Can vST cause syncope?

Vasovagal Syncope Can Cause Syncope

Yes, vasovagal syncope (VVS) is a common cause of syncope, characterized by a reflex causing hypotension and bradycardia that leads to cerebral hypoperfusion and loss of consciousness. 1

Pathophysiology of Vasovagal Syncope

VVS occurs through a reflex mechanism triggered by:

• Prolonged standing
• Emotional stress
• Pain
• Medical procedures (including venous access)
• Fear

The underlying mechanism involves:

1. Initial trigger activates the vasovagal reflex
2. Increased parasympathetic tone → bradycardia (sometimes severe, including asystole)
3. Reduced sympathetic tone → vasodilation and hypotension
4. Cerebral hypoperfusion → syncope

In young patients, reduced systemic vascular resistance is the predominant mechanism (75% of cases), while reduced cardiac output is less common (25% of cases) 2.

Clinical Presentation and Diagnosis

VVS typically presents with:

• Prodromal symptoms: diaphoresis, warmth, pallor, nausea
• Positional relationship: Often occurs when standing or sitting
• Recovery phase: Fatigue after the event

The European Society of Cardiology guidelines provide specific historical clues that suggest VVS 1:

• Occurs during prolonged standing
• Triggered by fear, pain, or medical procedures
• Associated with nausea, sweating, and pallor
• May occur after physical exercise, especially in young people

Distinguishing Features from Other Causes of Syncope

VVS must be differentiated from other causes of syncope:

• Cardiac syncope: Usually associated with palpitations, occurs during exertion, has minimal prodrome
• Orthostatic hypotension: Occurs shortly after standing
• Situational syncope: Specific triggers like coughing, micturition, defecation
• Arrhythmic syncope: Often associated with palpitations before syncope

Management Approach

For patients with VVS, management includes:

1. Patient education about the diagnosis and prognosis (Class I recommendation) 1

2. Physical counter-pressure maneuvers for patients with sufficient prodrome (Class IIa recommendation):

   • Leg crossing
   • Limb/abdominal contraction
   • Squatting

3. Pharmacological therapy when needed:

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

4. Acute management during an episode:

   • Assume supine position
   • Intravenous fluids if available
   • Atropine for severe bradycardia/asystole
   • Trendelenburg position 3

Special Considerations

• Asystole: Some patients with VVS may experience severe bradycardia with asystole, which can be potentially dangerous, especially in older patients or those with cardiovascular disease 3

• Mixed mechanisms: VVS can coexist with other conditions like postural orthostatic tachycardia syndrome (POTS) 4

• Fever: Can unmask or exacerbate syncope in certain conditions (like Brugada syndrome), requiring careful evaluation 5

Pitfalls and Caveats

• Not all syncope during procedures is vasovagal - consider cardiac arrhythmias in patients with concerning history
• Medications can exacerbate VVS, particularly beta-blockers which may cause postural hypotension 6
• Cerebral autoregulation impairment may play a role in some cases of VVS, even without severe drops in blood pressure 7
• Implantable loop recorders may be needed to distinguish between VVS and arrhythmic causes in unclear cases 8

VVS is generally benign but can significantly impact quality of life through injuries and psychological distress. Proper diagnosis and management can substantially improve outcomes for affected individuals.