DELIVERY OF NONCOMMITTED SHOCKS FOR NONSUSTAINED VENTRICULAR ARRHYTHMIAS BY A NEW IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR WITH ABORTIVE SHOCK CAPABILITY

Shock Delivery Despite Abortive Shock Capability. Introduction: To des cribe the delivery of noncommitted implantable cardioverter defibrilla tor (ICD) shocks despite self-termination of ventricular arrhythmias. Abortive shock capability should eliminate the delivery of shocks for self-terminating ventricular arrhythmias. The delivery of noncommitted shocks despite abortive shock capability is, therefore, unexpected an d previously unreported. Methods and Results: Among 118 patients who r eceived the Transvene nonthoracotomy lead system and the Jewel ICD (mo del 7219D), three patients (1.7%) experienced spurious, noncommitted s hocks for self-terminating arrhythmias, Only one detection zone (i.e., ventricular fibrillation) had been programmed in the defibrillator in each patient. Ln all three patients, the ventricular arrhythmias self -terminated during the charging period, One patient received seven sho cks during periods of asystole, and the other two patients received on e shock each. Two different mechanisms for shock delivery in this sett ing were identified: one occurring in the absence of electrical activi ty at the end of the bradycardia escape interval (i.e., associated wit h bradyarrhythmias), and the other when two sensed electrical events ( i.e., escape beats) occurred during the so-called ''synchronization'' window of the defibrillator. Conclusions: In rare patients with the Je wel defibrillator, shocks may be delivered for self-terminating arrhyt hmias despite abortive shock capability. Patients who are dependent up on pacing from their implanted defibrillator are at particular risk fo r shock in the aftermath of self-terminating ventricular arrhythmias. Defibrillator programming strategies aimed at eliminating or diminishi ng the incidence of this problem are discussed.