The diagnosis of syncope poses unique challenges. Syncope has multiple etiologies, with most carrying benign prognoses, and a few less common causes carrying a risk of serious morbidity or death. The history at first glance carries few clues. Faced with this many patients are heavily investigated with tests known to be both useless and expensive. For these reasons considerable emphasis has been placed on developing evidence-based and quantitative histories that might distinguish among the main causes of syncope. Quantitative histories were first developed in populations of several hundred patients with definite diagnoses of various losses of consciousness. Their derivation and use mirror those of experienced clinicians. The first score - the Calgary Syncope Seizures Score - discriminates between epileptic convulsions and syncope with a sensitivity and specificity of about 94%. The second score, the Calgary Syncope Score for normal hearts, discriminates between vasovagal syncope and other causes of syncope with a sensitivity and specificity of about 90%. The third score, the Calgary Syncope Score for Structural Heart Disease, diagnoses ventricular tachycardia with 98% sensitivity and 71% specificity. It also accurately predicts serious arrhythmic outcomes and all cause death. Gaps in the accuracy of the second score have been identified and are being addressed. These scores are proving useful in the clinic, and as entry criteria for observation studies, genetic studies, and randomized clinical trials. A very simple score predicts vasovagal syncope recurrences, based on the number of faints in the preceding year. Work from several centres indicates that scores will distinguish among competing causes of syncope in select populations, such as those with bifascicular heart block, Brugada syndrome, and Long QT syndrome.
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