TREATMENT OF VENTRICULAR-TACHYCARDIA AND FIBRILLATION WITH LOW-ENERGY CARDIOVERSION BY THE IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR (ICD)

Programmable implantable cardioverter-defibrillators (ICD) with low energy capabilities for the treatment of ventricular tachycardia were introduced to increase patients acceptance and lengthen battery life. However, no data about efficacy and safety of low energy cardioversion with subsequent defibrillation in ventricular tachycardia and fibrillation are available. Nineteen of 42 patients with documented or inducible ventricular tachycardia before ICD implantation were studied. In all patients the effectiveness of low-energy cardioversion (less-than-or-equal-to 4 joules) with subsequent high-energy defibrillation was evaluated in monomorphic ventricular tachycardia and/or ventricular fibrillation. During predischarge programmed stimulation in 13/19 patients, a total of 32 monomorphic ventricular tachycardias occurred, and in only six patients could ventricular fibrillation be induced. A tachycardia-related efficacy of 69 % and patient-related efficacy of 46 % of the low-energy cardioversion less-than-or-equal-to 4 joules was observed. Ten tachycardias were accelerated to ventricular fibrillation or remained unchanged (n = 2). The second shock (energy > 17 joules) terminated seven arrhythmias, whereas a third (30 joules) shock or an external defibrillation (n = 2) was necessary for termination of the remaining three arrhythmias. After induction of ventricular fibrillation as the primary arrhythmia, the first (low-energy) shock terminated 2/16 episodes, whereas the second (high-energy) shock reverted ventricular fibrillation in 11/16 episodes. In one patient, a second high energy shock and in two patients external defibrillation was necessary for conversion of ventricular fibrillation. In one patient, an increase of the defibrillation threshold induced by amiodarone could be identified. In the remaining patients, ongoing arrhythmia and delay of definite therapy caused by low-energy cardioversion was responsible for defibrillation failure. During a follow-up of 13 +/- 7 months 23/29 tachycardia episodes were converted by low energy cardioversion. One patient died suddenly 11 months after ICD implantation due to electromechanical dissociation during idioventricular tachycardia (120 bpm). Sudden death was preceded by two episodes with low-energy cardioversion. Twenty-one months after ICD implantation, a second patient required cardiopulmonary resuscitation during ventricular fibrillation because the ICD failed to defibrillate. Hence, low-energy cardioversion for treatment of ventricular tachycardia may cause substantial risk for the patient and should not be programmed.