Syncope accounts for up to 2% of all emergency department (ED) visits and 6% of hospital admissions. Syncope is defined as a transient loss of consciousness accompanied by loss of postural tone, followed by complete resolution without intervention. Although syncope often is a benign vasovagal event, it may represent a life-threatening dysrhythmia or other condition, particularly in the elderly. Near-syncope, or feeling an impending loss of consciousness without syncope, may carry the same risk as syncope. In up to half of syncope cases presenting to the ED, there is no definite etiology established for the syncopal episode.
Cardiac-related syncope can be due to a structural cardiac lesion that limits the heart's ability to appropriately increase cardiac output. Examples of structural cardiac disease that can cause syncope include hypertrophic cardiomyopathy, aortic stenosis, pulmonary embolism, and myocardial infarction. Tachydysrhythmias such as ventricular tachycardia, torsades des pointes, and supraventricular tachycardia are common causes of syncope, but bradycardic syndromes may cause it as well. Syncope from a dysrhythmia is typically sudden and without prodrome. In young people, familial dysrhythmias such as Brugada or QT syndromes are uncommon but potentially serious causes of syncope.
Syncope is most commonly caused by vasovagal reflexes. Inappropriate vagal or sympathetic tone may lead to bradycardia, hypotension, or both. The hallmark of vasovagal syncope is a slow progressive prodrome of dizziness, nausea, pallor, diaphoresis, and diminished vision. The history should include a search for possible stimuli that are known to be associated with vasovagal syncope, such as phlebotomy, prolonged standing in a warm place, or fear. In situational syncope, the autonomic reflexive response results from a specific physical stimulus such as micturition, defecation, or extreme coughing. Carotid sinus hypersensitivity is another type of reflex-mediated syncope that is suggested by a history of presyncope when shaving, head-turning, or wearing of a constricting collar. This should be considered as a potential cause in elderly patients with recurrent syncope despite a negative cardiac workup.
Orthostatic syncope occurs when a sudden change in posture after recumbence is associated with inadequate compensatory increases in heart rate and peripheral vascular resistance. Orthostatic syncope can be due to decreased intravascular volume or poor vascular tone, which has a myriad of potential causes such as peripheral neuropathy, spinal cord injury, or medication side-effects. Since orthostatic changes can also be associated with other serious illnesses, alternative causes of syncope should still be considered even in the presence of orthostatic changes in blood pressure.
Neurologic syncope is rarely the primary cause of syncopal episodes, as patients with loss of consciousness with persistent neurological deficits or altered mental status do not meet the usual diagnostic criteria for syncope. When brainstem ischemia or vertebrobasilar insufficiency is the cause of syncope, patients will often report other posterior circulation deficits such as diplopia, vertigo, focal neurological deficits, or nausea associated with the syncopal episode. If patients report that upper ...