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).