Usefulness of 123I-MIBG scintigraphy for prediction of effect of β-blocker therapy in dilated cardiomyopathy

To determine whether 123I-MIBG (MIBG) scintigraphy is useful for predicting the effect of β-blocker therapy in patients with dilated cardiomyopathy (DCM), we studied MIBG scintigraphy in 11 controls and 9 patients with DCM before starting β-blocker therapy. First, initial and delayed heart-to-mediastinum ratios (H/M ratio) of MIBG activity in patients with DCM were significantly lower than those in 11 controls, respectively (initial H/M; 1.8±0.3 vs. 2.1±0.3, p<0.02, delayed H/M; 1.6±0.3 vs. 2.4±0.2, p<0.0001), and MIBG washout rate from the heart was significantly higher in patients than in controls (washout rate; 33±7% vs. 22±4%, p<0.0005). Second, β-blocker therapy improved LVEF in 7 patients (improved group), while it resulted in deterioration of heart failure, followed by death in 2 patients (deteriorated group). Although initial and delayed H/M ratios in the improved group were not significantly different from those in the deteriorated group, respectively, MIBG washout rate was significantly higher in the deteriorated group than in the improved group (45±8% vs. 30±3%, p=0.04). Our study suggests that DCM patients with markedly rapid MIBG clearance may be deteriorated by β-blocker therapy. In contrast, there were no differences in LVEF and plasma norepinephrine between improved and deteriorated groups. In conclusion, 123I-MIBG scintigraphy is useful for predicting the effects of β-blocker therapy in patients with DCM. (author)