Syncope
What is Syncope?
Syncope occurs when there is a sudden and brief interruption of blood flow to the brain, leading to a temporary loss of responsiveness and muscle tone. It affects approximately 1 million Americans annually, accounting for 3% of all ER visits and 6% of hospital stays. Unexplained sudden syncope should prompt further medical examination. There are various types and causes of syncope, including vasomotor, orthostatic, and cardiovascular syncope.
Causes of Syncope
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, resulting in 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 side effects
- 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 of developing 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 of 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.
Diagnosing Syncope
A comprehensive medical history and physical exam are vital in determining the correct diagnosis. Non-cardiac vasomotor syncope can have unique presentations that make cardiac causes less probable. A complete exam, which includes taking a patient's sitting and standing blood pressure in both arms, should be performed. Your physician may order a study known as a tilt table test if they suspect 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, a physician may order a cardiac echocardiogram (ultrasound) or MRI to assess your heart structure and function. 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.
Treatments for Syncope
The best approach to treating syncope will depend on the cause. Vasomotor syncope can be treated with specific medications and by avoiding triggering situations. Many patients find that treatment provides 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, is 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 catheter ablation (in benign forms) or an ICD is also necessary.
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