Seventh Try's a Charm

Abstract

A 49-year-old man consulted our department 3 months after having several implantable cardioverter-defibrillator (ICD) shocks with subsequent syncope. A CRT-D device (Boston Scientific, Cognis 100-D) and a single-element subcutaneous array (Medtronic, model 6996 SQ) had been implanted 2 years previously for primary prevention of sudden cardiac death caused by symptomatic (New York Heart Association class III) nonischemic dilated cardiomyopathy with severely impaired left ventricular function (left ventricular ejection fraction, 10%) and a left bundle-branch block (QRS width, 176 ms). ICD interrogation revealed a prolonged episode of tachyarrhythmia starting with a fast monomorphic ventricular tachycardia (VT cycle length, 230 ms). Antitachycardia pacing (ATP) during charging led to discrete VT acceleration, followed by degeneration into ventricular fibrillation (VF) caused by the first 41-J shock. Another 5 ineffective ICD shocks were delivered. Eventually, the seventh shock was able to terminate VF (Figure 1). Chest radiographic examination revealed a dislodged SQ array requiring surgical revision (Figure 2). After positioning of a new SQ array, the intraoperative defibrillation threshold (DFT) was determined at 21 J. No perioperative complications occurred, and the patient could be discharged home after recovery. On follow-up 6 weeks later, the patient remained in stable condition with no arrhythmia recurrence. DiscussionOur current understanding conceives ventricular defibrillation as a probabilistic event that can be described by a sigmoidal probability-of-success curve. 1 Consequently, a true DFT above which defibrillation will always succeed cannot be defined. Instead, the goal of DFT testing is to determine an energy level that has a reasonable likelihood to terminate future ventricular tachyarrhythmias. An empirically established 10-J safety margin is then added to the DFT, expecting it to compensate for the probabilistic nature of defibrillation.The value of intraoperative DFT testing has been the topic of much debate. No standardized protocol exists, and clinical practice varies with each institution. With modern left pectoral high-output ICDs, the probability of successful DFT testing with a 10-J safety margin is estimated at 95%.However, it can be demonstrated with bayesian analysis that a high proportion of failed DFT tests with modern ICDs will be false-negative results possibly resulting in unnecessary revision. 1 Nevertheless, implant testing occasionally will correctly identify a system failure and indicate a necessary system revision that saves a patient's life-a circumstance that has been described as "the implanter's dilemma." 1 Because of a high DFT (Ͼ41 J in any shock vector configuration) at the time of implantation of the CRT-D device, a single-element subcutaneous array had been implanted in our patient to obtain an acceptable DFT. VF induced by T-wave shock had been successfully terminated twice at 21-J with a reversed wave form polarity (ie, RV coilϭanode, canϩSQ arrayϭcathode). The dev...

Fundamental Concepts in Electrophysiology in Cases and Reviews

“…32 Seventh try's a charm: Ventricular fibrillation terminated by the seventh shock. Li J, et al 33 Transvenous implantable defibrillators are highly effective in terminating ventricular tachycardia and fibrillation. Li et al describe a patient who required multiple shocks and review features associated with increased energy requirements for defibrillation.…”

“…Li et al describe a patient who required multiple shocks and review features associated with increased energy requirements for defibrillation. 33 Right coronary artery fistula as a result of delayed right atrial perforation by a passive fixation lead. Khoueiry G,et al 34 Cardiac perforation is an important risk of transvenous lead placement, that usually occurs acutely and often requires only lead repositioning, although tamponade and pericarditis can occur.…”