Importance of abortive shock capability with electrogram storage in cardioverter-defibrillator devices

This study evaluates the ability of a third-generation cardioverter-defibrillator to abort energy delivery and the importance of electrogram storage in analyzing the aborted events.

In the Cadence Tiered Therapy Defibrillator, when a tachycardia satisfies detection criteria for cardioversion or defibrillation therapy, high voltage capacitors begin charging. The Cadence defibrillator continues monitoring the rhythm during charging and if the rate decreases to below the rate triggering therapy, charging is terminated. This event is registered as an aborted shock. The defibrillator also has the ability to store intracardiac electrogram recordings of the electrical events that precipitate device therapy or aborted shocks.

During a mean follow-up interval of 10 +/- 7 months, 55 aborted events were registered by the Cadence defibrillator in 18 of the 49 patients who received it. Thirty-two stored ventricular electrograms of events leading to aborted shocks were available for analysis in 15 patients.

Intracardiac electrogram recordings demonstrated the probable electrical events leading to these aborted shocks included nonsustained ventricular tachycardia (n = 10), nonsustained rapid polymorphic ventricular tachycardia/ventricular fibrillation (n = 2), atrial fibrillation (n = 5), supraventricular tachycardia (n = 2) and electrical noise (n = 13). Eleven patients had a therapeutic intervention initiated as a consequence of the diagnostic information provided by analysis of intracardiac electrogram recordings. Four of the 15 patients had no changes made. During a follow-up period of 9 +/- 5 months after therapy was altered, no patient had subsequent aborted shocks. Five patients have had seven appropriate shocks for sustained ventricular tachycardias.

The ability of Cadence defibrillator to continue tachycardia sensing during capacitor charging and to abort shock therapy for self-terminating events prevented unnecessary shocks in 18 (37%) of the 49 patients. Intracardiac electrogram recordings were critical for instituting appropriate therapy that may have prevented unnecessary device charging and inappropriate discharges.