What is the initial approach to a patient presenting with near syncope?

Differential Diagnosis for Near Syncope

Near syncope should be evaluated identically to syncope, as both conditions carry similar prognostic implications and require the same systematic diagnostic approach to identify potentially life-threatening cardiac causes. 1, 2

Organizing Framework by Mechanism and Risk

The differential diagnosis must be organized into three primary categories, with cardiac causes representing the highest mortality risk requiring immediate exclusion 1, 3:

1. Cardiac Syncope (Highest Risk - 20-30% one-year mortality)

Arrhythmic Causes:

• Bradyarrhythmias: Sinus bradycardia, sinoatrial blocks, 2nd or 3rd degree AV block, bundle branch blocks, bifascicular block 4, 1
• Tachyarrhythmias: Ventricular tachycardia, supraventricular tachycardia, inherited channelopathies (Long QT syndrome, Brugada syndrome) 1, 3
• Device malfunction: Pacemaker or ICD malfunction 1

Structural Heart Disease:

• Severe aortic stenosis 4, 1
• Hypertrophic cardiomyopathy 1, 3
• Arrhythmogenic right ventricular cardiomyopathy 1
• Severe ostial left main stenosis 1
• Acute myocardial infarction 4
• Pulmonary embolism 4
• Cardiac tamponade 1
• Atrial myxoma 1

2. Reflex-Mediated (Neurally-Mediated) Syncope

Vasovagal Syncope (Most Common Overall):

• Triggered by emotional stress, pain, fear, prolonged standing, warm crowded environments 1, 3
• Characterized by prodromal symptoms: nausea, diaphoresis, blurred vision, dizziness 1, 3

Situational Syncope:

• Micturition, defecation, cough, swallowing, post-exercise 4, 3

Carotid Sinus Hypersensitivity:

• Triggered by neck turning, tight collars, pressure on carotid sinus (primarily in elderly) 4, 3

3. Orthostatic Hypotension

Medication-Induced (Most Common):

• Antihypertensives, diuretics, vasodilators, phenothiazines, tricyclic antidepressants, QT-prolonging agents 4, 1

Volume Depletion:

• Hemorrhage, dehydration, anemia 1

Autonomic Failure:

• Primary autonomic failure (Parkinson disease, multiple system atrophy) 4, 1
• Secondary autonomic failure (diabetic neuropathy, amyloidosis) 1

Critical Initial Evaluation Components

Every patient requires three mandatory assessments 1, 5:

History (Most Important Diagnostic Tool)

Circumstances Before the Event:

• Position: Supine suggests cardiac cause; standing suggests reflex or orthostatic 1, 3
• Activity: Exertional syncope is HIGH-RISK and mandates immediate cardiac evaluation 1, 3
• Triggers: Warm crowded places/prolonged standing suggest vasovagal; urination/defecation suggest situational 1, 3

Prodromal Symptoms:

• Presence of nausea, diaphoresis, blurred vision, dizziness favors vasovagal syncope 1, 3
• Absence of prodrome suggests cardiac arrhythmia or neurodegenerative disorder 4, 1
• Palpitations before event strongly suggest arrhythmic cause 1, 3

Witness Account:

• Tonic-clonic movements can occur with both cardiac and neurological causes 4
• Rapid, complete recovery without confusion confirms syncope (not seizure) 1

Past Medical History:

• Known structural heart disease or heart failure (95% sensitivity for cardiac syncope) 1
• History of myocardial infarction raises possibility of ventricular arrhythmias 4
• Repaired congenital heart disease 4

Family History:

• Sudden cardiac death or inherited arrhythmia syndromes (Long QT, Brugada, hypertrophic cardiomyopathy) 1, 3

Medications:

• Review for antiarrhythmics (proarrhythmia), antihypertensives (orthostasis), QT-prolonging agents 4, 1

Physical Examination

Orthostatic Vital Signs (Mandatory in ALL patients):

• Measure in lying, sitting, and standing positions 1, 5
• Positive if systolic BP drop ≥20 mmHg or to <90 mmHg 1

Cardiovascular Examination:

• Murmurs, gallops, rubs indicating structural heart disease 4, 1
• Signs of heart failure 3

Carotid Sinus Massage (in patients >40 years):

• Positive if asystole >3 seconds or systolic BP drop >50 mmHg 1, 3
• CONTRAINDICATION: Recent TIA/stroke, carotid bruit, or known carotid stenosis 4

Neurological Examination:

• Focal neurological signs suggest stroke or TIA (rare cause of syncope) 4, 6

12-Lead ECG (Mandatory in ALL patients)

High-Risk ECG Findings Requiring Admission:

• Sinus bradycardia <50 bpm, sinoatrial blocks 1
• 2nd or 3rd degree AV block, bifascicular block 4, 1
• QT prolongation (Long QT syndrome) 1, 3
• Brugada pattern 1
• Signs of ischemia or prior MI 1, 3
• Pre-excitation (Wolff-Parkinson-White) 4
• Any abnormality is an independent predictor of cardiac syncope and increased mortality 1

Risk Stratification for Disposition

HIGH-RISK Features (Require Hospital Admission) 1, 3:

• Age >60-65 years 1, 3
• Abnormal ECG findings 1, 3
• Known structural heart disease or heart failure 1, 3
• Syncope during exertion or in supine position 1, 3
• Brief or absent prodrome 1
• Palpitations before syncope 1
• Family history of sudden cardiac death 1, 3
• Systolic BP <90 mmHg 1
• Low number of episodes (1-2 lifetime) more concerning than many episodes 1

LOW-RISK Features (Appropriate for Outpatient Management) 1, 3:

• Younger age with no cardiac disease 1, 3
• Normal ECG 1, 3
• Syncope only when standing 1, 3
• Clear prodromal symptoms (nausea, diaphoresis, dizziness) 1, 3
• Specific situational triggers 1, 3
• Positional change triggers 1

Directed Testing Based on Initial Evaluation

When Structural Heart Disease is Suspected:

• Transthoracic echocardiography immediately for valvular disease, cardiomyopathy, ventricular function 1, 3

When Arrhythmic Syncope is Suspected:

• Continuous cardiac telemetry monitoring immediately for patients with abnormal ECG or palpitations 1, 3
• Holter monitor for suspected arrhythmic etiology 1
• External loop recorder or implantable cardiac monitor for less frequent symptoms 1

When Exertional Syncope:

• Exercise stress testing is MANDATORY for syncope during or immediately after exertion 1, 3

When Vasovagal Syncope Suspected but Not Diagnostic:

• Tilt-table testing for young patients without heart disease with recurrent unexplained syncope 1, 3

Tests NOT Routinely Recommended

The following have extremely low diagnostic yield and should NOT be ordered without specific clinical indication:

• Brain imaging (CT/MRI): 0.24-1% diagnostic yield; only if focal neurological findings or head trauma 1, 6
• EEG: 0.7% diagnostic yield; only if seizure suspected 1
• Carotid ultrasound: 0.5% diagnostic yield; not recommended routinely 1
• Comprehensive laboratory panels: Low yield; only order targeted tests based on clinical suspicion (e.g., hematocrit if bleeding suspected, electrolytes if dehydration suspected) 1

Common Pitfalls to Avoid

• Failing to distinguish true syncope from seizure, stroke, or metabolic causes - syncope has rapid, complete recovery without post-event confusion 1, 5
• Ordering brain imaging without focal neurological findings - extremely low yield 1
• Overlooking medication effects as contributors to syncope 1, 3
• Using Holter monitoring for infrequent events - use event monitors or implantable loop recorders instead 5
• Missing exertional syncope as HIGH-RISK - always requires cardiac evaluation 1, 3
• Not performing orthostatic vital signs in all patients 1, 5
• Ordering comprehensive laboratory testing without clinical indication 1

Age-Dependent Considerations

Pediatric/Young Patients:

• Most likely neurocardiogenic syncope, conversion reactions, primary arrhythmic causes (Long QT, Wolff-Parkinson-White) 4

Middle-Aged Patients:

• Neurocardiogenic syncope remains most frequent; also consider situational syncope, orthostasis, panic disorders 4

Elderly Patients:

• Higher frequency of cardiac causes: obstructions to cardiac output (aortic stenosis, pulmonary embolus), arrhythmias from underlying heart disease 4
• Consider carotid sinus hypersensitivity 4, 3