What is vasovagal syncope?

Vasovagal Syncope: The Most Common Form of Reflex Syncope

Vasovagal syncope (VVS) is the most common form of reflex syncope mediated by the vasovagal reflex, characterized by transient loss of consciousness due to cerebral hypoperfusion resulting from vasodilation and/or bradycardia. 1

Definition and Characteristics

Vasovagal syncope is defined by several key features:

1. Triggering factors:

   • Upright posture (standing or seated)
   • Emotional stress, fear, or pain
   • Medical settings or procedures
   • Prolonged standing in warm, crowded places

2. Typical symptoms:

   • Prodromal symptoms: diaphoresis, warmth, nausea, pallor
   • Vasodepressor hypotension and/or inappropriate bradycardia
   • Post-syncopal fatigue

3. Diagnostic criteria:

   • Based primarily on thorough history, physical examination, and eyewitness accounts
   • Absence of structural heart disease
   • Characteristic prodrome and triggers 1

Pathophysiology

The underlying mechanism involves a reflex response that causes:

• Vasodilation (vasodepressor response)
• Bradycardia (cardioinhibitory response)
• Or both (mixed response)

These responses lead to systemic hypotension and cerebral hypoperfusion, ultimately causing transient loss of consciousness. The contribution of each component (vasodilation vs. bradycardia) varies considerably between individuals 1.

Clinical Presentation

Classical vs. Atypical Presentation

• Classical VVS: Typically occurs in young adults with clear triggers and prodromal symptoms
• Atypical VVS: More common in older adults, often with short or absent prodrome and amnesia for loss of consciousness 2

Important distinction from other conditions:

• Cardiac syncope: Due to arrhythmias or structural heart disease
• Orthostatic hypotension: Sustained BP drop within 3 minutes of standing
• Situational syncope: Associated with specific actions (coughing, swallowing, etc.)
• Carotid sinus syndrome: Associated with carotid sinus hypersensitivity 1

Management Approach

Initial Management

• Patient education and reassurance are the cornerstone of treatment (Class I recommendation) 1
• Physical counter-pressure maneuvers are useful in patients with sufficient prodromal warning (Class IIa recommendation) 1
  • Leg crossing
  • Limb and/or abdominal contraction
  • Squatting

Pharmacological Management

• Midodrine may be reasonable in patients with recurrent VVS without history of hypertension, heart failure, or urinary retention (Class IIa recommendation) 1

Prevention Strategies

• Recognize and avoid triggers when possible
• Maintain adequate hydration and salt intake
• Assume supine position when prodromal symptoms occur to prevent injury 1

Special Considerations

Risk Assessment

• While generally benign, VVS can cause serious injuries due to falls during loss of consciousness 3
• Frequency of episodes and impact on quality of life should guide treatment intensity

Age-Related Differences

• Typical features may be absent in older patients
• In older adults, VVS may overlap with autonomic dysfunction and other forms of orthostatic intolerance 4

Common Pitfalls in Diagnosis and Management

1. Misdiagnosis as seizures due to myoclonic jerks during syncope
2. Failure to recognize atypical presentations in older adults
3. Overtreatment of infrequent, benign episodes
4. Underappreciation of impact on quality of life in patients with frequent episodes

VVS is generally not considered a disease but rather a physiological response that occurs in susceptible individuals. However, when occurring frequently or causing significant impact on quality of life, it requires appropriate management to prevent injuries and improve patient outcomes 4.