Although rare, death can occur due to a vagal reflex. A reflex is an automatic and involuntary reaction that occurs in a living being in response to certain stimuli. If a sensory nerve ending is stimulated, the current travels along the nerve to the spinal cord or brain stem. From there, an involuntary motor nerve current then emerges.
The typical example of a reflex is when we hit the patellar tendon (which is in the knee) and an automatic reaction of leg extension occurs. Similarly, reflexes occur in other parts of the body, both in the skeletal muscles and in the musculature of the internal organs.
There are many reflexes that control all the automatic activities of our organs. For example, if food reaches the intestine, the nerve endings in the intestinal wall are stimulated and, by reflex, bile and pancreatic juice are released. Similarly, if the amount of oxygen in the air decreases (for example at high altitudes), the reflex that occurs causes us to breathe more frequently.
What is the vagal reflex?
The vagal reflex is present in all people and is involved in regulating heart rate and blood pressure. It is called “vagal” because it involves the vagus nerve, which innervates the heart and causes the heart rate to decrease. There are many stimuli that can trigger a vagal reflex. This reflex causes the heart rate and blood pressure to decrease.
Normally, the vagal reflex intervenes normally in cardiac and vascular regulation. This does not produce major changes or symptoms, as it is necessary to maintain a normal hemodynamic situation. However, there are people in whom the vagal reflex is excessive and is triggered by minor stimuli. In such cases, these people suffer dizziness or syncope due to the drop in blood pressure and heart rate produced by the vagal reflex.
It is known that some people lose consciousness when they see blood. This can also happen when they see a surgical procedure or when they are pricked for a blood sample. It can also happen when they perceive unpleasant smells, when they are standing for a long time or when they are under emotional stress. This loss of consciousness is called “vasovagal syncope”.
Can the vagal reflex cause death?
- It is always possible that a very intense vagal reflex can reduce the heart rate so much that cardiorespiratory arrest occurs, although this is exceptional. Vasovagal syncope is usually benign. The decrease in blood pressure and heart rate does not typically last long. The patient often regains consciousness within a few seconds.
- We physicians know that there are diagnostic and therapeutic procedures that can trigger the vagal reflex and cause complications. In rare cases, these are serious. It is relatively common for the most sensitive individuals to trigger the vagal reflex when an artery is punctured for catheterization. Otolaryngologists are well aware that manipulation of the pharynx or the instillation of anesthetic into it can lead to a severe vagal reaction.
- The intense vagal reflex can be triggered by many other reasons. Various medical procedures that require surgical punctures or cuts can trigger the vagal reflex. That is why it is always recommended to give a good local anesthetic and to reassure the patient. The patient should suffer as little as possible and thus reduce the risk of the vagal reaction occurring.
- As with medical procedures, physical aggression, pain, and intense fear may trigger an excessive vagal reflex. This can lead to syncope or even cardiac arrest. Some animals die when captured due to a vagal reflex. In ancient times and in certain tribes, people were sometimes punished with rituals that provoked terror. Some people even died.
Diagnosis of vagal reflex at autopsy.
As mentioned, a reflex is an automatic and involuntary reaction that occurs in a living being when faced with certain stimuli. Therefore, it cannot be diagnosed by autopsy. Once dead, the body no longer has nervous activity and, therefore, lacks reflexes.
However, it is possible that signs of aggression may be seen on the corpse, which would justify an intense vagal reflex that caused death. But this is only a supposition. There are many other causes of death by cardiac arrest in which no abnormality is observed at autopsy. This may occur in tako-tsubo syndrome and in electrical abnormalities of the heart (such as Brugada syndrome, Wolff-Parkinson-White syndrome, long QT syndrome, or short QT syndrome).
Sudden unexplained death typically occurs in people under 40 years of age. Younger people are less likely to have structural heart disease, but have a higher prevalence of electrical cardiac abnormalities. If these people die suddenly, the autopsy usually reveals a structurally normal heart. In these cases, sudden cardiac death should be suspected as a result of an electrical abnormality of the heart.
Sudden unexplained death typically occurs in previously healthy young people with no known pathology, and the autopsy does not provide a diagnosis. Very few have been previously studied, and some are known to have had a cardiac condition. In others, however, the previous study shows no abnormality that suggests a risk of sudden death. Approximately 30% of patients who suffer sudden unexplained death have mutations in cardiac ion channels.
If a person has one of these abnormalities, a situation of intense psychological stress could trigger a cardiac arrest. In such a case, the autopsy would not show the exact cause of death. The heart would be normal, and no other serious pathology would be detected. Therefore, the diagnosis of the cause of death would be a probability, but not a certainty. It could be a vagal reaction in a previously healthy person or cardiac arrest due to severe arrhythmia in a person with a previously unknown electrical abnormality of the heart.
Pathophysiology of the vasovagal response
