Fainting and Blackouts (Syncope)

A fainting spell can be frightening, both for you and for those around you. Most often, however, there is no reason to panic. A fainting spell—the medical term is syncope—is a symptom, not a disorder. When you pass out or faint, it means that your brain is not getting sufficient oxygen to function properly. The signs of impending syncope may include nausea, perspiration, or a "graying-out" of your vision. The key sign, however, is a loss of consciousness.

Causes:

Syncope usually is the result of a malfunction in either the cardiovascular or the nervous system. Various heart problems can produce fainting spells. Among them are arrhythmias of the heart, especially an excessively rapid heart rate. In this case, the heart pumps insufficient blood to the brain, resulting in syncope. A narrowing of the aortic valve (Aortic Stenosis) that feeds blood from your heart to your main artery, sudden decreases in blood pressure, and slowing of the heart also can pro duce syncope.

The involuntary (autonomic) nervous system controls the pumping of your heart and the pressure in your blood vessels. When it fails to function properly or if too little blood is being pumped, the autonomic nervous system may malfunction and fainting spells may occur.

What Are the consequences?

Once you are lying flat, blood flow is quickly restored, and you usually regain consciousness. Recovering consciousness quickly after a fainting spell means that little or no damage is sustained by your brain due to the shortage of oxygen. In fact, the most serious risk of syncope is usually from the fall itself: fractures or head injuries may result.

Management:

If you experience a fainting spell, consult your physician. He or she will first identify the cause of the syncope. Your physician then will treat the cause with appropriate means, which may mean heart medications or, rarely, a pacemaker.

If the problem involves the autonomic nervous system, garments that constrict the circulation in your leg veins may help maintain an adequate supply of blood to your heart.

Vasovagal Fainting and Dizziness

Vasovagal fainting (neurocardiogenic syncope) is believed to be the most common type of syncope. It is estimated that 3 percent of emergency room visits in the United States are for this type of fainting. Vasovagal technically refers to the effect the vagus nerve has on the blood vessels, but in a broader sense it refers to the effects various nerves have on the heart and blood vessels.

The two types of nerves that affect the heart and blood vessels are called sympathetic nerves and parasympathetic nerves (like the vagus nerve). If these nerves are too sensitive, they can cause episodes of low blood pressure or slow heart rate or both. This may temporarily starve the brain of blood.

One test used to determine if a vasovagal reaction is the cause of fainting is called the tilt-table test. The patient lies flat on the back on a special table and is connected to an electrocardiogram machine. Under close observation by a physician, the table rotates to an upright position that may cause a vasovagal reaction or other neurologically related type of fainting.

Several medications can effectively treat these types of problems. Occasionally these patients may need a heart pacemaker.