Syncope: Types

The four main types of syncope are:

  1. Situational
  2. Carotid sinus hypersensitivity
  3. Cardiac (heart, blood vessels and other related structure problems)
  4. Orthostatic and neurocardiogenic syncope
  5. Other conditions that can mimic syncope

Situational syncope

Reflex syncope is the most common. It accounts for more than 50 percent of unexplained syncope. You may hear it called vasovagal or neurocardiogenic syncope.

It occurs when the part of the nervous system that regulates heart rate and blood pressure malfunctions in response to a trigger such as pain or fear. It causes the heart rate to slow, the blood pressure to drop and the blood to pool in the legs rather than going to the brain. This sudden decrease in blood flow to the brain causes the person to faint. Most people with this type of syncope recover quickly once they lie down and raise their legs. Some of the triggers for reflex syncope are:

  • coughing, sneezing or laughing
  • eating or swallowing
  • emotional distress such as fear and pain
  • exercise
  • prolonged standing
  • straining to go to the bathroom
  • urinating

Most people with this type of syncope have warning signs and symptoms before they faint. They can include severe dizziness, nausea and sweating. Reflex syncope can be harmless and require no treatment. If it affects your quality of life, it may require treatment. 

Carotid sinus hypersensitivity or carotid sinus syndrome

A less-common reflex syncope involves overly sensitive pressure receptors in the carotid arteries in the neck. These receptors can be stimulated by an increase in blood pressure or direct pressure to the arteries because of a tight shirt collar, shaving or neck massage.

Cardiac syncope

Cardiac syncope is the next most common cause of syncope. It involves either:

  • An abnormal heart rhythm
  • A problem with the structure or function of the heart, or major blood vessels

Abnormal heart rhythms

Two main categories of abnormal heart rhythms can cause cardiac syncope. Both can prevent enough blood from getting out of the heart to the brain, causing symptoms.

  • Tachycardias or very fast heart rates usually coming from the lower chambers of the heart
  • Bradycardias or very slow heart rates.

Abnormal heart structures or blood vessels

Abnormal heart structures also can prevent or slow the blood flow out of the heart to the brain. This can cause dizziness or syncope.

  • Heart valve problems
    The valves can become narrowed (valve stenosis) or leaky (valve regurgitation).
  • Heart muscle problems
    The heart muscle can’t normally contract, which pushes blood out of the heart, or it can’t normally relax, which allows the heart to fill with blood normally. Syncope may occur in up to 30 percent of people with a heart muscle condition known as hypertrophic obstructive cardiomyopathy.
  • Heart sac problems
    The thin, strong sac around the heart is called the pericardium. It can become irritated or diseased, causing it to become stiff or filled with fluid. This prevents the heart from beating normally. 
  • Heart artery problems
    The coronary arteries, which bring blood and oxygen to the heart, are abnormal. This can damaged the heart and cause it to malfunction.
  • Masses or tumors inside the heart
    A mass or tumor anywhere inside the heart can prevent the flow of blood out of the heart to the brain.

Other related structure problems

  • The lungs
    The lungs sit right next to the heart and help put oxygen into the blood. Without oxygen, the brain can’t function, and syncope occurs. Pulmonary embolism is one example: A blood clot can lodge in one of the vessels of the lung damaging lung tissue. Pulmonary hypertension is another example: The blood pressure running through the lungs can be too high.
  • The aorta
    Another important structural problem involves the aorta – the big artery that carries blood away from the heart to the rest of the body. If one or more layers of the wall of the aorta tear, blood flow to the brain can quickly reduce.

Orthostatic and neurocardiogenic syncope

These types of syncope involve the autonomic nervous system or ANS. The ANS regulates a series of reflexes that increase and decrease your heart rate and blood pressure when you change position. When you stand up, the ANS should automatically increase your blood pressure and heart rate to make sure that enough blood and oxygen get to your brain. If your ANS is not working correctly, you can experience dizziness or syncope with position changes.

Orthostatic syncope is a type of syncope that involves an abnormal ANS blood pressure response. It is triggered by position changes — particularly standing up after lying down for a while. Instead of increasing when standing, the blood pressure suddenly decreases, causing you to faint. Orthostatic syncope may be a sign of disorders or diseases that damage the ANS such as Parkinson’s disease, diabetes, amyloidosis and spinal cord injuries.

Neurocardiogenic syncope is another type of syncope that involves an abnormal ANS reflex among the heart, brain and the blood vessels. It is usually triggered by prolonged standing that causes the blood to pool in the legs. Instead of the normal reflex, which causes the heart rate and blood pressure to increase, an abnormal reflex causes the heart rate to slow and blood vessels to relax, making the blood pressure too low and causing syncope.

Other conditions that mimic syncope

Some medicines, alcohol, blood loss and dehydration can all cause low blood pressure and syncope. Neurological, metabolic or psychiatric problems can mimic syncope. Some of these problems include seizures, mini-strokes, panic attacks and conditions that cause low blood sugar, low blood oxygen or hyperventilation.