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.