3.7 Syncope: Cardiac Versus Non-Cardiac Causes and Workup
Key Takeaways
- Syncope is transient loss of consciousness from global cerebral hypoperfusion with rapid onset, short duration and complete spontaneous recovery; cerebral function fails after roughly 6-8 seconds of interrupted flow, and brief myoclonic jerks after collapse are convulsive syncope, not seizure.
- Syncope during exertion or while supine, absent prodrome, preceding palpitations, known structural heart disease, an abnormal ECG, or a family history of sudden death under age 50 are the red flags that define cardiac syncope and mandate a monitored bed.
- Orthostatic vitals are measured supine after 5 minutes then at 1 and 3 minutes standing; a positive result is a systolic fall of 20 mmHg or more, a diastolic fall of 10 mmHg or more, or systolic under 90 mmHg, and a heart-rate rise under about 15 beats/min despite a large drop suggests neurogenic autonomic failure.
- Monitor choice follows symptom frequency: Holter for daily events, a 14-30 day patch or event recorder for weekly events, mobile cardiac telemetry for real-time alerting, and an implantable loop recorder recording up to about 3 years when events occur less than monthly.
- Counter-pressure maneuvers such as leg crossing with muscle tensing or isometric handgrip raise systolic pressure by roughly 10-40 mmHg and can abort a vasovagal episode, but liberalized sodium and fludrocortisone are contraindicated in heart failure.
Defining Syncope Precisely
Syncope is a transient loss of consciousness caused by global cerebral hypoperfusion, with rapid onset, short duration and complete spontaneous recovery. Every element of that definition does work. Cerebral function fails after roughly 6-8 seconds of interrupted cerebral blood flow, or when systolic pressure at the level of the brain falls to about 50-60 mmHg. Recovery must be spontaneous and complete - if someone intervened, or the patient did not return to baseline, it was not syncope.
CMC tests this because cardiac syncope carries a mortality several times that of reflex syncope, and because the nurse is often the person who obtains the one history detail that reclassifies a patient from discharge to telemetry.
What syncope is not
| Mimic | Discriminating features |
|---|---|
| Generalized seizure | Aura, tonic-clonic activity from the onset rather than after collapse, lateral tongue biting, head turning, prolonged postictal confusion beyond 5 minutes |
| Convulsive syncope | Brief myoclonic jerks lasting under 15 seconds that begin after the patient is already down; occurs in up to 90% of syncope and is not epilepsy |
| Hypoglycemia, hypoxia, intoxication | Gradual onset, no rapid spontaneous recovery, correctable metabolic cause |
| TIA or stroke | Focal deficit; vertebrobasilar TIA can rarely cause loss of consciousness but never in isolation |
| Psychogenic pseudosyncope | Eyes held closed, episodes lasting many minutes, high frequency, absence of injury, normal blood pressure during the event |
| Drop attack, cataplexy, falls | No loss of consciousness at all |
| Cardiac arrest | Does not resolve spontaneously; requires intervention |
Urinary incontinence is nonspecific and occurs with both syncope and seizure, so it should never be used to distinguish them.
The Three Mechanistic Categories
| Category | Mechanism | Typical setting |
|---|---|---|
| Reflex (neurally mediated) | Inappropriate vagal surge and/or sympathetic withdrawal causing bradycardia, vasodilation or both | Vasovagal: prolonged standing, heat, crowds, pain, emotion, venipuncture, with a prodrome of nausea, warmth, diaphoresis and tunnel vision. Situational: cough, micturition, defecation, swallowing, post-exercise. Carotid sinus hypersensitivity: neck turning, tight collar, shaving, typically men over 60 |
| Orthostatic hypotension | Failure to compensate for the 500-1,000 mL that pools in the legs and splanchnic bed on standing | Volume depletion (bleeding, diuresis, vomiting), drug-induced (alpha blockers, nitrates, diuretics, ACE inhibitors/ARBs/ARNI, tricyclics), autonomic failure (diabetes, Parkinson disease, amyloidosis), post-prandial, alcohol, hot shower, deconditioning |
| Cardiac | Abrupt fall in cardiac output from arrhythmia or a fixed/dynamic obstruction | Arrhythmic: sinus node dysfunction, high-grade AV block, ventricular tachycardia, inherited channelopathy, device malfunction. Structural: severe aortic stenosis, hypertrophic obstructive cardiomyopathy, pulmonary embolism, tamponade, aortic dissection, atrial myxoma, prosthetic valve thrombosis, pulmonary hypertension |
Orthostatic vital signs are a nursing skill with a defined technique: measure supine after 5 minutes of rest, then at 1 minute and 3 minutes of standing. A positive result is a systolic fall of at least 20 mmHg, a diastolic fall of at least 10 mmHg, or a systolic pressure below 90 mmHg. Note the heart rate response - a blunted rise (under about 15 beats/min) despite a large pressure drop suggests neurogenic autonomic failure, whereas a compensatory tachycardia suggests hypovolemia or hemorrhage. A heart rate increase of 30 beats/min or more within 10 minutes of standing without hypotension is postural orthostatic tachycardia syndrome, not orthostatic hypotension.
Carotid sinus massage is considered in patients over 40 with unexplained syncope: 5-10 seconds of massage with continuous ECG and beat-to-beat blood pressure, supine and then upright. A ventricular pause of 3 seconds or longer and/or a systolic fall of 50 mmHg or more that reproduces symptoms is diagnostic. It is contraindicated with a carotid bruit or known stenosis, and after myocardial infarction, stroke or TIA within the preceding 3 months.
Four patients present to a chest pain unit after a syncopal episode. Which one most warrants admission to a telemetry bed?
Red Flags: Separating Cardiac From Reflex Syncope
| Feature | High-risk (suggests cardiac) | Low-risk (suggests reflex) |
|---|---|---|
| Trigger and position | During exertion, or while supine or seated | Prolonged standing, heat, crowd, pain, emotion, venipuncture, cough, micturition |
| Prodrome | Absent or under 5 seconds; abrupt "lights out" | 10 seconds or more of nausea, warmth, diaphoresis, blurred or tunnel vision |
| Preceding symptoms | Palpitations, chest pain, dyspnea | None, or a long history of identical benign episodes |
| Injury | Facial, dental or head injury from an unprotected fall | Little or no injury; the patient recalls getting to the floor |
| Cardiac history | Prior MI, ejection fraction 35% or below, heart failure, known arrhythmia, prior cardiac surgery, congenital disease | Structurally normal heart, first episode in adolescence or young adulthood |
| Family history | Sudden cardiac death under age 50, inherited channelopathy or cardiomyopathy, unexplained drowning or single-vehicle crash | None |
| Examination | New murmur, signs of heart failure, hypotension, bradycardia, rectal bleeding | Entirely normal |
| ECG | Abnormal (see below) | Normal |
| Age | Older, with comorbidity | Under 40 |
High-risk ECG findings
| Finding | Concern |
|---|---|
| Type 1 Brugada pattern: coved ST elevation of 2 mm or more with inverted T waves in V1-V2 | Polymorphic VT and ventricular fibrillation |
| QTc above 480-500 ms | Torsades de pointes; congenital or acquired long QT |
| QTc below 340 ms | Short QT syndrome |
| Short PR with a delta wave (WPW pre-excitation) | Pre-excited atrial fibrillation degenerating to VF |
| Epsilon wave, T-wave inversion in V1-V3, prolonged S-wave upstroke | Arrhythmogenic right ventricular cardiomyopathy |
| Marked LVH with deep narrow Q waves or giant T-wave inversions | Hypertrophic cardiomyopathy |
| Bifascicular block, QRS 120 ms or wider, Mobitz II, 2:1 or complete AV block | Intermittent complete heart block |
| Sinus bradycardia under 40 while awake, or a sinus pause longer than 3 seconds off rate-controlling drugs | Sinus node dysfunction |
| Pathologic Q waves of prior infarction | Scar-related monomorphic ventricular tachycardia |
Structural causes that produce exertional syncope
Severe aortic stenosis (mean gradient 40 mmHg or higher, peak velocity 4 m/s or greater, valve area under 1.0 cm2) classically presents with the triad of angina, syncope and dyspnea, and exertional syncope historically predicts a survival measured in a few years without valve replacement. Hypertrophic obstructive cardiomyopathy produces a dynamic left ventricular outflow gradient of 30 mmHg or more at rest or 50 mmHg or more with provocation, worsened by anything that reduces preload or afterload - standing suddenly, Valsalva, dehydration, nitrates, diuretics. Also consider pulmonary embolism (a meaningful minority of patients hospitalized for a first syncopal episode have one), cardiac tamponade, aortic dissection, atrial myxoma with positional obstruction and a tumor plop, and prosthetic valve thrombosis.
Risk Stratification and Disposition
Two tools appear repeatedly. The Canadian Syncope Risk Score predicts 30-day serious adverse events using nine variables: predisposition to vasovagal symptoms (minus 1), history of heart disease (plus 1), any systolic pressure below 90 or above 180 mmHg (plus 2), elevated troponin (plus 2), abnormal QRS axis under minus 30 or over 100 degrees (plus 1), QRS duration over 130 ms (plus 1), QTc over 480 ms (plus 2), an emergency department diagnosis of vasovagal syncope (minus 2), and an emergency department diagnosis of cardiac syncope (plus 2). Scores run from minus 3 to plus 11 and fall into five bands: minus 3 to minus 2 is very low risk (0.4-0.7% 30-day serious outcome), minus 1 to 0 is low (1.2-1.9%), 1 to 3 is medium (3.1-8.1%), 4 to 5 is high (12.9-19.7%), and 6 or above is very high (28.9-83.6%).
The San Francisco Syncope Rule uses the CHESS mnemonic - Congestive heart failure history, Hematocrit under 30%, ECG abnormal, Shortness of breath, Systolic blood pressure under 90 mmHg - with any positive item flagging risk of a 7-day serious outcome. It is sensitive but not specific.
Neither score replaces clinical judgment, and current US guidance treats them as supportive rather than determinative. Practically: high-risk features, an abnormal ECG, known structural disease or syncope during exertion earn a monitored bed; a young patient with a classic vasovagal history, a normal ECG, a normal examination and no structural disease can be discharged with outpatient follow-up.
A patient with a structurally normal heart, a normal ECG and roughly one unexplained syncopal episode every 8 to 10 months has already had a negative 48-hour Holter and a negative 30-day event monitor. Which monitoring strategy is most appropriate next?
The Workup Ladder
- 12-lead ECG on every patient - it is the only universally indicated test and it drives disposition.
- Orthostatic vital signs using the technique above, plus point-of-care hemoglobin and a rectal examination when bleeding is plausible.
- Continuous telemetry for anyone admitted with high-risk features; review the full disclosure rather than only the alarms.
- Targeted labs: troponin if ischemia is plausible, hemoglobin, electrolytes including magnesium, glucose, and a pregnancy test where relevant. Routine broad panels add nothing.
- Echocardiography when structural disease is suspected or the ECG is abnormal - it finds severe aortic stenosis, hypertrophic cardiomyopathy, low ejection fraction, tamponade and myxoma.
- Ambulatory rhythm monitoring, chosen by symptom frequency, which is the most commonly missed decision point.
| Symptom frequency | Appropriate monitor | Duration |
|---|---|---|
| Daily or near-daily | Holter monitor | 24-48 hours, or an adhesive patch up to 14 days |
| Every few days to weekly | Patch or external event recorder | 14-30 days |
| Weekly to monthly, with a need for real-time alerting | Mobile cardiac outpatient telemetry | Up to 30 days, auto-transmitting |
| Less often than monthly, unexplained after full workup | Implantable loop recorder | Up to about 3 years |
| Hospitalized with high-risk features | Continuous inpatient telemetry | Until diagnosis or disposition |
- Tilt-table testing for suspected reflex syncope or delayed orthostatic hypotension when the diagnosis remains unclear; it is not a test for suspected arrhythmic syncope.
- Exercise stress testing when syncope occurred during or immediately after exertion.
- Electrophysiology study for syncope with bifascicular block, prior infarction with preserved but abnormal ventricular function, or suspected bradyarrhythmia not captured by monitoring.
Medication review - a nursing responsibility
Two categories matter. QT-prolonging agents include amiodarone, sotalol, dofetilide, ibutilide, procainamide, haloperidol, methadone, ondansetron, fluoroquinolones, macrolides and citalopram; the risk multiplies with hypokalemia, hypomagnesemia, bradycardia and renal impairment, all common in the cardiac patient. Hypotensive agents include alpha blockers such as tamsulosin and doxazosin, nitrates, diuretics, ACE inhibitors, ARBs and sacubitril/valsartan, beta blockers, calcium channel blockers, SGLT2 inhibitors through volume depletion, mineralocorticoid antagonists, tricyclics and opioids. Ask specifically about timing: an alpha blocker taken in the morning before a hot shower, or a diuretic plus a nitrate on a hot day, explains many episodes without any further testing.
Nursing Priorities
- Fall and injury prevention first. Bed in low position, call-light and personal items within reach, non-skid footwear, bed or chair alarm, assisted ambulation on the first mobilization after an event, and a documented post-fall protocol. Head injury risk is what makes syncope dangerous even when the cause is benign.
- Continuous telemetry with deliberate review - correlate every symptom the patient reports with the strip, and teach the patient to press the event marker.
- Counter-pressure maneuver teaching for reflex syncope with a warning prodrome: at the first symptom, cross the legs and tense the thigh, buttock and abdominal muscles, or interlock the hands and pull the arms apart while tensing, or squeeze a ball, holding until symptoms resolve. These raise systolic pressure by roughly 10-40 mmHg and can abort an episode. Lying down and elevating the legs is the fallback when the setting allows.
- Volume and physical countermeasures, adjusted for cardiac comorbidity: 2-3 L of fluid daily and liberalized sodium help autonomic and vasovagal patients, but liberalized sodium is contraindicated in heart failure, uncontrolled hypertension and renal disease - this is exactly where a CMC item will test judgment. Graduated compression stockings of 30-40 mmHg or an abdominal binder, slow staged position changes, avoidance of hot showers, large carbohydrate meals and alcohol.
- Pharmacologic support when non-pharmacologic measures fail: midodrine 2.5-10 mg three times daily with the last dose at least 4 hours before bedtime to limit supine hypertension, or fludrocortisone 0.1-0.2 mg daily with monitoring of potassium, edema and supine pressure - both problematic in heart failure and used cautiously.
- Driving counselling and documentation. Restrictions after syncope are set by state law and vary widely, and commercial licensing is stricter than private. The nurse's role is to confirm that the restriction has been discussed, document the conversation, provide it in writing, and arrange alternative transportation rather than to quote a national rule that does not exist. Similar counselling applies to swimming alone, working at heights, and operating machinery until the cause is established.
- Discharge instructions should name the suspected mechanism, list the specific triggers to avoid, describe the counter-pressure maneuvers, specify which medications were changed and why, and give explicit return precautions for syncope with chest pain, palpitations, dyspnea, exertional onset or injury.
A 40-year-old with recurrent vasovagal syncope preceded by a 20-second prodrome, a structurally normal heart and no other comorbidity is being discharged. Which teaching point is most appropriate?