2.2 Analysis of RR interval variability of VT
Of the 608 true VT/VF episodes mentioned above, only cycle lengths of ≥240 ms were considered as VT episodes in this study.
VT cycle length variability was determined based on a previous report; 10 RR intervals, from 2 seconds after the onset of VT on intracardiac electrograms, were obtained by automatic reading of the devices, with an accuracy of 10 ms.12 VT was judged as irregular if any difference between two successive beats was > 20 ms at least once in 10 RR intervals; otherwise it was classified as regular.12 When ATP was administered more than once in an episode, evaluation of the RR interval variability after the first therapy session was performed using the 10 RR intervals occurring immediately before any subsequent ATP therapy.