What is a Pre-Syncope Episode?
Pre-syncope (near-syncope) is a condition in which patients experience symptoms of impending loss of consciousness—including lightheadedness, dizziness, nausea, visual disturbances, and weakness—but do not actually lose consciousness, caused by transient cerebral hypoperfusion that remains above the threshold required to maintain awareness. 1
Core Pathophysiology
Pre-syncope occurs when cerebral blood flow decreases below the normal range of 50-60 ml/100g tissue/min but remains sufficient to prevent complete loss of consciousness 2, 3. The mechanism involves either:
- Decreased cardiac output from reduced venous return, arrhythmias, or structural heart disease 2
- Decreased peripheral vascular resistance from excessive vasodilation or impaired vasoconstriction 2
A drop in systolic blood pressure to approximately 60 mmHg typically triggers syncope, but lesser decreases cause pre-syncope 1, 2.
Typical Symptoms
Patients describe a constellation of warning signs that signal impending loss of consciousness 1:
- Faintness and extreme lightheadedness 1, 3
- Dizziness and feeling unsteady 1, 3
- Nausea and abdominal discomfort 1
- Feeling warm/hot or cold 1
- Visual disturbances including black spots, blurred vision, "tunnel vision," or "graying out" 1, 3
- Generalized weakness 1, 3
Observable Signs
Bystanders or clinicians may observe physical manifestations 1:
- Pallor (paleness) and sweating 1
- Vomiting and shivering 1
- Diminished postural tone 1
- Confusion 1
- Audible sighing 1
Critical Clinical Point: Pre-Syncope Carries the Same Risk as Syncope
Do not dismiss pre-syncope as less serious than syncope—both conditions share similar short-term serious outcomes and mortality rates and require identical evaluation. 2, 4 The prevalence of short-term serious outcomes varies from 4% to 27% among emergency department patients with pre-syncope, with arrhythmia being the most common serious outcome 4.
Most Common Causes
Neurally-mediated (vasovagal) pre-syncope accounts for 21.2% of cases and is triggered by emotional stress, pain, prolonged standing, or fear 2. This involves decreased blood return to the heart, leading to decreased cardiac output and cerebral perfusion 1.
Orthostatic hypotension occurs in 9.4% of cases and results from inadequate blood pressure response to standing 2. This is particularly common in elderly patients taking diuretics, beta-blockers, calcium antagonists, ACE inhibitors, nitrates, antipsychotic agents, tricyclic antidepressants, or dopamine agonists/antagonists 2.
Cardiac arrhythmias carry the highest morbidity and mortality risk and include bradyarrhythmias (sinus node dysfunction, AV block) and tachyarrhythmias (supraventricular or ventricular tachycardia) 2.
High-Risk Features Requiring Urgent Cardiac Evaluation
The following features mandate immediate cardiac work-up 2:
- Age >60 years 2
- Male gender 2
- Known underlying cardiac disease 2
- Palpitations prior to the episode 2
- Occurrence during exertion 2
- Occurrence in supine position 2
- Family history of sudden cardiac death 2
Immediate Management
At the first sign of pre-syncope, the patient should immediately assume a safe position—sitting or lying down—to prevent falls and improve cerebral perfusion. 1
Physical counter-pressure maneuvers (PCMs) should be initiated immediately 1:
Lower-body PCMs are preferable to upper-body and abdominal PCMs because they more effectively sustain arterial pressure. 1
If symptoms do not improve within 1-2 minutes, worsen, or recur, activate emergency medical services immediately. 1
Critical Pitfall to Avoid
Do not use physical counter-pressure maneuvers when symptoms of a heart attack or stroke accompany pre-syncope, as this may cause harm. 1 In these cases, immediate emergency medical evaluation is required.