Reflex syncope

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Reflex syncope
Other namesNeurally mediated syncope, neurocardiogenic syncope [1] [2]
Gray793.png
Vagus nerve
Specialty Neurology, cardiovascular
Symptoms Loss of consciousness before which there may be sweating, decreased ability to see, ringing in the ears [1] [2]
Complications Injury [1]
DurationBrief [1]
TypesVasovagal, situational, carotid sinus syncope [1]
Diagnostic method Based on symptoms after ruling out other possible causes [3]
Differential diagnosis Arrhythmia, orthostatic hypotension, seizure, hypoglycemia [1]
TreatmentAvoiding triggers, drinking sufficient fluids, exercise, cardiac pacemaker [2]
Medication Midodrine, fludrocortisone [4]
Frequency> 1 per 1,000 people per year [1]

Reflex syncope is a brief loss of consciousness due to a neurologically induced drop in blood pressure and/or a decrease in heart rate. [5] [6] [7] [8] [9] [10] [2] Before an affected person passes out, there may be sweating, a decreased ability to see, or ringing in the ears. [1] Occasionally, the person may twitch while unconscious. [1] Complications of reflex syncope include injury due to a fall. [1]

Contents

Reflex syncope is divided into three types: vasovagal, situational, and carotid sinus. [2] Vasovagal syncope is typically triggered by seeing blood, pain, emotional stress, or prolonged standing. [11] Situational syncope is often triggered by urination, swallowing, or coughing. [2] Carotid sinus syncope is due to pressure on the carotid sinus in the neck. [2] The underlying mechanism involves the nervous system slowing the heart rate and dilating blood vessels, resulting in low blood pressure and thus not enough blood flow to the brain. [2] Diagnosis is based on the symptoms after ruling out other possible causes. [3]

Recovery from a reflex syncope episode happens without specific treatment. [2] Prevention of episodes involves avoiding a person's triggers. [2] Drinking sufficient fluids, salt, and exercise may also be useful. [2] [4] If this is insufficient for treating vasovagal syncope, medications such as midodrine or fludrocortisone may be tried. [4] Occasionally, a cardiac pacemaker may be used as treatment. [2] Reflex syncope affects at least 1 in 1,000 people per year. [1] It is the most common type of syncope, making up more than 50% of all cases. [2]

Signs and symptoms

Episodes of vasovagal syncope are typically recurrent and usually occur when the predisposed person is exposed to a specific trigger. Before losing consciousness, the individual frequently experiences early signs or symptoms such as lightheadedness, nausea, the feeling of being extremely hot or cold (accompanied by sweating), ringing in the ears, an uncomfortable feeling in the heart, fuzzy thoughts, confusion, a slight inability to speak or form words (sometimes combined with mild stuttering), weakness and visual disturbances such as lights seeming too bright, fuzzy or tunnel vision, black cloud-like spots in vision, and a feeling of nervousness can occur as well. The symptoms may become more intense over several seconds to several minutes before the loss of consciousness (if it is lost). Onset usually occurs when a person is sitting up or standing.[ citation needed ]

When people lose consciousness, they fall down (unless prevented from doing so) and, when in this position, effective blood flow to the brain is immediately restored, allowing the person to regain consciousness. If the person does not fall into a fully flat, supine position, and the head remains elevated above the trunk, a state similar to a seizure may result from the blood's inability to return quickly to the brain, and the neurons in the body will fire off and generally cause muscles to twitch very slightly but mostly remain very tense.[ citation needed ]

The autonomic nervous system's physiological state (see below) leading to loss of consciousness may persist for several minutes, so

Causes

Reflex syncope occurs in response to a trigger due to dysfunction of the heart rate and blood pressure regulating mechanism. When heart rate slows or blood pressure drops, the resulting lack of blood to the brain causes fainting. [12]

Vasovagal

Typical triggers include:

Situational

Carotid sinus

Pressing upon a certain spot in the neck. [11] This may happen when wearing a tight collar, shaving, or turning the head. [11]

Pathophysiology

Regardless of the trigger, the mechanism of syncope is similar in the various vasovagal syncope syndromes. The nucleus tractus solitarii of the brainstem is activated directly or indirectly by the triggering stimulus, resulting in simultaneous enhancement of parasympathetic nervous system (vagal) tone and withdrawal of sympathetic nervous system tone.[ citation needed ]

This results in a spectrum of hemodynamic responses:[ citation needed ]

  1. 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.
  2. 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 dilation of the blood vessels, probably as a result of withdrawal of sympathetic nervous system tone.
  3. 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.

Vasovagal syncope may be part of an evolved response, specifically, the fight-or-flight response. [16] [17]

Diagnosis

In addition to the mechanism described above, a number of other medical conditions may cause syncope. Making the correct diagnosis for loss of consciousness is difficult. The core of the diagnosis of vasovagal syncope rests upon a clear description of a typical pattern of triggers, symptoms, and time course.[ citation needed ]

It is pertinent to differentiate lightheadedness, seizures, vertigo, and low blood sugar as other causes.[ citation needed ]

In people with recurrent vasovagal syncope, diagnostic accuracy can often be improved with one of the following diagnostic tests:

Treatment

Treatment for reflex 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.[ citation needed ]

Lifestyle changes

Medications

Types of long-term therapy for vasovagal syncope include [18]

Prognosis

Brief periods of unconsciousness usually cause no lasting harm to health. Reflex syncope can occur in otherwise healthy individuals, and has many possible causes, often trivial ones such as prolonged standing with the legs locked.[ citation needed ]

The main danger of vasovagal syncope (or dizzy spells from vertigo) is the risk of injury by falling while unconscious. Medication therapy could possibly prevent future vasovagal responses; however, for some individuals medication is ineffective and they will continue to have fainting episodes. [29]

See also

Related Research Articles

Orthostatic hypotension, also known as postural hypotension, is a medical condition wherein a person's blood pressure drops when they are standing up (orthostasis) or sitting down. Primary orthostatic hypotension is also often referred to as neurogenic orthostatic hypotension. The drop in blood pressure may be sudden, within 3 minutes or gradual. It is defined as a fall in systolic blood pressure of at least 20 mmHg or diastolic blood pressure of at least 10 mmHg after 3 minutes of standing. It occurs predominantly by delayed constriction of the lower body blood vessels, which is normally required to maintain adequate blood pressure when changing the position to standing. As a result, blood pools in the blood vessels of the legs for a longer period, and less is returned to the heart, thereby leading to a reduced cardiac output and inadequate blood flow to the brain.

Baroreceptors are stretch receptors that sense blood pressure. Thus, increases in the pressure of blood vessel triggers increased action potential generation rates and provides information to the central nervous system. This sensory information is used primarily in autonomic reflexes that in turn influence the heart cardiac output and vascular smooth muscle to influence vascular resistance. Baroreceptors act immediately as part of a negative feedback system called the baroreflex, as soon as there is a change from the usual mean arterial blood pressure, returning the pressure toward a normal level. These reflexes help regulate short-term blood pressure. The solitary nucleus in the medulla oblongata of the brain recognizes changes in the firing rate of action potentials from the baroreceptors, and influences cardiac output and systemic vascular resistance.

<span class="mw-page-title-main">Cerebral edema</span> Excess accumulation of fluid (edema) in the intracellular or extracellular spaces of the brain

Cerebral edema is excess accumulation of fluid (edema) in the intracellular or extracellular spaces of the brain. This typically causes impaired nerve function, increased pressure within the skull, and can eventually lead to direct compression of brain tissue and blood vessels. Symptoms vary based on the location and extent of edema and generally include headaches, nausea, vomiting, seizures, drowsiness, visual disturbances, dizziness, and in severe cases, death.

<span class="mw-page-title-main">Dysautonomia</span> Any disease or malfunction of the autonomic nervous system

Dysautonomia, autonomic failure, or autonomic dysfunction is a condition in which the autonomic nervous system (ANS) does not work properly. This may affect the functioning of the heart, bladder, intestines, sweat glands, pupils, and blood vessels. Dysautonomia has many causes, not all of which may be classified as neuropathic. A number of conditions can feature dysautonomia, such as Parkinson's disease, multiple system atrophy, dementia with Lewy bodies, Ehlers–Danlos syndromes, autoimmune autonomic ganglionopathy and autonomic neuropathy, HIV/AIDS, mitochondrial cytopathy, pure autonomic failure, autism, and postural orthostatic tachycardia syndrome.

<span class="mw-page-title-main">Hypotension</span> Abnormally low blood pressure

Hypotension, also known as low blood pressure, is a cardiovascular condition characterized by abnormally reduced blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood and is indicated by two numbers, the systolic blood pressure and the diastolic blood pressure, which are the maximum and minimum blood pressures within the cardiac cycle, respectively. A systolic blood pressure of less than 90 millimeters of mercury (mmHg) or diastolic of less than 60 mmHg is generally considered to be hypotension. Different numbers apply to children. However, in practice, blood pressure is considered too low only if noticeable symptoms are present.

<span class="mw-page-title-main">Carotid sinus</span> Dilated area near internal carotid artery above bifurcation

In human anatomy, the carotid sinus is a dilated area at the base of the internal carotid artery just superior to the bifurcation of the internal carotid and external carotid at the level of the superior border of thyroid cartilage. The carotid sinus extends from the bifurcation to the "true" internal carotid artery. The carotid sinus is sensitive to pressure changes in the arterial blood at this level. It is the major baroreception site in humans and most mammals.

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<span class="mw-page-title-main">Postural orthostatic tachycardia syndrome</span> Abnormally high heart rate after a postural change

Postural orthostatic tachycardia syndrome (POTS) is a condition characterized by an abnormally large increase in heart rate upon sitting up or standing. POTS is a disorder of the autonomic nervous system that can lead to a variety of symptoms, including lightheadedness, brain fog, blurred vision, weakness, fatigue, headaches, heart palpitations, exercise intolerance, nausea, diminished concentration, tremulousness (shaking), syncope (fainting), coldness or pain in the extremities, numbness or tingling in the extremities, chest pain, and shortness of breath. Other conditions associated with POTS include myalgic encephalomyelitis/chronic fatigue syndrome, migraine headaches, Ehlers–Danlos syndrome, asthma, autoimmune disease, vasovagal syncope, and mast cell activation syndrome. POTS symptoms may be treated with lifestyle changes such as increasing fluid, electrolyte, and salt intake, wearing compression stockings, gentle and slow postural changes, avoiding prolonged bedrest, medication, and physical therapy.

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<span class="mw-page-title-main">Prazosin</span> Antihypertensive drug

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Lightheadedness is a common and typically unpleasant sensation of dizziness or a feeling that one may faint. The sensation of lightheadedness can be short-lived, prolonged, or, rarely, recurring. In addition to dizziness, the individual may feel as though their head is weightless. The individual may also feel as though the room is "spinning" or moving (vertigo). Most causes of lightheadedness are not serious and either cure themselves quickly or are easily treated.

<span class="mw-page-title-main">Tilt table test</span> Medical procedure often used to diagnose dysautonomia or syncope

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<span class="mw-page-title-main">Syncope (medicine)</span> Transient loss of consciousness and postural tone

Syncope, commonly known as fainting or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from low blood pressure. There are sometimes symptoms before the loss of consciousness such as lightheadedness, sweating, pale skin, blurred vision, nausea, vomiting, or feeling warm. Syncope may also be associated with a short episode of muscle twitching. Psychiatric causes can also be determined when a patient experiences fear, anxiety, or panic; particularly before a stressful event, usually medical in nature. When consciousness and muscle strength are not completely lost, it is called presyncope. It is recommended that presyncope be treated the same as syncope.

Blood-injection-injury (BII) type phobia is a type of specific phobia characterized by the display of excessive, irrational fear in response to the sight of blood, injury, or injection, or in anticipation of an injection, injury, or exposure to blood. Blood-like stimuli may also cause a reaction. This is a common phobia with an estimated 3-4% prevalence in the general population, though it has been found to occur more often in younger and less educated groups. Prevalence of fear of needles which does not meet the BII phobia criteria is higher. A proper name for BII has yet to be created.

<span class="mw-page-title-main">Dopamine beta hydroxylase deficiency</span> Medical condition

Dopamine beta (β)-hydroxylase deficiency is a human medical condition involving inadequate dopamine beta-hydroxylase. It is characterized by increased amounts of serum dopamine and the absence of norepinephrine (NE) and epinephrine.

Orthostatic syncope refers to syncope resulting from a postural decrease in blood pressure, termed orthostatic hypotension.

A frequent type of syncope, termed vasovagal syncope is originated by intense cardioinhibition, mediated by a sudden vagal reflex, that causes transitory cardiac arrest by asystole and/or transient total atrioventricular block. It is known as “Vaso-vagal Syncope”, “Neurocardiogenic Syncope” or “Neurally-mediated Reflex Syncope”. Although many different therapies have been tried in this condition, severe and refractory cases have been treated with pacemaker implantation despite great controversies about its benefit.

Neurocardiology is the study of the neurophysiological, neurological and neuroanatomical aspects of cardiology, including especially the neurological origins of cardiac disorders. The effects of stress on the heart are studied in terms of the heart's interactions with both the peripheral nervous system and the central nervous system.

References

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