Impedance rise, only clue to severe insulation damage in a transvenous single-lead AICD-system

We report a case of severe insulation damage 10 months after implantation of a fourth-generation single-lead implantable cardioverter defibrillator in a 45-year-old patient with dilative cardiomyopathy. The measured impedance was > 2000 Ohm and decreased to < 100 Ohm after slight pressure was applied to the device. All other parameters including intracardiac ECGs and markers were normal. Despite this delicate finding operative exploration revealed severe insulation damage of the pace-sense arm of the plug and insulation loss proximal to the distal coil of the lead.