Unusual manifestations of severe sick sinus syndrome.

An extremely athletic 56-year-old male physician was found to have profound sinus bradycardia. His only symptom was markedly increased alertness while actively exercising. During pacemaker insertion he had an episode of prolonged sinus arrest terminated by a precordial thump. This case suggests that exercise can alter autonomic tone and increase cardiac output in sick sinus syndrome, causing improvement in possibly unrecognized, subtle, cerebral symptoms. It also appears that patients with profound sinus bradycardia should be given a substantial dose of atropine prior to pacemaker insertion in an effort to prevent prolonged sinus arrest.