DEMONSTRABLE CARDIAC REINNERVATION AFTER HUMAN HEART-TRANSPLANTATION BY CAROTID BAROREFLEX MODULATION OF RR INTERVAL

Background After heart transplantation, respiration-synchronous fluctu ations (0.18 to 0.35 Hz, high frequency [HF]) in RR interval may resul t from atrial stretch caused by changes in venous return, but slower f luctuations (0.03 to 0.15 Hz, low frequency [LF]) not due to respirati on suggest reinnervation. In normal subjects, sinusoidal neck suction selectively stimulates carotid baroreceptors and causes reflex oscilla tions of RR interval. Methods and Results To evaluate the presence of reinnervation, we measured the power of RR-LF and RR-HF in 26 heart tr ansplant recipients and 16 control subjects before and during sinusoid al neck suction at 0.1 Hz and 0.20 Hz (similar to but distinct from th at of controlled respiration, 0.25 Hz) and before and during administr ation of atropine or beta-blocker (esmolol hydrochloride) by spectral analysis. All transplant recipients showed small respiratory HF fluctu ations. Nonrespiratory LF fluctuations were present in 13 of 26 transp lant recipients and increased with months since transplantation (r=.53 , P<.01). HF neck suction induced a 0.20-Hz component in all 16 contro l subjects and none of the 26 transplant subjects. LF neck suction inc reased RR-LF (from 0.73+/-0.20 to 1.30+/-0.26 ln ms(2), P<.001), simil ar to but less than in control subjects (from 6.12+/-0.21 to 8.27+/-0. 21 ln ms(2), P<.001). Atropine reduced all fluctuations in control sub jects and blocked the HF increase caused by 0.20-Hz neck suction but n ot the LF increase during 0.10-Hz stimulation. Neck suction-induced ch anges in LF fluctuations persisted after administration of atropine in transplant recipients but were attenuated by esmolol hydrochloride, s uggesting sympathetic rather than vagal reinnervation. Conclusions The presence of baroreceptor-induced RR oscillations is evidence of funct ional, although incomplete, autonomic reinnervation.