Whole-body distribution of iodine 123 metaiodobenzylguanidine in hypertrophic cardiomyopathy: significance of its washout from the heart.

Whole-body distribution of iodine 123 metaiodobenzylguanidine (123I-mIBG) was evaluated in 27 patients with hypertrophic cardiomyopathy (HCM). At 1 and 4 h after injection, anterior and posterior whole-body images were obtained with a dual-headed, camera-computer system. Patients were classified into three groups based on the septal wall thickness as determined by echocardiography: group 1 consisted of 7 patients with less than or equal to 15 mm septal thickness, group 2 included 12 patients with 16-19 mm septal thickness, and group 3 included 6 patients with greater than or equal to 20 mm septal thickness. Although the myocardial mIBG uptakes at 1 h were similar among these groups (1.84% +/- 0.19%, 1.95% +/- 0.38%, 1.98% +/- 0.57%, respectively; NS), mIBG washout from the heart in group 3 was faster than in groups 1 and 2 (31.5% +/- 13.0% vs. 15.8% +/- 11.0% (group 1, P less than 0.05), 17.6% +/- 7.3% (group 2, P less than 0.01)). There was a significant positive correlation between mIBG washout from the heart and septal thickness, with correlation coefficient r = 0.52 (P less than 0.01). The liver, lung, parotid gland, spleen and skeletal muscle showed similar mIBG uptake and washout among the three groups. We conclude from these data that mIBG washout from the heart in HCM was faster in patients with severe hypertrophy than in patients with mild to moderate hypertrophy, and hence it may be a useful parameter for evaluating the severity of altered adrenergic innervation and activities.