What is the difference between syncope and presyncope?

Syncope vs. Presyncope: Definition and Differences

Syncope is defined as a transient, self-limited loss of consciousness due to global cerebral hypoperfusion, characterized by rapid onset, short duration, and spontaneous complete recovery, while presyncope refers to symptoms that occur before syncope but without complete loss of consciousness. 1

Syncope Definition and Characteristics

• Syncope involves a complete loss of consciousness with an inability to maintain postural tone, followed by rapid and spontaneous recovery 1
• The underlying mechanism is transient global cerebral hypoperfusion 1
• Typical syncope is brief, with complete loss of consciousness in reflex syncope usually lasting no longer than 20 seconds 1
• Recovery is usually accompanied by almost immediate restoration of appropriate behavior and orientation, although retrograde amnesia may occur 1
• Post-recovery period may be marked by fatigue 1

Presyncope Definition and Characteristics

• Presyncope (near-syncope) refers to symptoms that resemble the prodrome of syncope but are not followed by complete loss of consciousness 1
• Common symptoms include extreme lightheadedness, visual sensations such as "tunnel vision" or "graying out," and variable degrees of altered consciousness 1
• The term "pre-syncopal" is used to indicate symptoms and signs that occur before unconsciousness in syncope, making it synonymous with "warning" and "prodromal" symptoms 1
• Presyncope occurs when cerebral perfusion decreases but not enough to cause complete loss of consciousness 2

Key Differences

• The primary difference is that syncope involves complete loss of consciousness, while presyncope does not 1
• Both conditions share similar prodromal symptoms (lightheadedness, nausea, sweating, weakness, visual disturbances) 1
• Both conditions involve the same underlying pathophysiology of decreased cerebral perfusion, but to different degrees 2
• Patients with presyncope have similar prognoses to those with syncope and should undergo a similar evaluation 3

Pathophysiological Mechanisms

• Normal cerebral blood flow ranges from 50-60 ml/100g tissue/min (12-15% of resting cardiac output) 1, 2
• Cerebral hypoperfusion can result from:
  • Decreased cardiac output due to venous pooling, diminished blood volume, arrhythmias, or valvular disease 1, 2
  • Decreased peripheral vascular resistance due to excessive vasodilatation or impaired capacity to increase vascular resistance during standing 1, 2
• A decrease in systolic blood pressure to around 60 mmHg is typically associated with complete syncope 2

Clinical Implications

• Understanding whether a patient experienced syncope or presyncope is important for diagnostic evaluation and risk stratification 3
• Both conditions require similar evaluation approaches, including detailed history, physical examination, and electrocardiography 3
• The distinction is important for accurate diagnosis, but both conditions should prompt investigation into the underlying cause 1, 3
• High-risk features that warrant more urgent evaluation include age >60 years, known cardiac disease, occurrence during exertion, and abnormal ECG findings 2, 3

Understanding the difference between syncope and presyncope is essential for proper clinical assessment, but both conditions require thorough evaluation to identify the underlying cause and determine appropriate management strategies.