Pulmonary embolism occurs in approximately 1 in 6 patients who are hospitalized for a first episode of syncope, according to data published in the New England Journal of Medicine.

Paolo Prandoni, MD, PhD, from the Department of Cardiovascular Sciences, Vascular Medicine Unit, University of Padua, Italy, and colleagues performed a systematic workup for 560 patients (mean age: 76 years) admitted to 11 hospitals in Italy with a first episode of syncope to determine the prevalence of pulmonary embolism in this patient population.

The researchers measured the pretest clinical probability of pulmonary embolism with a simplified Wells score, which classifies pulmonary embolism as being likely or unlikely. They ruled out pulmonary embolism among patients who had a low pretest clinical probability and a negative D-dimer assay. Computed tomographic pulmonary angiography or ventilation-perfusion lung scanning was performed in patients who had a high pretest clinical probability, a positive D-dimer assay, or a combination of both.

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Pulmonary embolism was ruled out in 58.9% of patients with a low pretest clinical probability and a negative D-dimer assay. The researchers identified pulmonary embolism in 97 of the 230 remaining patients (42.2%). The prevalence rate of pulmonary embolism for the entire cohort was 17.3%.

The investigators also found evidence of an embolus in a main pulmonary or lobar artery or evidence of perfusion defects greater than 25% of the total area of both lungs in 61 patients. They identified a pulmonary embolism in 45 of 355 patients (23.7%) who had an alternative explanation for syncope and in 52 of 205 patients (25.4%) who did not have an explanation of syncope.

“The unexpectedly high prevalence of pulmonary embolism among our patients with syncope contrasts with that reported elsewhere,” the study authors wrote. “Our study involved consecutive patients, all of whom underwent a guidelines-based workup for pulmonary embolism, regardless of whether another explanation was suggested clinically. Our study also involved multiple centers, and the results across the centers were consistent, with the prevalence of pulmonary embolism ranging from 15 to 20% across centers.”


  1. Prandoni P, Lensing AWA, Prins MH, et al. Prevalence of pulmonary embolism among patients hospitalized for syncope. N Engl J Med. 2016; doi: 10.1056/NEJMoa1602172.