Cardiac sympathetic dysfunction in an athlete's heart detected by I-123-metaiodobenzylguanidine scintigraphy

The athlete's heart is commonly characterized by an increase in left ventri cular mass because of an increase in the left ventricular diastolic cavity dimensions or wall thickness or both. Endurance exercise also induces numer ous cardiovascular adaptations, including increased vagal tone. However, th e sympathetic function has not yet been precisely elucidated, so the presen t study evaluated cardiac sympathetic nerve function from metaiodobenzylgua nidine (MIBG) images obtained 15 and 180 min after the injection of I-123-M IBG at a dose of 111 MBq. The ratio of heart/mediastinum count (H/M) and th e washout rates of I-123-MIBG (WR) were calculated in 25 consecutive patien ts who were athletes (aged 52 +/- 13 years) and 23 normal subjects. There w as a significant difference in the H/M between the athletic and normal hear ts (2.3 +/-0.3 vs 2.6 +/-0.3, p<0.01, Scheffe's test), An increased WR was observed in the athletes group when compared with the normal group (34<plus /minus>4 vs 28 +/-3, p<0.01), and there was a significant correlation betwe en WR and the left ventricular mass index (r=0.578, p<0.01). Prolonged exer cise training may alter cardiac sympathetic nerve function, which can be de tected by MIBG imaging.