What is the definition of syncope?

Definition of Syncope

Syncope is defined as a transient loss of consciousness due to global cerebral hypoperfusion characterized by rapid onset, short duration, and spontaneous complete recovery. 1, 2

Key Characteristics of Syncope

• Pathophysiological mechanism: Temporary cerebral hypoperfusion (approximately 35% reduction in cerebral blood flow or complete disruption for 5-10 seconds is sufficient to cause syncope) 2
• Duration: Relatively brief and self-limited 3
• Recovery: Spontaneous and complete without intervention 1
• Distinguishing features: Must be differentiated from other causes of transient loss of consciousness such as seizures, metabolic disorders, intoxication, and psychogenic pseudosyncope 2

Classification of Syncope

Syncope can be categorized into three main types based on underlying mechanisms:

1. Reflex (Neurally-Mediated) Syncope:

   • Vasovagal syncope (common faint)
   • Situational syncope (triggered by cough, micturition, defecation, etc.)
   • Carotid sinus syncope 2

2. Orthostatic Hypotension:

   • Primary or secondary autonomic failure
   • Drug-induced
   • Volume depletion 2

3. Cardiac Syncope:

   • Arrhythmias
   • Structural heart disease
   • Other cardiovascular conditions (pulmonary embolism, aortic dissection) 2

Epidemiology

• Affects approximately one-third of the population at least once during their lifetime 2
• Follows a trimodal distribution with peaks around ages 20,60, and 80 years 1, 2
• More common in females than males (22% versus 15%) 1
• Accounts for up to 3% of emergency department visits 2

Clinical Presentation

• Prodromal symptoms: May include lightheadedness, weakness, headache, blurred vision, diaphoresis, nausea, and vomiting seconds to minutes before loss of consciousness 2
• Post-syncopal symptoms: May include drowsiness, headache, dizziness, and nausea, but typically not confusion 2

Important Distinctions

• Syncope must be distinguished from other conditions that may cause apparent loss of consciousness but are not due to cerebral hypoperfusion 2
• Pseudosyncope is defined as "a syndrome of apparent but not true loss of consciousness that may occur in the absence of identifiable cardiac, reflex, neurological, or metabolic causes" 1

Prognostic Implications

The prognosis varies significantly based on the underlying cause:

• Reflex syncope is generally benign but may recur and cause injury
• Cardiac syncope carries a higher mortality risk and may indicate risk for sudden cardiac death 2, 3

Common Pitfalls in Diagnosis

• Misdiagnosing other causes of transient loss of consciousness as syncope
• Failure to identify potentially life-threatening cardiac causes
• Excessive diagnostic testing without a systematic approach
• Underestimating the impact of recurrent syncope on quality of life 2

Understanding the precise definition and characteristics of syncope is essential for proper diagnosis, risk stratification, and management to reduce morbidity and mortality associated with this common clinical condition.