From the Guidelines
A vasovagal episode occurs when the body overreacts to certain triggers, causing a sudden drop in heart rate and blood pressure that leads to reduced blood flow to the brain and temporary loss of consciousness, primarily due to the failure of protective mechanisms that maintain cerebral nutrient delivery, as described in the European Heart Journal guidelines 1.
Physiological Explanation
The physiological explanation of a vasovagal episode involves the activation of the vagus nerve, which releases acetylcholine, causing bradycardia and vasodilation of blood vessels, leading to a rapid drop in blood pressure 1. This response is triggered by various factors, including pain, emotional distress, or prolonged standing, and results in cerebral hypoperfusion, causing symptoms such as lightheadedness, tunnel vision, nausea, sweating, and potentially syncope.
Key Factors
Some key factors that contribute to the occurrence of vasovagal episodes include:
- Excessive vagal stimulation, which can be triggered by various factors, including pain, emotional distress, or prolonged standing 1
- Decreased cardiac output, which can be caused by bradyarrhythmias, tachyarrhythmias, or valvular disease 1
- Widespread and excessive vasodilatation, which can decrease arterial pressure and cerebral perfusion pressure 1
- Impaired capacity to increase vascular resistance during standing, which can cause orthostatic hypotension and syncope in patients using vasoactive drugs and in patients with autonomic neuropathies 1
Protective Mechanisms
The integrity of several control mechanisms is crucial for maintaining adequate cerebral nutrient delivery, including:
- Cerebrovascular 'auto-regulatory' capability, which permits cerebral blood flow to be maintained over a relatively wide range of perfusion pressures 1
- Local metabolic and chemical control, which permits cerebral vasodilatation to occur in the presence of either diminished pO2 or elevated pCO2 1
- Arterial baroreceptor-induced adjustments of heart rate, cardiac contractility, and systemic vascular resistance, which modify systemic circulatory dynamics in order to protect cerebral flow 1
- Vascular volume regulation, in which renal and hormonal influences help to maintain central circulating volume 1
Resolution and Prevention
The episode typically resolves quickly once the person falls or lies down, as horizontal positioning helps restore blood flow to the brain. No medication is typically needed for occasional vasovagal episodes, though staying hydrated, avoiding triggers, and using counter-maneuvers like leg crossing or muscle tensing can help prevent recurrences.
From the Research
Physiological Explanation of Vasovagal Syncope
The physiological explanation of a vasovagal syncope episode is related to a complex neurologic reflex that affects the body's blood pressure and heart rate regulation.
- Vasovagal syncope is characterized by an abrupt loss of consciousness in response to reduced perfusion to the brain 2.
- It results from a complex interplay between the nervous system and the cardiovascular system, leading to a sudden drop in blood pressure and heart rate 3.
- The exact mechanism is not fully understood, but it is thought to involve the activation of the vagus nerve, which can cause a decrease in heart rate and blood pressure 2.
Key Factors Involved
Some key factors involved in the physiological explanation of vasovagal syncope include:
- Reduced perfusion to the brain, leading to a loss of consciousness 2
- Activation of the vagus nerve, which can cause a decrease in heart rate and blood pressure 2
- Decreased systemic fluid volume, which can contribute to the development of vasovagal syncope 2
- Abnormalities in the sympathetic nervous system, which can affect the body's ability to regulate blood pressure and heart rate 2
Triggering Factors
Vasovagal syncope can be triggered by a variety of factors, including: