Iodine-123 metaiodobenzylguanidine scintigraphic assessment of the transplanted human heart: Evidence for late reinnervation

Objectives.This study attempted to determine whether cardiac sympathetic reinnervation occurs late after orthotopic heart transplantation.Background.Metaiodobenzylguanidine (MIBG) is taken up by myocardial sympathetic nerves. Iodine-123 (I-123) MIBG cardiac uptake reflects intact myocardial sympathetic innervation of the heart. Cardiac transplant recipients do not demonstrate I-123 MIBG cardiac uptake when studied <6 months from transplantation. However, physiologic and biochemical studies suggest that sympathetic reinnervation of the heart can occur >1 year after transplantation.Methods.We performed serial cardiac I-123 MIBG imaging in 23 cardiac transplant recipients early (<-1 year) and late (>1 year) after operation. In 16 subjects transmyocardial norepinephrine release was measured late after transplantation.Results.No subject had visible I-123 MIBG uptake on imaging <1 year after transplantation. However, 11 (48%) of 23 subjects developed visible cardiac I-123 MIBG uptake 1 to 2 years after transplantation. Only 3 (25%) of 12 subjects with a pretransplantation diagnosis of idiopathic cardiomyopathy demonstrated I-123 MIBG uptake compared with 8 (73%) of 11 with a pretransplantation diagnosis of ischemic or rheumatic heart disease (p = 0.04). All 10 subjects with a net myocardial release of norepinephrine had cardiac I-123 MIBG uptake; all 6 subjects without a net release of norepinephrine had no cardiac I-123 MIBG uptake.Conclusions.Sympathetic reinnervation of the transplanted human heart can occur >1 year after operation, as assessed by I-123 MIBG imaging and the transmyocardial release of norepinephrine. Reinnervation is less likely to occur in patients with a pretransplantation diagnosis of idiopathic cardiomyopathy than in those with other etiologies of congestive heart failure