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

Programmable implantable cardioverter-defibrillators (ICD) with low en ergy capabilities for the treatment of ventricular tachycardia were in troduced to increase patients acceptance and lengthen battery life. Ho wever, no data about efficacy and safety of low energy cardioversion w ith subsequent defibrillation in ventricular tachycardia and fibrillat ion are available. Nineteen of 42 patients with documented or inducibl e 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 eval uated in monomorphic ventricular tachycardia and/or ventricular fibril lation. During predischarge programmed stimulation in 13/19 patients, a total of 32 monomorphic ventricular tachycardias occurred, and in on ly six patients could ventricular fibrillation be induced. A tachycard ia-related efficacy of 69 % and patient-related efficacy of 46 % of th e low-energy cardioversion less-than-or-equal-to 4 joules was observed . Ten tachycardias were accelerated to ventricular fibrillation or rem ained unchanged (n = 2). The second shock (energy > 17 joules) termina ted seven arrhythmias, whereas a third (30 joules) shock or an externa l defibrillation (n = 2) was necessary for termination of the remainin g three arrhythmias. After induction of ventricular fibrillation as th e primary arrhythmia, the first (low-energy) shock terminated 2/16 epi sodes, whereas the second (high-energy) shock reverted ventricular fib rillation in 11/16 episodes. In one patient, a second high energy shoc k and in two patients external defibrillation was necessary for conver sion of ventricular fibrillation. In one patient, an increase of the d efibrillation threshold induced by amiodarone could be identified. In the remaining patients, ongoing arrhythmia and delay of definite thera py caused by low-energy cardioversion was responsible for defibrillati on failure. During a follow-up of 13 +/- 7 months 23/29 tachycardia ep isodes were converted by low energy cardioversion. One patient died su ddenly 11 months after ICD implantation due to electromechanical disso ciation during idioventricular tachycardia (120 bpm). Sudden death was preceded by two episodes with low-energy cardioversion. Twenty-one mo nths 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 vent ricular tachycardia may cause substantial risk for the patient and sho uld not be programmed.