Although we often think of syncope caused by PE in the setting of right ventricular failure and shock, less serious PE can also cause syncope by triggering a vaso-vagal reflex as supported by several case reports (1). Further supporting the potential role of neurogenic cause of syncope in at least some cases of PE is a study demonstrating that patients with syncope as a presenting symptom of PE did not show a more serious clinical picture (e.g. shock) than those without syncope (1). In another study of the clinical presentation of acute PE, EKG signs of acute right ventricle overload was found in only 25% of patients with syncope (2). So we shouldn’t rule out PE as cause of syncope just because signs of hemodynamic compromise are absent.
1. 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.
2. Miniati M, Cenci, Monti S, et al. Clinical presentation of acute pulmonary embolism: survey of 800 cases. PloS One 2012;7:e30891.