Causes of Fainting / Syncope

Causes of fainting could be reflex-mediated, cardiac, orthostatic or cerebrovascular.

Causes of syncope include:

  • Reflex-mediated Causes: Reflex-mediated syncope often occurs due to a failure with the normal reflexes to maintain blood supply to the brain with a change in posture. Types of reflex-mediated syncope are:
  • Vasovagal syncope: Vasovagal syncope is the common faint observed in many individuals. It is usually preceded by conditions like emotional stress, trauma, pain, sight of blood or prolonged standing. Initially, the patient experiences a prodrome phase. During this phase, the patient suffers from symptoms like excessive salivation, nausea and discomfort in the stomach, sudden tiredness, dizziness and yawning, which lasts for seconds to a few minutes. This is followed by the patient falling down. Following the syncope, the patient may experience confusion, disorientation and a feeling of being unwell.
  • Carotid sinus syncope: The carotid sinus is a bulb-like enlargement on the carotid artery, an artery that supplies to the brain. Stimulation of the carotid sinus with turning of the head, while shaving or wearing a tight collar, can result in syncope.
  • Situational syncope: Situational syncope is syncope that arises during certain situations like while passing urine, defecating or coughing.
  • Glossopharyngeal and trigeminal neuralgia: Inflammation affecting the Vth (trigeminal) and IX (glossopharyngeal) facial nerves can result in reflex-mediated syncope when these nerves are stimulated. These conditions are commonly associated with pain in the regions supplied by these nerves.
  • Cardiac Causes: Any condition affecting the heart could result in a decrease in blood supply to the brain, resulting in a syncopal attack. Some of the cardiac causes that could result in syncope are:
  • Mechanical or structural causes: Any condition that could affect the structure of the heart muscles, heart valves, pericardium or major arteries can result in syncope. Some of these conditions include valvular heart disease, heart attack, hypertension and congestive heart failure. The presence of these conditions may be known to the patient or may be diagnosed with ECG and other cardiac tests.
  • Arrhythmia: An arrhythmia is an abnormal heart rhythm, which could result in a disturbance in blood flow to the brain and thereby cause syncope. Drugs used to treat arrhythmia can also sometimes result in arrhythmias. Arrhythmias can be diagnosed on physical examination or continuous ECG monitoring.
  • Orthostatic Causes: Orthostatic syncope is a type of syncope that occurs due to sudden fall in blood pressure with change of position from lying or sitting to standing. It may be due to:
  • Primary causes: Neurological conditions like autonomic failure and Parkinson’s disease result in orthostatic syncope because of a failure of the nerves to adjust the blood pressure with standing position.
  • Secondary causes: Some underlying conditions can also result in orthostatic syncope. These include:
    • Reduced blood volume: Reduced blood volume due to dehydration or other conditions can result in orthostatic syncope. The heart rate is usually more than 100 beats per minute in these patients.
    • Medications and drugs: Some medications like those used for hypertension, depression and diuretics can result in orthostatic syncope. Illegal drugs as well as alcohol can also interfere with nerve function resulting in syncope.
    • Diabetes: Patients with diabetes may have abnormal nerve function, making them more prone to syncope.
  • Cerebrovascular Causes: Conditions interfering with the normal blood supply to the brain can result in fainting. Some of these conditions are:
  • Vertebrobasilar syncope: Reduced blood supply via the vertebrobasilar arteries to the brain can result in transient ischemic attacks and syncope. The patient may suffer from other symptoms like vertigo, headache, swaying while walking, difficulty with speech, double vision and sensory disturbances. Headache and dizziness during the recovery stage of a syncope should suggest vertebrobasilar insufficiency.
  • Vascular steal syndrome: Vascular steal syndrome like the subclavian steal syndrome is a consequence of reduced blood supply to the brain due to an obstruction or narrowing in a major artery like the subclavian artery. It may be diagnosed with arteriography or Doppler ultrasound.


  1. Miller TH, Kruse JE. Evaluation of Syncope. Am Fam Physician 2005;72:1492-500
  2. Benditt DG and Goldstein M. Fainting. Circulation. 2002;106:1048-1050

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