Cerebral attacks due to excessive vagal tone in heavily trained persons. A clinical and electrophysiologic study

Cardiac syncopes appeared in four heavily trained male patients without a history of cerebral or heart disease. Three were young athletes participating in competitive sport, one had trained intensively for years after poliomyelitis complicated by paraplegia. On admission all patients had sinus bradycardia; one had second degree atrioventricular (AV) block at rest, and one had transient sinoatrial (SA) block. His bundle studies demonstrated prolonged recovery time of the SA node (SAN) in two, prolonged atrio-His interval in three, and appearance of second degree AV block at abnormally low pacing rates in two. Refractory periods of the AV node (AVN), determined in three, tended to reach the upper limit of the normal range. The dysfunction of SAN and AVN was temporarily abolished in all patients by 1 mg of atropine i.v., and disappeared during exercise test, which was done by the three young athletes. The patient with paraplegia and one of the young athletes, who had second degree AV block at rest, were given atropine, 0.5 mg six times a day, and all three active sportsmen reduced training activity considerably. After 6--12 months all patients were re-examined. None had cerebral symptoms or other complaints. They were in regular sinus rhythm and in excellent physical condition.