Evaluation of beta-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 dy sfunction such as elevation of blood nor-epinephrine (NE) level, as a resul t of reduction in the number of sympathetic nerves, decrease in myocardial NE content, accelerated NE turnover or spillover of NE, and NE reuptake dis order 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 severi ty and prognosis. Methods and Results A total of 143 I-123-MIBG myocardial single-photon emis sion computed tomography (SPECT) images were taken at successive intervals on 58 patients with DCM (mean age 54 +/- 11 years), as well as before and a fter therapy to determine the severity of DCM and the therapeutic effect of beta -blocker. Patients were divided into group A (n = 20), in which left ventricular election fraction (LVEF) improved by 10% or more within 6 month s after the administration of beta -blocker, and group B (n = 20), in which there was less than a 10% change in LVEF. After I-123-MIBG myocardial SPEC T 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 f rom 17 healthy volunteers (mean age 35 +/- 5 years). There was a significan t correlation between LVEF and I-123-MIBG findings (extent score, severity score, and washout rate) obtained before and after beta -blocker therapy. A fter beta -blocker therapy, LVEF and I-123-MIBG findings significantly impr oved in group A. On the other hand, no change occurred in I-123-MIBG Findin gs 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 significa nt difference in the washout rate between group A (54.4% +/- 10.9%) and gro up B (52.9% a 7.2%). Comparison of I-123-MIBG images before beta -blocker t herapy of group A and group B revealed that the extent score (26.5 +/- 16.0 vs 44.5 +/- 21.1, respectively; P < .01 ) and the severity score (24.9 +/- 21.9 vs 58.2 +/- 35.2, respectively; P < .01) on the basis of the early I- 123-MIBG image was significantly lower for group A. Conclusions from the above findings, patients with DCM in which I-123-MIBG uptake is high on early images were expected to show improvement in cardiac function by beta -blocker therapy. Findings also suggested that I-123-MIBG was useful for examining the severity of DCM, determining the applicabilit y of beta -blocker therapy, estimating the maintenance dosage of beta -bloc ker, and evaluating prognosis.