Loss of consciousness is the most common sign of ventricular fibrillation.
Early signs and symptoms
A condition in which the lower chambers of your heart beat too fast (ventricular tachycardia) can lead to ventricular fibrillation. Signs and symptoms of ventricular tachycardia include:
- Chest pain
- Rapid heartbeat (tachycardia)
- Shortness of breath
- Loss of consciousness
When to see a doctor
If you or someone else is having the above signs and symptoms, seek emergency medical help immediately. Follow these steps:
- Call 911 or the emergency number in your area.
- If the person is unconscious, check for a pulse.
- If no pulse, begin CPR to help maintain blood flow to the organs until an electrical shock (defibrillation) can be given. Push hard and fast on the person's chest — about 100 compressions a minute. It's not necessary to check the person's airway or deliver rescue breaths unless you've been trained in CPR.
Portable automated external defibrillators (AEDs), which can deliver an electric shock that may restart heartbeats, are available in an increasing number of places, such as in airplanes, police cars and shopping malls. They can even be purchased for your home. Portable defibrillators come with built-in instructions for their use. They're programmed to deliver a shock only when it's needed.
To understand ventricular fibrillation, consider a normal heartbeat.
What's a normal heartbeat?
When your heart beats, the electrical impulses that cause it to contract follow a precise pathway through your heart. Interruption in these impulses can cause an irregular heartbeat (arrhythmia).
Your heart is divided into four chambers. The chambers on each half of your heart form two adjoining pumps, with an upper chamber (atrium) and a lower chamber (ventricle).
During a heartbeat, the smaller, less muscular atria contract and fill the relaxed ventricles with blood. This contraction starts after the sinus node — a small group of cells in your right atrium — sends an electrical impulse causing your right and left atria to contract.
The impulse then travels to the center of your heart, to the atrioventricular node, which lies on the pathway between your atria and your ventricles. From here, the impulse exits the atrioventricular node and travels through your ventricles, causing them to contract and pump blood throughout your body.
What causes ventricular fibrillation?
The cause of ventricular fibrillation isn't always known. The most common cause is a problem in the electrical impulses traveling through your heart after a first heart attack or problems resulting from a scar in your heart's muscle tissue from a previous heart attack.
Some cases of ventricular fibrillation begin as a rapid heartbeat called ventricular tachycardia (VT). This fast, regular beating of the heart is caused by abnormal electrical impulses that start in the ventricles.
Most VT occurs in people with a heart-related problem, such as scars or damage from a heart attack. Sometimes VT can last less than 30 seconds (nonsustained) and may not cause symptoms. But VT may be a sign of more-serious heart problems. If VT lasts more than 30 seconds, it will usually lead to palpitations, dizziness or fainting. Untreated VT will often lead to ventricular fibrillation.
Most cases of ventricular fibrillation are linked to some form of heart disease.
Factors that may increase your risk of ventricular fibrillation include:
- A previous episode of ventricular fibrillation
- A previous heart attack
- A heart defect you're born with (congenital heart disease)
- Heart muscle disease (cardiomyopathy)
- Injuries that cause damage to the heart muscle, such as electrocution
- Use of illegal drugs, such as cocaine or methamphetamine
- Electrolyte abnormalities, such as with potassium or magnesium