Syncope, commonly known as fainting or passing out, is a temporary loss of consciousness. This event occurs when there is a brief, sudden decrease in the amount of blood flowing to the brain. It is common, affecting many individuals at some point in their lives. While often not a sign of serious illness, understanding the different types of syncope is helpful for individuals and their healthcare providers.
Reflex Syncope
Reflex syncope, also known as neurally mediated or vasovagal syncope, is the most common type of fainting. It occurs when the body overreacts to triggers, causing a sudden drop in heart rate and blood pressure. This temporarily reduces blood flow to the brain, leading to loss of consciousness. Common triggers include intense emotional stress, physical pain, or prolonged standing; actions like coughing, straining during urination or defecation, or swallowing can also induce this type of fainting, known as situational syncope. It is generally considered benign and does not indicate a severe underlying health issue.
Orthostatic Syncope
Orthostatic syncope results from a sudden drop in blood pressure upon standing. When transitioning from lying or sitting to standing, gravity causes blood to pool in the lower extremities. The body usually compensates for this by increasing heart rate and constricting blood vessels to maintain adequate blood flow to the brain. However, in orthostatic syncope, these mechanisms fail, leading to insufficient blood supply to the brain and fainting. Dehydration, which reduces blood volume, can contribute, as can certain medications like those for high blood pressure, and conditions impairing the nervous system’s blood pressure regulation.
Cardiac Syncope
Cardiac syncope originates from a heart condition that impairs the heart’s ability to pump blood to the brain. This type of fainting can indicate a more serious health problem. Irregular heartbeats (arrhythmias) can cause the heart to beat too fast or too slow, disrupting blood flow. Structural heart problems also contribute, including issues with heart valves (e.g., aortic stenosis) or conditions like hypertrophic cardiomyopathy. A heart attack, which damages heart tissue, can also compromise pumping function, leading to a sudden reduction in blood to the brain and loss of consciousness.
Neurologic Syncope
Neurologic syncope is a less common category, where neurological conditions cause or mimic fainting. While most syncope cases relate to circulatory issues, certain brain disorders can temporarily reduce blood flow to the brain. Transient ischemic attacks (TIAs), or “mini-strokes,” and rare cerebrovascular diseases are examples where a temporary blockage reduces blood supply to a part of the brain, potentially causing syncope-like symptoms. It is important to distinguish true syncope from seizures; syncope involves a global lack of blood flow, while seizures are caused by abnormal electrical activity. Although some muscle twitching may occur during a syncopal episode, it differs from the sustained activity seen in a seizure, and neurological conditions can sometimes be mistaken for syncope.