Leong et al reported a
Leong et al. reported a similar case of a short circuit in the Riata 1570 defibrillator lead, which manifested as unsuccessful defibrillation . In this case, product analysis of generator indicated structural device damage owing to a short circuit in the defibrillation lead. Marenco et al. also reported an ICD system that failed to deliver additional shock therapy after a single 25-Joule shock. In this case, a high-voltage lead impedance alert was detected by interrogation and lead impedance was declared out of range with possible output circuit damage . Lakshmanadoss et al. presented two cases of failure of shock delivery in spite of apparently normal ICD leads and fluoroscopic appearance . In the case reported here, we did not perform the high-voltage lead impedance examination, which was conducted after the patient received an inappropriate shock 55 months earlier. Furthermore, the older generation St. Jude ICD (Atlas) being exchanged in our case did not have out of clinic high-voltage lead impedance daily measurement capabilities. Therefore, we could not determine whether the circuitry was damaged at the time of the earlier inappropriate shock therapy or at the time of shock delivery testing undertaken by our group. We are unable to explain the precise reason for the observed lead failure, as additional information has not yet been provided by the manufacturer. According to Hauser et al., Riata lead failure deaths were generally caused by short circuits between high-voltage components . Short-circuiting between the systems is also likely in our case. This case has raised important clinical issues. First, it BTL105 draws attention to a potential flaw in Riata leads with undetected externalization. Some published reports show a high prevalence of insulation failure with externalized cables. Parvathaneni et al. reported that 9 of 29 leads (31%) that showed externalized conductors had electrical abnormalities, including high-voltage circuit shorts . Theuns et al. also documented that 16 of 147 leads (11%) with lead excursion had abnormal electrical parameters compared to 3.5% of those without lead excursion . On the other hand, Cronin et al. suggested that fluoroscopy may lack the sensitivity to detect inside-out insulation failure and externalized conductors . Previous reports have suggested that leads with cable extrusion might not necessarily manifest overt electrical dysfunction [1,9]. Our case also highlights the role of high-voltage shock testing, including DFT testing, particularly at the time of generator change. The role of routine DFT testing in clinical practice has been recently questioned [1,8,15], because migration is associated with a mortality rate of 0.1–0.2% . However, the discussion of the utility of DFT testing in these cases is related to the need to determine the actual DFT or to conduct a demonstration on an adequate safety margin. The potential need to screen for HV cable dysfunction is completely different. In the case presented here, the lead failure would not have been recognized without high-voltage shock testing. Shock testing for identifying an unprotected individual may thus be required and even critical at the time of elective generator change. The role of shock testing should be clarified by additional confirmatory data and further research will be required to justify screening for HV cable dysfunction. For the time being, we propose that commanded high-voltage synchronized shock could be utilized for testing system integrity without the risk of VF induction. However, the risks and benefits of this approach need to be given adequate consideration in determining whether such a screening test should be performed. Finally, this patient showed a pronounced decrease in R-wave amplitude after shock testing, when lead fracture had already been manifested. Similar R-wave amplitude attenuations have been reported before [5,7]. Although it is uncertain whether the attenuation of R-wave amplitude is a reflection of latent lead insulation defects in Riata leads, this may be a marker of lead fracture. Currently, it is unknown how to manage patients with a Riata lead, with or without externalized conductors in the absence of abnormal electrical parameters. Although electric screening of these asymptomatic patients remains controversial, the complete abandonment of high-voltage shock testing needs to be cautioned against.