Abstract

Radiotracer kinetics were used to evaluate the activity of the sympathetic nervous system in 10 patients who had had unstable ischaemic symptoms within the previous 12 weeks and 10 with stable angina. Patients with recent unstable angina or angina after recent acute myocardial infarction had higher basal cardiac noradrenaline spillover than patients with stable angina. This represents a selective increase in cardiac sympathetic tone because whole body noradrenaline spillover was not significantly increased in the patients with recent unstable angina. Atrial pacing in 15 patients caused angina in 13 but did not significantly alter cardiac noradrenaline spillover in either patients with stable or unstable angina. The flow of plasma in the coronary sinus increased during pacing but because cardiac noradrenaline extraction decreased cardiac noradrenaline clearance was not significantly altered. Both whole body noradrenaline spillover and clearance were modestly increased by pacing, and arterial noradrenaline concentration was unchanged. Patients with recent symptoms of unstable ischaemia had a sustained and selective increase in cardiac efferent sympathetic tone compared with patients with stable angina, and angina induced by atrial pacing did not cause important cardiac sympathetic activation.