Depressed haart rate variability (HRV) is a powerful marker of future adverse
events in post-myocardial infarction patients (pts). The aim of our multicenter
study is to assess the cardiac autonomic tone using HRV analysis prior to the
onset of spontaneous and ICD-treated ventricular tachyarrhythmias (VTA) in pts
with implanted defibrillators. We performed time and frequency (FFT) analyses
on 1024 ICD-stored sinus RR intervals (average duration 12 min) preceding
VTA and compared the resuits to periods without VTA (ctrl). All episodes had
<5% premature beats.
Resuits: 61 episodes of ICD-stored VTA (maar) cycle length: 304 ± 63 ms)
from 40 pts (maan age: 55 ± 15 y, maan EF: 33 ± 16%) ware analyzed. The
following observations ware made: a significant iricrease in haart rate (VTA vs
ctrl: 711 ± 157 vs 791 ± 171 ms, p < 0.001) and reduction in total HRV (RR
interval standard deviation VTA vs ctrl: 43 ± 31 vs 52 ± 24 ms, p < 0.04),
decreased very low-frequency (InVLFpw VTA vs ctrl: 10.6 ± 1.4 vs 11.5 ± 1.3
ms2 , p < 0.001) and low-frequency fluctuations (InLFpw VTA vs ctrl: 9.4 ± 1.6
vs 9.9 ± 1.4 ms2 , p < 0.01). These findings are consistent with a sustained
adrenergic stimulation with reduced modulation of sympathetic inputs to the
haart prior to VTA onset. Moreover, the finding of low amplitude fluctuations in
the high-frequency band suggest a chronic vagal inhibition with an additional
vagal withdrawal prior to the onset of VTA (InHFpw VTA vs ctrl: 8.4 ± 1.8 vs
9.1 ± 1.6 ms2 , p < 0.001).
Conclusion: the analysis of HRV in pts suffering Erom repetitive VTA shows
at control a depressed cardiac parasympathetic activity with additional vagal
withdrawal and sympathetic activation within the 12-min window prior to the
onset of potentially fatal VTA.