Adverse effects of SVCI on CIED leads
RF application to the myocardium contiguous to CIED leads is needed to achieve electrical isolation of the SVC in some patients with previously implanted CIEDs; however, the general consensus of the Heart Rhythm Society is that direct contact between ablation catheters and CIED leads should be avoided.21 Potential interaction between SVCI and CIEDs may include the following: pulse generator malfunction, lead dislodgement during AF ablation, outer insulation damage, change in impedance, pacing, and sensing parameters because of RF application to the site closest to the leads. This study revealed no permanent pulse generator malfunction; however, the effects of RF application on the pulse generator, including noise reversion mode with asynchronous pacing, oversensing of electromagnetic interference, and mode switch or transient reset to elective replacement interval, have been previously reported.22 Previous studies have shown atrial lead dislodgement after catheter ablation of AF in patients with CIEDs and a rise in the pacing threshold after atrioventricular node ablation in these patients.23,24 AF ablation carries higher risks of lead dislodgement when performing transseptal puncture or catheter manipulation in the RA, compared with catheter ablation of arrhythmias other than AF. In the present study, impedance rise was observed in 2 patients. The mechanism of a pacing threshold rise remains unclear; however, micro-dislodgement or lead damage due to inductive current might contribute to a pacing threshold rise. The dislodgement of leads is a concern, especially given the current trend for fewer fluoroscopy AF ablation procedures using a 3-dimensional mapping system. Therefore, careful catheter manipulation on fluoroscopic imaging may be important. A previous study involving AF ablation in 86 patients with CIEDs reported atrial lead dislodgement in 2 patients with newly implanted leads of <6 months.23 Distal tip encapsulation within the myocardium has been reported to occur 2–6 weeks after implantation of leads.25,26 In our study, the median period from CIED implantation to AF ablation was 71.5 months, and the fluoroscopic time was significantly longer in the CIED group than in the control group. As a result, there was no lead dislodgement after SVCI. An adverse effect on lead insulation is another issue in SVCI for patients with CIEDs because the myocardium, when achieving electrical isolation of the SVC, might be close to the CIED leads. Lead insulation damage is one of the most common reasons for defibrillator lead failure.27 A previous in vitro study evaluated the adverse effect of direct application of RF on pacing and defibrillator lead function. In that study, CIED leads, including all commercially available lead insulation materials, were tested. RF energy was delivered at a maximum power of 50 W, with irrigated and non-irrigated tipped catheters. Significant changes in lead function and outer insulation were not observed.28 In another study that assessed the effects of electrocautery on lead insulation materials,29 lead insulation damage was shown to be more common in polyurethane and copolymer leads. In our study, no significant changes were found in lead parameters such as impedance, pacing threshold, and sensing. Sensing noise was observed in 1 patient, although whether RF application directly influenced lead insulation in that case remains unclear. The outer insulation material of the lead was silicone, which has been reported to be less susceptible to thermal damage from RF application.29 Moreover, the reported lead survival rate of the same model lead (Stelid BJ45D, ELA Medical, Montrouge, France) was 100% at 4.5 years after implantation, and that of ventricular leads (Stelid BT45D, ELA Medical, Montrouge, France) with the same structure, other than the proximal electrode position, was 99% at 20 years after implantation. Therefore, RF application might damage the outer insulation of the leads, and an association between RF ablations and sensing noises could not be completely ruled out, which is in contrast to the findings in the above-mentioned previous studies. There might be a difference between in vitro and in vivo studies. Micro-cracking resulting from environmental stress and metal-induced oxidation is known as outer insulation malfunction of leads implanted for a long time. Another possible reason for the sensing noises may be the unique structure of the lead. The lead (Stelid BJ45D, ELA Medical, Montrouge, France) had 2 electrodes, and the proximal electrode was positioned 70 mm from the distal tip (Figure 1B). RF energy might be applied to the proximal electrode when performing SVCI. Therefore, the safety of RF application to the CIED leads has been not fully guaranteed in the clinical setting.
This study had some limitations. First, this was a retrospective, single-center study. Second, the study population who had undergone both SVCI and CIED implantation prior to SVCI was relatively small. Third, the relationship between RF application and lead failure was not determined. The occurrence of sensing noise and an impedance increase might be compatible with lead degradation over time. Finally, the durability of SVCI in patients with CIED was not determined because not all study patients had undergone a second session.

Conclusion

SVCI could be achieved without lead failure and significant change of lead parameters in most patients with CIEDs; however, the 8.8% incidence of lead failure observed after SVCI should be noted. Careful RF application is essential to avoid not only sinus node injury and phrenic nerve damage but also lead damage for patients with CIEDs. In addition, lead structures, outer insulation materials, and the position of the leads or the defibrillator coil in the SVC must be carefully examined prior to SVCI. Further studies with a larger sample size are needed to confirm the safety and efficacy of SVCI for patients with CIEDs in the clinical setting.

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Figure legends