Sympathetic reinnervation of the sinus node and exercise hemodynamics after cardiac transplantation

Background-Sympathetic cardiac reinnervation occurs variably after cardiac transplantation (CT) in humans. We hypothesized that sinus node reinnervati on would partially restore normal chronotropic response to exercise. Methods and Results-Thirteen recent CT recipients, 28 late CT recipients (g reater than or equal to 1 year after CT), and 20 control subjects were stud ied. Sinus node sympathetic reinnervation was determined by heart rate (HR) change after tyramine injection into the artery that perfused the sinus no de. HR changes of <5 and less than or equal to 5 bpm were defined, respecti vely, as denervation and marked reinnervation. During treadmill exercise, H R, blood pressure, and expired O-2 and CO2 were measured. All early transpl ant recipients exhibited features typical of denervation (basal HR, 88+/-2 bpm; peak HR, 132+/-4 bpm, peaking 1.8+/-0.3 minutes after exercise cessati on and slowly declining after exercise). A similar pattern was found in the 12 late transplant recipients with persistent sinus node denervation. Howe ver, in patients with marked reinnervation, exercise HR rose more (peak HR, 142+/-4 and 141+/-2 bpm), peaked earlier after cessation of exercise (0.7/-0.4 and 0.3+/-0.1 minute), and fell more rapidly. Exercise duration and m aximal oxygen consumption were not related significantly to reinnervation s tatus, but a trend existed for longer exercise time in markedly reinnervate d patients. Conclusions-The present studies suggest that sympathetic reinnervation of t he sinus node is accompanied by partial restoration of normal HR response t o exercise. Both maximal oxygen consumption and exercise duration were mark edly shorter in CT patients than in control subjects, and most of the diffe rence was not related to innervation status.