Syncope and Presyncope Guidelines

Definition and Characteristics

• The American College of Cardiology and the European Heart Association define syncope as a transient, self-limited loss of consciousness due to global cerebral hypoperfusion, characterized by rapid onset, short duration, and spontaneous complete recovery 1, 2
• Syncope involves a complete loss of consciousness with an inability to maintain postural tone, followed by rapid and spontaneous recovery 1, 2
• The underlying mechanism is transient global cerebral hypoperfusion, which can result from decreased cardiac output or decreased peripheral vascular resistance 3, 4
• Typical syncope is brief, with complete loss of consciousness in reflex syncope usually lasting no longer than 20 seconds 3, 4
• The European Heart Association recommends that recovery is usually accompanied by almost immediate restoration of appropriate behavior and orientation, although retrograde amnesia may occur 4, 5
• Post-recovery period may be marked by fatigue, according to the European Heart Association 3, 6
• Presyncope (near-syncope) refers to symptoms that resemble the prodrome of syncope but are not followed by complete loss of consciousness, as defined by the American College of Cardiology and the European Heart Association 1, 2
• Common symptoms of presyncope include extreme lightheadedness, visual sensations such as "tunnel vision" or "graying out," and variable degrees of altered consciousness 1, 7
• 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, according to the European Heart Association 4, 8

Key Differences

• The primary difference between syncope and presyncope is that syncope involves complete loss of consciousness, while presyncope does not, as stated by the American College of Cardiology and the European Heart Association 1, 2
• Both conditions share similar prodromal symptoms, such as lightheadedness, nausea, sweating, weakness, and visual disturbances, according to the European Heart Association 3, 4
• Both conditions involve the same underlying pathophysiology of decreased cerebral perfusion, but to different degrees, as noted by the European Heart Association 3, 4

Pathophysiological Mechanisms

• Normal cerebral blood flow ranges from 50-60 ml/100g tissue/min, which is approximately 12-15% of resting cardiac output, according to the European Heart Association 3
• Cerebral hypoperfusion can result from decreased cardiac output due to venous pooling, diminished blood volume, arrhythmias, or valvular disease, as stated by the European Heart Association 3
• Decreased peripheral vascular resistance due to excessive vasodilatation or impaired capacity to increase vascular resistance during standing can also lead to cerebral hypoperfusion, according to the European Heart Association 3

Clinical Implications

• The American College of Cardiology recommends that understanding whether a patient experienced syncope or presyncope is important for diagnostic evaluation and risk stratification, although the strength of evidence for this recommendation is not specified 1
• The European Heart Association notes that high-risk features that warrant more urgent evaluation include age >60 years, known cardiac disease, occurrence during exertion, and abnormal ECG findings, with a moderate level of evidence supporting this recommendation 9