Vasovagal Episode


Article Author:
Rebecca Jeanmonod


Article Editor:
Michael Silberman


Editors In Chief:
Chaddie Doerr


Managing Editors:
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Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
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James Hughes
Beata Beatty
Nazia Sadiq
Hajira Basit
Phillip Hynes
Tehmina Warsi


Updated:
4/3/2019 10:16:46 PM

Introduction

A vasovagal episode or vasovagal syncope is the most common form of reflex syncope. Reflex syncope is a general term used to describe types of syncope resulting from a failure in autoregulation of blood pressure, and ultimately, in cerebral perfusion pressure resulting in transient loss of consciousness. The mechanisms responsible for this are complex and involve both depression of cardiac output as well as a decrease in vascular tone. Other types of reflex syncope include carotid sinus syncope and situational syncope, for instance, cough or micturition syncope. Vasovagal syncope may be triggered by pain or emotional upset, although frequently a specific trigger cannot be identified.[1][2][3][4]

Etiology

The etiology of vasovagal syncope is unclear. Some believe that the vasovagal reaction is an exaggeration of an adaptive response meant to assist in hemostasis in times of trauma. In other words, in the setting of physical trauma, the body reflexively lowers blood pressure and heart rate to reduce the amount of bleeding. Others have sought a genetic link for the syndrome. [5]Research elucidating a genetic predisposition for vasovagal syncope is challenging due to the high background incidence of the disease, but genomic analysis demonstrates some differences in copy number variations in families with a high burden of reflex syncope. More research in this area is warranted.

Epidemiology

Vasovagal syncope is the most common form of syncope in adults. More than 85% of syncopal events in people younger than 40 years are attributable to vasovagal syncope. Even in geriatric patients, more than 50% of syncopal episodes are due to vasovagal syncope. Vasovagal syncope requires an intact and functioning autonomic nervous system, and therefore, its incidence is low in populations with autonomic nervous system dysfunction, such as patients with Parkinson disease. The lifetime incidence of an episode of vasovagal syncope is more than 33%.

Pathophysiology

It is helpful to think about the pathophysiology of vasovagal syncope as a reflex arc, with an afferent limb and an efferent limb. Although the autonomic nervous system mediates vasovagal syncope,  pathophysiological mechanisms are not completely understood. The afferent limb of the reflex arc begins with a trigger. Although this trigger may be emotional stress or pain, it is often unidentifiable. It is believed that this trigger, usually in combination with central hypovolemia (from upright posture or dehydration) results in increased cardiac contractility in the setting of a relatively underfilled left ventricle. This may trigger mechanoreceptors in the ventricle that signal via vagal afferents to the central nervous system.

The efferent limb of the reflex arc is better understood. Increased vagal firing (increased parasympathetic activity) at the sinus node and the atrioventricular node causes a decrease in heart rate. This decrease in heart rate can be profound, with asystole that can be several seconds long. At the same time, decreased sympathetic activity results in decreased vascular tone in both arterioles and venules. The results in decreased preload, venous return, and ventricular volume. Since cardiac output is the product of stroke volume and heart rate, this reflex arc affects both factors in the equation: slowing the heart rate and decreasing the amount of volume. This results in a drop in the patient's mean arterial pressure. Cerebral autoregulation results in constant cerebral blood flow over a wide range of mean arterial pressures, but when the mean arterial pressure falls below the body's ability to autoregulate, the patient loses consciousness. Typically, if the patient falls or is laid supine, the increase in circulating blood volume from the lower extremities combined with the decreased work necessary to get blood to the brain (i.e., the heart does not have to pump "uphill" against gravity) will cause the patient to regain consciousness rapidly.

Toxicokinetics

Although vasovagal syncope occurs secondary to a reflex arc with an unclear trigger, in patients who are susceptible, medications that cause alterations in heart rate or vascular tone may exacerbate symptoms.

History and Physical

The differential diagnosis for syncope is broad and includes cardiac arrhythmia, acute blood loss, seizure, orthostasis, dehydration, dissection, subarachnoid hemorrhage, pulmonary embolus, ruptured ectopic pregnancy, trauma (concussion, epidural hematoma), toxins, and many other pathologies. History and physical exam should focus on ruling out life-threatening entities before a diagnosis of vasovagal syncope. Patients should be asked specifically about family and personal history of cardiovascular diseases, the potential for gastrointestinal blood loss, the potential for genitourinary blood loss, and medications that could be complicating the presentation (i.e., antihypertensives, antihistamines, anticholinergics, anticoagulants). Patients with syncope also frequently require a trauma evaluation to assess for injuries sustained during the syncopal event.

Most patients with vasovagal syncope present with a history of a syncopal prodrome. Patients will classically describe a feeling of lightheadedness. Feelings of warmth and nausea are common. Many patients describe tunnel vision, ringing in their ears, and profuse sweating. Patients should return to consciousness spontaneously. During the event, the patient will usually be bradycardic, hypotensive, pale, and diaphoretic. After the event, the patient should have an entirely normal physical exam. Abnormalities on physical exam (such as tongue biting, which suggests seizure, or ongoing pallor, which suggests symptomatic anemia) or atypical history should prompt a more thorough evaluation into the underlying cause of syncope.

Evaluation

Every patient with a complaint of syncope should have a complete history and physical exam, with attention to the presence or absence of pallor, cardiac abnormalities (murmurs, tachy/bradydysrhythmias, and irregular heartbeat), pulmonary abnormalities, and signs of trauma. Patients may require radiographic studies of trauma sustained during the vasovagal event.[6][7][8][6]

Every person undergoing evaluation for syncope including presumed vasovagal syncope should have an ECG to look for evidence of underlying arrhythmogenic cardiac abnormalities, such as Wolff-Parkinson-White syndrome, prolonged QT syndrome, Brugada syndrome, or heart blocks. It is also wise to check for pregnancy in women of childbearing potential. Strong consideration should be given to fecal blood testing in patients in whom blood loss anemia is suspected, as hemoglobin may be normal in patients with acute hemorrhage.

Further emergency evaluation for syncope is tailored based on the presentation of the patient and existing comorbid conditions. In healthy patients with a classic history of vasovagal syncope, a normal exam, and a normal ECG, no further testing is indicated, and laboratory testing is low yield. When a diagnosis is not certain, or when patients have multiple potential causes of syncope, serum electrolyte testing, complete blood count, and cardiac enzymes may be indicated.

In patients with recurrent syncope or when a diagnosis remains elusive, Holter monitoring, event monitoring, and tilt table testing may be used in an outpatient setting to define the etiology of syncope better.

Treatment / Management

Typically, vasovagal syncope is treated conservatively. When known and avoidable, patients are instructed to avoid triggers. Patients are also instructed to drink more fluids to improve their volume status (and therefore their preload) and to change positions slowly. Patients are educated as to the "warning signs" of a vasovagal event and instructed to place themselves in a supine position should they feel an event coming. This often prevents actual syncope and reduces traumatic risk from falling. In refractory or disabling cases and cases of prolonged asystole, cardiac pacing is a therapeutic option.[9][10][11][12]

Enhancing Healthcare Team Outcomes

The diagnosis and management of vasovagal syncope is very difficult because the differential is enormous. The symptom complex is best managed by a multidisciplinary team that includes the primary provider, nurse practitioner, cardiologist, endocrinologist, emergency department physician, and an internist.

Typically, vasovagal syncope is treated conservatively. When known and avoidable, patients are instructed to avoid triggers. Patients are also instructed to drink more fluids to improve their volume status (and therefore their preload) and to change positions slowly. Patients are educated as to the "warning signs" of a vasovagal event and instructed to place themselves in a supine position should they feel an event coming. This often prevents actual syncope and reduces traumatic risk from falling. In refractory or disabling cases and cases of prolonged asystole, cardiac pacing is a therapeutic option.[13]


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Vasovagal Episode - Questions

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When ear wax is removed, some people experience a fainting sensation due to stimulation of what nerve?



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A 15-year-old female is brought in after fainting while in line to buy concert tickets on a hot August weekend. The syncope was observed and not associated with tonic-clonic movements, incontinence, or tongue biting. The patient's exam, labs, and EKG are all normal. The caregiver notes that the patient is thin and mildly anxious. What was the most likely cause of the syncope?



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A 17 year old has a syncopal episode at the sight of her own blood while having it drawn for a test. What would be some of her symptoms?



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What is not a proper treatment for vasovagal syncope?



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What is the most likely cardiovascular etiology of vasovagal syncope?



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A 17-year-old female presents to the emergency department following a syncopal episode lasting less than 1 minute. There was no tongue biting, incontinence, twitching, or tonic-clonic movements. She denies palpitations or chest pain. Her physical exam is normal. Glucose and ECG are normal. What is the appropriate next step in management?



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A 17-year-old patient had her first syncopal event 10 minutes after a blood draw for laboratory testing. How should the patient be managed?



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Vasovagal Episode - References

References

Buszko K,Kujawski S,Newton JL,Zalewski P, Hemodynamic Response to the Head-Up Tilt Test in Patients With Syncope as a Predictor of the Test Outcome: A Meta-Analysis Approach. Frontiers in physiology. 2019;     [PubMed]
Heyer GL, Clinical features of prolonged tilt-induced hypotension with an apparent vasovagal mechanism, but without syncope. Autonomic neuroscience : basic     [PubMed]
Cheshire WP Jr,Goldstein DS, Autonomic uprising: the tilt table test in autonomic medicine. Clinical autonomic research : official journal of the Clinical Autonomic Research Society. 2019 Mar 5;     [PubMed]
Dockx K,Avau B,De Buck E,Vranckx P,Vandekerckhove P, Physical manoeuvers as a preventive intervention to manage vasovagal syncope: A systematic review. PloS one. 2019;     [PubMed]
Wu WJ,Goldberg LH,Rubenzik MK,Zelickson BR, Review of the Evaluation and Treatment of Vasovagal Reactions in Outpatient Procedures. Dermatologic surgery : official publication for American Society for Dermatologic Surgery [et al.]. 2018 Dec;     [PubMed]
Mizrachi EM,Sitammagari KK, Cardiac Syncope 2019 Jan;     [PubMed]
Ruzieh M,Grubb BP, Vasovagal syncope-role of closed loop stimulation pacing. Trends in cardiovascular medicine. 2018 Nov;     [PubMed]
Spiegel R,Kirsch M,Rosin C,Rust H,Baumann T,Sutter R,Friedrich H,Göldlin M,Müri R,Kalla R,Bingisser R,Mantokoudis G, Dizziness in the emergency department: an update on diagnosis. Swiss medical weekly. 2017;     [PubMed]
Caruana P,Hughes AR,Lea RA,Lueck CJ, Australian driving restrictions: how well do neurologists know them? Internal medicine journal. 2018 Sep;     [PubMed]
Golovina GA,Duplyakov DV, [Key Points of the 2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients With Syncope]. Kardiologiia. 2018 Aug;     [PubMed]
Williamson A,Muir S, Loss of consciousness, collapse and associated driving restrictions: a retrospective case note review - an important reminder regarding driving restrictions. Scottish medical journal. 2017 May;     [PubMed]
Cubera K,Stryjewski PJ,Kuczaj A,Nessler J,Nowalany-Kozielska E,Pytko-Polończyk J, The impact of gender on the frequency of syncope provoking factors and prodromal signs in patients with vasovagal syncope. Przeglad lekarski. 2017;     [PubMed]
Yau L,Mukarram MA,Kim SM,Arcot K,Thavorn K,Stiell IG,Taljaard M,Rowe BH,Sivilotti MLA,Thiruganasambandamoorthy V, Outcomes and emergency medical services resource utilization among patients with syncope arriving to the emergency department by ambulance. CJEM. 2018 Nov 21;     [PubMed]

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