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Fainting, also known as syncope, is a brief, sudden loss of consciousness, typically followed by a complete recovery. Fainting occurs when the brain is starved for oxygen due to temporarily inadequate blood flow.
In general, syncope is characterized as either cardiac syncope or noncardiac syncope. Cardiac syncope is caused by underlying heart disease, while non-cardiac syncope has a number of possible causes. Episodes of non-cardiac syncope may be triggered by standing up too quickly, working or playing too hard, stress, or various diseases. Cardiac syncope is associated with increased mortality, whereas most causes of noncardiac syncope are relatively benign. In fact, the patients' greatest risk may be injury from falling.
Importantly, syncope is not a disease by itself. It may be a symptom of an underlying condition. Or, in about a third of cases, episodes of syncope may prove impossible to explain. Episodes of syncope are more common with age, perhaps due to an increased prevalence of disease or an age-related inability to respond to stressors that would not have caused fainting at a younger age.
However, because of its link to serious cardiovascular problems, it is important for anyone experiencing syncope – especially patients with known heart disease – to report the episode to their physician as soon as possible. Common causes of cardiac syncope include:
- Arrhythmias. Abnormal heart rhythms, either too slow (bradycardia) or too fast (tachycardia) are the leading cardiovascular cause of syncope. The most common arrhythmias associated with syncope include ventricular tachycardia and sinus bradycardia. Ventricular fibrillation, a particularly dangerous abnormal heart rhythm, does not cause syncope. Structural heart disease (e.g., cardiomyopathy or heart failure) is a risk factor for arrhythmias that may lead to syncope.
- Heart block. Where the heart may suddenly stop for 10 to 30 seconds, or abruptly slow down, due to an abnormality in the flow of electricity through the heart.
- Valvular heart disease. Abnormal function of the heart’s valves can obstruct the flow of blood from the heart to the brain. The most common cause of valve-related syncope is aortic stenosis, which is characterized by reduced blood flow through the aortic valve that regulates blood flow between the left ventricle and the aorta. Less frequently, it may be caused by stenosis of the pulmonic valve, which regulates blood flow between the right ventricle and the pulmonary arteries.
- Cardiac ischemia. A lack of oxygen reaching the heart muscle, often caused by atherosclerosis, or "hardening of the arteries.”
- Hypertrophic cardiomyopathy. Characterized by an abnormal growth of muscle fibers on the heart muscle. This abnormal growth results, in many cases, in the thickening and stiffening of the septum – a muscular structure separating the right and left sides of the heart. Because of the rigidity of the muscle, the ventricle cannot relax properly. Patients with hypertrophic cardiomyopathy may faint due to arrhythmias (see above) or due to obstruction of blood flow out of the heart caused by the enlarged muscle of the septum.
- Heart medications. Some heart medications may cause syncope by dilating the blood vessels, resulting in a drop in blood pressure. Therefore, if any new medication is utilized and syncope occurs, one can be suspicious that it is caused by the medication. Patients should immediately alert their physician if this occurs.
- Long QT syndrome (LQTS), a rare heart abnormality, can be a cause of syncope. When an LQTS patient has periods of high emotional stress (e.g., when suddenly feeling afraid) or physical stress (e.g., during exercise), the heart may not be able to pump effectively. When the heart is no longer pumping as it should be, the blood flow to the brain is slowed and the patient may experience syncope without warning.
No one should disregard any sudden loss of consciousness. Fainting or “blacking out” is not a normal part of the aging process. Even “falling asleep at the wheel” may not be just fatigue, but may indicate a heart rhythm disorder (e.g., supraventricular tachycardia, ventricular tachycardia, heart block).
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