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 ms2, p  <  0.0001). Differences in the RR standard deviations persisted also on the last hundred beats (-100) (113  ±  54 versus 34  ±  17 ms2, 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.