THE CLINICAL SPECTRUM AND DIAGNOSIS OF SYNCOPE

Syncope is a symptom of a wide variety of underlying disorders. As suc h, it is a common and challenging clinical problem with different path ophysiologic mechanisms and prognostic implications. The clinical spec trum of etiologies of syncope includes disorders classified as cardiov ascular, noncardiovascular and unexplained. Generally, in patients in whom an initial diagnosis can be made. in the majority this is usually accomplished by a detailed history and thorough physical examination, that includes orthostatic vital signs and carotid sinus pressure. In the remaining cases, that can be as many as 50% of patients, the objec tive of subsequent noninvasive evaluation is to diagnose the cause of syncope, but also to stratify the patients in those with and those wit hout underlying structural heart disease. and selectively apply additi onal more specialized or invasive tests. Cardiac syncope. and particul arly when ventricular tachycardia is the cause, has the worst prognosi s with 20 to 30% one-year mortality. This realization prompts rigorous effort in diagnosing or excluding an arrhythmic cause and applying ag gressive therapy in such high risk patients. Thus, if after convention al noninvasive testing the etiology of syncope remains elusive in pati ents with underlying structural heart disease, electrophysiologic stud ies should be performed. Electrophysiologic studies identify a potenti al cause in up to two thirds of these patients. Treatment based on ele ctrophysiologic diagnoses is effective in preventing syncope recurrenc es but may also reduce cardiac mortality. In patients without structur al heart disease, head-up tilt testing has been very useful in diagnos ing neurally mediated syncope and guiding its therapy. Finally in pati ents with recurrent syncope which remains unexplained despite extensiv e testing. a loop monitor may record the rhythm during an episode and provide or exclude a diagnosis. The discussion in this article serves as a brief overview of the clinical spectrum of syncope and describes a stepwise and systematic approach to diagnosis of this common, albeit challenging, medical problem, with emphasis on recent developments in the syncope work-up.