Discussion
In this large, recent cohort of patients undergoing catheter ablation of
AVNRT, procedural outcomes in both study groups were excellent, with no
incidence of arrhythmia recurrence during follow-up. There was no
evidence of increased risk of AV nodal injury with irrigated RF
ablation. Use of ICFS ablation catheter was associated with successful
ablation with decreased total ablation and decreased need for ablation
in close proximity to the His region.
A previous, smaller, uncontrolled study has shown favorable outcomes for
irrigated radiofrequency ablation of AVNRT.7 The
present study, shows similarly favorable outcomes in a larger cohort
using a catheter with contact-force sensing capability. A case of
inadequate NI RF ablation for slow pathway modification with subsequent
successfully ablation using an ICFS ablation catheter has been
previously reported.8 Our study comparing these
ablation modalities demonstrates that slow pathway modification may be
successfully achieved with shorter duration RF application, and less
ablation in close proximity to the His region with ICFS catheters
relative to NI ablation catheters.
Safety and efficacy of lesion creation with both utilized catheter may
be better understood by examining details of RF delivery for each
catheter. In vivo studies have demonstrated that lesion size is
proportional to current density at the ablation
electrode.9 The surface area of the ablation
electrodes of the utilized NI 4mm catheter and the 3.5mm ICFS catheter
38 mm2 and 31 mm2, respectively
(catheter specifications obtained by personal correspondence with
medical affairs representative at Biosense Webster, Inc.). The resulting
power densities, which are proportional to current densities at a given
impedance, at goal 50W power with the 4mm NI catheter, and 35 W power
with the 3.5mm ICFS catheter are thus 1.3 W/ mm2, and
1.1W/ mm2, respectively. Additionally, “fast mode”
utilized with RF generator during ablation with 4mm NI catheter, and
“STSF mode” utilized with RF generator during ablation with 3.5mm ICFS
catheter, both result in achievement of goal power in
~3s if power delivery is not limited by electrode
temperature (RF generator specifications obtained by personal
correspondence with medical affairs representative at Biosense Webster,
Inc.). While irrigated RF ablation creates increased lesion diameter and
depth relative to NI RF ablation, the expected current density is
slightly lower using the ICFS compared to the NI catheter, and the
temporal characteristics if RF delivery are similar, thus lesion
creation under ideal conditions are likely similar with the two
approaches studied. The primary safety concern for adoption of ICFS
ablation is the possibility of greater risk of iatrogenic permanent AV
node block. We found no evidence of increased risk for iatrogenic AV
block with ICFS, with the single case of ablation related AV block in
our study cohort occurring in the NI ablation group. We hypothesize that
identification of inadequate contact-force results in reduced frequency
of ineffective RF application, while confirmation of adequate
contact-force during RF application and electrode irrigation to overcome
temperature-limited RF application facilitates effective lesion
creation, and successful ablation without encroachment of ablation
lesions into the region of the compact AV node. The substantially
decreased proportion of patients who required ablation within 10mm of
the His region suggests that risk of iatrogenic AV block may be lower
with ICFS ablation compared to NI ablation, although further studies are
required to confirm these findings.