Syncope

Syncope is a brief loss of consciousness caused by reduced blood flow to the brain. It happens quickly, lasts a short time, usually less than one minute, and consciousness returns fully on its own. Because the muscles lose their strength, the body falls or slumps. Fainting is different from seizures, stroke, low blood sugar, or head injury, which can also make a person unconscious but have other causes and treatments. This page helps you recognize possible causes and warning signs; it is not meant for working out the cause on your own.

Three Groups of Causes

The 2018 ESC guidelines divide syncope into three groups. The first is reflex syncope, which many people experience: a nerve reflex makes the blood vessels widen and the heart rate slow down, for example when standing for a long time, seeing blood, feeling pain, or after coughing or urinating. The type triggered by prolonged standing and emotions is covered on the Vasovagal Hypotension page. The second is syncope from a drop in blood pressure on standing, due to dehydration, blood pressure medicines, or autonomic nerve problems in diabetes and Parkinson's disease, covered on the Orthostatic Hypotension page. The third is cardiac syncope, meaning fainting caused by a heart problem, such as a heart rate that is too slow or too fast, narrowing of the aortic valve, hypertrophic cardiomyopathy, or a blood clot in the lungs.

Why Cardiac Syncope Needs to Be Recognized

Reflex and orthostatic syncope are usually not life-threatening, although they can cause injury from a fall. Cardiac syncope is different: fainting can be a warning before a more dangerous rhythm disorder. Signs that point to the heart include fainting during exercise or while lying down, fainting without warning signs, palpitations before fainting, existing heart disease, and family members who died suddenly at a young age.

For every person who faints, the doctor tries to answer two questions: was the event really syncope, and are there any high-risk signs? An account from someone who saw the event is very helpful, and an ECG is done for everyone who faints. People at low risk can usually have further evaluation as outpatients, while those at high risk need prompt testing in the hospital.

According to the 2018 ESC guidelines, the initial evaluation consists of the history of the event, a physical exam, blood pressure measurements lying down and standing, and an ECG. The doctor asks about your position and activity when you fainted, warning signs, how long you were unconscious, how you felt after waking up, your medicines, any heart disease, and your family history. An account from someone who saw the event is very helpful. From these steps, the cause can often already be identified, and the doctor assesses whether the risk is low or high.

If a heart cause is suspected, tests are chosen based on the suspected cause: rhythm monitoring in the hospital, a Holter monitor or rhythm recorder for several days, echocardiography to assess the valves and heart muscle, an exercise test if fainting happened during exercise, and an electrophysiology study in certain situations. For fainting that is rare but recurrent, a recorder under the skin can record the rhythm for two to three years. A tilt table test helps confirm reflex syncope or orthostatic hypotension when the history is unclear.

Any first-time fainting episode should be checked by a doctor. Call an ambulance (119) or go to the emergency room right away if fainting happens during exercise or while lying down, is preceded by palpitations or chest pain, or if the person does not wake up quickly. Make an appointment with a doctor if you have any of the following.

• Repeated fainting, or fainting that is becoming more frequent
• Often nearly fainting when standing
• Fainting that causes an injury
• Fainting after starting a new medicine
• You have heart disease, diabetes, or Parkinson's disease
• You work as a driver or in a place where fainting would be dangerous