Copyright © 1996 by the European Society of Cardiology.
© The European Society of Cardiology
Cardiac arrhythmias
Spectral analysis of short term R-Tapex interval variability during sinus rhythm and fixed atrial rate
Centro Ricerche Cardiovascolari, CNR; Medicina Interna II e Cardiologia, Ospedale ‘L. Sacco’, Università degli Studi Milano
*Dipartimento di Automazione Industriale, Università di Brescia
Dipartimento di Elettronica, Politecnico di Milano Italy
Received 30 May 1995; accepted 20 September 1995.
Correspondence: Federico Lombardi, MD, FESC, Medicina Interna II Ospedale ‘L.Sacco’, Via GB Grassi 74, 20157 Milano, Italy
Abstract
Analysis of heart rate variability has been proven useful in stratifying post myocardial patients at risk and in evaluating autonomic dysfunction. Recently augmented inter-lead variability of the QT interval has been associated with increased mortality as a result of arrhythmia and proposed as a marker of dispersion of ventricular repolarization. As the duration of the QT interval is largely dependent upon the length of the preceding cardiac cycle it is tempting to analyse whether neural mechanisms might also directly exert additional modulation.
Using autoregressive algorithms we therefore analysed RR and R-Tapex interval variabilities in 15 normal subjects during sinus rhythm and in six patients with a fixed atrial rate. In controls mean R-Tapex interval and variance meas ured on the vector magnitude were, respectively, 245±6 ms and 5·1±0·7 ms2 Spectral analysis of R-Tapex indicated the presence of two spectral components which corresponded to the low and high frequency components of heart rate variability. In R-Tapex variability, high frequency (44±4 nu) was predominant over low frequency (29±4 nu). During controlled respiration, a manoeuvre associated with enhanced vagal modulation of sinus node, there was a further increase in high frequency (58±4 nu) whereas during tilt the low frequency component of R-Tapex variability became predominant (57±6 nu). In patients with a fixed atrial rate, variance was extremely low (3±0·9 ms2 and only a respiration-related high frequency component was recognizable in spectral analysis of RR and R-Tapex variabilities. This component was likely to depend upon mechanically induced changes in cardiac vector orientation.
These data indicate that during sinus rhythm short-term R-Tapex interval variability is characterized by the same rhythmical components present in RR variability. However, the presence of a very low variance and of only a high frequency component in patients in whom the physiological variability of sinus node is abolished by atrial pacing, suggests that neural modulatory mechanisms do not exert a direct effect on the length of the R-Tapex interval.
Key Words: Spectral analysis • sympathetic modulation • ventricular repolarization
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