UNDERDETECTION OF VENTRICULAR-TACHYCARDIA BY ALGORITHMS TO ENHANCE SPECIFICITY IN A TIERED-THERAPY CARDIOVERTER-DEFIBRILLATOR

Objectives. The goal of this study was to determine the incidence and clinical significance of underdetection in 125 patients treated with a tiered therapy cardioverter defibrillator, the Medtronic PCD. Background. Underdetection, distinct from undersensing, is a unique, potential complication of new algorithms that enhance specificity in tiered therapy cardioverter defibrillators. These algorithms may delay or prevent recognition of ventricular tachy- cardia even though electrograms are sensed accurately and RR intervals meet the programmed interval criterion. Methods. Underdetection was defined as delay in detection >5 s at electrophysiologic study or symptomatic delay or detection failure at follow up of 15 +/- 8 months. Results. We identified six specific mechanisms of underdetection caused by algorithms to discriminate sustained ventricular tachycardia from sinus tachycardia, atrial fibrillation, ventricular fibrillation and nonsustained ventricular tachycardia. Underdetection caused detection delays in 13 (1.9%) of 677 induced ventricular tachyarrhythmia episodes in 12 patients (9.6%). During follow-up, underdetection occurred in 7 (9.9%) of 71 patients in whom ventricular tachycardia therapies were programmed. Failure to detect ventricular tachycardia occurred in 6 (0.6%) of 988 spontaneous ventricular tachycardia episodes in four patients (5.6%); 2 episodes required external cardioversion. After defibrillator reprogramming, underdetection did not occur. Conclusions. Algorithms to enhance specificity cause underdetection of ventricular tachycardia in a significant minority of patients with tiered-therapy cardioverter defibrillators. Optimal programming can minimize underdetection.