Although we often think of syncope caused by acute pulmonary embolism (APE) in the setting of submassive or massive APE and right ventricular failure or shock (1,2), less massive APE may potentially cause syncope as well by triggering a vaso-vagal reflex (3).
For sure, a significant association between submassive or massive APE and syncope has been reported (1,2). More specifically, patients with syncope and APE may be more likely to have systolic blood pressure <90 mmHg, right ventricular dilation and right ventricular hypokinesis (1). Another study reported a higher rate of central embolism (83% vs 43%), right ventricular dysfunction (91% vs 68%) and troponin positivity (80% vs 39%), but not 30 day mortality (2).
In contrast, 1 study found that patients with syncope as a presenting symptom of APE did not show a more serious clinical picture (e.g. shock) than those without syncope (3), while another found EKG signs of acute right ventricle overload in only 25% of patients with syncope (4).
So while massive APEs may be associated with syncope, they don’t seem to be a prerequisite for this condition.
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References
1. Omar HR, Mirsaeidi M, Weinstock MB, et al. Syncope on presentation is a surrogate for submassive and massive acute pulmonary embolism. Am J Emerg Med 2018;36:297-300. https://www.ncbi.nlm.nih.gov/pubmed/29146419
2. Altinsoy B, Erboy F, Tanriverdi H, et al. Syncope as a presentation of acute pulmonary embolism. Ther Clin Risk Manag 2016;12:1023-28. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4930221/
3. Castelli R, Tarsia P, Tantardini G et al. Syncope in patients with pulmonary embolism: comparison between patients with syncope as the presenting symptom of pulmonary embolism and patients with pulmonary embolism without syncope. Vascular Medicine 2003;8:257-261. https://journals.sagepub.com/doi/abs/10.1191/1358863x03vm510oa
4. Miniati M, Cenci, Monti S, et al. Clinical presentation of acute pulmonary embolism: survey of 800 cases. PloS One 2012;7:e30891.
