title: Stepwise evaluation of unexplained syncope in a large ambulatory population.
abstract: BACKGROUND
  Up to 60% of syncopal episodes remain unexplained. We report the results of a standardized, stepwise evaluation of patients referred to an ambulatory clinic for unexplained syncope.
  
  
  RESULTS
  We studied 939 consecutive patients referred for unexplained syncope, who underwent a standardized evaluation, including history, physical examination, electrocardiogram, head-up tilt testing (HUTT), carotid sinus massage (CSM) and hyperventilation testing (HYV). Echocardiogram and stress test were performed when underlying heart disease was initially suspected. Electrophysiological study (EPS) and implantable loop recorder (ILR) were used only in patients with underlying structural heart disease or major unexplained syncope. We identified a cause of syncope in 66% of patients, including 27% vasovagal, 14% psychogenic, 6% arrhythmias, and 6% hypotension. Noninvasive testing identified 92% and invasive testing an additional 8% of the causes. HUTT yielded 38%, CSM 28%, HYV 49%, EPS 22%, and ILR 56% of diagnoses. On average, patients with arrhythmic causes were older, had a lower functional capacity, longer P-wave duration, and presented with fewer prodromes than patients with vasovagal or psychogenic syncope.
  
  
  CONCLUSIONS
  A standardized stepwise evaluation emphasizing noninvasive tests yielded 2/3 of causes in patients referred to an ambulatory clinic for unexplained syncope. Neurally mediated and psychogenic mechanisms were behind >50% of episodes, while cardiac arrhythmias were uncommon. Sudden syncope, particularly in older patients with functional limitations or a prolonged P-wave, suggests an arrhythmic cause.
authors.affiliation: Unité des Troubles du Rythme, Service de Cardiologie, Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Juan F
authors.initials: JF
authors.lastname: Iglesias
authors.forename: Denis
authors.initials: D
authors.lastname: Graf
authors.forename: Andrei
authors.initials: A
authors.lastname: Forclaz
authors.forename: Juerg
authors.initials: J
authors.lastname: Schlaepfer
authors.forename: Martin
authors.initials: M
authors.lastname: Fromer
authors.forename: Etienne
authors.initials: E
authors.lastname: Pruvot
mesh_terms: D015984:Causality; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013557:Switzerland / Q000453:epidemiology; D013575:Syncope / Q000175:diagnosis* / Q000453:epidemiology*