Syncope

The term syncope means a sudden loss of consciousness. A simple fainting spell is the most common form of syncope. The term “near syncope” refers to the sensation of being dizzy or lightheaded and coming close to passing out although not completely.

There are a number of different causes of syncope.  Generally they can be broken down into one of three areas.  The first is a primary malfunction of the brain's electricity.  To remain awake and alert, one has to have a constant supply of electricity in the brain.  If this is short-circuited for some reason, then a person will suddenly lose consciousness.  The most common example of this is a seizure.  People that have seizures usually have sudden a sudden loss of consciousness, often accompanied by other abnormalities such as jerking of the extremities and loss of bowel or bladder control.

The second potential cause of syncope is a primary malfunction of the heart, which can cause a sudden decrease in blood flow to the brain.  When the brain is deprived of blood flow for even a short time, a loss of consciousness will result.  A primary malfunction of the heart can be due to poor contraction of the heart muscle or some electrical malfunction of the heart.  In an otherwise healthy young person, primary heart related causes of syncope are extremely uncommon.  They become more common the older ones gets.  In an elderly person they may cause up to half the cases of syncope.  However, in a child or young person they are very rare.

By far and away, the most common cause of syncope at all ages is “vasovagal” syncope. This most commonly occurs in someone who has been either standing for a while or has suddenly stood up from a sitting or lying position. With standing, gravity exerts a stronger effect on the body, pulling blood away from the brain and down towards the legs. If the brain doesn't respond properly by sending signals to the blood vessels in the legs causing them to constrict, an excess of blood will collect in the legs. This can result in a decrease in blood flow to the brain which causes dizziness. If the brain fails to correct the problem, then fainting can occur. Fainting in this situation can actually be thought of as a defense mechanism. It is the brain's way of getting the body flat again so it doesn't have to fight gravity!

The fainting reflex is mediated by the vagus nerve. The vagus nerve is a large nerve that originates from the brain and is distributed throughout the body. It supplies a number of different organs, including the heart, blood vessels, intestines, skin, as well as many other areas. When it is activated, it can cause a sudden decrease in heart rate as well as a dilation of blood vessels throughout the body. This results in a drop in blood pressure and, coupled with the decrease in heart rate, can cause a sudden decrease in blood flow to the brain. The vagus nerve can be activated by other things besides pooling of blood in the legs. Other triggers include emotion, such as fear or pain. Sometimes an upset stomach or viral infection can activate the vagus nerve and lead to a fainting episode. Occasionally an increase in pressure in the chest and abdomen can trigger the vagus nerve. This can be seen with coughing or vomiting.

Many individuals that have vasovagal syncope also have other associated symptoms. These include feelings of chest pain, dizziness, lightheadedness, and palpitations (a feeling that the heart is racing). Usually the majority of these symptoms are due to a release of adrenaline by the body as an attempt to counteract the movement of blood toward the legs due to gravity. Other potential symptoms include a chronic feeling of fatigue or tiredness. Often individuals will interpret these symptoms as some type of primary heart abnormality, when in reality the heart is completely fine.

The best way to prevent fainting due to vasovagal causes is to recognize the symptoms before fainting can occur. This means realizing when you are dizzy that blood is collecting in the legs. This should prompt you to sit or lie down immediately. Other factors which can help include staying very well hydrated. Rarely medications can be prescribed to increase the blood volume to prevent fainting.