Alternating myocardial sympathetic neural function of athlete's heart in professional cycle racers examined with iodine-123-MIBG myocardial scintigraphy

Myocardial sympathetic neural function in professional athletes who had the long-term tremendous cardiac load has not been fully investigated by myoca rdial iodine-123-metaiodobenzylguanidine (MIBG) uptake in comparison with p ower spectral analysis (PSA) in electrocardiography. Eleven male profession al cycle racers and age-matched 11 male healthy volunteers were enrolled in this study. The low frequency components in the power spectral density (LF ), the high frequency components in the power spectral density (HF), the LF /HF ratio and mean R-R interval were derived from PSA and time-domain analy sis of heart rate variability in electrocardiography. The mean heart-to-med iastinum uptake ratio (H/M ratio) of the MIBG uptake, in professional cycle racers was significantly lower than that in healthy volunteers (p < 0.01) and HF power in professional cycle racers was significantly higher than tha t in healthy volunteers (p < 0.05). In the group of professional cycle race rs, the H/M ratio showed a significant correlation with the R-R interval, a s indices of parasympathetic nerve activity (r = 0.80, p < 0.01), but not w ith the LF/HF ratio as an index of sympathetic nerve activity. These result s may indicate that parasympathetic nerve activity has an effect on MIBG up take in a cyclist's heart.