Vasovagal syncope
Encyclopedia
A vasovagal episode or vasovagal response or vasovagal attack (also called neurocardiogenic syncope) is a malaise
mediated by the vagus nerve
. When it leads to syncope
or "fainting", it is called a vasovagal syncope, which is the most common type of fainting.
There are a number of different syncope
syndromes which all fall under the umbrella of vasovagal syncope. The common element among these conditions is the central mechanism leading to loss of consciousness. The differences among them are in the factors that trigger this mechanism.
of symptoms such as lightheadedness, nausea
, the feeling of being extremely hot (accompanied by sweating), ringing in the ears (tinnitus
), uncomfortable feeling in the heart, fuzzy thoughts, a slight inability to speak/form words (sometimes combined with mild stuttering), weakness and visual disturbances such as lights seeming too bright, fuzzy or tunnel vision, and sometimes a feeling of nervousness can occur as well. These last for at least a few seconds before consciousness is lost (if it is lost), which typically happens when the person is sitting up or standing. When sufferers pass out, they fall down (unless this is impeded); and when in this position, effective blood flow to the brain is immediately restored, allowing the person to wake up. Short of fainting a person may experience an almost indescribable weak and tired feeling resulting from a lack of oxygen to the brain due to a sudden drop in blood pressure. Taber's Cyclopedic Medical Dictionary describes this as the "feeling of impending death" caused by expansion of the aorta, drawing blood from the head and upper body.
The autonomic nervous system
's physiologic state (see below) leading to loss of consciousness may persist for several minutes, so:
Typical triggers for vasovagal episodes include:
(vagal) tone and withdrawal of sympathetic nervous system
tone.
This results in a spectrum of hemodynamic responses:
One account for these physiological responses is the Bezold-Jarisch reflex
.
. Making the correct diagnosis for loss of consciousness is one of the most difficult challenges that a physician can face. The core of the diagnosis of vasovagal syncope rests upon a clear description by the patient of a typical pattern of triggers, symptoms, and time course.
It is also pertinent to differentiate lightheadedness, seizures, vertigo
, and hypoglycemia
as other causes.
In patients with recurrent vasovagal syncope, or defecation syncope, diagnostic accuracy can often be improved with one of the following diagnostic tests:
The main danger of fainting fits or vasovagal syncope (or dizzy spells from vertigo) is the risk of injury by falling while unconscious.
Malaise
Malaise is a feeling of general discomfort or uneasiness, of being "out of sorts", often the first indication of an infection or other disease. Malaise is often defined in medicinal research as a "general feeling of being unwell"...
mediated by the vagus nerve
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
. When it leads to syncope
Syncope (medicine)
Syncope , the medical term for fainting, is precisely defined as a transient loss of consciousness and postural tone characterized by rapid onset, short duration, and spontaneous recovery due to global cerebral hypoperfusion that most often results from hypotension.Many forms of syncope are...
or "fainting", it is called a vasovagal syncope, which is the most common type of fainting.
There are a number of different syncope
Syncope (medicine)
Syncope , the medical term for fainting, is precisely defined as a transient loss of consciousness and postural tone characterized by rapid onset, short duration, and spontaneous recovery due to global cerebral hypoperfusion that most often results from hypotension.Many forms of syncope are...
syndromes which all fall under the umbrella of vasovagal syncope. The common element among these conditions is the central mechanism leading to loss of consciousness. The differences among them are in the factors that trigger this mechanism.
Signs and symptoms
Among people with vasovagal episodes, the episodes are typically recurrent, usually happening when the person is exposed to a specific trigger. Prior to losing consciousness, the individual frequently experiences a prodromeProdrome
In medicine, a prodrome is an early symptom that might indicate the start of a disease before specific symptoms occur. It is derived from the Greek word prodromos or precursor...
of symptoms such as lightheadedness, nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
, the feeling of being extremely hot (accompanied by sweating), ringing in the ears (tinnitus
Tinnitus
Tinnitus |ringing]]") is the perception of sound within the human ear in the absence of corresponding external sound.Tinnitus is not a disease, but a symptom that can result from a wide range of underlying causes: abnormally loud sounds in the ear canal for even the briefest period , ear...
), uncomfortable feeling in the heart, fuzzy thoughts, a slight inability to speak/form words (sometimes combined with mild stuttering), weakness and visual disturbances such as lights seeming too bright, fuzzy or tunnel vision, and sometimes a feeling of nervousness can occur as well. These last for at least a few seconds before consciousness is lost (if it is lost), which typically happens when the person is sitting up or standing. When sufferers pass out, they fall down (unless this is impeded); and when in this position, effective blood flow to the brain is immediately restored, allowing the person to wake up. Short of fainting a person may experience an almost indescribable weak and tired feeling resulting from a lack of oxygen to the brain due to a sudden drop in blood pressure. Taber's Cyclopedic Medical Dictionary describes this as the "feeling of impending death" caused by expansion of the aorta, drawing blood from the head and upper body.
The autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
's physiologic state (see below) leading to loss of consciousness may persist for several minutes, so:
- If sufferers try to sit or stand when they wake up, they may pass out again
- The person may be nauseated, pale, and sweaty for several minutes
Cause
Vasovagal syncope occurs in response to a trigger, with a corresponding malfunction in the parts of the nervous system that regulate heart rate and blood pressure. When heart rate slows, blood pressure drops, and the resulting lack of blood to the brain causes fainting.Typical triggers for vasovagal episodes include:
- Prolonged standing or upright sitting
- Standing up very quickly
- StressStress (medicine)Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...
- P.O.T.S.(Postural Orthostatic Tachycardia SyndromePostural orthostatic tachycardia syndromePostural orthostatic tachycardia syndrome is a condition of dysautonomia, more specifically orthostatic intolerance, in which a change from the supine position to an upright position causes an abnormally large increase in heart rate, called tachycardia...
) Multiple chronic episodes are experienced daily by many patients diagnosed with this syndrome. Episodes are most commonly manifested upon standing up. - Any painful or unpleasant stimuli, such as:
- TraumaTrauma (medicine)Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...
- VenipunctureVenipunctureIn medicine, venepuncture, venopuncture or venipuncture is the process of obtaining intravenous access for the purpose of intravenous therapy or for blood sampling of venous blood. This procedure is performed by medical laboratory scientists, medical practitioners, some EMTs, paramedics,...
- Watching or experiencing medical procedures
- High pressure on or around the chest area after heavy exercise
- Trauma
- Arousal or stimulants, e.g. sex
- Sudden onset of extreme emotions
- Lack of Sleep
- DehydrationDehydrationIn physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
- UrinationUrinationUrination, also known as micturition, voiding, peeing, weeing, pissing, and more rarely, emiction, is the ejection of urine from the urinary bladder through the urethra to the outside of the body. In healthy humans the process of urination is under voluntary control...
("micturition syncopeMicturition syncopeMicturition syncope or post-micturition syncope is the name given to the human phenomenon of fainting shortly after or during urination.People often become pale, nauseated, sweaty and weak before they lose consciousness...
") or defecationDefecationDefecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid waste material from the digestive tract via the anus. Waves of muscular contraction known as peristalsis in the walls of the colon move fecal matter through the digestive tract towards the rectum...
, having a bowel movement ("defecation syncope") - Random onsets due to nerve malfunctions
- Pressing upon certain places on the throat, sinuses, and eyes (also known as vagal reflex stimulation when performed clinically)
- Use of certain drugs that affect blood pressure, such as amphetamineAmphetamineAmphetamine or amfetamine is a psychostimulant drug of the phenethylamine class which produces increased wakefulness and focus in association with decreased fatigue and appetite.Brand names of medications that contain, or metabolize into, amphetamine include Adderall, Dexedrine, Dextrostat,...
Pathophysiology
Regardless of the trigger, the mechanism of syncope is similar in the various vasovagal syncope syndromes. In it, the nucleus tractus solitarius of the brainstem is activated directly or indirectly by the triggering stimulus, resulting in simultaneous enhancement of parasympathetic nervous systemParasympathetic nervous system
The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
(vagal) tone and withdrawal of sympathetic nervous system
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
tone.
This results in a spectrum of hemodynamic responses:
- On one end of the spectrum is the cardioinhibitory response, characterized by a drop in heart rate (negative chronotropic effect) and in contractility (negative inotropic effect) leading to a decrease in cardiac output that is significant enough to result in a loss of consciousness. It is thought that this response results primarily from enhancement in parasympathetic tone.
- On the other end of the spectrum is the vasodepressor response, caused by a drop in blood pressure (to as low as 80/20) without much change in heart rate. This phenomenon occurs due to vasodilationVasodilationVasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...
, probably as a result of withdrawal of sympathetic nervous systemSympathetic nervous systemThe sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
tone. - The majority of people with vasovagal syncope have a mixed response somewhere between these two ends of the spectrum.
One account for these physiological responses is the Bezold-Jarisch reflex
Bezold-Jarisch reflex
The Bezold–Jarisch reflex involves a variety of cardiovascular and neurological processes which cause hypopnea and bradycardia .-Physiology:...
.
Diagnosis
In addition to the mechanism described above, a number of other medical conditions may cause syncopeSyncope (medicine)
Syncope , the medical term for fainting, is precisely defined as a transient loss of consciousness and postural tone characterized by rapid onset, short duration, and spontaneous recovery due to global cerebral hypoperfusion that most often results from hypotension.Many forms of syncope are...
. Making the correct diagnosis for loss of consciousness is one of the most difficult challenges that a physician can face. The core of the diagnosis of vasovagal syncope rests upon a clear description by the patient of a typical pattern of triggers, symptoms, and time course.
It is also pertinent to differentiate lightheadedness, seizures, vertigo
Vertigo (medical)
Vertigo is a type of dizziness, where there is a feeling of motion when one is stationary. The symptoms are due to a dysfunction of the vestibular system in the inner ear...
, and hypoglycemia
Hypoglycemia
Hypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...
as other causes.
In patients with recurrent vasovagal syncope, or defecation syncope, diagnostic accuracy can often be improved with one of the following diagnostic tests:
- A tilt table testTilt table testA tilt table test, occasionally called upright tilt testing, is a medical procedure often used to diagnose dysautonomia or syncope. Patients with symptoms of dizziness or lightheadedness, with or without a loss of consciousness , suspected to be associated with a drop in blood pressure or...
- Implantation of an insertable loop recorder
- A Holter monitorHolter monitorIn medicine, a Holter monitor is a portable device for continuously monitoring various electrical activity of the cardiovascular system for at least 24 hours...
or event monitor - An echocardiogram
- An electrophysiology studyElectrophysiology studyAn electrophysiology study is a minimally invasive procedure which tests the electrical conduction system of the heart to assess the electrical activity and conduction pathways of the heart. The study is indicated to investigate the cause, location of origin, and best treatment for various...
Treatment
Treatment for vasovagal syncope focuses on avoidance of triggers, restoring blood flow to the brain during an impending episode, and measures that interrupt or prevent the pathophysiologic mechanism described above.- The cornerstone of treatment is avoidance of triggers known to cause syncope in that person. However, new development in psychological research has shown that patients show great reductions in vasovagal syncope through exposure-based exercises with therapists.
- Because vasovagal syncope causes a decrease in blood pressure, relaxing the entire body as a mode of avoidance isn't favorable. A patient can cross his/her legs and tighten leg muscles to keep blood pressure from dropping so drastically before an injection.
- Before known triggering events, the patient may increase consumption of salt and fluids to increase blood volume. Sports and energy drinks may be particularly helpful.
- Discontinuation of medications known to lower blood pressure may be helpful, but stopping antihypertensive drugs can also be dangerous. This process should be managed by an expert.
- Patients should be educated on how to respond to further episodes of syncope, especially if they experience prodromalProdromeIn medicine, a prodrome is an early symptom that might indicate the start of a disease before specific symptoms occur. It is derived from the Greek word prodromos or precursor...
warning signs: they should lie down and raise their legs; or at least lower their head to increase blood flow to the brain. If the individual has lost consciousness, he or she should be laid down with his or her head turned to the side. Tight clothing should be loosened. If the inciting factor is known, it should be removed if possible (for instance, the cause of pain). - Wearing graded compression stockings may be helpful.
- There are certain orthostatic training exercises which have been proven to improve symptoms in people with recurrent vasovagal syncope. A technique called "Applied Tension" which involves learning to tense the muscles in your torso, arms, and legs is effective for vasovagal Syncope.
- Certain medications may also be helpful:
- Beta blockers (β-adrenergic antagonists) were once the most common medication given; however, they have been shown to be ineffective in a variety of studies and are thus no longer prescribed.
- Other medications which may be effective include: fludrocortisoneFludrocortisoneFludrocortisone is a synthetic corticosteroid with moderate glucocorticoid potency and much greater mineralocorticoid potency. The brand name in the U.S. and Canada is Florinef.-Uses:...
, midodrineMidodrineMidodrine is a vasopressor/antihypotensive agent. Midodrine was approved in the United States by the Food and Drug Administration in 1996 for the treatment of orthostatic hypotension...
, SSRIs such as paroxetineParoxetineParoxetine is an SSRI antidepressant. Marketing of the drug began in 1992 by the pharmaceutical company SmithKline Beecham, now GlaxoSmithKline...
or sertralineSertralineSertraline hydrochloride is an antidepressant of the selective serotonin reuptake inhibitor class. It was introduced to the market by Pfizer in 1991. Sertraline is primarily used to treat major depression in adult outpatients as well as obsessive–compulsive, panic, and social anxiety disorders in...
, disopyramideDisopyramideDisopyramide is an antiarrhythmic medication. It is a Class Ia antiarrhythmic used in the treatment of ventricular tachycardias...
, and, in health-care settings where a syncope is anticipated, atropineAtropineAtropine is a naturally occurring tropane alkaloid extracted from deadly nightshade , Jimson weed , mandrake and other plants of the family Solanaceae. It is a secondary metabolite of these plants and serves as a drug with a wide variety of effects...
.
- For people with the cardioinhibitory form of vasovagal syncope, implantation of a permanent pacemakerArtificial pacemakerA pacemaker is a medical device that uses electrical impulses, delivered by electrodes contacting the heart muscles, to regulate the beating of the heart...
may be beneficial or even curative.
Prognosis
Brief periods of unconsciousness do no harm and are seldom symptoms of disease.The main danger of fainting fits or vasovagal syncope (or dizzy spells from vertigo) is the risk of injury by falling while unconscious.