Kinetics of I-123-MIBG after acute myocardial infarction and reperfusion therapy

Metaiodobenzylguanidine (MIBG) washout from the myocardium has been thought to reflect sympathetic nerve tenet After acute myocardial infarction, howe ver, little is known about this parameter., The aim of this study was to de termine the significance of cardiac washout after myocardial infarction and early reperfusion by investigating MIBG kinetics and correlating those kin etics to clinical parameters. Methods: Sixty patients with acute myocardial infarction underwent planar MIBG and thallium imaging within 14 d of early reperfusion therapy. Global uptake and washout in myocardium, lungs and li ver were calculated from early and delayed images. A regional analysis of m yocardial kinetics in normal and infarcted myocardium and in an infarct bor der zone was alsb performed. Scintigraphic data were correlated with heart- rate variability as an electrophysiologic marker for autonomic tone and pre valence of arrhythmia in 52 patients. Heart-rate variability was described by time-domain indices from long-term electrocardiogram recordings. An age- matched normal control group for MIBG consisted of 10 individuals without h eart disease. Results: The infarct patients had preserved left-ventricular ejection fraction (LVEF) (56% +/- 17%). Although late myocardial uptake was expectedly lower in infarct patients compared with healthy volunteers (2.3 6 +/- 0.66 versus 2.80 +/- 0.55; P = 0.04), global myocardial MIBG washout was faster (11.6% +/- 7.9% versus 0.2% +/- 10.2%, respectively; P = 0.002). Lung and liver kinetics did not differ in patients and healthy volunteers. Global MIBG washout showed a-weak but significant positive correlation wit h the baseline heart rate (r = 0.28, P = 0.03) and an inverse correlation w ith LVEF (r = -0.28, P = 0.04). Washout was faster in a subgroup of 8 patie nts with reduced heart-rate variability (16.5% +/- 9.9% versus 10.3% +/- 8. 3%; P = 0.04). Regional analysis revealed similar degrees of enhanced MIBG washout for infarcted (low perfusion, low MIBG uptake) and remote myocardiu m (normal perfusion, high MIBG uptake), whereas the border zone (normal per fusion, low MIBG uptake) showed a nonsignificant trend toward higher washou t. Conclusion: After myocardial infarction, changes in MIBG kinetics occur specifically in the myocardium, whereas kinetics in lung and liver remain u nchanged. Even in patients with left-ventricular function preserved by repe rfusion therapy, MIBG washout is abnormal and globally increased, Enhanced washout:may reflect increased sympathetic nerve tone and represent increase d catecholamine turnover or impaired reuptake in the subacute phase of myoc ardial infarction.