br Case report An year old man with ischemic cardiomyopathy
Case report An 81-year-old man with ischemic cardiomyopathy underwent ICD smoothened for primary prevention in February 2007. The patient had never experienced spontaneous VF. A Riata™ 1570 dual-coiled lead (St. Jude Medical, Sylmar, CA) was passed through the left cephalic vein and connected to an Atlas™+ DR ICD (St. Jude Medical, Sylmar, CA). High-voltage lead impedance was 44Ω when a 5-Joule shock was inappropriately delivered due to sinus tachycardia 55 months earlier. Electrical lead parameters did not change before and after shock delivery. Over the preceding 10 months, all in-clinic routine device interrogations showed normal and stable sensing amplitudes (range 8.7–9.4mV), pacing lead impedances (range 335–370Ω), and capture thresholds (range 1.25–1.5V/1.0ms) (Fig. 1). Because this generator model did not allow for pain-free lead integrity testing, we did not examine high-voltage lead impedance except through the earlier inappropriately delivered shock. At 70 months post-implant follow-up, the patient was scheduled for ICD generator replacement because of battery depletion. Cine-fluoroscopy of the entire length of the lead conducted prior to exchanging the generator showed normal appearance without any apparent separation (Fig. 2). In order to detect possible lead-to-can abrasion, we manipulated the pocket during lead measurement, but found normal electrical lead parameters. We have been aware that defibrillation threshold (DFT) testing in this situation has been controversial [1,8]. However, as we were concerned about the possibility of lead malfunction despite an unremarkable interrogation showing a sensing amplitude of 8.7mV, pacing lead impedance of 335Ω, and a capture threshold of 1.5V/1.0ms, we attempted to deliver a 36-Joule test shock. The shock was delivered on the patient\'s intrinsic R-wave without inducing VF to see if it would unmask a potential insulation defect. After the first delivery, the device declared “possible output circuit damage.” Subsequent shock could not be delivered owing to a fault in the pulse generator or lead. High-voltage lead impedance was consistently below 20Ω, suggesting post-shock development of high-voltage cable abrasion. On the following day, the patient showed a significant decrease in R-wave amplitude (from 8.7mV to 6.1mV) despite a stable pacing impedance of 330Ω and pacing threshold of 1.25V/1.0ms (Fig. 1). In addition, no noise was recorded on the intra-cardiac monitor. A Protecta®XT DR ICD (Medtronic, Minneapolis, MN) was implanted and once again positioned within the subcutaneous pocket. No charring was apparent in the pocket area (Fig. 3). A new Sprint Quattro secure™ (Medtronic, Minneapolis, MN), bipolar, active-fixation defibrillator lead was implanted through the left subclavian vein and connected to the new generator. The old St. Jude Riata 1570 lead was not extracted, but the proximal portion of the lead was cut off and capped. On visual inspection, the extracted ICD can and cut-off ICD lead showed no charring. In addition, there was no obvious external abrasion at the proximal portion of the lead (Fig. 4). The device and lead were sent to the manufacturer for analysis, which yielded no additional information. After VF induction for DFT testing of the new device and lead, a 15-Joule shock resulted in successful defibrillation. High-voltage lead impedance was 41Ω.
Discussion This case demonstrates a potentially fatal inhibition of therapy because of the insulation breach. Electrical dysfunction of low-voltage circuitry can lead to oversensing with inappropriate shock and loss of capture, whereas damaged high-voltage circuitry can lead to short-circuiting with failure to defibrillate. Electrical shorts are particularly lethal because convergent evolution may occur abruptly during shock delivery, and thus failure to defibrillate may be the first and only sign of lead failure. Although numerous reports of a high incidence of insulation defects in Riata leads have been published [1–7], ours is a report of Riata lead failure with no abnormalities on interrogation and with no fluoroscopic evidence of insulation breach.