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Vasovagal Syncope

Vasovagal Syndrome

A vasovagal syncope is loss of consciousness associated with vagal activity. It may be triggered by pain, fright, stress, dehydration or trauma.


Before losing consciousness, some of the early signs and symptoms presented by vasovagal syncope patients include lightheadedness, nausea, extremely high or extremely low body temperature (often followed by sweating), tinnitus, palpitations, confusion, a slight inability to speak, often followed by mild stuttering, nervousness and visual disturbances are other symptoms that can occur as well [8].

The symptoms often last for a few seconds before the loss of consciousness begins. The loss of consciousness often happens when the individual is sitting up or standing. As soon as the sufferer passes out, they fall down. At this point blood flow to the brain is restored instantaneously. A seizure may result if the individual doesn’t fall into a fully flat supine position and the head stays elevated above the trunk as blood will unable to quickly return to the brain. 

  • These new data seem to indicate that some unexplained falls could be cases of atypical VVS/carotid sinus syncope with retrograde amnesia.[ncbi.nlm.nih.gov]
  • Her symptoms (falls) responded to the withdrawal of culprit medications.[ncbi.nlm.nih.gov]
  • In atypical vasovagal syncope, there is often a short or absent prodrome, and amnesia for loss of consciousness is common and it can, therefore, often be misdiagnosed, for example as falls.[ncbi.nlm.nih.gov]
  • Relying on falling heart rate is insufficient, probably because it occurs too late. Other algorithms which indirectly detect neuroendocrine changes earlier than heart rate fall may have useful application.[ncbi.nlm.nih.gov]
  • The major danger of vasovagal syncope is the risk of injury by falling while unconscious.[symptoma.com]
  • Synonym(s): vasodepressor syncope . vasovagal syncope See FAINTING . syncope a temporary suspension of consciousness due to cerebral anemia; fainting. cardiac syncope sudden loss of consciousness due to cerebral anemia caused by ventricular asystole,[medical-dictionary.thefreedictionary.com]
  • Mild blood loss, poor physical condition, prolonged bed rest, anemia, fever, organic heart disease , and fasting are other factors which increase the possibility of fainting in susceptible individuals.[healthcentral.com]
  • Susceptible individuals may be especially prone to these fainting episodes if any of the following conditions are present: mild blood loss; anemia; fever; hypoglycemia; or injury.[diversalertnetwork.org]
  • The lab can detect conditions like low blood sugar and anemia (a shortage of healthy red blood cells) that might cause a person to feel weak or faint. Tilt table test.[innerbody.com]
  • Children with VVS had symptoms of dizziness, pallor, blurred vision, nausea, and some had syncope. Erythrocyte H2S production was measured by a sulphur-sensitive electrode.[ncbi.nlm.nih.gov]
  • Clinical findings Abrupt loss of vascular tone; nausea; diaphoresis; pallor.[medical-dictionary.thefreedictionary.com]
  • The onset may be abrupt or gradual and is often associated with warning symptoms such as lightheadedness, dizziness, weakness, feeling hot or cold, fatigue, nausea, abdominal pain, sweating, pallor, visual disturbances or confusion.[pccoforegon.com]
  • In the second to minutes leading up to the fainting, the patient may feel weakness, nausea, pallor, and sweating.[courses.washington.edu]
  • RESULTS: SS was found in 55/1,401 (4.0%) syncope patients with follow-up data available in 47 patients: defecation (n 16), micturition (n 15), cough (n 10), swallow (n 3), laughter (n 1), sneeze (n 1), and cough plus laughter (n 1).[ncbi.nlm.nih.gov]
  • […] with stretching the arms upward with the spine extended. swallow syncope syncope associated with swallowing, a disorder of atrioventricular conduction mediated by the vagus nerve. tussive syncope brief loss of consciousness associated with paroxysms of coughing[medical-dictionary.thefreedictionary.com]
  • I bring this up, because heartburn/coughing can trigger it and I’ve learned that heartburn can be tied to gas putting pressure to push it back up and you cough and syncope.[earthclinic.com]
  • ., hot crowded environments, volume depletion, effects of cough, tight collars, etc.), recognition of premonitory symptoms, and manoeuvers to abort the episode.[escardio.org]
  • Patients with nausea or extreme anxiety should be watched carefully and their symptoms treated.[ncbi.nlm.nih.gov]
  • The vasovagal reaction, bradycardia and/or asystole, was preceded by abnormal EEG findings when the patient complained of feeling a headache, photophobia, and nausea.[ncbi.nlm.nih.gov]
  • Severe sinus bradycardia and hypotension accompanied by light-headedness, cold sweating, and nausea occurred at 80 degrees head-up position during 4 micrograms/min isoproterenol infusion.[ncbi.nlm.nih.gov]
  • Children with VVS had symptoms of dizziness, pallor, blurred vision, nausea, and some had syncope. Erythrocyte H2S production was measured by a sulphur-sensitive electrode.[ncbi.nlm.nih.gov]
  • Clinical findings Abrupt loss of vascular tone; nausea; diaphoresis; pallor.[medical-dictionary.thefreedictionary.com]
  • Presyncopal (near fainting) patients may also complain of vomiting, disorientation, and difficulty speaking or seeing.[pccoforegon.com]
  • , especially on hot days, or if you have been exercising or have had diarrhoea or vomiting. Your urine should be clear.[jpaget.nhs.uk]
  • Here's some really practical advice: The absolute best way to control the episodes is to effectively control the pain first and avoid the cramps which lead to the excrutiating screaming pain and then the fainting, vomiting, sweating etc.[steadyhealth.com]
  • You may even feel nauseous afterwards and vomit. Some people have only 1 or 2 episodes of vasovagal syncope in their life. For others, it happens more often and with no warning.[fairview.org]
  • U of Washington Study (2) Of those having symptoms Feeling of faintness or dizziness (85%) Nausea (50%) Feeling hot (31%) or cold (21%) Pallor (79%) Sweating (57%) Vomiting or loss of consciousness (0%) Pavlin, et. al. (1993) 16.[slideshare.net]
  • POTS has recently been conflated with VVS when excessive tachycardia is succeeded by hypotension during tilt testing.[ncbi.nlm.nih.gov]
  • CONCLUSION: Sinus acceleration along with high-grade AV block during syncope and hypotension can occur in some patients with neurocardiogenic syncope. The exact mechanism of this phenomenon is unclear.[ncbi.nlm.nih.gov]
  • It is commonly believed that the most frequent cause of recurrence of syncope in patients treated with a pacemaker is an associated hypotensive reflex. In these cases additional measures should be used to counteract hypotension.[ncbi.nlm.nih.gov]
  • Although a beta blocker was not effective in preventing tilt-induced hypotension and bradycardia, midodrine hydrochloride (alpha-1 stimulant) or atropine prevented it.[ncbi.nlm.nih.gov]
  • Vasovagally mediated hypotension and bradycardia are believed common, yet difficult to diagnose, causes of syncope in healthy children and adolescents.[ncbi.nlm.nih.gov]
Orthostatic Hypotension
  • Both types of syncope are associated with orthostatic hypotension and are nonlethal. The underlying pathophysiology manifests the vast symptoms suffered by the individual.[ncbi.nlm.nih.gov]
  • Past studies found that an Anti-Gravity suit (G-suit) can increase blood pressure and has been reported to prevent orthostatic hypotension effectively in patients with diabetes. It is possible that the G-suit can prevent VVS.[ncbi.nlm.nih.gov]
  • The highest recommended dose for orthostatic hypotension is 0.3 mg daily. The dose range in this study was 0.05-0.2 mg daily, so some patients may have been underdosed.[reliasmedia.com]
  • Orthostatic Hypotension (2) Treatment Lie down Trendelenberg position NS Regulate medications 24.[slideshare.net]
Left Ventricular Dysfunction
  • KEYWORDS: Autonomic nervous system; Head-up tilt; Left ventricular dysfunction; Vasovagal syncope[ncbi.nlm.nih.gov]
  • CASE REPORTS: A 16-year-old healthy boy had sometimes experienced dizziness when looking at the tips of pens. When he put his finger and the lens close to his eye to insert a soft contact lens, he felt sick and dizzy and fell unconscious.[ncbi.nlm.nih.gov]
  • It is also important for patient’s to recognize the feeling of dizziness so that they can react appropriately to their body's signals and either sit or lie down quickly. Once the dizziness has passed, they can slowly stand up again.[pediatricheartspecialists.com]
  • Children with VVS had symptoms of dizziness, pallor, blurred vision, nausea, and some had syncope. Erythrocyte H2S production was measured by a sulphur-sensitive electrode.[ncbi.nlm.nih.gov]
  • This causes blood pressure to fall and dizziness as less blood goes to the brain. This is usually relieved by lying down. Vasovagal syncope is not dangerous and usually gets better in time.[newcastle-hospitals.org.uk]
  • Patients usually feel unwell at this point with symptoms of lightheadedness, dizziness, queasiness, and may be nauseous and sick, sweaty and clammy, before passing out.[londoncardiovascularclinic.co.uk]
  • As soon as there is a slow-down in heart rate, the resulting lack of blood to the brain brings about fainting and confusion.[symptoma.com]
  • They may complain of symptoms including nausea, abdominal pain, clamminess, tremors, lightheadedness, headache, malaise, exhaustion and confusion.[pccoforegon.com]
  • After "blacking out," the person usually regains consciousness within minutes, but may experience a period of confusion or feeling weak for up to 24 hours. In 2002, former U.S. President George W.[cnn.com]
  • However, these fainting spells can be accompanied by confusion, jerking movements and loss of consciousness much like an epileptic seizure. At times, patients’ pupils may dilate and be noticed by others prior to fainting.[rscdiagnosticservices.com]
  • I find showering warm water on my abdomen area seems to confuse the cramping nerves sometimes a little and can interrupt it - not always, but worth trying if you're able.[steadyhealth.com]
Drop Attacks
  • It has many causes, and is distinct from vertigo, seizures, coma, falls, psychogenic pseudosyncope, drop attacks, transient ischaemic attacks, and states of altered consciousness. [3] Strickberger SA, Benson DW, Biaggioni I, et al.[bestpractice.bmj.com]
Myoclonic Jerking
  • During the session, the participant appeared to have a brief event involving fainting and myoclonic jerks of the upper extremities.[ncbi.nlm.nih.gov]


There are many medical conditions that may cause syncope. This is why making the correct diagnosis for loss of consciousness is one of the most difficult challenges facing health care providers. The core of the diagnosis of vasovagal syncope is dependent on a clear description by the patient for a particular pattern of triggers and time course. It is very important to differentiate vertigo, seizures, light-headedness, seizures, vertigo and hypoglycaemia as other causes.

For patients with recurring vasovagal syncope, the accuracy of diagnosis can often be improved with any one of the following diagnostic tests [9]:

  • Tilt table test
  • Echocardiogram
  • Holter monitor or event monitor
  • Implantation of an insertable loop recorder
  • Electrophysiology study
Epileptiform Activity
  • However, continuous electroencephalogram, blood pressure, and heart rate recordings during attacks indicated that in some episodes there was neither cardiovascular change nor epileptiform activity, implying feigned syncope (pseudosyncope) with pseudoseizures[ncbi.nlm.nih.gov]
Chloride Increased
  • Fludrocortisone and sodium chloride increase systemic fluid volume. Midodrine, β blockers and norepinephrine transport inhibitors modulate the sympathetic nervous system.[ncbi.nlm.nih.gov]
Sinus Arrest
  • Vasovagal syncope with concomitant ventricular asystole and sinus arrest is rare. Aggressive management with permanent pacemaker is strongly advocated in malignant vasovagal syncope.[ncbi.nlm.nih.gov]
  • Abstract Cardioinhibitory vasovagal syncope with sinus arrest and asystole of 28 seconds' duration occurred during rectosigmoidoscopy in a patient with frequent previous symptoms and a syncopal episode.[ncbi.nlm.nih.gov]
  • Facts While standing, approximately 300-700 ml of blood pools in the lower extremities which decreases intravascular volume Strong vagal stimulations may induce 4-10 seconds of sinus arrest 15 seconds of asystole is necessary to produce unconsciousness[slideshare.net]
  • In intrinsic sick sinus syndrome, syncope typically occurs secondary to long pauses caused by sinus arrest or sinoatrial block. 1 In the setting of tachyarrhythmia, syncope or near-syncope occurs at the onset of paroxysmal tachycardia, before vascular[clevelandclinicmeded.com]


In many cases of vasovagal syncope, treatment is relatively unnecessary as soon as the cause of syncope is identified and avoided [10]. Also medications for treatment of low blood pressure will also be helpful when medication in necessary. Therapies and surgery (often to insert an electrical pacemaker) may be needful in many cases.


Brief episodes of unconsciousness rarely do any harm and they are not the symptoms of a disease so patients often recover easily [7]. The major danger of vasovagal syncope is the risk of injury by falling while unconscious. In some people, medical therapy can prevent future vasovagal responses but for some others medication is ineffective and so they will always continue to have the vasovagal episodes.


Vasovagal syncope often occurs in response to a trigger and there is often a corresponding malfunction in the parts of the nervous system which regulate the heart rate and blood pressure [4]. As soon as there is a slow-down in heart rate, the resulting lack of blood to the brain brings about fainting and confusion.

Below are some of the main triggers for vasovagal episodes:

  • Sensitivity as a result of pain
  • Extreme menstural pains
  • Pressure on the chest after heavy exercising
  • Being present during medical procedures
  • Sight of blood
  • Biopsy procedures (pre and post)
  • Increased stress levels
  • Dehydration
  • Ingestion of certain medications and addcitive substances
  • Heavy emotional swings
  • Nervous malfucntions
  • In rare cases, low sugar level in blood


The incidence for this condition is 6.2 cases per 100 patient years in the United States [5]. Syncope also reoccurs in less than 3% of affected individuals and also, 10% of affected individuals have a cardiac etiology. Data from around the world also suggest a similar occurrence rate to what is obtainable in the United States.

Sex distribution
Age distribution


Vasovagal syncope occurs as a result of cerebral hypoperfusion [6]. Brain parenchyma is dependent on sustained blood flow to be able to provide a constant supply of glucose which is its major metabolic substrate. It is not possible for the brain tissue to store energy in form of high-energy phosphates as is seen in other areas of the body. This is why cerebral perfusion of between 3 to 5 seconds is enough to bring about syncope.

Cerebral perfusion is maintained relatively constant by an intricate and complex feedback system which typically involves arterial pressure, intravascular volume status, metabolic regulation and cerebrovascular resistance with intrinsic autoregulation. When there is a significant defect in any of these or subclinical defects in several of these systems, syncope may arise.


Even with treatment, not all cases of vasovagal syncope can be avoided. A common solution to prevent fainting is lying down and lifting your legs. This makes it possible for gravity to keep blood flowing to your brain. When lying down is not possible, sitting down and putting your head between your knees will make you feel better.


Syncope refers to a self-limited loss of consciousness accompanied by the inability to maintain postural tone. Most of the time, it is followed by spontaneous recovery [1]. The condition doesn’t include seizures, coma, shock or other such states of altered consciousness.

There are many recognised etiologies for syncope but categorization is made into reflex (neutrally mediated), orthostatic and cardiac so as to ensure proper initial evaluation [2]. Cardiac vasovagal syncope has the highest number of mortality while non-cardiac syncope doesn’t have such high mortality. Syncope can result in significant morbidity due to accidents or falls that may occur following its onset [3].

Patient Information

Vasovagal syncope refers to one of the most common causes of fainting. It occurs when the body begins to overreact to certain triggers. The most common triggers are sight of blood and extreme emotional distress.

The vasovagal syncope trigger kicks off a sudden drop in heart rate and blood pressure. This brings about a reduction in blood flow to the brain which leads to a momentary loss of consciousness.

The condition is often harmless requiring no treatment. However, it is possible for patients to get injured during an episode of the condition. The doctor may recommend tests to rule out more serious cases of fainting such as an underlying heart condition.



  1. Moya A, Sutton R, Ammirati F, et al. Guidelines for the diagnosis and management of syncope (version 2009): the Task Force for the Diagnosis and Management of Syncope of the European Society of Cardiology (ESC). Eur Heart J. Nov 2009;30(21):2631-71.
  2. Rockx MA, Hoch JS, Klein GJ, et al. Is ambulatory monitoring for "community-acquired" syncope economically attractive? A cost-effectiveness analysis of a randomized trial of external loop recorders versus Holter monitoring. Am Heart J. Nov 2005;150(5):1065.
  3. Gibson TC, Heitzman MR. Diagnostic efficacy of 24-hour electrocardiographic monitoring for syncope. Am J Cardiol. Apr 1 1984;53(8):1013-7.
  4. Chen L, Chen MH, Larson MG, Evans J, Benjamin EJ, Levy D. Risk factors for syncope in a community-based sample (the Framingham Heart Study). Am J Cardiol. May 15 2000;85(10):1189-93.
  5. Savage DD, Corwin L, McGee DL, Kannel WB, Wolf PA. Epidemiologic features of isolated syncope: the Framingham Study. Stroke. Jul-Aug 1985;16(4):626-9. 
  6. Task Force for the Diagnosis and Management of Syncope, European Society of Cardiology (ESC), European Heart Rhythm Association (EHRA), et al. Guidelines for the diagnosis and management of syncope (version 2009). Eur Heart J 2009; 30:2631.
  7. Kapoor WN. Evaluation and outcome of patients with syncope. Medicine (Baltimore) 1990; 69:160.
  8. Savage DD, Corwin L, McGee DL, et al. Epidemiologic features of isolated syncope: the Framingham Study. Stroke 1985; 16:626.
  9. Soteriades ES, Evans JC, Larson MG, et al. Incidence and prognosis of syncope. N Engl J Med 2002; 347:878.
  10. Lipsitz LA. Syncope in the elderly. Ann Intern Med 1983; 99:92.

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Last updated: 2018-06-22 06:24