From the Guidelines
Vasovagal stimulation can be recognized by a characteristic set of symptoms, including lightheadedness, dizziness, nausea, cold sweaty skin, blurred vision, and pallor, which often progress to fainting (syncope) if severe, as described in the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1. These symptoms typically occur in response to triggers such as emotional stress, pain, the sight of blood, prolonged standing, dehydration, or during medical procedures.
Key Symptoms
- Lightheadedness
- Dizziness
- Nausea
- Cold sweaty skin
- Blurred vision
- Pallor Before fainting, a person may experience warning signs called "prodromal symptoms" including yawning, feeling warm, nausea, and ringing in the ears.
Prodromal Symptoms
- Yawning
- Feeling warm
- Nausea
- Ringing in the ears During an episode, check for a slow pulse (bradycardia) and low blood pressure, as noted in the 2018 ESC guidelines for the diagnosis and management of syncope 1. Most episodes resolve quickly when the person lies down with legs elevated, allowing blood flow to return to the brain. Vasovagal reactions differ from other medical emergencies because consciousness typically returns quickly once horizontal, and there's no confusion afterward as might occur with seizures. If symptoms don't resolve promptly or occur frequently without clear triggers, medical evaluation is necessary to rule out cardiac or neurological conditions.
From the FDA Drug Label
Atropine-induced parasympathetic inhibition may be preceded by a transient phase of stimulation, especially on the heart where small doses first slow the rate before characteristic tachycardia develops due to paralysis of vagal control Adequate doses of atropine abolish various types of reflex vagal cardiac slowing or asystole The drug also prevents or abolishes bradycardia or asystole produced by injection of choline esters, anticholinesterase agents or other parasympathomimetic drugs, and cardiac arrest produced by stimulation of the vagus.
To recognize vasovagal stimulation, look for signs of parasympathetic stimulation, such as:
- Bradycardia (slow heart rate)
- Cardiac slowing or asystole (temporary stoppage of the heart)
- Vagal cardiac slowing These signs may be preceded by a transient phase of stimulation before atropine takes effect and abolishes the vagal stimulation 2.
From the Research
Recognising Vasovagal Stimulation
To recognise vasovagal stimulation, it is essential to understand the symptoms and mechanisms involved. Vasovagal syncope is characterised by a common autonomic reflex involving the cardiovascular system, associated with bradycardia and/or hypotension, likely mediated by parasympathetic activation and sympathetic inhibition 3.
Symptoms and Diagnosis
The symptoms of vasovagal syncope include:
- Profound bradycardia and hypotension 4
- Dizziness, nausea, sweating, bradycardia, hypotension, and, in some cases, syncope or convulsions 5
- Premonitory symptoms such as pallor, nausea, asthenia, yawns, hyperventilation, mydriasis, humming, lasting several minutes 6 The diagnosis of vasovagal syncope can be made based on history, and a tilt test can be used to confirm the diagnosis 7, 6.
Mechanisms
The mechanisms involved in vasovagal syncope include:
- A paradoxical reaction of the autonomic nervous system leading to hypotension and/or bradycardia 7
- A fall in the venous return, inducing an increased sympathetic drive to the heart and a lower ventricular filling 6
- Activation of ventricular mechanoreceptors, and through a reflex mechanism, a sudden increase in the vagal and a sudden reduction in the sympathetic drive 6
- Marked peripheral vasodilation, particularly in skeletal muscle, contributing to the fall in arterial pressure 4
Key Findings
Key findings in vasovagal syncope include:
- The temporal causative association of bradycardia with syncope in those with vasovagal syncope may help identify which patient could benefit from pacing 3
- The mode, rate, pacing algorithm and time to initiate dual-chamber pacing preferentially with respect to the vasovagal reflex may be important to prevent or ameliorate the faint 3
- Permanent pacing may have a role in managing select patients with vasovagal syncope 3, 7