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What is Syncope?

Syncope is an abrupt loss of consciousness or fainting. It can occur for any number of reasons including low blood pressure, either alone or in connection with an inappropriately slow (bradycardia) or fast (tachycardia) heart rate.  It affects approximately 1 million Americans every year and accounts for 3% of all ER visits and 6% of all hospital stays.  Unexplained sudden syncope should prompt further medical examination.

Non-cardiac causes

Non-cardiac episodes of syncope are the most common. Vasomotor syncope can occur when blood pools in the legs, causing a drop in blood pressure and blood supply to the brain, with resulting loss of consciousness. The pooling of blood in the lower veins of the body can occur when standing if the person’s body fails to narrow those vessels as a result of:

  • medication effect,
  • dehydration,
  • autonomic nervous system disease

The reflex causes the second form of vasomotor syncope. Various stimuli including emotions, pain, heat, urination/defecation, yawning, and nausea can bring about an unsuitable reflexive response with the pooling of blood in the legs and a varied heart rate response (usually improper slowing).

Cardiovascular Syncope

Cardiovascular syncope is the most dangerous type of fainting and is typically caused by an abnormal heart rhythm (arrhythmia) or severe cardiac valve disease.

The risk of cardiovascular syncope increases with age. People who have any of the following conditions may be at a higher risk to develop cardiovascular syncope.

  • Chest pain caused by angina
  • Coronary artery disease
  • Previous heart attack
  • Cardiomyopathy (malfunction or malformation of the heart muscle)
  • Ventricular dysfunction (weakness of the heart muscle)
  • An abnormal electrocardiogram
  • Recurrent episodes of fainting that come on rapidly and without warning
  • Fainting during exercise
  • Some congenital heart defects or syndromes
  • Defects of the electrical system of the heart such as Long QT syndrome and Brugada Syndrome

Symptoms of Cardiovascular Syncope

Cardiovascular syncope is usually a sudden event with little or no warning signs that a person is about to faint.  Some people do experience the following:

  • Heart palpitations
  • Shortness of breath
  • Pressure, pain, or tightness in the chest

Tachyarrhythmias (heart rhythms more than 100 beats per minute), can also lead to cardiac syncope.

Supraventricular tachycardia seldom causes syncope and a detailed evaluation is critical to exclude a more life-threatening cause.

Ventricular tachycardia and ventricular fibrillation can produce syncope and are potentially fatal conditions.  These are forms of sudden cardiac death.  A comprehensive medical history is required.


A comprehensive medical history and physical exam are vital in order to determine the correct diagnosis. Non-cardiac vasomotor syncope can have unique presentations that make cardiac causes less probable. A complete exam including sitting and standing blood pressures in both arms should be performed. A study, known as a Tilt Table Test, may be ordered by your physician if he suspects vasomotor insufficiency. Patients with a history of myocardial infarction and coronary artery disease are at an increased risk of developing ventricular arrhythmias. If symptoms are frequent, your physician will attempt to capture these incidents with a Holter or Event monitor Additionally, an assessment o

Tilt Table Test for Syncope

f your heart structure and function with a cardiac echocardiogram (ultrasound) or MRI may be ordered. An exercise stress test could also provide useful information. If you have indications of a tachycardia-related issue, your doctor may decide to perform a diagnostic electrophysiology study to study your cardiac conduction system and to determine if the tachycardia can be triggered.

How to treat the syncope will depend upon on the cause. Vasomotor syncope can be treated with specific medications and by avoiding triggering situations. Many patients do get relief, but not an absolute elimination of the episodes. Treatment for cardiac-related syncope is customized to the triggering mechanism. Bradycardia, or slow heart rates, are typically related to AV block or sick sinus syndrome and can be treated with a pacemaker if required. Supraventricular tachycardias can be treated with drugs or catheter ablation. Ventricular tachycardias can also be treated with medications, but usually, either a catheter ablation (in benign forms) or an ICD is also necessary.

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