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  • In the case reported by Goldstein et al a

    2019-04-19

    In the case reported by Goldstein et al. [2], a Riata ST lead (St. Jude Medical, Sylmar, CA, USA) was used. The authors did not mention whether the lead was a dual-coil system or not. If the lead was a single-coil system, the possibility of an HV short circuit between the RV coil conductor and the device could be expected. Evidence of the HV short circuit should exist in the device pocket. As, the authors did not find such evidence, the lead is likely to have been a dual-coil system. The investigators suspected that the HV short circuit occurred in relation to the RV coil. However, this speculation is contradicted by the results of our experiments. Failures of ICD leads are classified as conductor failures and insulation failures. There are two kinds of conductors in the ICD lead. Pace–sense conductors include the tip electrode conductor and the sensing ring conductor. In the integrated bipolar ICD lead, the sensing ring conductor is also the RV coil conductor, as described above. Conductor failure is caused by fracture of the conductor. Fractured pace–sense conductors are a source of noise. Maytin et al. showed the mechanism of noise generation in their report [4], which demonstrated that sensing conductor failure generated noise through changes in conductor impedance. The same authors showed that a pacing conductor failure generated noise. However, noise can also be generated by contact between a pace–sense conductor and any other conductor. In such a case, insulation failure must exist at the contact point between the two conductors. If HV conductors are fractured, the protection circuit in the ICD prevents therapeutic shocks from being delivered, so that the device will not be destroyed. HV conductor fractures are revealed by high shock impedance. New ICD devices are equipped with an alarm (beep sound or vibration). Insulation failures manifest various phenomena. An HV short circuit is evidence of insulation failure of an HV conductor. Insulation failure may involve either the HV anode EZ Cap Reagent GG as SVC coil, or the HV cathode as RV coil. In the device pocket, the ICD has no insulation by design. At this site, only RV conductor insulation failure is a requirement for an HV short circuit. The evidence of an HV short circuit in the pocket is arc marks on the surface of the device can. If the HV short circuit is inside the lead, there will be no arc marks on the device can. For arc marks to be seen, both the outer and the inner EZ Cap Reagent GG tetrafluoroethylene (ETFE) insulation layers of the ICD lead must be abraded to bare the metal of the RV coil conductor. In Goldstein׳s case [2], an inappropriate shock caused by noise was reported, suggesting an HV conductor fracture or failure of the pace–sense conductor [5]. However, the authors did not report any electrical abnormality in the pacing or shock systems, which argue against fracture of the conductors. Therefore, it seems likely that the noise was not generated by conductor fracture but by insulation failure. Their case lacks evidence of an intra-pocket short circuit. We must, therefore, suspect that the lesions related to the short circuit were inside the ICD lead and not visible. Unfortunately, the lead was not extracted and the mechanism of the short circuit was not found. An HV short circuit is a most dangerous complication of ICD therapy, and ICD leads still present a risk of HV short circuit. Gradaus et al. reviewed multi-luminal ICD lead configurations, based on two types of conductors, coiled and straight, running in parallel with a single insulating body [6]. There are risks of HV short circuits associated with multi-luminal ICD lead configurations. The first authors to discuss this risk were Bracke et al. [7]. They commented that an HV short circuit might be created when an insulation breach occurs between HV conductors that are located sufficiently close together. Haddad et al. also pointed out this risk with multi-luminal ICD leads [8], but they concluded that the overall incidence of HV short circuits was low. Contrary to their speculation, case reports of HV short circuits seem to be increasing [1–3,7,9–13], and this is probably attributable to an increase in the insulation failure of ICD leads. HV short circuits are caused by accidental contact between HV conductors. The HV conductor is sheathed in an ETFE layer. When an HV short circuit is created, insulation failure may be expected in the ETFE insulation. Borleffs et al. reported the failure rates of ICD leads implanted from 1992 to 2009. They observed 2069 ICD leads during this period and found a 3.8% lead failure rate [14]. Furthermore, Kleemann et al. observed 990 ICD leads from 1992 to 2005 [15]. They classified the implantation period as <3 years, 4–6 years, and >6 years. They found that sensing failure and exit block increased little with the years of implantation, in contrast to the number of conductor problems and insulation failures, which clearly increased with the duration of implant.