Use of iodine-123 metaiodobenzylguanidine myocardial imaging to predict the effectiveness of β-blocker therapy in patients with dilated cardiomyopathy

It is crucial to predict drug effectiveness in chronic disease, such as dilated cardiomyopathy (DCM), in which the left ventricular (LV) function might be improved by β-blocker therapy. As the functional improvement effected by β-blocker therapy takes more than 2 months, we investigated whether iodine-123 metaiodobenzylguanidine (123I-MIBG) imaging could be used to predict drug effectiveness. We studied 13 patients (11 men and two women; mean age, 43±13 years) with DCM and seven normal subjects (six men and one woman; mean age, 48±16 years). We obtained myocardial single-photon emission tomography (SPET) images 15 min and 4 h after administration of123I-MIBG (111 MBq). Studies were performed in the patients with DCM before and 1 and 3 months after the administration of metoprolol and in the normal subjects. We calculated the regional123I-MIBG washout rate (r-WR) in the SPET image, and the global123I-MIBG washout rate (g-WR) and heart-mediastinum activity ratio (H/M) using the anterior planar image. We classified patients into those showing a ≥5% increase in LV ejection fraction (LVEF) at 3 months compared with LVEF values before the treatment (group 1,n=7) and those showing a <5% increase in LVEF (group 11,n=6). In group I, the r-WR values at pretreatment and at 1 month and 3 months of treatment, respectively, were 36%±19%, 29%±14%* and 25%±13%* in the anterior segment, 39%±17%, 33%±17%** and 28%±17%* in the lateral segment, 36%±16%, 31%±14%* and 22%±12%** in the septal segment and 40%±11%, 37%±19% and 31%±18%* in the inferior segment; the g-WR was 45%±11%, 43%±10% and 34%±9%*, respectively (*P<0.05, **P<0.01 vs pretreatment). In group II, there were no significant changes in regional or global parameters during the 3-month period. In normal subjects, the r-WR values in each of the anterior, lateral, septal and inferior segments were significantly lower than those in groups I and II. These values were 18%±9%, 18%±15%, 20%±12% and 21%±15%, respectively. This study demonstrated that with regional assessment123I-MIBG SPET imaging can be used to predict the functional improvement of LVEF at 1 month of β-blocker therapy in patients with DCM.