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.