DIFFERENTIATION OF SINUS TACHYCARDIA FROM VENTRICULAR-TACHYCARDIA WITH 1/1-VENTRICULOATRIAL CONDUCTION IN DUAL-CHAMBER IMPLANTABLE CARDIOVERTER-DEFIBRILLATORS - FEASIBILITY OF A CRITERION BASED ON THE ATRIOVENTRICULAR INTERVAL

Tachycardia discrimination in future implantable cardioverter defibrillators (ICDs) is likely to be enhanced by the addition of an atrial sensing/pacing lead. However, differentiation of sinus tachycardia (ST) from ventricular tachycardia (VT) with 1:1 VA conduction will remain problematic. we assessed the use of the AV interval as a potential criterion for correctly differentiating ST from VT. Incremental V pacing at the right ventricular (RV) apex served as a ''VT'' model in each of 41 patients with 1:1 VA conduction to pacing cycle lengths less than or equal to 450 msec. High right atrial and RV apical electrograms during normal sinus rhythm (NSR) and during incremental V pacing were digitized (simulating ICD sensing). From these signals, AV interval versus pacing cycle length plots were computer generated to identify crossover cycle lengths, each defined as the cycle length at which the AV interval during V pacing equals the AV interval during NSR. At cycle lengths longer than the crossover value, the AV interval during ''VT'' exceeds the AV interval during NSR. In contrast, the AV interval during ST is physiologically shorter than the AV interval during NSR. Thus, ST can be readily differentiated from ''VT'' over a range of cycle lengths greater than the crossover value. The overall mean calculated crossover cycle length was 371 +/- 52 msec. In 11 patients paced multiple times, each crossover cycle length was reproducible (mean coefficient of variation was 1.2% +/- 0.9% per patient). AV intervals measured at the RV apex were also analyzed with incremental V pacing during catecholamine stimulation (isoproterenol, n = 5) and during alternate site ''VT'' (RV outflow tract [n = 8] and left ventricle [n = 2]). In all these cases, the new ''VT'' plots of AV interval versus pacing cycle length coincided with or fell to the left of those obtained during control RV apical pacing and recording (i.e., these AV interval values crossed the NSR baseline at cycle lengths less than or equal to the crossover cycle length). Thus, the cycle length range for recognizable differentiation of ST from ''VT'' remained valid. The data suggest that the described AV interval criterion relying on the crossover cycle length: (1) is a promising approach to improve differentiation of ST from relatively slow VTs with 1:1 VA conduction, and (2) can readily be automated in future dual chamber ICDs, given ifs computational simplicity.