What are the causes and management of syncope?

Causes and Management of Syncope

Syncope is primarily caused by transient global cerebral hypoperfusion resulting from decreased cardiac output, reduced peripheral vascular resistance, or both, with neurally-mediated reflexes, cardiac conditions, and orthostatic issues being the most common etiologies. 1

Major Categories of Syncope

1. Neurally-Mediated (Reflex) Syncopal Syndromes

• Vasovagal syncope (common faint) - triggered by emotional stress, pain, or prolonged standing, characterized by inappropriate vasodilation and bradycardia 1, 2
• Carotid sinus syncope - occurs with mechanical manipulation of carotid sinuses 1
• Situational syncope - associated with specific triggers:
  • Acute hemorrhage 1
  • Coughing or sneezing 1, 2
  • Gastrointestinal stimulation (swallowing, defecation, visceral pain) 1, 2
  • Micturition (post-micturition) 1, 2
  • Post-exercise 1
  • Others (brass instrument playing, weightlifting, post-prandial) 1

2. Orthostatic Syncope

• Autonomic failure:
  • Primary autonomic failure syndromes (pure autonomic failure, multiple system atrophy, Parkinson's disease with autonomic failure) 1
  • Secondary autonomic failure syndromes (diabetic neuropathy, amyloid neuropathy) 1
• Drug and alcohol-induced 1, 3
• Volume depletion 1

3. Cardiac Arrhythmias as Primary Cause

• Sinus node dysfunction (including bradycardia/tachycardia syndrome) 1, 4
• Atrioventricular conduction system disease 1
• Paroxysmal supraventricular and ventricular tachycardias 1
• Inherited syndromes (long QT syndrome, Brugada syndrome) 1, 5
• Implanted device (pacemaker, ICD) malfunction 1
• Drug-induced proarrhythmias 1

4. Structural Cardiac or Cardiopulmonary Disease

• Cardiac valvular disease (especially aortic stenosis) 1
• Acute myocardial infarction/ischemia 1
• Obstructive cardiomyopathy 1
• Atrial myxoma 1
• Acute aortic dissection 1
• Pericardial disease/tamponade 1
• Pulmonary embolus/pulmonary hypertension 1

5. Cerebrovascular Causes

• Vascular steal syndromes (most commonly subclavian steal) 1

Non-Syncopal Conditions Often Misdiagnosed as Syncope

• Disorders without impairment of consciousness: falls, cataplexy, drop attacks, psychogenic pseudo-syncope, TIAs of carotid origin 1
• Disorders with partial or complete loss of consciousness: metabolic disorders (hypoglycemia, hypoxia, hyperventilation), epilepsy, intoxication, vertebro-basilar TIA 1, 6

Diagnostic Approach

Initial Evaluation

• Detailed history: prodromal symptoms, triggers, position, duration, recovery 7
• Physical examination: vital signs, orthostatic measurements, cardiac and neurological examination 7
• 12-lead ECG: to identify arrhythmias, conduction abnormalities, or structural heart disease 7

Risk Stratification

High-risk features requiring hospitalization:

• Suspected or known significant heart disease 1
• ECG abnormalities suggesting arrhythmic syncope 1
• Syncope during exercise 1
• Syncope causing severe injury 1
• Family history of sudden death 1

Specialized Testing (Based on Initial Evaluation)

• Cardiac evaluation: echocardiography, stress testing, prolonged ECG monitoring 4, 5
• Autonomic testing: tilt-table testing for suspected neurally-mediated syncope 3, 6
• Neurological evaluation: only when loss of consciousness cannot be attributed to syncope 1

Management Approach

1. Neurally-Mediated Syncope

• Education and lifestyle modifications: avoiding triggers, maintaining hydration 3
• Physical counterpressure maneuvers for prodromal symptoms 2
• Pharmacological therapy in refractory cases: fludrocortisone, midodrine, beta-blockers 3

2. Orthostatic Syncope

• Non-pharmacological measures: gradual position changes, increased salt and fluid intake, compression stockings 3
• Medication adjustment: reducing or discontinuing vasodilators or diuretics 3
• Pharmacological therapy: fludrocortisone, midodrine, droxidopa 3

3. Cardiac Arrhythmic Syncope

• Bradyarrhythmias: pacemaker implantation 4
• Tachyarrhythmias: antiarrhythmic drugs, catheter ablation, ICD implantation 4, 5
• Inherited arrhythmia syndromes: specific management based on syndrome type 5

4. Structural Cardiac Disease

• Treatment directed at the underlying cardiac condition:
  • Valvular disease: valve repair/replacement 1
  • Ischemic heart disease: revascularization 1
  • Obstructive cardiomyopathy: surgical myectomy, alcohol septal ablation 1
  • Cardiac masses: surgical removal 1

5. Vascular Steal Syndromes

• Direct corrective angioplasty or surgery for subclavian steal syndrome 1

Clinical Pearls and Pitfalls

• Cardiac syncope carries higher mortality risk (24% one-year mortality) compared to non-cardiac causes (3-4%) 1
• Multiple mechanisms may contribute to syncope in patients with structural heart disease 1
• Avoid unnecessary neurological testing (EEG, brain imaging) unless specific neurological signs are present 1, 7
• Prodromal symptoms like nausea, sweating, and pallor suggest neurally-mediated syncope 2, 3
• Post-syncopal confusion is more suggestive of seizure than true syncope 3, 6