Serial change of ¹²³I-Metaiodobenzylguanidine (MIBG) myocardial concentration in patients with dilated cardiomyopathy

¹²³I-Metaiodobenzylguanidine (MIBG) is expected to be useful agent for functional evaluation of the myocardial sympathetic innervation. The aim of this paper is to investigate serial change of ¹²³I-MIBG myocardial concentration in patients (pts) with dilated cardiomyopathy (DCM) as compared with ²⁰¹Tl upatke. Eight pts with DCM and six non-cardiac subjects (controls) were examined. After injection of 111 MBq (3 mCi) ²⁰¹Tl and 111 MBq (3 mCi) ¹²³I-MIBG, simultaneous myocardial imaging in anterior view was performed for both tracers in every 30-60 minutes during 5 hours (6 images). Myocardial uptake ratio per pixel to the injected dose was calculated for each tracer with background and cross-talk correction on each image. In pts with DCM, myocardial uptake ratio of ¹²³I-MIBG did not differ significantly from that of control. The washout of ¹²³I-MIBG from the myocardium, however, was significantly increased in pts with DCM as compared with controls. The % decrease of radioactivity in 3 hours was 46.9±13.8% in DCM, whereas 18.0±7.7% in controls (p<0.05). Especially, the decrease in the early phase (<1 hour) was significantly larger than controls (21.2±7.5% vs 5.3±4.0%, p<0.01). For ²⁰¹Tl, on the other hand, neither uptake ratio nor washout rate, differed significantly between the two. In conclusion, the rapid washout of ¹²?3I-MIBG in the early phase may reflect some sympathetic dysfunction in pts with DCM.