Sympathetic reinnervation of cardiac allografts evaluated by 123I-MIBG imaging

Some heart-transplant patients present with improved heart rate response to exercise and anginal pain suggesting reinnervation of allografts. Studies performed up to 5 y post-transplantation have suggested that reinnervation is a slow process that occurs only after 1 y post-transplantation. The purpose of this study was to evaluate the extent of sympathetic reinnervation in heart-transplant patients and its relation to cardiac function. Methods: We performed I-123-metaiodobenzylguanidine (MIBG) studies and rest/exercise radionuclide ventriculography in 31 heart-transplant patients 6 mo to 12 y post-transplantation. Intensity of myocardial MIBG uptake was quantified by a heart-to-mediastinum ratio (HMR), and the regional distribution of MIBG was determined by tomographic studies. Results: HMR correlated positively with time after transplantation (r = 0.607, P < 0.001). Patients studied from 2 to 12 y post-transplantation had an HMR significantly higher than patients studied before 2 y posttransplantation (1.62 +/- 0.2 versus 1.34 +/- 0.2, P < 0.05). Myocardial MIBG uptake was anterolateral in 16 patients, anterior in 3 and anterolateral and septal in 3. Myocardial MlBG uptake was absent in 9 patients. Vasculopathy developed in 8 patients, and 5 of them (63%) had decreased myocardial MIBG uptake. Peak filling rate was higher in patients studied from 2 to 12 y post-transplantation (2.7 +/- 0.8 end-diastolic Volume (EDV)/s versus 2.16 +/- 0.5 EDV/s, P = 0.02). Conclusion: Sympathetic reinnervation increases with time after heart transplantation and is seen more frequently after 2 y post-transplantation. Complete reinnervation of the transplanted heart does not occur even up to 12 y post-transplantation. Early vasculopathy may delay the process of sympathetic reinnervation.