What is the definition of syncope?

Definition of Syncope

Syncope is defined as a sudden, transient, complete loss of consciousness associated with inability to maintain postural tone, with rapid and spontaneous recovery, presumed to be caused by cerebral hypoperfusion. 1

Key Characteristics of True Syncope

• Abrupt onset with complete loss of consciousness
• Brief duration (typically seconds to minutes)
• Spontaneous and complete recovery without therapeutic intervention
• No prolonged confusion following the event
• Inability to maintain postural tone (patient falls or slumps if not supported)
• Underlying mechanism: Cerebral hypoperfusion (approximately 35% reduction in cerebral blood flow or complete disruption for 5-10 seconds) 1

Distinguishing Syncope from Other Causes of Loss of Consciousness

Syncope must be differentiated from other conditions that may present with transient loss of consciousness:

• Seizures: Often associated with post-event confusion, tongue biting, incontinence
• Hypoglycemia: Gradual onset, associated with diaphoresis, hunger
• Concussion: Associated with head trauma
• Intoxication: History of substance use, gradual onset
• Metabolic disorders: Often more gradual onset with other systemic symptoms
• Psychogenic pseudosyncope: Apparent rather than true loss of consciousness

Pathophysiological Classification of Syncope

Syncope occurs when cerebral blood flow is temporarily insufficient. The main mechanisms include:

1. Reflex (neurally-mediated) syncope:

   • Vasovagal syncope (emotional distress, orthostatic stress)
   • Situational syncope (cough, micturition, defecation, etc.)
   • Carotid sinus syncope

2. Orthostatic hypotension:

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

3. Cardiac syncope:

   • Arrhythmias (bradycardia or tachycardia)
   • Structural heart disease (valvular disease, cardiomyopathy, etc.)
   • Other cardiovascular conditions (pulmonary embolism, aortic dissection, etc.)

Clinical Significance

Syncope is a common medical problem accounting for:

• Up to 3% of emergency department visits
• Approximately 6% of hospital admissions 1
• Prevalence varies by age with trimodal distribution (peaks around ages 20,60, and 80) 1

Common Pitfalls in Syncope Evaluation

• Misdiagnosis: Failing to distinguish syncope from other causes of transient loss of consciousness
• Overinvestigation: Ordering unnecessary tests (e.g., neuroimaging, EEG) when clinical presentation is typical for reflex syncope
• Underestimation of cardiac causes: Cardiac syncope carries higher mortality risk and requires thorough evaluation
• Ignoring recurrence risk: Even benign causes of syncope can recur and lead to injury

Key Diagnostic Considerations

When evaluating a patient with suspected syncope, remember:

• The definition requires complete loss of consciousness, inability to maintain posture, and spontaneous recovery
• The underlying mechanism is cerebral hypoperfusion
• Distinguishing syncope from seizures, metabolic causes, and psychogenic pseudosyncope is essential for proper management
• Risk stratification should guide the diagnostic approach and treatment decisions

By adhering to the proper definition and understanding the pathophysiology, clinicians can more effectively evaluate and manage patients with syncope.