Methods
Study population
We prospectively enrolled 136 patients who were undergoing radiofrequency catheter ablation for PSVT between January 2020 and June 2021. The study was conducted in two medical centers affiliated with the Catholic Medical Center. Patients with age <15 years and who were scheduled to undergo electrophysiology study for supraventricular tachycardia were screened. For inclusion, any AVNRT, AVRT, or WPW syndrome with atrial fibrillation had to be documented during the electrophysiologic study. The patients in whom supraventricular tachycardia (SVT) was not induced or only atrial tachycardia was induced were excluded. The study was registered in a public trials registry. (ClinicalTrials.gov number, NCT04215640) This study was approved by the Institutional Review Board of Catholic Medical Center. All patients provided written informed consent. No industry or public institution was involved in the design, reporting, or dissemination plans of our research.
Randomization and study protocol
Included patients were categorized into AVNRT or AVRT/WPW syndrome groups according to the induced SVT during procedures. When ≥2 arrhythmias were induced during the same procedure, categorization and data acquisition was based on the first SVT targeted for ablation. Patients were randomized at a 1:1 ratio into the ME group or the control group. Block randomization (block size 4) was used to assign the randomization sequence for each SVT category (AVNRT or AVRT/WPW syndrome) at each site. Patients assigned to the ME group received RFA for induced SVTs using a 4.5mm tip ablation catheter equipped with ME (IntellaTip MiFi OI, Boston Scientific, Boston, MA, USA), which has conventional bipolar electrodes and three additional MEs with irrigation holes at the distal tip (Figure 1A). Patients assigned to the control group received RFA using a 4 mm tip ablation catheter (Blazer II HTD, Boston Scientific, Boston, MA, USA) (Figure 1B).
Electrophysiology study and RFA
All antiarrhythmic drugs were discontinued at least 2 days before the procedure. Diagnostic mapping catheters were inserted through the femoral vein and positioned to the lateral side of the right atrium, coronary sinus, His area, and right ventricular apex. Electrograms were recorded using a digital recording system (CardioLab, GE Healthcare, Chicago, IL, USA). At baseline, ventricular and atrial programmed stimuli were delivered to identify the presence of AP and/or SP. If SVT was not induced, atrial and ventricular programmed stimuli were delivered again after intravenous isoproterenol infusion. Once SVT was induced, His-refractory ventricular premature beat was delivered and overdrive pacing from the right ventricular apex was performed. Differential diagnosis of the SVT was mainly based on the following criteria:
1) AVNRT: Absence of reset response to His-refractory ventricular premature beat and corrected post-pacing interval > 110ms after right ventricular overdrive pacing.
2) AVRT: Presence of AP on baseline study, positive reset response to His-refractory ventricular premature beat, and corrected post-pacing interval < 110 ms after right ventricular overdrive pacing.
If SVT was not sustained to complete above studies or the responses were conflicting, further studies to differentiate SVT were attempted including para-Hisian pacing, ventricular differential pacing and/or the assessment of ∆AH during sinus rhythm and SVT. After SVT diagnosis, the ablation catheters were advanced via femoral vein using long sheaths. RFA was performed targeting SP potentials in AVNRT or AP potentials in AVRT/WPW syndrome. When it was difficult to map the pathway potentials, RF energy was delivered to an anatomically expected SP location in AVNRT, and to a site showing earliest atrial activation during ventricular pacing in AVRT. In WPW syndrome with an absence of retrograde conduction via AP, a site with an earliest preexcited ventricular activation was targeted for ablation. In patients who were assigned to the ME group, three bipolar ME signals made between m1-2, m2-3, and m3-1 were shown in addition to conventional bipolar and unipolar electrograms at the distal ablation tip. Ablation was performed with a guidance of the ME signals. The radiofrequency (RF) generator was set at the non-irrigation mode in both groups, but minimal (2 mL/minute) saline irrigation was performed for the ME catheters to maintain patency. In AVNRT, the primary ablation endpoint was the emergence of junctional rhythm during ablation. In AVRT/WPW syndrome, the primary ablation endpoint was a conduction block of targeted AP. When the ablation endpoint was not achieved within 10 to 20 seconds of ablation, ablation was stopped, and repeated mapping was performed to find the optimal ablation site. Temperature controlled RF delivery with a target temperature of 60oC was performed with an initial power of 25W for SP ablation and 35W for AP ablation in both groups. When the primary ablation endpoint was achieved, RF power was gradually increased to 35 to 40W and the ablation was continued for 50 to 60 seconds. After successful initial RF energy delivery, consolidation ablation was performed at the operator’s discretion. SVT non-inducibility was confirmed using atrial and ventricular programmed stimulus maneuvers after a 20-minute waiting period. The procedure endpoint was ≤1 atrioventricular nodal echo beat during atrial programmed stimuli in AVNRT. In AVRT/WPW syndrome, the procedure endpoint was an absence of AP conduction at rest and after intravenous 12mg bolus injection of adenosine.
Study outcome definitions
To compare the mapping performance, the rate of discrete pathway electrogram identification at the ablation catheter was analyzed. The primary study outcomes were RF attempt number and cumulative ablation time to achieve the first ablation endpoint, which was defined as an emergence of junctional rhythm in AVNRT or AP block in AVRT/WPW syndrome. When multiple RFAs were needed to achieve the ablation endpoint, the ablation time to endpoint was defined as the sum of all ablation time spent during ineffective and effective ablation before achieving the endpoint. The secondary study outcomes were total ablation time, average RF power, average temperature, procedure time, acute SVT reinduction rate and dormant AP conduction rate. If ≥2 SVTs were induced or ≥2 APs were targeted for ablation in a single procedure, we recorded the study outcomes of the first ablated SVT or AP. All study outcomes were recorded during the index procedures.
Statistical analysis
Normally distributed continuous variables are presented as the mean ± standard deviation for normally distributed values and compared using Student’s t-tests. Non-normally distributed continuous variables are presented as the median (25th – 75th percentiles) and compared using Mann-Whitney U tests. Categorical variables are presented as the frequency with percentage (%) and were compared using chi-square or Fisher’s exact tests. All analyses were two-tailed, and a p-value <0.05 was considered statistically significant. All statistical analyses were performed using R version 3.6.2 (R Foundation).