Evaluating the Cause of Syncope

If you have had an episode of syncope (a transient loss of consciousness also referred to as fainting), it is important for you and your healthcare provider to figure out what caused the episode. There are many potential causes of syncope, and unless your healthcare provider approaches the diagnosis in a systematic way, things can get confusing in a hurry. This article discusses a straightforward and systematic approach to the diagnosis of syncope.

What to Know About Vasovagal Syncope
Verywell / Brooke Pelczynski

First Things First

In evaluating the cause of syncope, your healthcare provider has an immediate question to answer: Does the syncope in your case suggest an increased risk of sudden death? Fortunately, arriving at an answer to this question is usually pretty straightforward, and also fortunately, in the large majority of cases the answer to this question is “No.” Still, it is critical to address this question right away. Since life-threatening syncope is almost always cardiac in origin, this means your healthcare provider needs to determine whether you have, or are likely to have, a significant cardiac condition. If your healthcare provider decides that your syncope may have been due to a cardiac condition, an immediate evaluation is necessary—and it may be necessary to hospitalize you until a life-threatening cause is ruled out, or you are adequately treated.

If (as is much more often the case) your healthcare provider does not find any sign of a life-threatening condition, then they can perform a less hurried evaluation to find the cause of your syncope, and hospitalization is only rarely needed.

A Two-Phased Approach to Evaluating Syncope

Phase One: Medical History and Physical Examination

This is the most important step in diagnosing the cause of syncope. The history and physical examination give vital clues in diagnosing nearly all causes of syncope. In the large majority of cases, the healthcare provider should have an excellent idea as to the cause of syncope after talking to you and examining you.

Taking a careful medical history must include getting the details about any possible cardiac history you may have, including:

  • All information pertaining to any prior history of heart disease
  • If you have no history of heart disease, evaluating your risk factors for heart disease
  • Asking you about any family history you may have of heart disease, especially any family history of sudden death

In addition, the healthcare provider should ask you for the details of each and every one of your syncopal episodes—all the way back to childhood, if necessary—including information regarding:

  • When each one occurred
  • What you were doing just before, e.g., whether you were engaged in physical activity, what foods you had eaten
  • Whether there were any warning symptoms immediately before (prodromal symptoms), such as palpitations, nausea, or vomiting
  • Whether there were symptoms afterward
  • How long it lasted
  • Whether you have discovered a way to abort an episode

Any information you may have gotten from bystanders may be helpful, and if there’s any video of any of the episodes that might help as well.

The physical examination should include thorough neurological and cardiac exams. Your healthcare provider will check your blood pressure and heart rate while you are lying down, while you are sitting, immediately after you stand up, and after you’ve been standing for three minutes. They will also listen to your heart for abnormal sounds, such as a murmur.

By the end of the history and physical, your healthcare provider ought to have an excellent idea as to what is causing your syncope. In particular, at the very least your healthcare provider should know how likely it is that you have a cardiac problem causing the syncope—in which case, sudden death is a concern.

If cardiac disease is not suspected, then generally your healthcare provider will need to order no more than one or two directed tests to confirm her suspicions. They should be able to tell you what they think is the problem, and should be able to give you some idea of what the treatment will likely entail.

Phase Two: Directed Testing

After the history and physical exam:

  • If your healthcare provider suspects a cardiac cause for your syncope, a non-invasive cardiac workup should be done immediately. In most cases, this work-up will consist of an echocardiogram, and in some cases a stress test. If some form of obstructive heart disease is found (such as aortic stenosis), then treatment to relieve the obstruction should be planned as soon as possible. If this initial evaluation points to a cardiac arrhythmia as the cause of your syncope, you may need electrophysiologic testing. In this case, it is likely that you will need to remain on a hospital monitor until you receive definitive therapy.
  • If your healthcare provider suspects a neurological cause, then they will probably order a CT scan of the brain or electroencephalogram (EEG), or in some cases, angiography (a dye study to visualize the arteries to the brain) to confirm the diagnosis. Syncope due to neurological disorders, however, is relatively uncommon.
  • If your healthcare provider has diagnosed or strongly suspects vasomotor syncope (that is, orthostatic hypotension, POTS, or vasovagal syncope), usually no further testing is necessary. In some cases, a tilt table study may be useful in confirming the diagnosis. But generally, once this type of syncope is identified, your healthcare provider can immediately move toward instituting therapy. The great majority of people who have syncope turn out to have vasovagal syncope.
  • If your healthcare provider—despite taking a careful medical history and performing a thorough physical examination—still has no good presumptive explanation for your syncope, it is usually a good idea to perform non-invasive cardiac testing to rule out subtle cardiac disease. This testing generally will consist of an echocardiogram, often ambulatory monitoring (where you wear a cardiac monitor at home for several days or weeks), and possibly stress testing. A tilt table study may also be useful. If syncope remains undiagnosed after these studies, electrophysiologic testing may be considered.


Using this general two-phase approach, it is probable that your healthcare provider will be able to diagnose the cause of your syncope quickly and accurately, and will be able to initiate appropriate therapy in short order.

1 Source
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  1. Shen WK, 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. Circulation. 2017;136(5)e60-e122. doi:10.1161/CIR.0000000000000499

By Richard N. Fogoros, MD
Richard N. Fogoros, MD, is a retired professor of medicine and board-certified in internal medicine, clinical cardiology, and clinical electrophysiology.