Recently, polarity-dependent shock failures were reported in implantable cardioverter-defibrillators caused by structural failure in the high-voltage feedthrough. Short circuits may occur when the right ventricular coil is cathodal for phase 1 of biphasic shocks (cathodal shock). This viewpoint proposes a mechanism for observed polarity dependence and considers whether the same mechanism may apply in other shock-induced, short circuits. Implantable cardioverter-defibrillator connections to the lead traverse feedthroughs into the hermetically sealed housing (\"Can\"). The feedthrough comprises 2 concentric, conducting metal cylinders, the inner pin-conductor to the right ventricular coil and outer Can, separated by impermeable insulation. Shock failure depends on 3 conditions: 1) development of a fluid layer in the feedthrough, creating a conduction path in parallel with the shock pathway; 2) the radial gradient of the electric field in the fluid, so resistive heating during a shock vaporizes water to form a high-resistance gas bubble around the pin; and 3) field emission of electrons at the cathode, with rate and energy dependent on the field\'s strength and the cathode\'s potential-energy barrier to emission. For cathodal shocks, electrons emitted at the metal pin may initiate an ionization avalanche in the gas until it \"breaks down\" into a low-resistance plasma, resulting in a short circuit. For anodal shocks, the effective cathode is the liquid-gas interface, where the field is weaker than at the pin. Additionally, solvated electrons in aqueous solution must overcome a higher potential-energy barrier to be emitted. This permits the high-resistance gas bubble to stabilize so that the shock is completed.

BACKGROUND: Recent reports describe a high rate of premature lead failure in the St Jude/Abbott TendrilTM 2088 (St. Jude Medical Inc., St. Paul, MN, USA) pacing lead principally manifested by electrical noise. This finding awaits confirmation.
METHODS: We performed a retrospective analysis of 2088 TendrilTM leads among 362 patients implanted from 2010 to 2018. Eligible leads were those with device interrogations beyond one month from lead implantation. Review of serial device interrogations was conducted for each lead, particularly focussing on electrical noise as a marker of premature lead dysfunction.
RESULTS: Four hundred and eight (408) leads among 337 patients were included in this study, with an average patient age of 81±11 years at the time of lead implantation. Mean follow-up was 2.5±1.8 years. There were eight leads with electrical noise indicating premature lead failure. This reflects an overall 1.7% rate of lead dysfunction; the failure rate was 6.2% at 4 years. The majority of cases were detected during routine checks without adverse clinical consequences. Four (4) cases required device reprogramming to avoid interference or inhibition due to noise.
CONCLUSIONS: The rate of Tendril TM 2088 premature lead failure appears to be similar to recent local and international studies. This study reports a significantly higher rate of lead dysfunction at 4 years (6.2%) than the published Abbott product performance reports.

Noise oversensing encountered in patients with Abbott Tendril leads in our hospital triggered an internal investigation.
We retrospectively analyzed patients with a Tendril lead model 1688, 1788, 1888, and 2088. Most leads were connected to Abbott generators. To exclude a primary generator issue as the cause of noise oversensing, we enrolled a cohort of patients in whom Medtronic CapSureFix leads model 4076 and 5076 were prospectively connected to similar Abbott generators.
A total of 1063 Tendril leads were implanted in 869 patients. Noise was encountered in 66 leads (6.2%) during a follow-up of 3.9 years. Most affected leads had normal impedance and only a few of these patients were symptomatic. Reprogramming was attempted in 44 of 66 (67%), and reduced oversensing in 34 of 44 (77%) of these patients. Seventeen malfunctioning leads (1.5%) were replaced, including 16 of 66 (24%) of those with noise. Of the four leads with noise extracted and returned to the manufacturer, lead to device abrasion was identified in two and inner insulation breach in one. None of the 145 Medtronic CapSureFix leads connected to Abbott generators had noise during a follow-up of 3.6 years.
Noise oversensing was relatively common in Tendril leads, but was not detected in Medtronic leads despite connecting to Abbott generators. Although the majority of the affected leads did not show abnormal impedance, outer or inner insulation breach was identified in three of the four returned leads. As patients with affected leads are generally asymptomatic, most of them can be managed conservatively.

OBJECTIVE: Serious concerns have been recently raised about the reliability of the silicone-polyurethane copolymer (Optim™) lead insulation system. We sought to identify insulation defects and Optim-lead failures by systematic fluoroscopic and electrical assessment in a prospectively defined cohort of implantable cardioverter-defibrillator (ICD) patients.
RESULTS: Between July 2007 and December 2011, 234 patients were implanted with 413 optim-coated leads as part of an ICD system at a single centre. Fluoroscopic screening with high-resolution cine-fluoroscopy at 30 frames per second was offered to all patients. In addition, the electrical integrity of all implanted leads was assessed. Durata, Riata ST Optim, and low-voltage Optim leads were implanted in 199, 26, and 188 cases, respectively. During a total follow-up of 10 036 lead-months, there were 7 Optim-lead failures (defined as electrical malfunction resulting in lead replacement) and 31 deaths; no cases of electrical noises were encountered. The overall incidence of lead failure was 1.2 vs. 0.3 per 100 lead-years, for high- and low-voltage leads, respectively (P = 0.1). One hundred fifty-one patients agreed to undergo fluoroscopy screening; none of the 264 analysed Optim leads were found to have any fluoroscopically visible structural defects after an average of 31 months post-implant.
CONCLUSIONS: This study represents the first systematic screening of Optim-coated leads in a large unselected cohort of ICD patients. Over a 5-year period few lead failures were observed and normal fluoroscopic appearance was present in all patients.