STABILITY - AN ICD DETECTION CRITERION FOR DISCRIMINATING ATRIAL-FIBRILLATION FROM VENTRICULAR-TACHYCARDIA

Introduction: The purpose of this study was to review a new implantabl e cardioverter defibrillator (ICD) detection criterion, stability, to determine if it can effectively discriminate rapid rhythms of atrial f ibrillation from ventricular tachycardia. Inappropriate shocks for rap id atrial fibrillation limit the acceptance of ICDs. The advent of an additional detection criterion, stability, has been postulated to be o f value in discriminating rapid atrial fibrillation, which may not war rant treatment, from ventricular tachycardia, which obviously does war rant therapy delivery. Methods and Results: Twenty-six patients were s tudied during 32 episodes of rapid atrial fibrillation and 24 episodes of monomorphic ventricular tachycardia below 220 beats/min. Each rhyt hm was repeatedly evaluated by the device at each of the seven stabili ty values available (8, 16, 23, 31, 39, 47, and 55 msec) and then clas sified as stable or unstable. Upon completion of this acute study, 32 ICD patients had the stability feature activated and were followed for proper arrhythmia treatment by the device. Using stability windows fr om 8 to 47 msec, all atrial fibrillation rhythms were appropriately cl assified as unstable. Three of 6 were classified correctly for the 55- msec window. All ventricular tachycardia rhythms were appropriately cl assified as stable for all stability windows from 8 to 55 msec. Clinic al follow-up confirmed appropriate therapy delivery when coupled with sustained rate duration (SRD). Thirty-two patients followed for 292 pa tient-months had no episodes of untreated ventricular tachycardia with 428 successfully classified as stable and treated. Only three episode s of suspected atrial fibrillation resulted in therapy delivery as the rhythm duration exceeded the SRD of 30 seconds. Conclusions: The CPI Ventak PRx ICD is highly reliable in appropriately classifying atrial fibrillation as unstable and monomorphic ventricular tachycardia as st able for most stability windows evaluating tachycardias below 220 beat s/min. As a result, when testing of atrial fibrillation is not possibl e, we recommend the routine programming of this stability feature at t he 31-msec window with an SRD of 30 seconds. The reliability of this d evice in discriminating atrial fibrillation from monomorphic ventricul ar tachycardia may have important clinical implications for other tier ed therapy ICDs with this feature as well as for future ICDs in develo pment.