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 pretransplantation diagnosis of idiopathic cardiomyopathy demonstrated I-123 MIBG uptake compared with 8 (73%) of 11 with pretransplantation diagnosis of ischemic or rheumatic heart disease (p = 0.04). All 10 subjects with net myocardial release of norepinephrine had cardiac I-123 MIBG uptake; all 6 subjects without 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 pretransplantation diagnosis of idiopathic cardiomyopathy than in those with other etiologies of congestive heart failure.