Vasodepressor syncope.

Disorders of the autonomic nervous control mechanisms of heart rate and vascular tone may cause syncope. Notably these are carotid sinus and vasovagal syndromes. Knowledge of their aetiology is limited. Each presents cardioinhibition and vasodepression. Pacing offers benefit in cardioinhibition and the mode required is usually dual chamber (DDI) with rate hysteresis. Pacing is unable to control vasodepression. A wide variety of drugs has been proposed to combat the vasodepressor components of these syndromes but none is wholly successful.