No abstract

T his article discusses the clinical application and potentiality of a relatively new methodology, which in large part uses noninvasive recordings and appears to provide a quantitative evaluation of the sympathovagal interaction modulating cardiovascular function.As a result of this methodology, pathophysiological conditions of paramount importance, such as arterial hypertension, myocardial ischemia, sudden cardiac death, and heart failure, for which the promoting or aggravating role of neural factors is still largely unknown, might soon undergo a novel scrutiny with practical implications. Physiological BackgroundIn addition to cardiac cycle, two main rhythmic events affect the circulation: respiration and vasomotion. The respiratory activity has long been known to be accompanied by arterial pressure' and heart period fluctuations, whereas the finding of slow arterial pressure oscillations (also referred to as Mayer waves), having a period of approximately 10 seconds, has been more elusive.2-4 On the other hand, rhythmic discharges in phase with respiration have been described in the sympathetic5 and vagal6,7 outflows; similarly, a slower rhythm in phase with vasomotor waves has been found in the sympathetic8,9 and vagal10 efferent discharges.The neural regulation of circulatory function is mainly effected through the interplay of the sympathetic and vagal outflows. In most physiological conditions, the activation of either outflow is accompanied by the inhibition of the other. The sympathovagal balance is tonically and phasically modulated by the interaction of at least three major factors: central neural integration, peripheral inhibitory reflex mechanisms (with negative feedback characteristics), and peripheral excitatory reflex mechanisms (with positive feedback characteristics)"1-'3 (Figure 1).

The Task Force was established by the Board of the European Society of Cardiology and co-sponsored by the North American Society of Pacing and Electrophysiology. It was organised jointly by the Working Groups on Arrhythmias and on Computers of Cardiology of the European Society of Cardiology. After exchanges of written views on the subject, the main meeting of a

Spectral analysis of HRV, using nu or LF-to-HF ratio, appears to be capable of providing a noninvasive quantitative evaluation of graded changes in the state of the sympathovagal balance.

During sympathetic activation in normal humans, there is a predominance in the LF oscillation of blood pressure, RR interval, and sympathetic nerve activity. During sympathetic inhibition, the HF component of cardiovascular variability predominates. This relationship is best seen when power spectral components are normalized for total power. Synchronous changes in the LF and HF rhythms of both RR interval and MSNA during different levels of sympathetic drive are suggestive of common central mechanisms governing both parasympathetic and sympathetic cardiovascular modulation.