Further review of the case's figure disclosed appropriate VT detection, a high voltage impedance of 0 ohms, and an "aborted charge because of possible output circuit damage" on device interrogation after the event. Importantly, at the time of lead revision, "there was no fluoroscopic insulation breach and no obvious insulation breach in the pocket." Fluoroscopic screening of these leads, therefore, would not have detected pending lead failure. Further, as far as we can tell from the report, no antecedent device alerts were triggered before this event.A 60-year-old man had a single-chamber St.Jude Atlas VR defibrillator (St. Jude Medical, St. Paul, MN, USA) with a dual coil St. Jude Riata 7001 defibrillator lead (My note: this is actually a downsized, second-generation 7 Fr Riata ST model whose internal construct shares many similarities to St. Jude's currently-marketed third-generation 7 Fr Durata lead) placed in 2006 for primary prevention secondary to an ischemic cardiomyopathy and prior myocardial infarction. All routine device interrogations, both remote and in-office, had been normal with stable sensing amplitude, lead impedances, and capture thresholds. The device was programmed with two zones: a ventricular tachycardia (VT) zone from 340 ms (176 beats/min) and a ventricular fibrillation (VF) zone from 260 ms (231 beats/min). The VT zone had a morphology discriminator “on” with interval stability and sudden onset “passive.” Five years from implant, he presents with palpitations, light-headedness, and a single implantable cardioverter defibrillator (ICD) discharge. He has a friend drive him to the emergency room and is found to be in ventricular tachycardia over 200 beats/min. The ventricular tachycardia terminated with intravenous amiodarone bolus before need for external defibrillation. Device interrogation demonstrated an initial rhythm of atrial fibrillation with the appropriate detection of the onset of ventricular tachycardia with a cycle length of 245 ms, within the device’s VF zone (Fig. 1). Discriminators were not activated in the VF zone, but the morphology discriminator clearly demonstrates a failure of the electrogram signal to match the template (indicated by the “x” in the marker channel). After detection of 12 intervals (interval average) within the VF zone an episode is declared and a 25-Joule (693 V) shock is delivered, failing to restore sinus rhythm. No additional shocks are delivered despite appropriate redetection within the VF zone (Fig. 2). After a fifth detection, the device declares “no more therapies” with VT continuing indefinitely. Device interrogation in the emergency department reveals a pacing lead impedance was 465 ohms, signal amplitude 1.8 mV, and capture threshold 0.75 V at the rate of 0.5 ms. What is the differential diagnosis of failure to deliver appropriate therapy and why did this device fail to deliver more than a single shock?
This case report discloses several important issues. (1) High voltage coil damage in a 7Fr Riata ST lead can lead to either ineffective high voltage therapy delivery, withholding of further therapies, or both despite appropriate arrhythmia detection. St. Jude defibrillators are engineered to automatically withhold energy delivery in low high-voltage lead impedance situations to avoid excessive current delivery and device overheating in such circumstances (personal communication). (2) This failure mechanism, while curently very rare, may affect implanters decisions regarding whether or not to replace existing Riata leads irrespective of their performance characteristics and flouroscopic appearance at the time of battery change. Already there have been other reported high voltage failures in Riata leads with externalized wires. Some have advocated testing the high voltage leads as part of Riata lead follow-up to screen for this failure mechanism, especially since the therapeutic implications of high voltage lead failure is much more significant and difficult to detect than low-voltage (sensing lead) failures.
Perhaps most important for St. Jude going forward is how this case will influence implanters' choice of later-generation 7 Fr St. Jude defibrillator leads with their Optim coating but similarly-downsized inner lumen dimensions. I look forward to St. Jude's update of their Riata Communications website regarding these recently published case reports.
Marenco JP. "Failure to Deliver ICD Shocks after a Failed Discharge Despite Redetection of Rapid Ventricular Tachycardia? What Is the Cause?" PACE DOI: 10.1111/j.1540-8159.2012.03484.x Published online 21 July 2012.
For an excellent overview of the Riata ICD lead recall by Dr. Jay Schloss: http://cardiobrief.org/2012/02/22/guest-post-more-lessons-from-the-riata-icd-lead-recall/