Syncope is a common clinical presentation and establishing an etiology is often challenging. Pulmonary embolism (PE) has been thought to be an uncommon cause but a recent report suggested otherwise.

To establish the prevalence of PE in patients presenting with syncope to the emergency department (ED) and in hospitalized patients.

We systematically searched Medline, CINAHL, EMBASE, LILACS and Web of Science with relevant keywords and MeSH headings for syncope and PE. Inclusion criteria were patients presenting with syncope to ED or hospitalized due to syncope, and etiologies including PE.

Of 1329 titles and abstracts, 12 (other than Prandoni et al.) met inclusion criteria. Nine studies included 6608 ED patients and 3 included 975 hospitalized patients. The mean age was 62 (95% CI 54–69) for ED patients and 67 (95% CI 64–70) for hospitalized. The pooled estimate of PE prevalence in ED syncope patients was 0.8% (95% CI 0.5–1.3%, I²=0%). The pooled estimate of PE prevalence in hospitalized patients was 1.0% (95% CI 0.5–1.9%, I²=0). In contrast, the prevalence of PE in Prandoni et al. were 3.8% and 17.3% for ED and hospitalized patients respectively, both significantly higher than in other relevant studies (p<0.0001).

The estimated prevalence of PE in patients presenting with syncope is low. The Prandoni et al. estimates are significantly higher, suggesting a possible site effect, accrual bias, or investigation strategy. These and the prognostic impact of higher PE prevalence require understanding before changes in practice.