When blood flow to the brain is momentarily dropped, a person can briefly lose consciousness and lose control over one’s posture. Syncope is physiologically related to abrupt decrease in blood pressure, heart rate, and blood volume and distribution. To correctly diagnose the cause of syncope your doctor will run a thorough review of your heart, blood circulations, and nervous system.



Prior to the actual syncopal episode certain symptoms also called premonitory symptoms manifest. Patients with past syncopal experience can recognize these symptoms and sit down or lie down with their feet up to anticipate and prevent passing out.


Syncopal symptoms

“dizziness, drowsiness, grogginess, light-headedness, “blacking out,” falling for no reason, feeling weak when standing

If you’ve experienced syncope with any of the above symptoms you should visit a doctor to find out any underlying medical conditions. Most patients with syncope can recover with proper treatment.


Types of syncope

(1) Vasovagal syncope

Vasovagal syncope is the most common type of syncope. When a you stand up a big portion of your blood moves below the diaphragm towards the lower part of your body due to gravity. With less blood returning to the heart, blood pressure is registered as reduced and the heart will compensate by raising the sympathetic response. The central nervous system will respond through vasovagal nerves to reduce this heightened “fight or flight” response by reducing the blood pressure (hypotension) and slowing the heart rate (bradycardia) which result in syncope.


(2) Situational syncope

Situational syncope is also a type of vasovagal syncope. The vasovagal response is triggered through particular kinds of situations related to physiological changes such as dehydration or hunger, intense emotions such as stress or fear, and use of substance such as alcohol or drugs. Some more extreme situations that cause panic attacks can cause you to hyperventilate (breathing too fast or too deeply that brings in too much oxygen expels carbon dioxide too quickly) can also lead to syncope. Other stimuli include forceful coughing, urinating (micturition syncope), and turning the neck or wearing a tight collar (carotid sinus hypersensitivity).

(3) Cardiac syncope

When there is an abnormality directly on the heart or blood vessel that prevents proper blood flow to the brain you can lose consciousness which is called cardiac syncope. You can have cardiac syncope when there are abnormal heart rhythm (arrhythmia), obstructed blood flow in the heart or blood vessels, valve disease, aortic stenosis, blood clot, or heart failure.

(4) Neurologic syncope

Neurological condition such as seizure, stroke, transient ischemic attack (TIA), and psychiatric symptoms can lead to loss of consciousness as well.

A good majority of the syncope cases ranging from 18 to 41 % depending on the clinical studies reported causes to be unknown. 

Evaluation of syncope patients

Initially a physician should identify presence of any life threatening causes and apply stabilizing management if necessary while finding a more thorough diagnoses and treatment plan. The emphasis should be doing a careful history taking and physical examination focusing on vital signs and the neurologic and cardiac examination. Concurrently any external or internal secondary injuries from fall should be identified especially in the head (i.e. subdural hematoma), wrist, or hip. 

After the initial evaluation additional tests are recommended.

  • Carotid sinus massage in patients >40 years old
  • Echocardiogram when there is previous known heart disease or data suggestive of structural heart disease or syncope secondary to cardiovascular cause.
  • Orthostatic challenge (lying to standing orthostatic test or head-up tilt testing) when syncope is related to the standing position or there is suspicion of a reflex mechanism.
  • Other less specific tests such as neurologic evaluation or blood tests are indicated only when there is suspicion of nonsyncopal transient loss of consciousness.


Treatment of syncope patients

Treatment is based upon addressing the underlying cause of syncope and prevention of recurrence.

  • Metabolic disorders — Low blood sugar (hypoglycemia) or low blood oxygen state (hypoxemia) have potential to cause syncope. Metabolic abnormalities, anemia, and hypovolemia can be effectively managed by specific therapy to correct these abnormalities.
  • Iatrogenic syncope — Iatrogenic syncope resulting from drug therapy is a preventable and treatable condition. It is especially common in elderly patients and those with coexisting chronic diseases, and diminished or blunted cardiovascular reflexes. In this setting, effective interventions include the elimination of the offending agent, substitution of an alternative agent, changing the dose, or altering the timing of drug administration.
  • Orthostatic hypotension — Identifying the underlying cause is crucial to appropriate treatment of orthostatic hypotension. Orthostatic hypotension associated with evidence of volume depletion should be treated with volume expansion and avoidance of precipitating factors (such as diuretic use). Orthostatic hypotension in the absence of volume depletion is most often due to an autonomic neuropathy or the administration of antidepressant drugs.
  • Cardiovascular disease with obstruction — Cardiac diseases that obstruct the outflow of blood generally require surgical correction or attenuation of the obstruction. As an example, aortic valve replacement for aortic stenosis will alleviate symptoms, prevent syncope, and prolong survival.Dynamic outflow obstruction resulting from hypertrophic cardiomyopathy is treated pharmacologically with beta blockers or calcium channel blockers. Refractory obstructive symptoms may be treated with nonpharmacologic methods such as septal myectomy or septal ablation. The cause of syncope in such patients may be due to undiagnosed ventricular arrhythmias that may increase the risk of death and may require therapy with an implantable cardioverter-defibrillator (ICD).
  • Implantable cardioverter-defibrillator therapy — ICD therapy is indicated in patients with who have syncope that is due to potentially life-threatening ventricular tachycardia that is otherwise not treatable. ICD therapy should also be considered for patients who have syncope due to an unknown cause but have underlying structural heart disease that places them at risk of sudden cardiac death.



  • Cleveland Clinic – Syncope (Cleveland Clinic)
  • Approach to the adult patient with syncope in the emergency department (UptoDate)
  • Evaluation of syncope in adults (UptoDate)
  • Management of the patient with syncope (UptoDate)


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