Vasovagal Syncope (Common Fainting)

What happens in a vasovagal faint

When you stand, blood pools in your legs, and your body normally tightens blood vessels and speeds the heart to keep blood flowing to the brain. In vasovagal syncope, a trigger sets off an abnormal reflex: instead, the vagus nerve slows the heart and blood vessels relax. Blood pressure drops, the brain gets less oxygen, and you lose consciousness. Once you fall or lie flat, blood flows back to the brain and you wake quickly.

Triggers

• standing for a long time, especially in heat or crowds
• getting up quickly, especially after lying down or eating
• dehydration, skipped meals or alcohol
• pain or fear
• the sight of blood, needles or medical procedures
• straining, coughing or urinating (situational syncope)
• hot showers or baths
• intense emotion

Symptoms

Warning signs (prodrome)

Usually seconds to a few minutes before fainting:

• lightheadedness or dizziness
• nausea or stomach discomfort
• sweating, feeling hot or clammy
• pale or gray skin
• blurred, dimmed or tunnel vision
• muffled hearing or ringing
• yawning
• weakness

During and after

• brief loss of consciousness, usually less than a minute
• a few jerking movements are common and do not mean a seizure
• tiredness, nausea or feeling washed out for some time afterward
• quick return of normal awareness, unlike after a seizure

What to do

If you feel faint

• lie down immediately and raise your legs, or sit and put your head between your knees
• counter-pressure maneuvers: cross your legs and squeeze your thigh and buttock muscles, or grip your hands together and pull your arms apart, to push blood back to the heart
• stay down until you feel fully better, then get up slowly

If someone faints

• lay them on their back with their legs raised
• check breathing. If they do not breathe normally, call 911 and start CPR
• loosen tight clothing
• once awake, keep them lying down for 10 to 15 minutes, then sit up slowly
• if they vomit or remain drowsy, turn them onto their side
• call 911 if they do not wake within a minute or two, or if any red flags are present

Vasovagal syncope vs other causes of fainting

Diagnosis

A doctor will take a detailed history, which is the most important part, including triggers, warning signs, what witnesses saw and how quickly you recovered. Tests are chosen based on risk:

• ECG for everyone with a faint
• orthostatic blood pressure measurements lying and standing
• blood tests if dehydration, anemia or blood sugar problems are suspected
• echocardiogram, heart monitoring or exercise test if heart disease is possible
• tilt-table test: you lie on a table that tilts upright while heart rate and blood pressure are monitored. It can confirm vasovagal syncope when the diagnosis is uncertain

Prevention and treatment

Most people need no medicine. Effective measures:

• drink 2 to 3 liters of fluid a day, unless your doctor advises otherwise
• increase salt in the diet if you do not have high blood pressure, heart or kidney disease (ask your doctor)
• avoid triggers: prolonged standing, overheating, skipping meals
• move your legs when standing for long periods
• compression stockings
• lie down for blood tests and injections if needles trigger fainting, and tell staff in advance
• counter-pressure maneuvers at the first warning sign
• tilt training in some people

For frequent, troublesome episodes:

• midodrine or fludrocortisone may be prescribed
• review medicines that lower blood pressure
• cardiac pacing only in selected older patients with very slow heart rates during episodes

Outlook

Vasovagal syncope is not dangerous to the heart. The main risk is injury from falling, or fainting while driving or in dangerous places. Episodes are often clustered and may become less frequent with time. Many people learn to recognize warning signs and prevent faints.

Frequently asked questions

What is vasovagal syncope?

Vasovagal syncope is the most common type of fainting. A trigger such as standing too long, heat, pain or the sight of blood causes the heart rate and blood pressure to drop suddenly, briefly reducing blood flow to the brain and causing loss of consciousness.

What are the warning signs of a vasovagal faint?

Common warning signs include lightheadedness, nausea, sweating, feeling hot or cold, pale skin, blurred or tunnel vision, muffled hearing and yawning. Lying down with your legs raised as soon as these start can often prevent fainting.

Is vasovagal syncope dangerous?

Usually not. It does not damage the heart or brain. The main risks are injuries from falling and fainting in hazardous situations. Fainting during exercise, without warning, or with heart symptoms needs evaluation because other causes may be serious.

Why do I faint at the sight of blood?

Seeing blood or needles can trigger a strong emotional and nervous system response that slows the heart and widens blood vessels in some people. This blood-injury phobia response is a classic vasovagal trigger. Lying down during procedures and applied tension techniques help.

How can I stop vasovagal syncope?

Drink plenty of fluids, increase salt if your doctor agrees, avoid long standing and overheating, and learn your warning signs. At the first sign, lie down or use counter-pressure maneuvers like crossing your legs and tensing your muscles. Medicines help in some frequent cases.