Evaluation of β-blocker therapy in patients with dilated cardiomyopathy—Clinical meaning of iodine 123–metaiodobenzylguanidine myocardial single-photon emission computed tomography

Background Patients with heart failure show signs of cardiac sympathetic dysfunction such as elevation of blood norepinephrine (NE) level, as a result of reduction in the number of sympathetic nerves, decrease in myocardial NE content, accelerated NE turnover or spillover of NE, and NE reuptake disorder at sympathetic nerve endings. In dilated cardiomyopathy (DCM), iodine 123–metaiodobenzylguanidine (MIBG) used clinically as a tracer for imaging of the sympathetic function was found to be useful in evaluation of severity and prognosis. Methods and Results A total of 143 123I-MIBG myocardial single-photon emission computed tomography (SPECT) images were taken at successive intervals on 58 patients with DCM (mean age 54 ± 11 years), as well as before and after therapy to determine the severity of DCM and the therapeutic effect of β-blocker. Patients were divided into group A (n = 20), in which left ventricular ejection fraction (LVEF) improved by 10% or more within 6 months after the administration of β-blocker, and group B (n = 20), in which there was less than a 10% change in LVEF. After 123I-MIBG myocardial SPECT was taken, the washout rate for the entire left ventricle was calculated from early and delayed images. The estimations of extent score and severity score were based on the polar map prepared from short axial images taken from 17 healthy volunteers (mean age 35 ± 5 years). There was a significant correlation between LVEF and 123I-MIBG findings (extent score, severity score, and washout rate) obtained before and after β-blocker therapy. After β-blocker therapy, LVEF and 123I-MIBG findings significantly improved in group A. On the other hand, no change occurred in 123I-MIBG findings in group B. There was no significant difference in LVEF between group A (32.1% ± 8.0%) and group B (29.5% ± 7.2%). Also, there was no significant difference in the washout rate between group A (54.4% ± 10.9%) and group B (52.9% ± 7.2%). Comparison of 123I-MIBG images before β-blocker therapy of group A and group B revealed that the extent score (26.5 ± 16.0 vs 44.5 ± 21.1, respectively; P