PO-05-144 WHERE DID THE JUICE GO ON MY ICD?

Abstract

Implantable cardioverter defibrillators (ICDs) have become standard therapeutic tools in patients with life-threatening ventricular arrhythmias. ICD leads are the most susceptible component and are still the weakest link of this system. In this case we present an interesting case of subtherapeutic shock delivery. A 58-year-old male with a history of syncope, ventricular tachycardia and prior dual chamber ICD placement presented to the outpatient clinic due to an episode of three ICD shocks noted on remote interrogation. The day of presentation, the patient mentions he was helping ring a cow and he used his arms to swing a lasso. As the device appropriately identified the ventricular event to have fallen in the VF zone, a standard algorithm of anti-tachycardia pacing followed by defibrillation was delivered. Interestingly however, during this episode two out of three shocks delivered had subtherapeutic energy delivery at 10.9 J and 7 J respectively as shown in figure 1. Upon review of the episode, the shock impedance was noted to be <20 ohms for both episodes with subtherapeutic energy delivery. At this point we were suspicious of a lead integrity issue resulting in a low shock impedance. All previous ICD checks prior to this episode were unremarkable. A device interrogation performed the following day showed no significant change in the shock impedance, however, did reveal a significant drop in the pace/sense impedance of both the right ventricular and right atrial leads from around 400 ohms to 200 ohms. A chest x-ray was ordered to evaluate for lead integrity issues but was unremarkable. NA Ultimately due to a significant drop in lead impedance and concern for issues with lead integrity, a decision was made for whole system extraction with a new system implantation. Our case is unique in that the first sign of an insulation breach or low lead impedance was subtherapeutic energy delivery for an event that occurred in the VF zone. These findings can be described by the Medtronic short circuit protection algorithm. Wherein, a low detected shock impedance will prevent further energy delivery due to concern for an open circuit and energy leakage. These findings were likely induced by the sudden jerking movements involved with ringing a cow. While this algorithm is specific to Medtronic, all major device companies have similar algorithms built when the device suspects an open circuit and this should be kept as a differential for subtherapeutic shock delivery.