Vasovagal syncope.

BACKGROUND: Vasovagal syncope is the most common type of syncope and is one of the most difficult types to manage.
PURPOSE: This article reviews the status of mechanisms, diagnosis, and management of vasovagal syncope. DATA SOURCES: MEDLINE search for English-language and German-language articles on vasovagal syncope published up to June 1999. STUDY SELECTION: Case reports and series, clinical trials, research investigations, and review articles from peer-reviewed journals. DATA EXTRACTION: Findings were summarized and discussed individually. Summaries were made in table format. Statistical analysis of combined data was inappropriate because of differences among studies in patient selection, testing, and follow-up. DATA SYNTHESIS: The population of patients with vasovagal syncope is highly heterogeneous. Triggers of vasovagal syncope are likely to be protean, and many potential central and peripheral triggers have been identified. The specific mechanisms underlying the interactions among decreased preload, sympathetic and parasympathetic modulation, vasodilation, and cardioinhibition remain unknown. Tilt-table testing is a widely used diagnostic tool. The test results should be interpreted in the context of patients' clinical presentations and with an understanding of the sensitivity and specificity of the test. Assessment of therapeutic outcomes has been difficult, primarily because of patient heterogeneity, the large number of pharmacologic agents available for therapy, and the sporadic nature of the syndrome complex.
CONCLUSIONS: Vasovagal syncope is a common clinical syndrome that has complex and variable mechanisms and is difficult to manage. Advancements are being made in laboratory investigations of its triggering mechanisms. Randomized, controlled trials of pharmacologic and nonpharmacologic interventions are needed. Mechanism-targeted therapeutic trials may improve clinical outcomes.