Iodine 123-metaiodobenzylguanidine imaging reflect generalized sympathetic activation in patients with left...

Iodine 123-metaiodobenzylguanidine (MIBG) imaging has been used to assess cardiac sympathetic nerve abnormalities. To determine the role of MIBG imaging as a measure of generalized sympathetic nerve activity, MIBG imaging was evaluated with muscle sympathetic nerve activity (MSNA) and plasma norepinephrine (noradrenaline) level in patients with old myocardial infarction.

Myocardial MIBG scintigraphy, MSNA and plasma norepinephrine measurement were performed within 3 days in 35 patients with old myocardial infarction. Patients were divided into three groups according to their ejection fraction (EF); preserved (EF > or = 50%, 12 patients), intermediate (35% < EF < 50%, 13 patients), or depressed (EF < or = 35%, 10 patients). The heart to mediastinum (H/M) ratio was obtained 4 h after tracer injection from the chest anterior view image. MIBG washout rate was calculated from the early and delayed images. MSNA was recorded by microneurography.

Plasma norepinephrine level had weak negative correlations with early H/M ratio (r = 0.37, P<0.05) and delayed H/M ratio (r = 0.33, P<0.05), and a positive correlation with MIBG washout rate (r = 0.54, P<0.01). MSNA had weak negative correlations with early H/M ratio (r = 0.51, P<0.05) and delayed H/M ratio (r = 0.52, P<0.05). However, a strong correlation was found between MSNA and MIBG washout rate (r = 0.88, P<0.001). Despite no significant differences in plasma norepinephrine level and H/M ratio, patients with intermediate and depressed EF had higher MIBG washout rate and MSNA compared with those with preserved EF.

Increased in cardiac sympathetic nerve activity was associated with augmented sympathetic outflow of the skeletal muscle and hence, MIBG washout rate allow the assessment of general sympathetic nerve activity.