A 74-year-old man, recipient of a Virtuoso DR dual chamber defibrillator for ischemic cardiomyopathy and syncope due to VT, was seen in the ambulatory department after receiving several shocks in absence of symptoms.
Extracardiac signals are recognizable by the absence of their correlation with the intrinsic cardiac cycle. A <200 Ohms pacing and <25 Ohms shock impedance (not observed in this example) would increase the likelihood of a breakdown in lead insulation as the source of extracardiac signals. On the other hand, the normal impedance found in this case does not exclude this diagnosis. The anomaly may be a result of a sharp variation of the impedance curve not recorded by the device. Mobilization of the arm or shoulder can reproduce the extracardiac signals. In this example, the low impedance, combined with the sensing of <150 ms signal to signal cycles and, perhaps, the low amplitude of the signals, suggest a breakdown of insulation.
In this patient, 1) remote monitoring could enable an earlier diagnosis of the lead dysfunction, and 2) the only treatment is the implantation of a new RV lead.
Detection of 3 episodes of VF prompting the delivery of maximum energy shocks.
