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Many Causes

There are many causes of syncope.

  • If blood does not circulate the way it should
  • The autonomic nervous system does not work properly
  • Changes in blood pressure
  • Changes in heart rate
  • Heart problems
  • Metabolic abnormalities
  • Anemia

Types of Syncope

There are a number of types of syncope.

Vasovagal Syncope

Blood Pressure Drops Suddenly

This is the most common type of syncope and occurs when your blood pressure drops suddenly, reducing blood flow to your brain. When you stand up, gravity causes blood to pool in the lower part of your body, below the diaphragm. In response, the heart and autonomic nervous system (ANS) react to maintain your blood pressure.

Situational Syncope

Triggered by Particular Situations

This is a type of vasovagal syncope that takes place only during particular situations. Certain situations "trigger" an exaggerated neurological reflex. These can include such things as dehydration, intense emotional stress, anxiety, fear, pain, hunger, the sight of blood or use of alcohol or drugs. Hyperventilation associated with panic or anxiety also can cause syncope. Other triggers may include coughing forcefully, turning the neck or wearing a tight collar.

Postural Syncope

Blood Pressure Drops Suddenly Due to Quick Position Change

This occurs when your blood pressure drops suddenly due to a quick change in position, such as from lying down to standing. Postural syncope can be related to certain medications or dehydration.

Cardiac Syncope

Heart or Blood Vessel Problem Interferes with Blood Flow to Brain

This involves a loss of consciousness due to a heart or blood vessel problem that interferes with blood flow to your brain. Among these are an abnormal heart rhythm (arrhythmia), obstructed blood flow in the heart or blood vessels, valve disease, aortic stenosis, blood clot, or heart failure. Syncope caused by heart problems can be life-threatening.

Neurologic Syncope

Triggered by Neurological Condition

This is the result of a neurological condition such as stroke, transient ischemic attack (TIA) or seizure.

Contact Information

Cardiovascular Medicine
Division of the CardioVascular Institute
Beth Israel Deaconess Medical Center
330 Brookline Avenue
Boston, MA 02215