The Autonomic Laboratory for Evaluating Syncope/Collapse: Investigations and Their Implications
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Syncope and collapse may result from a number of causes—neurological (autonomic and non-autonomic), cardiac, and metabolic. In addition, syncopal behaviour (loss of postural tone and unresponsiveness) may manifest in the form of a conversion disorder (functional non-syncopal collapse or pseudosyncope). There are many autonomic nervous system causes of syncope and they vary across the entire age spectrum. Intermittent and transient autonomic dysfunction, classed as autonomic mediated syncope (AMS), include those in all age groups (e.g., vasovagal syncope), in the >50’s (e.g., carotid sinus hypersensitivity/syndrome), and in different predisposing situations (situational syncope). An increasingly recognised new millennium autonomic cause of pre-syncopal symptoms (principally palpitations and dizziness) when upright is the postural tachycardia syndrome (PoTS), that can be associated with fainting. Many diseases and disorders within the brain, spinal cord, or periphery, although less common can result in autonomic damage and failure, often with orthostatic (postural) hypotension. Drugs also can cause or contribute to syncope. This chapter will provide an overview of the role of the autonomic laboratory in the evaluation of syncope/collapse, with the key aims being able to confirm (or exclude) an autonomic condition, to ascertain the cause or associated disorder contributing, and to determine additional factors that aid the management of autonomic mediated syncope/collapse.