How do you differentiate the etiology of syncope?

Differentiating the Etiology of Syncope

A thorough history and physical examination with targeted questions about circumstances, triggers, prodromal symptoms, and recovery pattern is the most effective approach to differentiate the etiology of syncope. 1

Initial Classification Framework

Syncope can be classified into three major categories:

1. Neurally-mediated (reflex) syncope

   • Vasovagal syncope (common faint)
   • Carotid sinus syncope
   • Situational syncope

2. Cardiac syncope

   • Arrhythmias
   • Structural heart disease

3. Orthostatic hypotension

   • Primary/secondary autonomic failure
   • Volume depletion
   • Drug-induced

Key Historical Features to Differentiate Etiology

Features Suggesting Cardiac Syncope 1

• Age >60 years
• Male sex
• Known heart disease (ischemic, structural, arrhythmias)
• Brief or absent prodrome
• Syncope during exertion
• Syncope in supine position
• Low number of episodes (1-2)
• Family history of sudden cardiac death
• Palpitations before syncope

Features Suggesting Neurally-Mediated Syncope 1

• Younger age
• No known cardiac disease
• Syncope only in standing position
• Positional change from supine/sitting to standing
• Clear prodrome: nausea, vomiting, feeling warm
• Specific triggers: dehydration, pain, emotional distress
• Situational triggers: cough, micturition, defecation, swallowing
• Frequent recurrence with similar characteristics

Features Suggesting Orthostatic Hypotension 1

• Symptoms upon standing
• Temporal relationship to medication changes
• Autonomic neuropathy symptoms
• Post-prandial timing
• Volume depletion history

Physical Examination Elements

1. Cardiovascular Assessment

   • Heart rate and rhythm
   • Murmurs, gallops, or rubs suggesting structural heart disease
   • Carotid bruits

2. Orthostatic Vital Signs

   • Measure BP and HR lying, sitting, immediately upon standing, and after 3 minutes
   • Orthostatic hypotension: drop in systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg within 3 minutes of standing

3. Neurological Examination

   • Basic assessment to rule out focal deficits

Diagnostic Tests

First-Line Testing 1

• 12-lead ECG (mandatory)
• Look for:
  • Conduction abnormalities (bifascicular block, QRS >0.12s)
  • AV block
  • Bradycardia/tachycardia
  • Pre-excitation
  • Prolonged QT
  • Brugada pattern
  • Arrhythmogenic right ventricular dysplasia signs
  • Q waves suggesting infarction

Additional Testing Based on Initial Evaluation

• Suspected cardiac cause: Echocardiogram, prolonged ECG monitoring
• Suspected reflex mechanism: Tilt table testing
• Suspected orthostatic hypotension: Formal orthostatic challenge
• Age >40 years: Consider carotid sinus massage

Diagnostic Algorithm

1. Initial evaluation: History + Physical exam + ECG

2. If diagnostic:

   • Classic vasovagal: Emotional trigger + prodrome
   • Situational: During specific activities (micturition, defecation, coughing)
   • Orthostatic: Symptoms upon standing + BP drop
   • Cardiac arrhythmia: ECG evidence or palpitations + sudden LOC

3. If non-diagnostic:

   • High-risk features present (cardiac disease, abnormal ECG, exertional syncope, family history of SCD):
     • Cardiac evaluation (echocardiogram, monitoring)
   • Low-risk features (recurrent episodes, prodrome, triggers):
     • Consider tilt testing for reflex syncope
     • Consider orthostatic testing

Common Pitfalls to Avoid

1. Misdiagnosing seizures as syncope

   • Look for: prolonged LOC, postictal confusion, tongue biting, tonic-clonic movements

2. Missing cardiac causes

   • Always obtain ECG
   • Consider monitoring in unexplained cases

3. Inadequate orthostatic testing

   • Measure BP at appropriate intervals
   • Consider medication effects

4. Overlooking situational triggers

   • Ask specifically about activities preceding syncope

5. Ignoring red flags

   • Syncope during exertion
   • Family history of sudden death
   • Syncope without prodrome

By systematically evaluating patients using this approach, the etiology of syncope can be determined in 23-50% of cases during initial evaluation 1. For unexplained cases after initial assessment, risk stratification should guide further specialized testing.