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. Backgro und. Underdetection, distinct from undersensing, is a unique, potentia l complication of new algorithms that enhance specificity in tiered th erapy cardioverter defibrillators. These algorithms may delay or preve nt recognition of ventricular tachy- cardia even though electrograms a re sensed accurately and RR intervals meet the programmed interval cri terion. 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 sust ained ventricular tachycardia from sinus tachycardia, atrial fibrillat ion, ventricular fibrillation and nonsustained ventricular tachycardia . Underdetection caused detection delays in 13 (1.9%) of 677 induced v entricular tachyarrhythmia episodes in 12 patients (9.6%). During foll ow-up, underdetection occurred in 7 (9.9%) of 71 patients in whom vent ricular tachycardia therapies were programmed. Failure to detect ventr icular tachycardia occurred in 6 (0.6%) of 988 spontaneous ventricular tachycardia episodes in four patients (5.6%); 2 episodes required ext ernal cardioversion. After defibrillator reprogramming, underdetection did not occur. Conclusions. Algorithms to enhance specificity cause u nderdetection of ventricular tachycardia in a significant minority of patients with tiered-therapy cardioverter defibrillators. Optimal prog ramming can minimize underdetection.