In this small study of 17 patients with an implantable cardioverter defibrillator (ICD), it was found that in patients undergoing a I-123 MIBG scan, a low uptake of MIBG was associated with an increase in need for defibrillator discharges. Comment: MIBG is a norepinephrine analog that is taken up by sympathetic nerve endings. After a myocardial infarction, those patients with myocardium where there is perfusion (by Tl-201) but denervation (a lack of MIBG uptake), are more likely to suffer ventricular arrhythmias. A common statistic obtained from MIBG scanning is the heart to mediastinal ratio. In this study, a HMR of > 1.54 was associated with no need for defibrillator discharges. In patients with heart failure, a HMR of less than about 1.5 (range = 1.2 to 1.74) is highly predictive of death. The current study combined findings from holter monitoring, specifically heart rate variability, and combined these results with MIBG scanning. The numbers involved in their study are too low to make any definite conclusion, but nonetheless this is an interesting study. [ J Nucl Cardiol 2003;10:121-31 ]