Syncope – Causes, Symptoms, Diagnosis, Treatment

Syncope a sudden, transient loss of consciousness and postural tone, is a phenomenon estimated to affect 30% to  40% of the population, and those numbers are likely underestimated given the high prevalence of patients with syncope who do not present to a hospital or urgent care setting.

Syncope is a sudden transient loss of consciousness associated with loss of postural tone. “Blackout spells,” “passing out,” or “fainting” are terms occasionally used by patients and refer to syncope only if associated with loss of consciousness.

Syncope, also known as fainting, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery.[rx] It is caused by a decrease in blood flow to the brain, typically from low blood pressure.[rx] 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.[rx][rx] When consciousness and muscle strength are not completely lost, it is called presyncope.[rx] It is recommended that presyncope be treated the same as syncope.

Types of Syncope

Vasodepressor syncope

  • It occurs in all age groups, although it is more common in younger patients and rare in the elderly. Vasodepressor syncope occurs in response to sudden emotional stress or in a setting of real, threatened, or imagined injury. Some of the situations commonly leading to vasodepressor syncope include pain, the sight of blood, instrumentation, and venipuncture.
  • Vasodepressor syncope occurs primarily in the standing position and less frequently in the sitting position. Patients usually experience several minutes of prodromal symptoms including weakness, pallor, sweating, nausea, increased peristalsis, yawning, belching, and dimming of vision followed by a loss of consciousness associated with hypotension and sinus bradycardia.

Vasovagal syncope (also called cardio-neurogenic syncope)

  • Vasovagal syncope is the most common type of syncope. It is caused by a sudden drop in blood pressure, which causes a drop in blood flow to the brain. When you stand up, gravity causes blood to settle in the lower part of your body, below your diaphragm. When that happens, the heart and autonomic nervous system (ANS) work to keep your blood pressure stable.
  • Some patients with vasovagal syncope have a condition called orthostatic hypotension. This condition keeps the blood vessels from getting smaller (as they should) when the patient stands. This causes blood to collect in the legs and leads to a quick drop in blood pressure.

Situational syncope

Situational syncope is a type of vasovagal syncope. It happens only during certain situations that affect the nervous system and lead to syncope. Some of these situations are:

  • Dehydration
  • Intense emotional stress
  • Anxiety
  • Fear
  • Pain
  • Hunger
  • Use of alcohol or drugs
  • Hyperventilation (breathing in too much oxygen and getting rid of too much carbon dioxide too quickly)
  • Coughing forcefully, turning the neck, or wearing a tight collar (carotid sinus hypersensitivity)
  • Urinating (miturition syncope)

Postural syncope (also called postural hypotension)

  • Postural syncope is caused by a sudden drop in blood pressure due to a quick change in position, such as from lying down to standing. Certain medications and dehydration can lead to this condition. Patients with this type of syncope usually have changes in their blood pressure that cause it to drop by at least 20 mmHg (systolic/top number) and at least 10 mmHg (diastolic/bottom number) when they stand.

Micturition syncope

  • It occurs in healthy, young-to-middle-aged men and also elderly men and women. Syncope usually occurs in the middle of the night during or immediately following voiding, often without premonitory symptoms. In the young, the predisposing factors include excessive alcohol consumption, a recent viral infection, fatigue, or recent reduced food intake.
  • In the elderly, the predisposing factors are diuretics and chronic orthostatic hypotension. Syncope is usually not recurrent; however, recurrent micturition syncope has been reported with bladder neck obstruction, severe chronic orthostatic hypotension, and paroxysmal complete atrioventricular block.

Defecation syncope

  • It occurs in elderly patients, usually in the early morning hours. There are no known predisposing factors. The evaluation of defecation syncope is similar to other patients with syncope in whom a cause is not known.
  • Syncope in association with swallowing is rare and generally occurs in patients with structural diseases of the esophagus or the heart. Esophageal diseases that can cause swallow syncope include esophageal spasm, a diverticulum, or other lesions. Transient atrioventricular block or bradycardias associated with swallowing are also reported to cause swallow syncope.

Cough syncope

  • It is usually middle-aged men who are mildly obese, and heavy smokers and alcohol users who often have associated pulmonary conditions such as chronic obstructive pulmonary disease, asthma, bronchiectasis, pneumoconiosis, sarcoidosis, or tuberculosis. Cough syncope has also been associated with hypertrophic cardiomyopathy and herniation of cerebellar tonsils.

Orthostatic hypotension

  • It is one of the most common causes of syncope. Orthostatic hypotension occurs in a variety of clinical situations with volume depletion or decreased venous return. Various pharmacologic agents can predispose patients to orthostatic hypotension. Orthostatic hypotension is also a symptom of many central and peripheral nervous system disorders.

Drug-induced syncope

It rapidly acting medications (e.g., sublingual nitroglycerin) may cause syncope immediately after ingestion. More commonly, drugs may lead to effects on blood pressure or arrhythmias, leading to syncope. Some of the drug effects include the following:

  • Postural hypotension. In this category are drugs such as antihypertensives, diuretics, nitrates, other arterial vasodilators, l-dopa, phenothiazines, or other tranquilizers.
  • Anaphylactic reaction. Drugs may lead to an anaphylactic reaction with associated symptoms of anaphylaxis and hypotension leading to syncope.
  • Drug overdose.
  • Drug-induced ventricular tachycardia. This group includes drugs that lead to Q-T interval prolongation and torsades de pointes. The most commonly implicated drugs leading to torsades de pointes include quinidine, disopyramide, procainamide, psychotropic drugs, phenothiazines, and tricyclic antidepressants. In addition, drug-induced hypokalemia and hypomagnesemia may lead to prolonged Q-T interval and development of torsades de pointes.

Reflex (Neurogenic)

  • Vasovagal – typically preceded by an inciting stressful event such as fear, seeing blood, hearing bad news, emotional stress, or pain
  • Situational – preceded by a specific action such as sneezing, laughing, coughing, urinating, defecating, eating, or exercise
  • Carotid sinus stimulation

Orthostatic Hypotension

  • Autonomic dysfunction – usually a symptom of another degenerative disease such as Parkinson disease, multiple system atrophy, Lewy body dementia or can be a primary disease on its own; can also occur as a direct result of diabetes, amyloidosis, and spinal cord trauma
  • Drug-induced – in the setting of diuretics, vasodilating agents, alcohol, antidepressants or any other medications that reduce cardiac output or vascular resistance
  • Volume depletion – traumatic hemorrhage, atraumatic blood loss, diarrhea, vomiting, sweating, decreased oral hydration

Causes of Syncope

The following is a brief list of the more common etiologies of cardiac syncope. Further discussion regarding how to recognize and manage these etiologies will follow.


  • Ischemic cardiomyopathy (most common structural cardiac etiology of syncope)
  • Valvular abnormalities (second most common structural etiology, most commonly aortic stenosis)
  • Nonischemic/Dilated cardiomyopathy (third most common structural etiology)
  • Hypertrophic obstructive cardiomyopathy
  • Aortic dissection
  • Cardiac tamponade
  • Obstructive cardiac tumors
  • Pericardial disease
  • Pulmonary hypertension
  • Pulmonary emboli
  • Arrhythmogenic right ventricular cardiomyopathy



  • Supraventricular (examples: atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia (PSVT), PSVT in the setting of pre-existing accessory conduction pathways)
  • Ventricular (often secondary to mechanical/structural heart disease or channelopathies, such as Brugada)
  • PR interval disorders/accessory conduction pathways (WPW, LGL, Mahaim syndrome, Breijo syndrome).


  • Sinus node dysfunction
  • Atrioventricular conduction block (typically second or third degree)
  • Pacemaker malfunction

Inherited channelopathies

  • QT interval disorders (Long or short QT)

    • Romano-Ward syndrome: Autosomal dominant congenital long QT syndrome
    • Jervell and Lange-Nielsen syndrome: autosomal recessive long QT syndrome associated with deafness
  • Brugada syndrome

    • An autosomal dominant mutation in the SCN5A gene, which encodes for voltage-gated sodium channels found in the heart
  • Catecholaminergic polymorphic ventricular tachycardia

    • Autosomal dominant mutation of hRyR2 gene, which encodes for ryanodine receptors
    • Autosomal recessive mutation of CASQ2 gene, which encodes for calsequestrin-2
    • Drug-Induced(bradycardias, tachycardias, QT interval prolongation, cardiotoxins, etc.).

Cardiovascular disorders

  • Cardiac arrhythmias (both tachy and bradyarrhythmias)
  • Structural and obstructive disorders (valvular abnormalities, HOCM, MI, PE)
  • Cerebrovascular causes (vertebrobasilar insufficiency)

Disorders of blood flow and vascular tone

  • Vasovagal (neurocardiogenic)
  • Orthostatic hypotension (medications, autonomic failure, peripheral neuropathy, decreased blood flow)
  • Situational (cough, micturition, defecation, post prandial, deglutition)
  • Carotid sinus syncope

Others that mimic syncope

  • Seizures
  • Metabolic (hypoglycemia, hypoxia, symptomatic anemia)
  • Psychogenic (panic attacks)

Neurally mediated causes include conditions that cause either primary or secondary failure of the autonomic system

  • Peripheral neuropathy as seen in diabetes mellitus, alcoholics, nutritional (vitamin B12 deficiency), amyloidosis
  • Idiopathic postural hypotension
  • Multisystem atrophies (parkinsonism, progressive cerebellar degeneration, dementia with Lewy bodies)
  • Acute dysautonomia (seen in a variant of Guillain-Barre syndrome)
  • Toxin, drug or infection-induced neuropathy

Non-neurally mediated causes include

  • Medications (antihypertensives, vasodilators)
  • Decreased blood volume (adrenal insufficiency, blood loss, dehydration, hypovolemia or decreased effective intravascular volume)
  • Physical deconditioning
  • Sympathectomy

Symptoms of syncope

The most common symptoms of syncope include:

  • Blacking out
  • Feeling lightheaded
  • Falling for no reason
  • Feeling dizzy
  • Feeling drowsy or groggy
  • Fainting, especially after eating or exercising
  • Feeling unsteady or weak when standing
  • Changes in vision, such as seeing spots or having tunnel vision
  • Headaches
  • Pale skin
  • Lightheadedness
  • Tunnel vision — your field of vision narrows so that you see only what’s in front of you
  • Nausea
  • Feeling warm
  • A cold, clammy sweat
  • Yawning
  • Blurred vision

Diagnosis of Syncope

Tests to determine causes of syncope include

  • Laboratory testing – Blood work to check for anemia or metabolic changes.
  • Electrocardiogram (EKG or ECG) – A test that records the electrical activity of your heart. Electrodes (small sticky patches) are applied to your skin to collect this information.
  • Exercise stress test – A test that uses an ECG to record your heart’s electrical activity while you are active. This is done on a treadmill or stationary bike, which helps you reach a target heart rate.
  • Ambulatory monitor – You will wear a monitor that uses electrodes to record information about your heart’s rate and rhythm.
  • Echocardiogram – A test that uses high-frequency sound waves to create an image of the heart structures.
  • Tilt table (head-up tilt test) – A test that records your blood pressure and heart rate on a minute-by-minute or beat-by-beat basis while the table is tilted to different levels as you stay head-up. The test can show abnormal cardiovascular reflexes that cause syncope.
  • Blood volume determination – A test to see if you have the right amount of blood in your body, based on your gender, height and weight. A small amount of a radioactive substance (tracer) is injected through an intravenous (IV) line placed in a vein in your arm. Blood samples are then taken and analyzed. The blood volume analyzer system used at Cleveland Clinic can provide accurate test results within 35 minutes.
  • Hemodynamic testing – A test to check the blood flow and pressure inside your blood vessels when your heart muscle contracts and pumps blood throughout the body. A small amount of a radioactive substance (tracer) is injected through an intravenous (IV) line placed in a vein in your arm and three sets of images are taken.
  • Autonomic reflex testing – A series of different tests are done to monitor blood pressure, blood flow, heart rate, skin temperature and sweating in response to certain stimuli. These measurements can help your doctor determine if your autonomic nervous system is working normally or if there is nerve damage.
  • Tilt-table test – During a tilt-table test, you’ll be secured to a special table. Your heart rate and blood pressure are measured as you’re rotated from lying down to upright.
  • Carotid sinus massage – Your doctor will gently massage your carotid artery, which is located in your neck. They’ll check to see if symptoms of faintness occur when they do this.
  • Stress test – A stress test assesses how your heart responds to exercise. The electrical activity of your heart will be monitored via ECG while you exercise.
  • Echocardiogram – An echocardiogram uses sound waves to create a detailed image of your heart.
  • Imaging tests – These tests can include a CT scan or MRI, which capture images inside your body. These tests are most often used to look at the blood vessels in your brain when a neurologic cause of fainting is suspected.
  • Pulse oximetry – should be done during or immediately after an episode to identify hypoxemia (which may indicate pulmonary embolism). If hypoxemia is present, CT or a lung scan is indicated to rule out pulmonary embolism.
  • Invasive electrophysiologic testing – is considered if noninvasive testing does not identify arrhythmia in patients with any of the following ->A negative response defines a low-risk subgroup with a high rate of remission of syncope. The use of electrophysiologic testing is controversial in other patients. Exercise testing is less valuable unless physical activity precipitated syncope.

Treatment of Syncope

Nonpharmacological treatment

Nonpharmacological treatment measures aim at either increasing venous return to the heart while decreasing venous pooling in the lower extremities or increasing blood volume to maintain blood pressure in the supine position and include:

Avoiding physical deconditioning in the elderly which helps maintain muscle tone in lower extremities
  • External compression devices such as waist-high compression stockings, abdominal binders
  • Physical maneuvers such as lunges, calf-raise, squatting, leg crossing
  • Review of home medications and discontinue diuretics and vasodilators if possible
  • Increase water and fluid intake to about 2-3 liters per day, avoid dehydration, bolus water ingestion of 500mls of water in 2 to 3 minutes especially in the morning
  • Dietary measures including liberal salt diet 6-10g/day, eating small frequent low carbohydrate meals a day in case of postprandial orthostatic hypotension, avoid alcohol intake
  • In patients with autonomic dysfunction and supine hypertension, raising the head of the bed to 10 degrees at night reduces nocturnal diuresis
  • Lifestyle modification by avoiding activities that increase core temperature and cause peripheral vasodilatation such as avoiding saunas, spas, hot tubes, prolonged hot showers and excessive high-intensity exercise


The goal of pharmacological treatment is to increase blood volume or peripheral vascular resistance and includes:

  • Midodrine 2.5 to 15mg – orally once to thrice daily
  • Fludrocortisone 0.1 to 0.2mg – daily in the morning titrated up to 1mg daily if needed
  • Pyridostigmine 30 to 60 mg – orally trice daily
  • Yohimbine 5.4 to 10.8mg – orally trice daily
  • Octreotide 12.5 to 50 ug – subcutaneously twice daily
  • Cafergot – such as caffeine 100mg and ergotamine 100mg

Treatment of underlying cause is the focus of treatment in syncope. During acute an acute episode, patients should be made to sit or lay down quickly and raising the legs help recovery in patients with reflex postural hypotension event. Placing patients in a horizontal position after the acute event and preventing rising too soon. Treatment of any injuries sustained during a sudden fall from syncope warrants immediate attention.

Vasovagal syncope

  • Conservative measure includes avoiding situations or stimuli that have caused them, Tilt training and increasing use of salt and fluid.
  • Drug therapy with beta-blockers, SSRIs, Hydrofludrocortisone, Proamantine and few other medications might be useful if conservative measures fail.

Orthostatic hypotension

  • Rising slowly from supine and sitting position, a gradual change in posture.
  • Avoiding medications that can cause orthostatic hypotension (diuretics, vasodilators).
  • Use of compression stocking to improve venous return.
  • Intravenous fluids in patients who are intravascularly volume depleted.
  • Use proamantine in refractory cases.

Cardiovascular disorders

Treating underlying condition by Cardiology.

  • Disposition is often the most difficult task in caring for emergency department patients with syncope. Admission rates vary in patients presenting with syncope. In the United States, about 80% of patients presenting to the emergency department following a syncopal event will be admitted.
  • Catheter ablation – procedure to cauterize the specific heart cells that cause abnormal heart rhythms
  • Pacemakers – device inserted under the skin below the collarbone to deliver regular electrical pulses through thin, highly durable wires attached to the heart; used to treat bradycardia, heart block and some types of heart failure
  • Implantable cardioverter-defibrillators (ICDs) – a small implanted device that delivers an electrical pulse to the heart to reset a dangerously irregular heartbeat; often used to treat ventricular tachycardia or heart failure


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