RR INTERVAL VARIABILITY IN IRREGULAR MONOMORPHIC VENTRICULAR-TACHYCARDIA AND ATRIAL-FIBRILLATION

Background Algorithms to reject irregular tachyarrhythmias are availab le in implantable cardioverter-defibrillator devices to discriminate v entricular tachycardia (VT) from atrial fibrillation (AF). The hazard of underdetection of irregular monomorphic VTs using these algorithms has not yet been fully evaluated. The purpose of this study was to det ermine the ability of a commonly used stability algorithm to reject AF and to correctly detect VT with a high RR interval variability. Metho ds and Results The electrophysiological studies from 232 patients with induced monomorphic VT (cycle length >250 ms) and 21 with AF were rev iewed. A preliminary analysis was performed to classify the VT episode s in irregular (successive RR differences >20 ms after 4 seconds from onset) or regular (otherwise). Three study groups were defined: group 1 (27 patients with irregular VT), group 2 (22 randomly selected patie nts with regular VT), and group 3 (21 patients with AE). A computer pr ogram analyzed the first 50 RR intervals of the induced VT (AF), reset ting a VT counter if the interval was greater than a tachycardia detec tion interval (TDI) or if its absolute difference with the preceding t hree beats exceeded a programmed stability value (STAB). The VT was de tected when the VT counter reached a preset number of intervals (NIDs) . Different combinations of TDI, STAB, and NID were analyzed. All VTs in group 2 were correctly detected. In contrast, up to 10 VTs from gro up 1 were not detected when high NIDs and low STAB parameters were pro grammed. With usual values (10 to 16 beats and 50 to 60 ms, respective ly), only 1 to 2 VTs remained undetected, but 20% to 50% had a detecti on delay >8 seconds. Undetected VTs were significantly slower than ear ly detected VTs for most STAB and NID combinations. With usual stabili ty and NID values, 10% to 20% of episodes of AF were inappropriately d etected. Changes in TDI had a small impact on sensitivity and specific ity when currently used values for stability were programmed. Conclusi ons An implantable cardioverter-defibrillator tachycardia detection al gorithm with a stability criterion of 50 to 60 ms and 12 to 14 RR inte rvals is able to detect over 90% of monomorphic irregular VTs. Neverth eless, significant VT detection delays may arise, and inappropriate de tection of AF cannot be totally prevented.