PROGRAMMABLE VT DETECTION ENHANCEMENTS IN IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR THERAPY

This report describes the distribution of automatically measured value s of enhanced arrhythmia detection parameters such as ''rate stability '' and ''rate onset'' in various forms of spontaneous arrhythmia episo des in patients treated with a new, third-generation, tiered therapy i mplantable cardioverter defibrillator (ICD). The study population cons isted of 27 patients who received the Ventak PRxII cardioverter defibr illator, which provides extensive diagnostic options such as electrogr am storage capabilities, and the ability to store measured values of a dditional arrhythmia detection parameters such as rate stability and r ate onset during spontaneous arrhythmia episodes. During a follow-up p eriod of 11.1 +/- 5.2 months, this device defected 264 arrhythmia epis odes. The analysis of stored electrograms revealed 13 episodes of sin us tachycardia, 52 episodes of atrial tachyarrhythmias, and 201 episod es of monomorphic ventricular tachycardias (VTs). The mean measured va lues of rate stability and rate onset were: 2.2 +/- 0.9 msec, 0% in si nus tachycardias; 41.0 +/- 24.1 msec, 8.5% +/- 9.5% in atrial tachyarr hythmias; and 7.8 +/- 6.0 msec, 30.6% +/- 12.1% in monomorphic VTs. Th ere was a wide zone of overlapping measured values for rate stability and rate onset in ventricular and nonventricular rhythms. No episode o f VT showed a measured rate stability criterion > 35 msec. The subanal ysis of arrhythmia episodes presenting with a heart rate < 160 beats/m in revealed no episode of VT with a rate stability value > 24 msec. Th e calculated rate dependent specificities for these programmed rate st ability parameters in detecting VTs were 46.2% and 81.8%, respectively . The analysis of the rare onset algorithm revealed no comparable rela tionship between sensitivity and specificity in the detection of VTs. Additional arrhythmia detection algorithms such as rate stability and rate onset may contribute to a significant enhancement in the specific ity of ICD therapy.