Clinical insights into syncope and presyncope during graded exercise testing: A 40,715-test experience

Syncope and presyncope during graded exercise testing (GXT) are uncommon but clinically important events that may reflect hemodynamic, autonomic, conductionrelated, or arrhythmic mechanisms. We reviewed all clinically significant syncope and presyncope occurring during non-imaging GXTs performed at Mayo Clinic between January 2006 and December 2010. All clinically significant events underwent detailed chart review incorporating exercise findings, clinical documentation, and longitudinal follow-up to systematically adjudicate the most likely mechanism. Among 40,715 GXTs performed in 33,885 unique patients, eight episodes of syncope (0.20 per 1000 tests) and five episodes of hemodynamically significant presyncope (0.12 per 1000 tests) required test termination. Five additional patients with transient lightheadedness without exercise-induced hypotension or clinically significant arrhythmia and five mechanical treadmill events without hemodynamic compromise were excluded from the primary analysis. Only two events were attributed to a documented arrhythmic mechanism. Most episodes were adjudicated as hemodynamic, autonomic/neurocardiogenic, or indeterminate. Syncope occurred predominantly in younger women and was generally associated with sinus rhythm and hypotensive or autonomic mechanisms, whereas presyncope occurred predominantly in older men with underlying cardiovascular disease, atrial arrhythmias, bradycardia, or chronotropic incompetence. Clinically significant syncope and presyncope during supervised GXT were exceedingly uncommon and were rarely associated with a documented arrhythmic mechanism. These findings support the safety of supervised exercise testing in appropriately monitored settings and improve understanding of the mechanisms underlying these uncommon exercise laboratory events.