Diagnosing syncope. Part 2: Unexplained syncope

Purpose: To review the literature on diagnostic testing in syncope that remains unexplained after initial clinical assessment. Data Sources: MEDLINE search. Study Selection: Published papers were selected if they addressed diagnostic testing in syncope, near syncope, or dizziness. Data Extraction: Studies were identified as population studies, referral studies, or case series. Data Synthesis: After a thorough history, physical examination, and electrocardiography, the cause of syncope remains undiagnosed in 50% of patients. In such patients, information may be derived from the results of carefully selected diagnostic tests, especially 1) electrophysiologic studies in patients with organic heart disease, 2) Holter monitoring or telemetry in patients known to have or suspected of having heart disease, 3) loop monitoring in patients with frequent events and normal hearts, 4) psychiatric evaluation in patients with frequent events and no injury, and 5) tilt-table testing in patients who have infrequent events or in whom vasovagal syncope is suspected. Hospitalization is indicated for high-risk patients, especially those with known heart disease and elderly patients. Conclusions: A flexible, focused approach is required to diagnose syncope. Features of the initial history and physical examination help guide diagnostic testing.