SYMPATHETIC REINNERVATION AND HEART-RATE-VARIABILITY AFTER CARDIAC TRANSPLANTATION

Background-Heart rate variability is thought to measure autonomic modu lation, but the relation has never been demonstrated directly in human s. Aim-To test the hypothesis that increased low frequency heart rate variability reflects sympathetic reinnervation after cardiac transplan tation. Patients-24 cardiac transplant recipients at the time of routi ne surveillance coronary angiography two Or more years after cardiac t ransplantation, and 10 controls with normal coronary arteries undergoi ng angiography for investigation of chest pain. Setting-Regional cardi othoracic centre. Methods-Sympathetic effector function at the sinus n ode was assessed by measuring the fall in cycle length for two minutes after injection of tyramine to the artery supplying the sinus node. H eart rate variability was measured from three-minute RR interval seque nces at rest, during metronomic respiration, and before and after atro pine. Results-The logarithm of the low frequency component of heart ra te variability during metronomic respiration was linearly related to t he logarithm of the change in cycle length after injection of tyramine (R-2 = 0.28, P = 0.007). Absolute units more accurately reflected sym pathetic effector function than did normalised units or the ratio of l ow frequency to high frequency. Atropine did not affect high frequency heart rate variability in transplant recipients. Conclusions-The low frequency component of heart rate variability is directly related to s ympathetic reinnervation to the sinus node.