5 LIMITATIONS
First, the number of VT episodes per individual varies. Multilevel logistic regression was applied to estimate the odds ratio, since VT episodes were nested within individuals. Second, the VT evaluation period was limited to 10 RR intervals of 2 seconds after the onset, to simplify clinical usage. In some episodes, RR interval variations may have changed after the assessment. Third, we could not perform multivariate analysis for spontaneous termination without therapy since the number of target episodes was small. Fourth, these results may not hold true for slow VT because the programming of VT detection for each monitor and therapy zone was set at approximately 150 bpm in most episodes.