Independent autonomic modulation of sinus node and ventricular myocardium in healthy young men during sleep

Autonomic Modulation of Sinus Node and Ventricle, Introduction: The aim of this study was to investigate whether autonomic modulation of ventricular r epolarization may spontaneously differ from that of the sinoatrial node. Methods and Results: Onset of P waves, QRS complexes, and the apex and end of T waves were detected beat to beat in high-resolution ECGs from nine hea lthy young men during the night. There were time-dependent fluctuations in the QT/RR slopes of consecutive 5-minute segments that could not be explain ed by the mean RR cycle length of the respective segment. Because the varia bility found in QT intervals could not be explained by either possible effe cts of rate dependence or hysteresis, autonomic effects were obvious. Power spectral analysis was performed for consecutive 5-minute segments of PP an d QT tachograms, In a given subject, trends in the time course of low-frequ ency (LF) and high-frequency (HF) power in PP and QT often were similar, bu t they were quite different at other times. The mean LF/HF ratio for QT(end ) (0.75 +/- 0.1) was different from that of PP (1.8 +/- 0.2; P = 0.002), in dicating differences in sympathovagal balance at the different anatomic sit es. Furthermore, at a given mean heart rate, averaged QT intervals were dif ferent on a time scale of several minutes to hours. The QT/RR slope of 5-mi nute segments correlated significantly with the HF power of QT variability but not with that of PP variability, indicating effects of the autonomic ne rvous system on ventricular action potential restitution. Conclusion: These differences demonstrate that changes in sinus node automa ticity are not necessarily indicative of the autonomic control of ventricul ar myocardium.