Syncope—Are We Missing an Important Cause?

Nurses examining an ill senior patient during a home visit.

By Adam Schaffer, MD
April 19, 2017

As a hospitalist, syncope is an admitting diagnosis that I consider a challenge. Syncope is a presentation that we see frequently, and so can start to seem routine. Though published estimates of the causes of syncope vary, most have shown that the etiologies of syncope that we are most concerned about—such as bradyarrhythmias or ventricular tachyarrhythmias—make up a minority of cases. In one retrospective cohort study of the causes of syncope in 987 patients who were referred for cardiac electrophysiology evaluation, bradyarrhythmias accounted for 13.6% of cases and ventricular tachyarrhythmias accounted for 12.1% of cases.1  Vasovagal syncope, among the more benign etiologies of syncope, accounted for 47.0% of cases. These numbers come from a population of patients who were referred for electrophysiology evaluation, and so it is very possible that cardiac arrhythmias were overrepresented in this population compared to an unselected group of patients. Thus clinicians who evaluate syncope patients need to remain vigilant in order to correctly identify the minority of syncope patients who have a potentially serious cause of their syncopal episode.

There have been two recent important developments in the published syncope literature. An ACC/AHA/HRS Guideline for the Evaluation and Management of Patients with Syncope was issued in 2017.2  Among the helpful features of this guideline is a list of characteristics more often associated with cardiac causes of syncope—such as older age, brief or absent prodrome, syncope during exertion, or a small number of syncopal episodes (one or two).  Though this list and guideline are helpful, it still comes down to clinical judgment in deciding who is more likely to have a cardiac cause of syncope and so warrants a more extensive workup, such as with extended cardiac rhythm monitoring, cardiac echo, and electrophysiology referral.

One cause of syncope that was, until recently, not given prominent consideration is pulmonary embolism (PE). Indeed, PE is discussed only a handful of times in the main text of the recent syncope guideline. However, the possibility that PE is an underappreciated cause of syncope was raised by an article published in the October 20, 2016, issue of NEJM by Prandoni et al.3 Including 560 patients admitted to 11 Italian hospitals for an initial episode of syncope, this study examined how often PE was present. A decision rule using the dichotomized Wells score and negative D-dimer testing was used to exclude PE in 58.9% of patients. The remaining 229 patients, with high pretest probability (Wells score >4), positive D dimer or both, underwent further testing, either with a PE-protocol chest CT (78.6% of patients) or ventilation–perfusion scanning (21.4% of patients). Of these 229 syncope patients who underwent radiographic evaluation for PE, 97 (42.4%) were diagnosed with a PE, a percentage that is surprisingly high. Perhaps most disconcertingly, among patients who were felt to have an alternative explanation for their syncope, 12.7% of them were nonetheless diagnosed with a PE.

This study that has already changed how I approach patients with syncope.  Now, when I am evaluating a patient with syncope and am considering the possibility of a PE, I am more likely to go ahead an order a PE CT so as to definitively assess for this possibility.


1. Chen LY, Gersh BJ, Hodge DO, Wieling W, Hammill SC, Shen W-K. Prevalence and Clinical Outcomes of Patients with Multiple Potential Causes of Syncope. Mayo Clinic Proceedings. 2003;78(4):414-420.

2.  Shen W-K, Sheldon RS, Benditt DG, et al. 2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients with Syncope: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines, and the Heart Rhythm Society.

3. Prandoni P, Lensing AWA, Prins MH, et al. Prevalence of Pulmonary Embolism among Patients Hospitalized for Syncope. New England Journal of Medicine. 2016;375(16):1524-1531.

Prepare for your board review in internal medicine online with Harvard Medical School:

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Adam Schaffer is an instructor in medicine at Harvard Medical School as well as an attending physician on the Brigham and Women’s hospital medicine unit in Boston, where he is director of the general medicine consultation service.

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