Defibrillator Implantation Without Induction of Ventricular Fibrillation

Abstract

An increasing number of cardiac electrophysiologists are fortunate not to have endured the challenges of implanting monophasic waveform cardioverter-defibrillators (ICDs). With early technology, ICDs were routinely tested during the implantation procedure and then again before discharge, with a not-infrequent need for system revisions. With transvenous, high-output devices and biphasic shocks, the number of patients who have an inadequate defibrillation safety margin (DSM) has become so small that questions have been raised about the need for testing at all. However, given the fact that ICDs are designed to be potentially lifesaving, it is incumbent on physicians to obtain a high level of assurance that the device will work as designed if needed. It also should be noted that all clinical trials of ICD therapy for the prevention of sudden cardiac death incorporated testing for the adequacy of the DSM. Article p 2382 Despite the fact that we usually call the sequence of induction of ventricular fibrillation (VF) and defibrillation at different energies in the electrophysiology laboratory “defibrillation threshold testing,” it is, in fact, usually a DSM that is determined.1 Particularly with the typical protocol of 2 defibrillations at a minimum of 10 J below the maximum output of the device, a true probability curve for defibrillation success cannot be constructed. Regardless, this protocol is well accepted in practice. An alternative approach is upper limit of vulnerability testing, which closely correlates with the defibrillation threshold.2 This method requires only 1 initiation of VF, but strictly performed, multiple shocks may need to be delivered before VF is induced and the energy corresponding to the upper limit of vulnerability is determined. In the present issue of Circulation , Day et al3 present the results of the Arrhythmia Single Shock Defibrillation Threshold Testing Versus Upper Limit of Vulnerability: Risk Reduction Evaluation (ASSURE) …