There is the possibility that asymptomatic patients with Wollf-Parkinson-White syndrome develops fatal tachyarrhythmia and this is because such patients have well conducting accessory pathways for atrial fibrillation. In the control state, 13% of such asymptomatic patients was found to have short effective refractory period of antegrade conduction of accessory pathway. When isoproterenol was administered to simulate exercise loading, effective refractory period became shorter and more than half of patients belonged to the short effective refractory period group; 250 msec or shorter.
　Reciprocating tachycardia was also induced in some patients after isoproterenol. Such potential abnormality (or risk) can be disclosed only by electrophysiological study. Among paroxysmal supraventricular or ventricular tachycardias, there are many apparently healthy subjects and some attack of tachycardia was also associated with exercise or isoproterenol administration. Again, tachycardia can be diagnosed only after episode of an attack which may be fatal. These facts raise some limitations in the medical check or health examination to detect subjects with potential risk.

DESCENTE SPORTS SCIENCE Vol.10/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE