Age and gender differences in normal myocardial adrenergic neuronal function evaluated by iodine-123-MIBG imaging

Myocardial sympathetic nervous function has been evaluated with 123I-metaiodobenzylguanidine (MIBG) imaging in various cardiac diseases. Heterogeneous distribution of this tracer has been reported. This study was undertaken to assess whether such heterogeneity is related to age and gender.

Twenty-nine subjects (18 men, 11 women; age range, 21 to 79 yr; mean age 42 +/- 17 yr) with no cardiac disorders were studied. Early (15 min) and late (3-4 hr) planar images were taken, and SPECT images were also obtained 3-4 hr after MIBG injection (111 MBq). The mean counts of the whole heart, mediastinum and the anterior and inferior regions of the heart were obtained to calculate heart-to-mediastinum count ratios, myocardial washout rates and the inferior-to-anterior wall count ratio. On a bull's-eye map of the SPECT images, the left ventricular myocardium was divided into nine sectors to calculate the inferior-to-anterior wall count ratio.

There were no significant differences in the heart-to-mediastinum count ratio based on age or gender, but there was a significant inverse correlation between the inferior-to-anterior wall count ratio and age (r = -0.51 on late planar images and r = -0.69 on SPECT; p < 0.01 and p < 0.001, respectively). This correlation was valid in men (r = -0.74 and -0.83, respectively; both p < 0.001), but not in women (r = -0.25 and -0.34, respectively; p = ns).

Inferior wall uptake of MIBG decreased with age in individuals without cardiac diseases, especially men. Such age- and gender-related heterogeneity should be considered in the interpretation of MIBG images.