vasovagal

Vasovagal refers to a reflex that can cause fainting (vasovagal syncope) due to a temporary drop in blood flow to the brain. It is the most common cause of syncope and is often described as a neurocardiogenic or reflex-mediated collapse.

Mechanism and triggers: The vasovagal response involves an abnormal autonomic reflex where stimuli such as prolonged standing, heat, dehydration, emotional distress, pain, or fear trigger a surge of vagal (parasympathetic) activity and withdrawal of sympathetic tone. This leads to vasodilation and, in some cases, slowed heart rate, reducing cerebral perfusion and producing loss of consciousness followed by rapid recovery.

Clinical features: Typical episodes begin with prodromal symptoms such as lightheadedness, nausea, pallor, sweating, and blurred vision. Fainting usually occurs after a trigger and is followed by rapid recovery once lying flat, which restores blood flow to the brain.

Diagnosis: Diagnosis is mainly clinical, based on history and exam. An ECG is often performed to exclude cardiac arrhythmias. Additional testing, such as tilt-table testing, may be used in selected cases to confirm susceptibility and guide management.

Management: Primary treatment focuses on education and lifestyle adjustments. Nonpharmacologic measures include recognizing triggers, staying hydrated, maintaining adequate salt intake where appropriate, and using physical counterpressure maneuvers (such as leg crossing and tensing muscles) at the first signs of prodrome. For recurrent cases, clinicians may consider pharmacologic options (for example, midodrine or fludrocortisone) on an individualized basis, though evidence varies.

Prognosis: Vasovagal syncope is usually benign with a good prognosis. Recurrence is possible but can often be reduced with trigger avoidance and preventive strategies.