What are the main types and causes of syncope?

Main Types and Causes of Syncope

Syncope is primarily classified into three major categories: neurally-mediated (reflex) syncope, orthostatic hypotension, and cardiac syncope, with neurally-mediated being the most common and cardiac being the most concerning for mortality. 1

Neurally-Mediated (Reflex) Syncope

• Vasovagal syncope (common faint) - The most prevalent form of syncope, characterized by a reflex that causes inappropriate vasodilation and bradycardia, resulting in systemic hypotension and cerebral hypoperfusion 1, 2

  • Typically triggered by emotional stress, fear, pain, blood phobia, or prolonged standing 2, 3
  • Often preceded by prodromal symptoms including lightheadedness, dizziness, nausea, diaphoresis, and pallor 1, 2
  • More common in younger patients but can occur at any age 1

• Carotid sinus syncope - Occurs when mechanical manipulation of the carotid sinuses triggers the vasovagal reflex 1

  • More common in older adults 3
  • Can be reproduced by carotid sinus massage 1

• Situational syncope - Associated with specific scenarios 1:

  • Cough or sneeze-induced syncope 1, 2
  • Gastrointestinal stimulation (swallowing, defecation, visceral pain) 1, 2
  • Micturition syncope (particularly post-micturition) 1, 2
  • Post-exercise syncope 1, 2
  • Post-prandial syncope 1, 2
  • Other triggers (brass instrument playing, weightlifting) 1

Orthostatic Hypotension

• Classic orthostatic hypotension - Sustained reduction of systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg within 3 minutes of assuming upright posture 1, 3

• Initial (immediate) orthostatic hypotension - Transient BP decrease within 15 seconds after standing 1

• Delayed orthostatic hypotension - Sustained reduction of BP that takes >3 minutes of upright posture to develop 1

• Causes of orthostatic hypotension:

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

Cardiac Syncope

• Arrhythmias as primary cause 1:

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

• Structural cardiac or cardiopulmonary disease 1:

  • Obstructive cardiac valvular disease (e.g., 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

Cerebrovascular Causes

• Vascular steal syndromes 1
• Basilar artery or severe bilateral carotid artery disease - Rarely causes syncope but when it does, it's usually associated with focal neurological symptoms 1

Age-Related Patterns in Syncope Etiology

• Pediatric and young patients - Most commonly experience neurocardiogenic syncope, conversion reactions (psychiatric causes), and primary arrhythmic causes such as long QT syndrome and Wolff-Parkinson-White syndrome 1

• Middle-aged patients - Neurocardiogenic syncope remains most frequent, with increased prevalence of situational syncope (deglutition, micturition, defecation, cough), orthostasis, and panic disorders 1

• Elderly patients - Higher frequency of cardiac causes including obstructions to cardiac output (aortic stenosis, pulmonary embolus) and arrhythmias resulting from underlying heart disease 1

Clinical Implications and Diagnostic Approach

• Cardiac syncope is associated with increased morbidity and mortality compared to neurally-mediated syncope, which generally has a benign course 4

• The initial evaluation should include a detailed history, physical examination including orthostatic blood pressure measurements, and standard ECG 1

• Careful attention to prodromal symptoms, circumstances surrounding the event, and post-event symptoms can help differentiate between types of syncope 1, 2

• Patients with structural heart disease or abnormal ECG findings should be evaluated for cardiac causes of syncope due to higher risk of mortality 5, 4

• Tilt-table testing can be useful for diagnosing neurally-mediated and orthostatic syncope when the diagnosis remains unclear after initial evaluation 6, 7