From the Guidelines
Vasovagal syncope is a common type of fainting that occurs when the body overreacts to certain triggers, causing a sudden drop in heart rate and blood pressure, reducing blood flow to the brain, as defined by the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1. This condition is triggered by various stimuli such as the sight of blood, extreme emotional distress, prolonged standing, dehydration, or pain. When an episode occurs, individuals might experience warning signs like nausea, sweating, pale skin, and lightheadedness before briefly losing consciousness. The diagnosis of vasovagal syncope is made primarily on the basis of a thorough history, physical examination, and eyewitness observation, if available, as stated in the 2017 ACC/AHA/HRS guideline 1. Some key features of vasovagal syncope include:
- It may occur with upright posture or with exposure to emotional stress, pain, or medical settings
- It is typically characterized by diaphoresis, warmth, nausea, and pallor
- It is associated with vasodepressor hypotension and/or inappropriate bradycardia
- It is often followed by fatigue Most cases of vasovagal syncope are benign and don't require specific medication. Management typically involves:
- Avoiding known triggers
- Staying hydrated
- Increasing salt intake if appropriate
- Learning to recognize warning signs to sit or lie down immediately to prevent falling For recurrent episodes, physical counterpressure maneuvers like leg crossing or hand gripping may be recommended to maintain blood pressure. In severe cases that significantly impact quality of life, medications such as fludrocortisone, midodrine, or beta-blockers might be prescribed, though these are not first-line treatments, as noted in the guidelines on management of syncope 1. Vasovagal syncope occurs due to an imbalance in the autonomic nervous system, where the vagus nerve inappropriately signals the heart to slow down while blood vessels dilate, causing blood to pool in the legs rather than return to the heart and brain. According to the European Heart Journal guidelines on management of syncope, the initial evaluation of syncope should include a thorough history, physical examination, and ECG, and the diagnosis of vasovagal syncope can be made if precipitating events are associated with typical prodromal symptoms 1. Additionally, pacing therapy may be considered for patients with refractory neurocardiogenic syndromes associated with severe bradycardia or asystole, but its effectiveness is still a topic of debate, as discussed in the American Family Physician indications and recommendations for pacemaker therapy 1.
From the Research
Definition of Vasovagal Syncope
- Vasovagal syncope is a condition characterized by an abrupt loss of consciousness in response to reduced perfusion to the brain, resulting from a complex neurologic reflex 2.
- It is also known as neurocardiogenic syncope, and its treatments aim to modulate aspects of this reflex to prevent recurrence.
Pathophysiology and Triggers
- Reduced venous return is an important trigger of vasovagal syncope, and treatments such as elastic compression stockings (ECS) can modify venous return and be of therapeutic interest 3.
- The condition involves a complex interplay of neural and cardiovascular factors, including the sympathetic nervous system, which can be modulated by pharmacologic treatments such as midodrine, β blockers, and norepinephrine transport inhibitors 2.
Treatment Options
- Conservative measures, such as lifestyle modifications, are the first line of treatment for vasovagal syncope, and may include increasing fluid and salt intake, and practicing counter-pressure maneuvers 4, 3.
- Pharmacologic treatments, such as midodrine and fludrocortisone, may be effective in preventing recurrence of vasovagal syncope, although the evidence is not yet conclusive 2, 4, 5, 6.
- Midodrine has been shown to substantially reduce the likelihood of positive head-up-tilt (HUT) test outcomes and clinical syncope in patients with recurrent vasovagal syncope 6.
- Fludrocortisone has been found to have a marginally nonsignificant reduction in syncope in some studies, although it may have a significant effect after dose stabilization 5.
Ongoing Research and Future Directions
- Several ongoing and planned studies, such as the COMFORTS and COMFORTS-II trials, aim to evaluate the efficacy of midodrine and fludrocortisone in preventing recurrence of vasovagal syncope, and to compare their effects with lifestyle modifications and other treatments 4, 3.
- Further research is needed to fully understand the pathophysiology of vasovagal syncope and to develop effective treatments for this condition.