Syncope is characterized by a transient loss of consciousness due to cerebral hypoperfusion, loss of postural tone, varying degrees of recall of events surrounding the syncopal spell, and absence of neurologic sequelae. Syncope is extremely common, constituting up to 3% of all visits to emergency departments and up to 5% to 6% of all hospital admissions. A carefully performed history review (including family history) and physical examination (Table 1) of the patient with syncope suggests a diagnosis in about 45% of patients. Many of these patients will have structural heart disease suggested or identified in this manner; in others, this initial evaluation will be unrevealing. Although in some cases the 12-lead electrocardiogram can establish or suggest a diagnosis (as in, for example, congenital complete atrioventricular block or long QT syndrome), in many instances the 12-lead electrocardiogram, chest radiograph, and echocardiogram can fail to indicate cardiac abnormalities (Table 2).
Goldschlager N, Epstein AE, Grubb BP, Olshansky B, Prystowsky E, Roberts WC, Scheinman MM, for the Practice Guidelines Subcommittee, North American Society of Pacing and Electrophysiology. Etiologic Considerations in the Patient With Syncope and an Apparently Normal Heart. Arch Intern Med. 2003;163(2):151–162. doi:10.1001/archinte.163.2.151