Time- and frequency-domain analysis of beat to beat P-wave duration, PR interval and RR interval can predict asystole as form of syncope during head-up tilt

To seek possible differences in short-period temporal RR interval, P-wave and PR interval dispersion and spectral coherence in patients with a head-up tilt test positive for vasovagal syncope with or without prolonged asystole, severe symptoms and at high risk of trauma. We retrospectively reviewed 5 min ECG and blood pressure recordings obtained at baseline, at rest and during head-up tilt in 40 patients diagnosed as having recurrent vasovagal syncope confirmed at a head-up tilt test. We analysed autoregressive spectral power for all the ECG-derived variables, focusing on temporal P-wave and PR interval dispersion indexes as well as their spectral coherence calculated on the same 5 min recordings at rest and during tilt. ECG recordings obtained during tilt before syncope showed significantly lower P → PR spectral coherence and higher RR standard deviations in patients with tilt-induced asystole than in those without (0.567 ± 0.097 versus 0.670 ± 0.127, p : 0.010 and 84 ± 36 versus 46 ± 22 ms 2 , p < 0.0001). Differences in the RR standard deviations persisted also on the last hundred beats ( −100 ) (113 ± 54 versus 34 ± 17 ms 2 , p < 0.0001). Multiple regression analysis identified a significantly negative association between the maximum RR intervals and P → PR coherence at rest ( β : −0.3, p < 0.05) and positive association with RR −100 standard deviation during tilt-induced syncope ( β : 0.621, p < 0.001). P → PR spectral coherence could be used to assess the risk of prolonged asystole in patients with tilt-induced vasovagal syncope as well as as a possible surrogate for tilt-testing during these patients' follow-up.