Syncope, commonly known as fainting, is a sudden and temporary loss of consciousness caused by reduced blood flow to the brain. Although it often lasts only seconds to minutes, syncope can be alarming both to the patient and those around them.
While many episodes are benign, some forms of syncope indicate serious underlying conditions such as cardiac arrhythmias or neurological disorders. Therefore, correctly identifying the cause of syncope is crucial in clinical practice.
To simplify differential diagnosis, medical educators often rely on the SYNCOPE mnemonic, which neatly organizes the main categories of causes:
- S – Situational syncope
- Y – Young fainter (Vasovagal syncope)
- N – Neurogenic syncope
- C – Cardiac syncope
- O – Orthostatic syncope
- P – Psychogenic syncope
- E – Endocrine-related causes
This article will take you through each of these differentials, exploring their mechanisms, clinical relevance, diagnostic strategies, and management approaches.
The Physiology of Syncope
To understand why fainting occurs, we must first look at the brain’s energy requirements. The brain depends almost entirely on a continuous supply of oxygen and glucose through cerebral blood flow. If cerebral perfusion falls below critical levels for even 6–8 seconds, loss of consciousness occurs.
Syncope results from transient global cerebral hypoperfusion. This can occur due to:
- Reduced cardiac output (e.g., arrhythmias, structural heart disease)
- Peripheral vasodilation or pooling of blood (e.g., vasovagal, orthostatic hypotension)
- Impaired vascular resistance control (e.g., neurogenic causes)
- Metabolic disturbances (e.g., hypoglycemia)
Now, let us break down the mnemonic SYNCOPE.
S – Situational Syncope
Situational syncope refers to fainting episodes that occur in specific circumstances, often due to exaggerated reflexes that cause sudden vasodilation and bradycardia.
Common triggers include:
- Coughing (cough syncope)
- Urination (micturition syncope)
- Defecation (defecation syncope)
- Swallowing (swallow syncope)
- Post-exercise syncope
The underlying mechanism is a reflex-mediated drop in systemic vascular resistance and heart rate, leading to cerebral hypoperfusion.
Clinical Clue: Patients usually report a reproducible pattern – for example, fainting during urination at night in elderly men with prostate issues.
Management: Avoidance of triggers, hydration, and in severe cases, medications like midodrine may help.
Y – Young Fainter (Vasovagal Syncope)
Also called neurally mediated syncope, vasovagal syncope is the most common type of fainting, especially in adolescents and young adults.
Triggers include:
- Emotional stress (fear, pain, blood sight)
- Prolonged standing in hot environments
- Fatigue or dehydration
Pathophysiology:
A sudden surge in vagal activity leads to bradycardia and vasodilation, causing hypotension and fainting.
Symptoms:
- Prodrome (lightheadedness, sweating, nausea, blurred vision)
- Sudden collapse
- Rapid recovery without confusion
Management: Patient reassurance, lying supine with elevated legs, and long-term education about hydration and counterpressure maneuvers (e.g., leg crossing, hand grip).
N – Neurogenic Syncope
Neurogenic causes involve dysregulation of the autonomic nervous system, often due to neurological conditions.
Common causes:
- Seizure disorders (though seizures are distinct from syncope, they may mimic it)
- Stroke or transient ischemic attack (TIA) affecting brainstem perfusion
- Migraine-associated syncope
- Autonomic neuropathies (e.g., in diabetes, Parkinson’s disease)
Clinical Distinction:
Unlike vasovagal syncope, neurogenic syncope may have accompanying focal neurological deficits.
Management: Address underlying neurological disorder, manage risk factors like diabetes or hypertension, and use medications that improve autonomic balance.
C – Cardiac Syncope
Cardiac syncope is the most dangerous form, often indicating life-threatening conditions.
Mechanisms:
- Arrhythmias – tachyarrhythmias (e.g., ventricular tachycardia) or bradyarrhythmias (e.g., complete heart block)
- Structural heart disease – aortic stenosis, hypertrophic cardiomyopathy
- Ischemic heart disease – myocardial infarction
- Pulmonary embolism – obstructing right heart blood flow
Red flags for cardiac syncope:
- Occurs suddenly, without prodrome
- Happens during exertion or while lying down
- Family history of sudden cardiac death
Management: Hospital admission, ECG, echocardiography, and often device implantation (pacemaker/ICD).
O – Orthostatic Syncope
Orthostatic hypotension is defined as a drop in systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg within 3 minutes of standing.
Causes:
- Hypovolemia (dehydration, blood loss)
- Medications (antihypertensives, diuretics, antidepressants)
- Autonomic dysfunction (diabetes, Parkinson’s disease, aging)
Clinical Presentation: Patients faint after rising from bed or standing for prolonged periods.
Management: Adequate hydration, compression stockings, gradual position changes, and medication review.
P – Psychogenic Syncope
Psychogenic pseudosyncope mimics true syncope but is not caused by cerebral hypoperfusion.
Features:
- Often prolonged unresponsiveness
- Absence of typical prodrome or pallor
- More common in young women with anxiety, depression, or conversion disorder
Diagnosis: Exclusion after ruling out organic causes, tilt-table testing may help.
Management: Psychological support, cognitive-behavioral therapy (CBT), and addressing comorbid psychiatric conditions.
E – Endocrine-Related Causes
Metabolic and endocrine conditions can also cause transient loss of consciousness.
Common causes:
- Hypoglycemia – most important, especially in diabetics on insulin
- Adrenal insufficiency (Addison’s disease)
- Hypothyroidism with myxedema crisis
- Electrolyte imbalances (e.g., hyponatremia)
Management: Rapid correction of glucose, electrolyte replacement, and long-term management of endocrine disorders.
Quick Reference Table: SYNCOPE Mnemonic
| Letter | Type of Syncope | Key Causes | Clinical Clues | Management |
|---|---|---|---|---|
| S | Situational | Cough, micturition, defecation, swallowing | Trigger-specific fainting | Avoid triggers, hydration |
| Y | Young fainter | Vasovagal | Stress, heat, prolonged standing | Education, counterpressure maneuvers |
| N | Neurogenic | Seizure, stroke, autonomic neuropathy | Focal deficits, recurrent episodes | Neurological workup |
| C | Cardiac | Arrhythmias, structural heart disease | Sudden, exertional, no prodrome | ECG, pacemaker/ICD |
| O | Orthostatic | Hypovolemia, meds, autonomic failure | Postural fainting | Hydration, compression stockings |
| P | Psychogenic | Conversion disorder, anxiety | Prolonged, atypical episodes | Psychological therapy |
| E | Endocrine | Hypoglycemia, adrenal insufficiency | Confusion, metabolic signs | Glucose, endocrine management |
Diagnostic Approach to Syncope
- History and Examination – most important; ask about triggers, prodrome, family history.
- Vital signs and orthostatic BP measurement.
- ECG – for arrhythmias.
- Echocardiography – structural causes.
- Tilt-table testing – for vasovagal and psychogenic syncope.
- Blood glucose and metabolic profile.
- Neuroimaging if neurological signs present.
Management Principles
- Identify and treat underlying cause.
- Risk stratify: benign vasovagal vs dangerous cardiac causes.
- Educate patients on lifestyle modification and preventive measures.
- Hospitalize if high risk (cardiac suspicion, injury during syncope, elderly with comorbidities).
FAQs on Syncope
Q1: What is the difference between syncope and seizure?
Syncope is due to reduced cerebral blood flow, usually with rapid recovery and no post-ictal confusion. Seizures often involve tonic-clonic movements, tongue-biting, incontinence, and post-ictal drowsiness.
Q2: When should fainting be considered dangerous?
If it occurs suddenly during exertion, at rest, or with no prodrome, cardiac causes should be suspected. A family history of sudden death also raises concern.
Q3: Can stress cause syncope?
Yes, vasovagal syncope is often triggered by emotional stress, fear, or anxiety.
Q4: How is orthostatic syncope prevented?
By standing up slowly, staying hydrated, and avoiding medications that worsen hypotension.
Q5: What is the first test in evaluating syncope?
A detailed clinical history and an ECG form the cornerstone of syncope evaluation.
