Syncope: about 40% had an unknown cause.

Clinical bottom line (level 2b)

  1. About 40% of patients with syncope had no identified cause, 30% had noncardiac causes and around 30% had cardiac causes.
  2. A third of patients had recurrent syncope.
  3. About a third of patients died; a tenth suddenly. Those with a cardiac cause for syncope were at greater risk.
Kapoor : Medicine 1990; 69 (3): 160-175
Expires October 2004

The study

Prospective cohort study with objective outcomes, adjusted for confounding factors, not validated in an independent set of patients.

Setting: emergency room, admissions and outpatients, university hospital, USA

433 patients (aged mean 56 years, 60% female) syncope- defined as sudden transient loss of consciousness associated with an inability to maintain postural tone that was not compatible with seizure, vertigo, dizziness, coma, shock or other status of altered consciousness

Excluded if
  • required pharmacologic or electrical cardioversion at initial presentation
  • tonic-clonic movements, post-ictal state or aura




    • Cox proportional hazards model was used to adjust for confounding factors.

    99.7 followed for mean 40 months
    Outcomes studied:
  • noncardiac cause
  • vasodepressor syncope
  • situational syncope
  • drug-induced syncope
  • orthostatic hypotension
  • conversion reaction
  • neurological cause: seizure
  • transient ischaemic attack
  • subclavian steal syndrome
  • cardiac cause
  • ventricular tachycardia
  • sick sinus syndrome
  • bradycardia
  • supraventricular tachycardia
  • complete heart block
  • Mobitz II atrioventricular block
  • pacemaker malfunction
  • carotid-sinus syncope
  • aortic stenosis
  • myocardial infarction
  • pulmonary embolism
  • unknown cause
  • death
  • sudden death occurred within 24 hours of onset of terminal symptoms
  • recurrent syncope

    • All patients underwent a basic evaluation:
      • complete history, physical and neurologic examination
      • baseline laboratory evaluation
      • 12-lead ECG
      • prolonged ECG monitoring of at least 24 hours
      • evaluation of clinical or historical findings suggestive of cause of syncope

    The evidence

    outcome time to outcome number of patients/total number %
    (95% CI)
    noncardiac cause mean 40 months 144/433 33%
    (29% to 38%)
    vasodepressor syncope mean 40 months 35/433 8.1%
    (5.5% to 11%)
    situational syncope mean 40 months 36/433 8.3%
    (5.7% to 11%)
    drug-induced syncope mean 40 months 9/433 2.1%
    (0.74% to 3.4%)
    orthostatic hypotension mean 40 months 43/433 9.9%
    (7.1% to 13%)
    conversion reaction mean 40 months 3/433 0.69%
    (0.0% to 1.5%)
    neurological cause: seizure mean 40 months 7/433 1.6%
    (0.43% to 2.8%)
    transient ischaemic attack mean 40 months 8/433 1.9%
    (0.58% to 3.1%)
    subclavian steal syndrome mean 40 months 2/433 0.46%
    (0.0% to 1.1%)
    cardiac cause mean 40 months 110/433 35%
    (21% to 30%)
    ventricular tachycardia mean 40 months 49/433 11%
    (8.3% to 14%)
    sick sinus syndrome mean 40 months 15/433 3.5%
    (1.7% to 5.2%)
    bradycardia mean 40 months 4/433 0.92%
    (0.02% to 1.8%)
    supraventricular tachycardia mean 40 months 5/433 1.2%
    (0.15% to 2.2%)
    complete heart block mean 40 months 6/433 1.4%
    (0.29% to 2.5%)
    Mobitz II atrioventricular block mean 40 months 2/433 0.46%
    (0.0% to 1.1%)
    pacemaker malfunction mean 40 months 3/433 0.69%
    (0.0% to 1.5%)
    carotid-sinus syncope mean 40 months 5/433 1.2%
    (0.15% to 2.2%)
    aortic stenosis mean 40 months 8/433 1.9%
    (0.58% to 3.1%)
    myocardial infarction mean 40 months 6/433 1.4%
    (0.29% to 2.5%)
    pulmonary embolism mean 40 months 2/433 0.46%
    (0.0% to 1.1%)
    unknown cause mean 40 months 179/433 41%
    (37% to 46%)
    death mean 40 months 116/433 27%
    (23% to 31%)
    sudden death mean 40 months 43/433 10%
    (7.1% to 13%)
    recurrent syncope mean 40 months 153/433 35%
    (31% to 40%)

    • After adjustment for age and co-morbid conditions, cardiac cause for syncope was a significant predictor of mortality at 5 years (RR = 2.2; 95% CI 1.45 to 3.22)
    • Recurrent syncope was not a significant predictor of mortality, after adjustment for age, prior medical history and comorbid conditions (RR = 1.4; 95% CI 0.9 to 2.1)

    Citation

    1. Kapoor WN, : Evaluation and outcome of patients with syncope. Medicine 1990; 69 (3): 160-175
    Contributor: Clare Wotton and Bob Phillips, October 2000
    Reviewer:

    Clinical Question.
    Patient syncope
    Intervention or Exposure prevalence
    Outcome causes