Cerebral Attacks due to Excessive Vagal Tone in Heavily Trained Persons

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Abstract
Cardiac syncope appeared in 4 heavily trained male patients with no history of cerebral or heart disease. Three were young athletes participating in competitive sport, 1 had trained intensively for years after poliomyelitis complicated by paraplegia. On admission all patients had sinus bradycardia; 1 had 2nd degree atrioventricular (AV) block at rest and 1 had transient sinoatrial (SA) block. His bundle studies demonstrated prolonged recovery time of the SA node (SAN) in 2, prolonged atrio-His interval in 3 and appearance of 2nd degree AV block at abnormally low pacing rates in 2. Refractory periods of the AV node (AVN), determined in 3, reached 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 of 3. The paraplegic patient and 1 who had 2nd degree AV block at rest, were given atropine, 0.5 mg 6 times a day, and all 3 reduced training activity considerably. After 6-12 mo. all patients were re-examined. None had cerebral symptoms or other complaints. They were in regular sinus rhythm and in excellent physical condition.