Physiological Changes in Human Cardiac Sympathetic Innervation and Activity Assessed by ¹²³I-Metaiodobenzylguanidine (MIBG) Imaging

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Background Physiologic changes in the human sympathetic nervous system (SNS) may be associated with cardiovascular diseases, so the present study assessed the age and gender differences in global cardiac SNS in normal subjects. Methods and Results The 163 subjects (74 men, 89 women; age range 40-89 years) whose coronary arteriogram was normal, and who had no other cardiac or neurohormonal diseases, and no medication affecting the autonomic nervous system were included. All study subjects underwent metaiodobenzylguanidine imaging. Both initial and delayed heart-to-mediastinum (H/M) ratios had a significant gender difference and showed a progressive decrease with aging. In addition, the initial H/M ratio had a significant positive correlation with the delayed H/M ratio (r=0.89, P<0.0001). Females (50-59 years) demonstrated significantly higher delayed H/M ratio than males of the same age. After the age of 60, the delayed H/M ratio in females progressively decreased with aging, similar to males. As for the washout rate, both genders had a significantly progressive increase with aging. In addition, there was a significant decrease in the delayed H/M ratio in 10 females with surgical menopause compared with 15 age-matched females without surgical menopause. Conclusion Cardiac SNS appears to be regulated by various physiological factors. (Circ J 2009; 73: 310 - 315)