Clinical Methods to Assess Cardiac Sympathetic Innervation and Function

Abstract

Physiological, pharmacologic, neurochemical, and neuroimaging methods enable evaluation of cardiac sympathetic noradrenergic innervation and function in humans. This lecture provides examples of each approach. Low frequency power of heart rate variability, adjusted for total or high frequency power, has been used to examine cardiac sympathetic “tone” or “sympathovagal balance” but seems related more closely to baroreflex modulation of autonomic outflows than to the outflows themselves. Effects drugs on cardiac contractility can separate pre‐ from post‐ganglionic noradrenergic lesions. Measurement of norepinephrine and its main neuronal metabolite during infusion of tracer‐labeled norepinephrine provides a means to examine key aspects of cardiac sympathetic function in heart failure. Cardiac sympathetic imaging is very powerful for detecting dysfunction or loss of cardiac sympathetic nerves. Using this technology we described cardiac sympathetic denervation in Parkinson disease and obtained evidence for decreased vesicular uptake of intra‐neuronal catecholamines in Lewy body diseases. Clinical laboratory evaluation therefore can provide important clues to the pathophysiology of neurocardiologic disorders.