Morphology discriminator feature for enhanced ventricular tachycardia discrimination in implantable cardioverter defibrillators

The Morphology Discriminator (MD) feature is an electrogram template matchi ng algorithm that intends to improve tachycardia discrimination in implanta ble cardioverter defibrillators (ICDs). The aim of this study was to evalua te the performance of this feature during spontaneously occurring ventricul ar and supraventricular tachyarrhythmias and exercise induced sinus tachyca rdia. Twenty-three patients (20 men, 3 women; mean age 54.3 +/- 13.8 years) with pectorally implanted Ventritex Contour MD, Angstrom MD, and Profile M D ICDs were studied. The stability of the acquired morphology template and performance of the algorithm during spontaneous tachyarrhythmias were evalu ated at follow-up. A treadmill exercise test was performed in 16 patients a long with continuous telemetric monitoring of matching scores. A satisfacto ry template could be acquired at baseline in 22 (96%) patients. Variations in electrogram morphology necessitated new template acquisition in seven (3 0%) patients at first follow-up (6-8 weeks postimplant). During a mean foll ow-up of 9.1 +/- 3.7 months, 56 ventricular tachycardia (VT) and 15 suprave ntricular tachycardia episodes (sinus tachycardia in two-thirds) in 11 pati ents were all appropriately discriminated by the MD feature. Exercise testi ng showed appropriate discrimination of sinus tachycardia in 15 (94%) of 16 patients. A common observation was postshock changes in electrogram morpho logy that resulted in transient mismatch with the template. In the recently introduced MD feature in ICDs has a high sensitivity for detection of VT a nd high specificity for rejection of sinus tachycardia. Postshock changes i n electrogram morphology have been observed that may cause inappropriate re detection. Marked variations of electrogram morphology over time may be a c oncern in some patients, especially during lead maturation.