USE OF I-123 METAIODOBENTYLGUANIDINE MYOCARDIAL IMAGING TO PREDICT THE EFFECTIVENESS OF BETA-BLOCKER THERAPY IN PATIENTS WITH DILATED CARDIOMYOPATHY

It is crucial to predict drug effectiveness in chronic disease, such a s dilated cardiomyopathy (DCM), in which the left ventricular (LV) fun ction might be improved by beta-blocker therapy. As the functional imp rovement effected by beta-blocker therapy takes more than 2 months, we investigated whether iodine-123 metaiodobenzylguanidine (I-123-MIBG) imaging could be used to predict drug effectiveness. We studied 13 pat ients (11 men and two women; mean age, 43+/-13 years) with DCM and sev en normal subjects (six men and one woman; mean age, 48+/-16 years). W e obtained myocardial single-photon emission tomography (SPET) images 15 min and 4 h after administration of I-123-MIBG (111 MBq). Studies w ere performed in the patients with DCM before and 1 and 3 months after the administration of metoprolol and in the normal subjects. We calcu lated the regional I-123-MIBG washout rate (r-WR) in the SPET image, a nd the global I-123-MIBG washout rate (g-WR) and heart-mediastinum act ivity ratio (H/M) using the anterior planar image. We classified patie nts into those showing a greater than or equal to 5% increase in LV ej ection fraction (LVEF) at 3 months compared with LVEF values before th e treatment (group I, n=7) and those showing a <5% increase in LVEF (g roup II, n=6). In group I, the r-WR values at pretreatment and at 1 mo nth and 3 months of treatment, respectively, were 36%+/-19%, 29%+/-14% and 25%+/-13%* in the anterior segment, 39%+/-17%, 33%+/-17%** and 2 8%+/-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%, re spectively (P<0.05, **P<0.01 vs pretreatment). In group II, there wer e no significant changes in regional or global parameters during the 3 -month period. In normal subjects, the r-WR values in each of the ante rior, lateral, septal and inferior segments were significantly lower t han those in groups I and II. These values were 18%+/-9%, 18%+/-15%, 2 0%+/-12% and 21%+/-15%, respectively. This study demonstrated that wit h regional assessment I-123-MIBG SPET imaging can be used to predict t he functional improvement of LVEF at 1 month of beta-blocker therapy i n patients with DCM.