Exercise-induced syncope and Holter-documented asystole in an endurance runner with moderate aortic stenosis

The case of an endurance runner with moderate aortic stenosis, who had recurrent syncope, is reported. A Holter recording during syncope revealed asystole lasting 57 s. Head-up tilt table test with isoproterenol was abnormal. No important abnormality was found in sinus or atrioventricular nodal functions. It was postulated that the syncope was due to exaggerated left ventricular baroreflex response, probably aggravated by the increased vagal tone in an endurance runner. The patient was given a beta-adrenergic blocker, and a pacemaker was implanted because of the profound cardio- inhibitory response. The arguments for this approach are discussed.