Presyncope
Synonyms and keywords: Faintness; generalized weakness; lightheadedness; near blackout; near fainting; near syncope

# Overview
Presyncope is the sensation of feeling faint, lightheadedness and muscular weakness without actually losing consciousness. The presyncope stage may occur for only a few seconds as a prodrome before losing consciousness. Presyncope is most often due to cardiovascular etiology.

# Classification
Presyncope may be classified into following subtypes based on the inciting mechanism leading to the final event of transient global hypoperfusion. Presyncope suggests global cerebral hypoperfusion or a toxic/metabolic derangement. Hypoperfusion usually results from a drop in blood pressure (BP).

# Pathophysiology
It is thought that presyncope is the result of the interaction between the circulatory system and the autonomic nervous system. The autonomic nervous system is vital for the maintenance of internal homeostasis including regulation of blood pressure, heart rate, fluid and electrolyte balance, and body temperature. Syncope or presyncope occurs as a result of brain hypoxia, which is usually secondary to a reduction of cerebral perfusion pressure. However, not every reduction in blood pressure leads to brain hypoxia. This is because the cerebral circulation is autoregulated so that brain perfusion is maintained in the face of significant changes in mean blood pressure. This homeostatic mechanism allows regional cerebral blood flow to remain constant over a range of cerebral perfusion pressure (CPP) of 50 to 150 mm Hg or mean arterial pressure (MAP) of 60 to 160 mm Hg. So, as MAP or CPP increases, resistance in small cerebral arteries increases via vasoconstriction and vice versa. Blood pressure below the lower level result in syncope secondary to brain hypoxia.
When standing, initially the force of gravity pools 500 to 800 mL of blood in the distensible veins below heart level. This increases capillary pressure and plasma is lost to interstitial fluid. Pooling of blood in the veins decreases venous return to the heart with subsequent reduction of cardiac output, which in turn, triggers compensatory mechanisms to prevent the reduction of arterial pressure. Compensatory mechanisms include: sympathetic outflow upregulation by the central autonomic network (CAN); and the venoarterial reflex, leg pumping of skeletal muscles, the cerebral autoregulatory mechanism, and to a lesser extent, the renin angiotensin aldosterone system (RAAS).
The autonomic supply to the cardiovascular system is coordinated at the CAN located in the brain stem. The sympathetic nervous system acts as the main effector in the hemodynamic response to postural stressors. Upon standing, there is an initial reduction of cardiac filling and thus, of stroke volume. Pressure receptors in the heart, carotids, and aortic arch sense the perturbation and send impulses to the CAN. This initiates sympathetic vasomotor outflow and norepinephrine is released to vascular beds in the skeletal muscles and cutaneous vasculature; causing vasoconstriction, venoconstriction, as well as increased heart rate and contractility. Venoconstriction causes a correction of orthostasis by increasing cardiac filling for a given amount of gravitational pooling of blood. At the same time, leg pumping of skeletal muscles enhances venous return to the heart and the venoarterial reflex augments arterial vasoconstriction in response to venous distention.
Postural stress in the atrium is sensed by mechanoreceptors as a decreased in atrial stretch. This causes increase of arginine vasopressin (AVP) and decrease in A-type atrial natriuretic peptide (ANP) secretion. This results in anti-natriuresis that leads to an increase of ECF volume and cardiac filling.
The pathophysiology of syncope is summarized as a reduction in systemic blood pressure that causes a decrease in the global cerebral blood flow, which results in loss of consciousness. A sudden cessation of cerebral blood flow for 6 to 8 seconds has been shown to cause loss of consciousness.

# Causes
Presyncope may be caused by
- a temporary drop in blood pressure
- dehydration
- prolonged standing
- intense nausea or pain
- hypoglycemia, or low blood sugar, which may or may not be due to diabetes
- neurally mediated hypotension, which causes blood pressure to drop when a person stands up from a sitting or lying position
- Vagal presyncope
- side effect of some medications
- Cardiac arrhythmia

# Differentiating Presyncope from other Diseases
The differentiation between syncope and non-syncopal conditions with real or apparent LOC can be achieved in most cases with a detailed clinical history,   but sometimes can be extremely difficult.

# Epidemiology and Demographics
Patients of all age groups may develop presyncope. The prevalence of the causes of syncope is different depending on the clinical settings in which the patient is evaluated and the age of the patients. Furthermore, other differences depend on diagnostic definitions, geographical factors, and local care pathways, making a comparison between different studies difficult.19% of the United States population will experience a syncopal event in their lifetime, with the majority occurring in either the early adult years or after age 70; almost 58% of patients with syncope are female.    3% of visits to emergency departments and up to 6% of admissions to hospitals in the United States are for syncope.   Reflex syncope is the most frequent cause of syncope in any setting. Syncope secondary to cardiovascular disease is the second most common cause. The number of patients with a cardiovascular cause varies widely between studies; higher frequencies are observed in emergency settings mainly in older subjects, and in settings oriented toward cardiology. In patients <40 years OH is a rare cause of syncope; OH is frequent in very old patients. Non-syncopal conditions, misdiagnosed as syncope at initial evaluation, are more frequent in emergency referrals and reflect the multifactorial complexity of these patients. The high unexplained syncope rate in all settings justifies new strategies for evaluation and diagnosis. In the elderly multiple causes are often present and the medical history may be less reliable than in the young.   .

# Risk Factors
There are no established risk factors for .
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Common risk factors in the development of  include , , , and .
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Common risk factors in the development of  may be occupational, environmental, genetic, and viral.

# Screening
There is insufficient evidence to recommend routine screening for presyncope.

# Natural History, Complications, and Prognosis
If left untreated, patients with presyncope may progress to develop syncope which leads to actual loss of consciousness.
Common complications of presyncope include major trauma due to falls, sudden cardiac death, seizure, recurrent hospitalization.
Prognosis  of presyncope depends on the underlying cause. Patients with presyncope with structural heart disease and primary electrical disease are at high risk of overall mortality and sudden cardiac death. Young patients with reflex presyncope have an excellent prognosis.Morbidity in patients with presyncope is associated with recurrence of episodes and physical injury. Young patients with psychiatric disease have high rates of recurrence of pseudosyncope.
In patients with presyncope presenting to the emergency department, 29.1% have minor trauma, 4.7% have major trauma, and in older patients with carotid disease, 43% have major trauma. Morbidity is particularly high in the elderly, and is associated with loss of confidence, fear of falling, depression, fractures, and institutionalization.

# Diagnosis
The diagnosis of presyncope is made based on complete medical history of the patient including preexisting conditions such as diabetes and heart disease, and medications the patient takes. Physical exam will help guide further diagnostic testing, which may include:
- complete blood count and basic metabolic panel
- urinalysis
- thyroid function tests
- glucose test
- electrocardiogram
- Holter monitoring
- tilt table test
- echocardiogram

## History and Symptoms
The majority of patients with presyncope report:
- lightheadedness, general weakness
- dizziness
- confusion
- tunnel vision, blurry vision
- slurred speech
- trouble hearing
- sweating
- nausea or vomiting
- headache
- heart palpitations
These symptoms can last from just a few seconds to several minutes before they pass.

## Physical Examination
Patients with complains of presyncope usually appear normal. A careful and comprehensive physical examination is essential in a patient presenting with presyncope. Blood pressure should to be checked in both arms, and in the supine and standing positions. Signs to look for in the physical exam are dehydration, flushing, carotid bruits, cardiac murmurs, abdominal masses, varicose veins, and signs of endocrine disorders in skin, eyes and thyroid.

## Carotid sinus massage
Carotid sinus massage (CSM) is indicated in patients older than 40 years with presyncope of unknown etiology after initial evaluation.

## Electrocardiogram
An ECG may be helpful in the diagnosis of cause of presyncope. ECG monitoring is indicated in patients who have clinical or ECG findings suggestive of arrhythmic presyncope and is diagnostic when a correlation between pesyncope and an arrhythmia is detected. Several ECG ambulatory monitoring methods are available: conventional ambulatory Holter monitoring, in-hospital monitoring, event recorders, external or implantable loop recorders (ILRs), and remote (at home) telemetry.

## Echocardiography or Ultrasound
Echocardiography/ultrasound  may be helpful in the diagnosis of presyncope due to structural heart disease such as severe aortic stenosis, obstructive cardiac tumor or thrombi, pericardial tamponade, aortic dissection, and congenital anomalies of coronary artery. It is a class IIa recommendation from the American College of Cardiology/American Heart Association if there is clinical suspicion of structural heart disease and it is of no benefit unless cardiac etiology is suspected.

## Orthostatic challenge
The tilt table test is a simple test that moves a patient from a supine to an upright position using a tilt table. It is used to examine autonomic neural regulation of cardiovascular orthostatic responses.

## Other Diagnostic Studies
Assessment of global autonomic function may be helpful in the diagnosis of etiology of presyncope. This entails a number of maneuvers, pressor testing, Valsalva maneuver, phenylephrine test, amyl nitrite inhalation. These are performed while heart rate variability and blood pressure are monitored.

# Treatment
The mainstay of treatment for presyncope are 2 main treatment strategies: conservative/nonpharmacologic therapy and medical treatment. The treatment varies based on the cause of presyncope.
- Pharmacologic medical therapy is recommended among patients with recurrent episodes despite adequate conservative therapy. This list includes beta blockers, fludrohydrocortisone, midodrine, calcium channel blockers, anticholinergic agents, and serotonin transporter inhibitors.
- Conservative therapy includes lifestyle modifications like avoidance of provocative triggers such as heat, prolonged standing, decongestants, excess caffeine, large meals, and alcohol; increased salt and fluid intake; reduction or withdrawal of antihypertensive medications, and physical counterpressure maneuvers. Physical counter maneuvers and simple postural maneuvers like leg crossing, leg raising, genuflexion, toe-raising to contract calf/gastrocnemius muscle, squatting, and isotonic contraction of the thighs/quadriceps muscle are easy to teach to patients and may be useful in mild orthostatic symptoms. Compression support stockings are also effective in patients with postural hypotension and those with accentuated postural venous pooling. An abdominal binder and small frequent meals are advised in patients with post-prandial hypotension. In patients with supine hypertension and postural hypotension, elevation of the head-of-bed by 6 to 8 inches may also be helpful.

## Secondary Prevention
Effective measures for the secondary prevention of presyncope include patient education and treatment. Patients need to be aware of triggers that may predispose to or precipitate syncopal spells and orthostatic intolerance.

## Causes by Organ System

## Causes in Alphabetical Order

# Clinical test
The tilt table test is an evaluative clinical test to help identify presyncope or syncope. A tilt angle of 60 and 70 degrees is optimal and maintains a high degree of specificity.  A positive sign with the tilt table test must be taken in context of patient history, with consideration of pertinent clinical findings before coming to a conclusion.