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A 52 year old male patient with an implantable cardioverter/defibrillator (ICD) and a transvenous ICD lead (Endotac 0062, Guidant Inc, St Paul, Minnesota, USA), who presented with electrical lead desintegrity with inappropriate shock delivery, received a new transvenous ICD lead (Sprint 6942, Medtronic Inc, Minneapolis, Minnesota, USA) without extraction of the old lead. The implantation of the new ICD lead was complicated by difficulties in finding a position with satisfactory sensing and pacing properties and adequate defibrillation efficacy. The final lead position was in very close proximity to the distal coil of the former implanted lead (below left). During device based intraoperative testing high frequency noise signals were observed in the rate sensing channel after shock delivery of defibrillation energies from 31 J down to 6 J (below right, arrows). The sensing of these artefacts led to inappropriate redetection of ventricular fibrillation with consecutive shock delivery.
By reducing the maximum sensitivity level of the device (MINI IV, Guidant Inc) from 0.14 mV to 0.28 mV, sensing of induced ventricular fibrillation was not influenced but noise detection after shock delivery could be completely prevented.
Since 1990 12 patients underwent implantation of a second ICD lead without extraction of the old lead in our hospital. This is the first case of electrical interference of the two leads, which can be explained by their very close proximity.
Thus, if the implantation of a second ICD lead is necessary, positioning the leads too close to one another should be avoided. Post-shock intracardiac electrograms should be analysed carefully to exclude electrical interference between the two implanted leads.