CARDIAC I-123 MIBG UPTAKE IS AFFECTED BY VARIABLE UPTAKE IN REFERENCEREGIONS - IMPLICATIONS FOR INTERPRETATION IN CLINICAL-STUDIES

Cardiac I-123-meta-iodobenzyl guanidine (I-123-MIBG) uptake, using the mediastinal region as a reference, is a predictor of outcome in heart failure. Constant uptake in a reference region is required when study ing the pharmacotherapeutic effects on the integrity of the cardiac ad renergic system. The aim of this study was to verify the assumption of constant uptake in reference regions and their relation to establishe d predictors of clinical outcome. Planar I-123-MIBG images were obtain ed in 28 patients with heart failure. The left ventricular ejection fr action correlated with the heart-to-mediastinum (H/M) ratio but not wi th myocardial I-123-MIBG uptake. Plasma noradrenaline correlated with the H/M ratio, the heart-to-lung (H/L) ratio, mediastinal uptake and a ge, but not with uptake in the myocardium and lung. Age correlated wit h the H/M ratio, H/L ratio, mediastinal uptake and lung uptake, but no t with myocardial uptake. In a regression model, after the inclusion o f age, the H/M ratio and mediastinal uptake were not related to noradr enaline. We conclude that changes in the H/M and H/L ratios are predom inantly due to confounding changes in mediastinal uptake or lung uptak e. In pharmacological intervention studies, myocardial I-123-MIBG upta ke should be assessed using single photon emission tomography or posit ron emission tomography, which do not rely on reference regions in med iastinum or lung.