Evaluation of a programming algorithm for the third tachycardia zone in a fourth-generation implantable cardioverter-defibrillator.

The clinical efficacy of electrical algorithms for termination of slowventricular tachycardia (VT) and ventricular fibrillation (VF) inimplantable cardioverter-defibrillators (ICDs) is well established. Suchalgorithms have not been equally well defined for fast VT reversion. Wereport the testing of a prospectively designed algorithm for ICDs to treatfast VT that is inherently less responsive to antitachycardia pacing thanslow VT. Fourth-generation ICD devices were programmed to threeprospectively defined tachycardia detection zones as follows: cyclelengths≤ ms for VF, 270-330 ms for fast VT, and >330 ms for slow VT.The initial selected therapy for the VF zone was a high-energy biphasicshock (>15J), while a 3- or 5-J biphasic shock was usually administered forfast VT, and antitachycardia pacing was initially attempted for slow VT.Initial therapy was followed by backup therapy with high-energy shocks.Twenty-eight patients, 24 of whom were males, all with organic heartdisease, with a mean age of 65 ± 9 years, received either a Medtronic7219D (23 patients), 7219C (2 patients), 7218SP1 (2 patients), or 7218C (1patient) ICD with a nonthoracotomy lead system. The defibrillation thresholdwas 10 ± 5 J. At predischarge electrophysiologic testing, a single 3-or 5-J shock terminated all episodes of fast VT tested. During a follow-upof 18 ± 9 months, there were four nonarrhythmic deaths. Fourteenpatients (50%) had a total of 21 VF, 44 fast VT, and 202 slow VTepisodes. Twenty-three of 24 (96%) VF, 33 of 39 (84%) fast VT,and 193 of 202 (95.5%) slow VT episodes were terminated with thefirst delivered therapy in each therapy algorithm (p=NS). The overallefficacy of the entire electrical therapy algorithm was 100% for VF,100% for fast VT, and 98% for slow VT episodes (p=NS).No patient experienced syncope or presyncope during fast VT or VF in thisstudy. We conclude that a third detection and therapy zone can besuccessfully programmed in ICDs to define a range of fast VT episodes thatcan be effectively terminated with lower energy cardioversion shocks withcomparable success and freedom from arrhythmic symptoms to electricaltherapies used for slow VT and VF..