Clinical usefulness of 123I meta-iodobenzylguanidine imaging in predicting the effectiveness of beta blockers for patients with idiopathic dilated cardiomyopathy before and soon after treatment.

OBJECTIVE To investigate the value of iodine-123 meta-iodobenzylguanidine (MIBG) myocardial imaging for defining high risk patients with idiopathic dilated cardiomyopathy from among candidates for beta blocker treatment, and for predicting functional improvement of the left ventricle in the early stages of treatment. METHODS Echocardiographic indices, neurohormonal measurements, and myocardial MIBG distribution were assessed at baseline and after one month and three months of treatment in 27 patients with idiopathic dilated cardiomyopathy. Patients were classified into two groups, based on whether they reached a daily dose of > 20 mg of metoprolol without deterioration of heart failure at three months (group A, n = 20) or not (group B, n = 7). RESULTS There were no significant differences in the echocardiographic indices or neurohormonal activity at baseline between the two groups, but MIBG uptake was higher, and the washout rate lower, in group A than in group B. After one month, though there were no significant changes in echocardiographic and neurohormonal variables, the heart to mediastinal (H/M) ratio on the delayed image was increased in group A but not in group B. In group A, the degree of increase in the H/M ratio on the delayed image after one month was also correlated with the degree of reduction in plasma concentrations of noradrenaline after three months. CONCLUSIONS MIBG myocardial imaging may be useful for predicting the outcome of beta blocker treatment for heart failure patients with idiopathic dilated cardiomyopathy.