HEART RATE VARIABILITY ANALYSIS

Abstract

S109 Heart rate variability (HRV), as measured by changes in RR intervals, traditionally has been used to quantify autonomic tone and the relative contributions of the sympathetic and parasympathetic nervous systems. Decreases in HRV have been reported to be associated with disease states such as diabetes and myocardial dysfunction, and acute changes have been associated with severe ischemia and impending death. Acute changes in HRV are also associated with the administration of anesthetic agents since these agents may affect automaticity and conduction [1]. As presently determined, HRV simply assesses the overall RR interval. However, the SA node and AV node receive different innervation [2]. We sought to determine if, during a process designed to activate vagal reflexive (baroreceptor) mechanisms, alterations in atrial/atrioventricular conduction - as opposed to sinoatrial automaticity alone - may contribute to HRV. Methods: Five healthy volunteers (28-35 years old) were monitored with an automated noninvasive blood pressure device and an EKG which sampled at 250 Hz during a baseline period and then during an infusion of phenylephrine which was titrated to provide a 20% increase in mean arterial pressure (average rate 0.8 [micro sign]g/kg/min). The beat-to-beat PR and RR intervals then were determined during 60-sec artifact-free intervals in each subject. Results: The data indicate that, in addition to previously documented changes in the automaticity of the SA node, RR variability is also influenced by changes in atrial/atrioventricular conduction. As shown in Figure 1 and Figure 2, beat-to-beat percent change of PR (top) was less than that of RR (bottom), but nonetheless substantial.Figure 1Figure 2Conclusion: Time and frequency domain analyses of HRV as assessed by RR interval changes have traditionally been used to assess autonomic tone. We have shown that changes in autonomic outflow dynamically affect intra-atrial/AV nodal conduction as well as SA automaticity, suggesting that perhaps both PR and RR variability should be analyzed to gain a more complete assessment of autonomic tone and of the effects of disease states, anesthetic agents, and therapies on cardiac function.