Value of ventricular electrogram recordings in the diagnosis of arrhythmias precipitating electrical device shock therapy. An antitachycardia pacemaker-cardioverter-defibrillator that is capable of storing ventricular electrograms before and after delivery of device shock therapy was implanted in 16 patients. Three of the patients experienced out-of-hospital device shock therapy preceded by minimal symptoms. Although limitations of electrogram analysis exist and are discussed, careful analysis and registration of electrograms during all supraventricular and ventricular rhythms observed during in-hospital testing served as an important reference for subsequent arrhythmia diagnosis. By analyzing the electrogram rate and RR interval stability and configuration, a definitive diagnosis was established in all three patients (atrial fibrillation, polymorphic ventricular tachycardia and rate-sensing lead disruption, respectively). Thus, the ability to store ventricular electrograms before shock therapy represents a major advance in the management of patients who receive an electrical device to treat ventricular tachyarrhythmia. 