What are the causes and management of sporadic near syncope (near fainting)?

Causes of Sporadic Near Syncope

Sporadic near syncope (presyncope) has the same underlying causes as syncope itself and warrants the same systematic evaluation, as patients with presyncope have similar prognoses and outcomes to those with complete syncope. 1

Primary Causes

Neurally Mediated (Reflex) Syncope

• Vasovagal syncope is the most common cause, triggered by prolonged standing, emotional stress, pain, fear, or specific situations like blood draws 1, 2
• Situational syncope occurs with micturition, defecation, coughing, sneezing, or post-prandial states 3
• Carotid sinus hypersensitivity should be considered in older patients (>40 years) with episodes during head turning or neck pressure 2
• These episodes typically occur when standing, have clear prodromal symptoms (lightheadedness, nausea, sweating, visual changes), and have a benign long-term prognosis 1, 2

Orthostatic Hypotension

• Classic orthostatic hypotension develops within 3 minutes of standing with a sustained drop in systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg 1
• Initial orthostatic hypotension occurs within 15 seconds of standing with transient BP decrease 1
• Delayed orthostatic hypotension takes >3 minutes to develop 1
• Common causes include volume depletion, medications (antihypertensives, diuretics, vasodilators), autonomic dysfunction, and prolonged bed rest 3

Cardiac Arrhythmias

• Bradyarrhythmias: sinus node disease with pauses, second-degree Mobitz II AV block, advanced or complete AV block 1
• Tachyarrhythmias: supraventricular tachycardia (SVT), ventricular tachycardia (VT), rapid atrial fibrillation 1
• These are particularly concerning when episodes occur during exertion, in supine position, or without prodrome 1, 2

Structural Cardiac Disease

• Critical aortic stenosis, hypertrophic cardiomyopathy, cardiac masses (atrial myxoma), acute myocardial infarction, pulmonary embolism, aortic dissection 1
• Pacemaker or ICD malfunction including battery depletion, lead failure, or pacemaker syndrome 1

Non-Cardiovascular Causes

• Metabolic: severe anemia, hypoglycemia, hypoxia 1
• Neurological: autonomic failure (Parkinson's disease, multiple system atrophy), peripheral neuropathy 1
• Psychiatric: anxiety disorders, panic attacks, hyperventilation syndrome (though true syncope must be excluded first) 1

Critical Evaluation Approach

Initial Assessment (All Patients)

• Detailed history focusing on: position at onset, activity (exertion vs. rest), prodromal symptoms, eyewitness accounts, recovery time, frequency of episodes, medication review, family history of sudden cardiac death 2
• Physical examination including cardiac auscultation for murmurs/gallops, neurological assessment for focal deficits 2
• Orthostatic vital signs measured supine and at 1 and 3 minutes of standing 2
• 12-lead ECG is mandatory for all patients to identify conduction abnormalities, pre-excitation, QT prolongation, or ischemic changes 2

Risk Stratification

High-risk features requiring urgent cardiac evaluation 1, 2:

• Syncope during exertion or while supine
• Sudden onset without prodrome
• Known structural heart disease or reduced ventricular function
• Abnormal cardiac examination (murmurs, gallops)
• Family history of sudden cardiac death before age 50
• Concerning ECG findings (bundle branch block, QTc >500ms, Brugada pattern, arrhythmogenic right ventricular cardiomyopathy pattern)

Low-risk features suggesting benign neurally mediated syncope 1, 2:

• Episodes only when standing
• Clear prodromal symptoms (nausea, warmth, diaphoresis, visual changes)
• Specific triggers (prolonged standing, emotional stress, pain)
• Younger age without cardiac disease
• Recurrent episodes with similar characteristics

Targeted Diagnostic Testing

For suspected cardiac causes 2:

• Echocardiography to evaluate structural heart disease
• Prolonged cardiac monitoring (external loop recorder for episodes every few weeks, implantable loop recorder for less frequent episodes)
• Electrophysiological studies in patients with bundle branch block and unexplained syncope

For suspected neurally mediated syncope 2:

• Tilt-table testing as first-line in younger patients (<40 years) with recurrent episodes
• Carotid sinus massage in older patients (>40 years)

Avoid unnecessary testing 2:

• Routine comprehensive laboratory panels have low yield unless volume loss or specific metabolic cause suspected
• Brain imaging (CT/MRI) and EEG are not indicated unless focal neurological findings, head trauma, or features suggesting seizure rather than syncope 1, 2

Common Pitfalls

• Do not assume a single negative Holter monitor excludes arrhythmic causes—if clinical suspicion remains high, consider longer-term monitoring with loop recorders 2
• Do not attribute episodes to psychiatric causes without excluding cardiac and neurological causes first, as psychiatric disorders can coexist with true syncope 1
• Do not overlook medication review—polypharmacy, especially antihypertensives, diuretics, and QT-prolonging drugs, is a frequent contributor 3
• Do not dismiss recurrent episodes in young patients as "just vasovagal" without proper evaluation if high-risk features are present 2