Clinical Performance of the Implantable Cardioverter Defibrillator: Electrocardiographic Documentation of 101 Spontaneous Discharges

Records of 105 patients, who received an automatic implantable cardioverter defibrillator (AICD), were studied to investigate the causes of spontaneous AICD discharges and to correlate the symptoms with the arrhythmias triggering AICD discharges. During a follow-up period of 13 +/- 8 months, 46/105 (44%) patients had 566 spontaneous AICD discharges. A total of 101 discharges were documented with Holter monitoring in 23 patients. In this study group, there were 8 (8%) AICD discharges for 5 episodes of ventricular fibrillation, and 68 (67%) discharges for 63 episodes of sustained ventricular tachycardia. Patients lost consciousness in all episodes of ventricular fibrillation, but were symptomatic prior to only 36 (53%) discharges in ventricular tachycardia. Nonsustained ventricular tachycardia persisting for a period of 7.5 +/- 2 seconds resulted in 20 AICD discharges; patients were symptomatic prior to 13 (65%) discharges. Supraventricular tachycardias triggered three discharges. One patient had two spurious discharges during sinus rhythm. In conclusion, most of the spontaneous AICD discharges were appropriate for the detected rhythms, but only clinically appropriate for the management of arrhythmias in 75% of the cases. A significant portion of the patients with sustained or nonsustained ventricular tachycardias triggering AICD discharges were asymptomatic prior to discharge, which requires further assessment of the physiology of the arrhythmia as a component of the detection algorithm.