Clinical experience with downsized lower energy output implantable cardioverter defibrillators

Background and study objective: Technical improvements in cardioverter defibrillators technology has resulted in decrease in can size coupled with improved electrodes technology. A decrease in maximum energy output allows further decrease in device size. The aim of this study was to evaluate the feasibility of a single lead transvenous implant employing a downsized cardioverter-defibrillator (volume 59 cm3), with a related decrease in maximum energy output (29–31 joules as stored energy and 25–27 joules as delivered energy). Methods and results: Fifty-five patients with ventricular tachyarrhythmias were enrolled in 17 European institutions for implantation. At implantation step-down defibrillation threshold (DFT) was determined and the device was implanted only if a safety margin ≥10 joules was maintained between DFT and maximum programmable output. Implantation was performed in 54 of the 55 referred patients (98%) in a single electrode-device configuration. Step-down DFT testing was performed in 44 patients (43 finally implanted) and DFT was 7.77±4.41 joules (range 3–20). In 20 of the tested patients (45%) DFT was ≤5 joules, in 26 patients (59%) was ≤8 joules and in 34 patients (77%) it was ≤10 joules. No differences were found in DFT comparing patients with left ventricular ejection fraction ≤ or >40% or patients treated or not with antiarrhythmic drugs or β-blockers. Mean implant duration was 85±34 min. Conclusions: Employing a downsized cardioverter defibrillator, successful transvenous implantation can be achieved in 98% of the patients, with maintenance of adequate defibrillation safety margins despite a reduction in stored energy to 29 joules. Implantation of the device with a lead-alone configuration allows short implant times and few perioperative complications.