A syncopal episode, medically termed syncope, is a sudden, temporary loss of consciousness and muscle tone, commonly called fainting or “passing out.” This transient event is short-lived and followed by spontaneous recovery. Syncope represents a temporary failure of the circulatory system to maintain adequate blood flow to the brain. While many episodes are not linked to severe underlying disease, any sudden loss of consciousness warrants attention to determine the cause and mitigate the risk of injury.
Understanding the Physiology of Syncope
The cause of syncope is transient global cerebral hypoperfusion—a temporary reduction of blood flow to the brain. Brain tissue requires a constant supply of oxygen and glucose, and it cannot store energy like other organs. A cessation of adequate cerebral perfusion lasting only three to five seconds is enough to result in a loss of consciousness.
Cerebral blood flow is maintained by a complex system involving cardiac output, systemic vascular resistance, and blood pressure. When this system fails momentarily, the brain is starved of its energy source. The resulting loss of postural tone causes the person to fall down, which is a protective mechanism. When the body is horizontal, blood flow returns to the brain, quickly restoring consciousness.
Categorizing the Most Common Causes
The most frequent causes of syncope are benign and fall into the category of neurally mediated syncope, often called reflex syncope. This includes vasovagal syncope, the most common form, often triggered by emotional distress, severe pain, or the sight of blood. This reflex involves the vagus nerve, causing the heart rate to slow (bradycardia) and blood vessels to dilate (vasodepression). This combination leads to a sharp drop in blood pressure, causing the temporary lack of cerebral perfusion.
Another common type is orthostatic hypotension, which occurs when a person stands up too quickly. This rapid change in posture causes blood to pool in the lower extremities, and the body’s autonomic nervous system is unable to compensate fast enough to maintain blood pressure. Dehydration, low blood volume, or certain medications like vasodilators and diuretics can exacerbate this effect, making the drop in pressure more pronounced.
Situational syncope is a form of reflex syncope linked to specific bodily actions. Triggers include straining during a bowel movement, coughing fits, or micturition (urination). These activities temporarily increase pressure in the chest or abdomen, which reflexively slows the heart rate or lowers blood pressure, reducing blood flow to the brain.
Recognizing Warning Signs and Immediate Action
Many syncopal episodes are preceded by warning signs, collectively known as the prodrome. These symptoms occur because the brain is already experiencing reduced blood flow before the complete loss of consciousness. Common prodromal symptoms include feeling dizzy or lightheaded, sudden nausea, or developing a cold, clammy sweat.
Visual disturbances are common, such as “tunnel vision,” blurred sight, or seeing spots. The person may also feel a sudden sense of warmth or have muffled hearing, indicating the circulatory system is struggling to maintain pressure. Recognizing these signs is an opportunity to prevent the full syncopal episode and potential injury from falling.
The immediate action when experiencing these warning signs is to lie down immediately, bringing the head level with the heart. Elevating the legs above the heart, by propping them on a chair or wall, helps shunt pooled blood back toward the brain. If lying down is not feasible, sitting down and placing the head between the knees is an alternative way to quickly increase cerebral blood flow. If a person has already fainted, ensure they are lying flat and check that their breathing is normal until they regain full consciousness.
When Syncope Signals a Serious Underlying Problem
Although many cases of fainting are benign, syncope can sometimes be the first sign of a serious condition, often related to the heart. Certain features are considered “red flags” that mandate a prompt medical evaluation. Fainting that occurs during or immediately after physical exertion may point to structural heart disease or an arrhythmia.
Syncope that happens while the person is lying down (supine position) is a strong indicator of a serious issue, as this position should naturally maximize blood flow to the brain. Other worrisome signs include episodes accompanied by chest pain or heart palpitations. A failure to regain consciousness quickly, or a family history of sudden, unexplained cardiac death at a young age, should prompt immediate medical attention. These features suggest a possible cardiac cause, such as an abnormal heart rhythm or an obstruction of blood flow, requiring specialized diagnostic testing.