Sympathetic Nervous Activation and Failure

Background Although heart rate variability (HRV) at 0.1 Hz has been proposed as a noninvasive clinical measure of cardiac sympathetic nerve firing, this premise has not been sufficiently validated by comparison with techniques such as microneurography and the measurement of norepinephrine spillover from the heart that more directly reflect presynaptic sympathetic activity. Methods and Results We compared the three techniques under conditions of effective cardiac sympathetic denervation, pure autonomic failure (n=4), dopamine 83-hydroxylase deficiency (n= 1), and after cardiac transplantation (n=9) as well as in the context of sympathetic nervous activation in cardiac failure (n= 15) and with aging (n= 10). Age-matched comparisons were made in each case with healthy individuals drawn from a pool of 52 volunteers. In pure autonomic failure and early after transplantation, cardiac norepinephrine spillover was negligible, and HRV was low. Late after transplantation, however, cardiac norepinephrine spillover returned to normal levels, and HRV remained low. In comparison to younger