Changes in cycle length at the onset of sustained tachycardias—importance for antitachycardiac pacing

Abstract

We analyzed changes in the spontaneous cycle length of sustained tachycardia during the first 100 beats after electrophysiologic initiation of sustained monomorphic ventricular tachycardia (VT), atrioventricular nodal tachycardia (AVNT), and circus movement tachycardia incorporating an accessory pathway (CMT). The mean cycle length of VT was 288 ± 75 msec, for AVNT this value was 388 ± 63 msec, and for CMT this value was 348 ± 76 msec. After initiation, in all three types of tachycardia changes in cycle length of up to ± 15% to 25% were observed. The changes in cycle length ranged from +12% to −18% in patients with VT, from +17% to −15% in patients with AVNT, and from +17% to −15% in patients with CMT. The mean percentage of changes during the first 100 beats of tachycardia was 7.0 ± 4.7% (VT), 9.5 ± 5.4% (AVNT) and 8.3 ± 5.4% (CMT). Patients with VT and AVNT showed both a constant increase or decrease or alteration of the rate of tachycardia. In no patient with CMT was there a constant decrease in cycle length after initiation. The mean time to achieve the maximal increase or decrease in cycle length was 13 ± 6 and 11 ± 9 seconds in patients with VT and 16 ± 3 and 20 ± 7 seconds in patients with AVNT. In patients with CMT, the mean time to achieve the maximal increase (10 ± 7 seconds) or decrease (20 ± 9 seconds) varied markedly. These results indicate that in all types of sustained tachycardia, changes in cycle length after initiation of the tachycardia are a common finding and have to be carefully considered when antitachycardia pacing systems are designed.