Syncope accounts for 1% of emergency department (ED) visits, yet few experience a serious adverse event (SAE). Two-thirds of syncope patients are transported to the ED by ambulance, placing considerable burden on emergency medical services (EMS), and many of these transports may be unnecessary. We estimated the proportion of syncope patients who fell into a low-risk category based on an ED diagnosis of vasovagal syncope and the absence of EMS intervention, hospitalization, or SAE.

We conducted a multicentre prospective cohort study enrolling adult syncope patients transported to the ED by ambulance over 13 months. We collected demographics and EMS interventions, and followed patients for 30 days to identify all SAE, including death, dysrhythmia, myocardial infarction, aortic dissection, pulmonary embolism, subarachnoid hemorrhage, significant hemorrhage, and related procedural interventions.

Of 990 (67.2%) patients transported to the ED by ambulance, 121 had EMS interventions, 137 suffered 30-day SAE, 393 (39.7%; 95%CI 36.6, 42.8) were deemed low risk, 41 patients with vasovagal syncope were lost to follow-up, and 298 patients were diagnosed with non-vasovagal syncope. During transport, 121 (12.2%; 95%CI 10.2, 14.3) patients underwent some EMS intervention, and 137 (14.6%; 95%CI 12.4, 16.9) suffered SAEs within 30 days.

About 40% of patients transported to the ED by ambulance are at low risk and may not benefit from paramedic care or transport to a hospital. A robust clinical decision tool would help identify patients safe for treat-and-release, diversion to alternative care, or rapid offload into low-acuity ED areas, potentially reducing EMS workload and cost.