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Scientific letters
The relative contribution of the sinus and AV node to heart rate variability
  1. J O Schwab1,
  2. G Eichner2,
  3. H Schmitt3,
  4. S Weber4,
  5. M Coch4,
  6. B Waldecker4
  1. 1Department of Medicine – Cardiology, University of Bonn, Bonn, Germany
  2. 2Mathematical Institute, University of Giessen, Giessen, Germany
  3. 3Department of Medicine, Upstate University Medical Center, New York, USA
  4. 4Medizinische Klinik I, Universitaetsklinikum Giessen, Giessen, Germany
  1. Correspondence to:
    Joerg O Schwab, MD, Department of Medicine – Cardiology, University of Bonn, Sigmund-Freud-Str. 25, 53105 Bonn, Germany;
    joerg.schwab{at}ukb.uni-bonn.de

https://doi.org/10.1136/heart.89.3.337

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    In vivo hearts show fine beat to beat temporal variation during normal sinus rhythm (NSR). These changes have been termed “heart rate variability” (HRV). Accurate measurements of the beat to beat variation have enable investigators to determine the parameters of HRV.1 Routine assessment of HRV is derived from measurements of QRS-to-QRS (RR) intervals in the surface ECG. Activation of the heart starts with impulse formation in the sinus node and ends with excitation of the ventricular myocardium resulting in a QRS complex. Therefore, RR interval variation is likely to be the result of both sinus and atrioventricular (AV) node action. However, the relative contribution of each structure to HRV is not known.

    We hypothesised that, by calculating and comparing HRV during NSR and different pacing manoeuvres, we would be able to elucidate the relative contribution of both nodes to HRV. Therefore, we measured and compared HRV during AAI pacing (elimination of impulse formation in the sinus node) and VAT pacing (elimination of contribution of the AV node).

    METHODS

    Twenty consecutive patients were studied during diagnostic electrophysiological testing. Informed written consent was obtained from all subjects. A time period of 600 seconds was used to calculate HRV during each pacing manoeuvre and NSR. HRV of NSR was calculated twice before and after the pacing manoeuvres. AAI pacing was done at a pacing rate 15% faster than the sinus rate, and VAT pacing with an AV delay of 80 ms. For pacing manoeuvres, an external AV …

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