Differentiating Syncope: A Few Pearls

Syncope. To a fresh-faced student, it’s a snappy word for fainting. To someone with experience, it’s a heavy sigh, because we take a lot of calls for “syncope” and most of them are no big deal. But to a veteran provider, syncope is a deep, dark diagnostic hole—because syncope can be caused by countless different disorders, and although some are benign, a few of them are deadly.

Comprehensive diagnosis and treatment of syncope deserves its own dedicated series, and one of these days we’ll try and work through it from A to Z. Every etiology is unique and has its own distinct pathophysiology, presentation, and treatment considerations. Syncope sucks.

But for now, we’ll just talk about a few take-home pearls that can pay dividends in the everyday management of your next syncope call. We don’t support simplistic rules of thumb ’round these parts, but sometimes 95% of the work can be done by 5% of the know-how, and that’s just fine.

Here are a few dead-simple roadsigns to help guide you through the most common and most important causes of syncope.


Did they pass out and fall, or did they fall and then pass out?

Syncope means that somebody passed out and fell down. It doesn’t mean that they fell down and then lost consciousness. If they tripped on an oil can, fell over and smacked their head on a rock, they may have blacked out, but there’s no mystery there—it’s a simple trauma call.

So, our first step should be to take the raw he passed out and sift it into a more precise description. One problem is that people who lose consciousness often have a poor or unreliable memory of those events, so they may not always be helpful; this is why it’s nice to have witnesses who can tell the story. Of course, witnesses aren’t always reliable either.


Okay, so what do they remember?

To the extent that the patient remembers it, how do they describe the event?

A prodrome is an early, sometimes subtle set of symptoms that warn of a problem developing. Prodromes are our friend, because although they can be very brief or non-obvious, when present they can help indicate what happened. So, ask! It’s the O in OPQRST, and it’s the E in SAMPLE, so it’s the beginning and end of our patient history—no excuses!

Vasovagal syncope is one of the most common causes of syncope, involving a transient drop in blood pressure, and vasovagal syncope is usually preceded by a prodrome. If you’ve never had the experience of standing up too fast and getting briefly faint, here’s the gist: you become light-headed, your vision blurs or darkens, you feel weak, you may stumble, and finally you go down. There may also be broad neurological symptoms, such as visual disturbances (“seeing spots”), strange sensations, shaking, and more. (Basically, your brain isn’t getting enough oxygen, so odd stuff happens.)

How about seizures? Many seizures are preceded by a prodrome known as an “aura,” which can manifest as various unusual neurological abnormalities; read more in our piece on seizures. Did the patient truly lose consciousness, or do they claim that they remained somewhat aware? In a simple partial seizure, the patient will remain aware of their surroundings (although these often don’t cause a “syncopal” collapse); in most others they will experience a gap in consciousness.

Syncope caused by cardiac arrhythmias, such as a run of V-tach or a Stokes-Adams attack, will sometimes be preceded by a palpable sensation of weakness, or palpitations  (“fluttering”) in the chest. However, in many cases there will be no warning whatsoever.


What did the witnesses see?

It’s one thing to hear about a prodrome from the patient, but you may get a different story from the bystanders.

What did they see before he went down? Did he become absent, demonstrate tics or tonic immobility, perhaps complain of an aura? Did he demonstrate obvious clonic jerking of the muscles or urinary incontinence? If he’s acting normally now, was there a period after the event where he demonstrated sluggish activity or unusual behavior, consistent with a post-ictal period? These are all suggestive of a seizure.

Were his eyes open or closed for the duration? Closed is typical of classic syncope, such as a vagal event; open is more appropriate for a seizure. If open, were they rolled back? This also suggests seizure.

Did the patient say, do, or complain of anything before or after the event, which he may no longer recall? Dizziness, headache, chest pain?

Did he stumble, lean against something, or seem to become dizzy? After he went down, did he regain consciousness almost immediately? These are suggestive of vasovagal; once a horizontal position is reached, perfusion to the brain is restored and the problem resolves. If he remained unconscious for a prolonged period while prone—or his initial episode occurred while already seated or reclined—this is highly unusual for vasovagal.

Was he walking and moving normally, in no distress, when he suddenly collapsed like a marionette with its strings cut, hitting the ground with no attempt to protect himself? This is strongly suggestive of a cardiac event and these patients should be considered high-risk for sudden death.


Is there a suggestive history or surrounding circumstances?

Sometimes, the chain of events or the patient’s medical history may suggest an etiology.

Is there a known history of a seizure disorder like epilepsy? How about diabetes? (Take a blood sugar if you’re capable of it; in my book, everybody with an altered mental status is diabetic.) Do they have often pass out or become light-headed?

Have they been eating and drinking as normal? Have they had the flu, and been unable to keep down fluids for the past two days? Were they partying all night? Vomiting? Are they a marathon runner who collapsed in 110 degree weather? Dehydration is a common cause of syncope, particularly in the young, healthy population.

Is there a known condition which may have neurological or metabolic involvement? Cancer with metastases to the brain? A recent infection? A congenital heart condition, such as Long QT, hypertrophic cardiomyopathy, or Brugada? For that matter, are they currently drunk or using drugs? If they take psychotropic or other medications, are they compliant with these, or could there have been an under- or over-dose?

Has there been any recent trauma, such as a fall, motor vehicle collision, or assault with injury?

Have there been repeated lapses in and out of consciousness, rather than a single event? This is an ominous sign suggesting a significant problem.


Are there frank clinical signs that suggest a diagnosis?

This is less likely to be useful than the history, but it can help rule in or rule out major, acute emergencies.

Cardiac abnormalities may manifest with irregular pulses, and active decompensation may be revealed in the blood pressure. Whenever possible these patients should receive ECG monitoring, including a 12-lead. Orthostatic vital signs can be considered if vagal, orthostatic, or hypovolemic etiologies are suggested.

All syncope patients, including suspected seizures, should get a neurological workup, particularly a Cincinatti Stroke Scale.

Respiratory adequacy, including pulse oximetry where available, should be assessed.

Evaluate the abdomen for signs of hemorrhage, and inquire about blood in the stool or emesis as well.

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