Serial assessment of denervated but viable myocardium following acute myocardial infarction in dogs using iodine-123 metaiodobenzylguanidine and thallium-201 chloride myocardial single photon emission tomography

Iodine-123 metaiodobenzylguanidine (mIBG) is taken up by sympathetic nerve endings, allowing scintigraphic imaging of myocardial sympathetic innervation. We investigated the denervated but viable canine myocardium after acute myocardial infarction by serial mIBG and thallium-201 chloride (²⁰¹TIC1) single photon emission tomography (SPET). In 12 dogs, acute myocardial infarction was produced by ligation of the left circumflex coronary artery. Images of mIBG and thallium SPET were obtained 6 h, 1, 4 and 6 weeks later. The defect size was calculated in percentage points from short axial views, and the ¹²³I-mIBG/²⁰¹TlCl ratio was determined. The uptake ratio was high at 1 week but gradually decreased. Three dogs were killed at each time point, and tissue samples were obtained from infarcted (both ²⁰¹TICl and ¹²³I-mIBG defects), peri-infarcted (¹²³I-mIBG defect and ²⁰¹TICl normal) and normal myocardium (both mIBG and ²⁰¹TIC1 normal). The changes in tissue content of noradrenaline in these lesions were measured. Noradrenaline tissue content gradually recovered in the peri-infarcted area. However, no recovery was noted in the infarcted area at 6 weeks. We conclude that sympathetic denervation and re-innervation occur following acute myocardial infarction, and the denervated but viable myocardium could be detected non-invasively by combined mIBG and thallium SPET. Offprint requests to: T. Nishimura