach the target LSI in a shorter time. We also showed that a 50 W RF application reached a target lesion (LSI of 5.0) within a mean of 12.9 seconds at each site. Therefore, the HPSD ablation shortened the BOXI creation, procedure, and fluoroscopic times without reducing the acute and chronic effects in terms of the number of pacing capture sites, atrial tachyarrhythmia-free rate, and incidence of PV reconnections and line gaps. That is meaningful because longer ablation times increase the incidence of heart failure due to an increased fluid load 23 and cognitive dysfunction. 24 Also, shorter procedure and fluoroscopic times are preferable for patients, operators, and the staff.

| Study limitations
First, this was a single-center study and the number of patients was too small to evaluate for the safety issue. Second, we did not perform esophagogastroscopies to assess esophageal injury after ablation, because no patients had significant gastrointestinal symptoms.
Therefore, we cannot deny the gastric hypofunction and asymptomatic esophageal lesions. Third, it was possible that asymptomatic recurrences were undetected. Finally, the follow-up period was relatively short. Further long-term follow-up studies are necessary.

| CON CLUS IONS
Box isolation with HPSD ablation is effective, feasible, and safe and provides a shorter procedure time and smaller amount of total RF energy deliveries without reducing the clinical outcomes.

CO N FLI C T O F I NTE R E S T
Authors declare no conflict of interests for this article.