Ventricular fibrillation is a type of abnormal heart rhythm (arrhythmia). During ventricular fibrillation, disorganized heart signals cause the lower heart chambers (ventricles) to twitch (quiver) uselessly. As a result, the heart doesn't pump blood to the rest of the body.

Ventricular fibrillation is an emergency that requires immediate medical attention. It's the most frequent cause of sudden cardiac death.

Emergency treatment for ventricular fibrillation includes cardiopulmonary resuscitation (CPR) and shocks to the heart with a device called an automated external defibrillator (AED). Medications, implanted devices or surgery may be recommended to prevent episodes of ventricular fibrillation.

Collapse and loss of consciousness is the most common symptom of ventricular fibrillation.

Warning signs and symptoms

Before a ventricular fibrillation episode, you may have signs and symptoms of an abnormally fast or erratic heartbeat (arrhythmia). These warning signs may include:

• Chest pain
• Very fast heartbeat (tachycardia)
• Dizziness
• Nausea
• Shortness of breath

When to see a doctor

Make an appointment with a heart doctor (cardiologist) if you have an unexplained, fast or pounding heartbeat.

If you see someone collapse, seek emergency medical help immediately. Follow these steps:

• Call 911 or your local emergency number.
• If the person is unconscious, check for a pulse.
• If no pulse, begin CPR to help keep blood flowing through the body until an automated external defibrillator (AED) is available. The American Heart Association recommends hands-only CPR. Push hard and fast on the person's chest — about 100 to 120 times a minute. It's not necessary to check the person's airway or deliver rescue breaths. Continue until emergency medical help arrives.
• Use an AED as soon as it's available. Deliver a shock following the prompts on the device.

To understand how ventricular fibrillation occurs, it may be helpful to know how the heart normally beats.

The normal heartbeat

Your heart is made up of four chambers — two upper chambers (atria) and two lower chambers (ventricles).

The heart's rhythm is normally controlled by a natural pacemaker (the sinus node) in the right upper chamber (atrium). The sinus node sends electrical signals that normally start each heartbeat. These electrical signals move across the atria, causing the heart muscles to squeeze (contract) and pump blood into the ventricles.

Next, the signals arrive at a cluster of cells called the AV node, where they slow down. This slight delay allows the ventricles to fill with blood. When the electrical signals reach the ventricles, the lower heart chambers contract and pump blood to the lungs or to the rest of the body.

In a healthy heart, this heart signaling process usually goes smoothly, resulting in a normal resting heart rate of 60 to 100 beats a minute.

The heart during ventricular fibrillation

Ventricular fibrillation is caused by either a problem in the heart's electrical properties or by a disruption of the normal blood supply to the heart muscle. Sometimes, the cause of ventricular fibrillation is unknown.

Things 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 being struck by lightning
• Drug misuse, especially with cocaine or methamphetamine
• A severe imbalance of potassium or magnesium

Without immediate treatment, ventricular fibrillation can cause death within minutes. The condition's rapid, erratic heartbeats cause the heart to abruptly stop pumping blood to the body. Your blood pressure drops suddenly and significantly. The longer the body lacks blood, the greater the risk of damage to your brain and other organs.

Ventricular fibrillation is the most frequent cause of sudden cardiac death. The risk of other long-term complications depends on how fast you receive treatment.

Ventricular fibrillation is always diagnosed in an emergency situation. A pulse check will reveal no pulse if sudden cardiac death occurred.

Tests to diagnose and determine the cause of ventricular fibrillation include:

• Electrocardiogram (ECG or EKG). This quick and painless test measures the electrical activity of your heart. Sticky patches (electrodes) are placed on your chest and sometimes your arms and legs. Wires connect the electrodes to a computer, which displays the test results. An ECG can show if your heart is beating too fast, too slow or not at all. If you're having an episode of ventricular fibrillation, the ECG usually shows a heartbeat of about 300 to 400 beats a minute.
• Blood tests. Blood tests can be done to check for enzymes that leak into the bloodstream when the heart is damaged by a heart attack.
• Chest X-ray. An X-ray image of your chest allows your doctor to check the size and shape of your heart and its blood vessels.
• Echocardiogram. This noninvasive test uses sound waves to produce images of your heart's size, structure and motion.
• Coronary catheterization (angiogram). To determine if your coronary arteries are narrowed or blocked, a dye is injected through a long, thin tube (catheter) that's inserted through an artery, usually in your groin area, to the heart's arteries. The dye makes your arteries show up more clearly on X-ray, revealing areas of blockage.
• Cardiac computerized tomography (CT). During a cardiac CT scan, you lie on a table inside a doughnut-shaped machine. An X-ray tube inside the machine rotates around your body and creates images of your heart and chest.
• Cardiac magnetic resonance imaging (MRI). This test uses a magnetic field and computer-generated radio waves to create detailed images of blood flow in the heart. During a cardiac MRI, you lie on a table that slides into a long tubelike machine.

Ventricular fibrillation requires emergency medical treatment to prevent sudden cardiac death. The goal of emergency treatment is to restore blood flow as quickly as possible to prevent organ and brain damage.

Emergency treatment for ventricular fibrillation includes:

• Cardiopulmonary resuscitation (CPR). CPR mimics the pumping motion of the heart and keeps blood flowing through the body. First call 911 or your local emergency number. Then start CPR by pushing hard and fast on the person's chest — about 100 to 120 compressions a minute. Let the chest rise completely between compressions. Continue CPR until an automated external defibrillator (AED) is available or emergency personnel arrive.
• Defibrillation. This treatment is also called cardioversion. An automated external defibrillator (AED) delivers shocks through the chest wall to the heart. It can help restore a normal heart rhythm. As soon as an AED is available, apply it and follow the prompts. If you're not trained to use an AED, a 911 operator or another emergency medical operator may be able to give you instructions. Public-use AEDs are programmed to recognize ventricular fibrillation and send a shock only when needed.

Other treatments for ventricular fibrillation are given to prevent future episodes and reduce your risk of arrhythmia-related symptoms. Treatment for ventricular fibrillation includes medications, medical devices and surgery.

Medications

Drugs to control your heart rhythm (anti-arrhythmics) are used for emergency or long-term treatment of ventricular fibrillation. If you're at risk of ventricular fibrillation or sudden cardiac death, your doctor may prescribe medications to slow and control your heartbeat.

Surgery or other procedures

Surgery or medical procedures to treat ventricular fibrillation include:

• Implantable cardioverter-defibrillator (ICD). An ICD is an implanted device that constantly monitors your heart rhythm. If it detects a very fast heartbeat or a quivering heart, it sends out shocks to stop the episode and reset your heart's rhythm. The battery-powered device is implanted near your left collarbone during a minor surgery. One or more flexible, insulated wires (leads) from the ICD run through veins to your heart.
• Cardiac ablation. This procedure uses heat or cold energy to create tiny scars in your heart to block the abnormal electrical signals that cause ventricular fibrillation. It's most often done using thin, flexible tubes called catheters inserted through the veins or arteries. It may also be done during heart surgery.

• Coronary angioplasty and stent placement. If your ventricular fibrillation was caused by a heart attack, this procedure may reduce your risk of future episodes of ventricular fibrillation.

  Doctors insert a long, thin tube (catheter) through an artery, usually in the groin, to a blocked artery in your heart. A balloon on the tip of the catheter briefly inflates to widen the artery, restoring blood flow to the heart. During the procedure, the doctor may place a metal mesh stent into the artery to help it stay open.

• Coronary bypass surgery. This open-heart surgery improves blood flow to the heart. It may be done if your ventricular fibrillation was caused by coronary artery disease. During bypass surgery, the surgeon takes a healthy blood vessel from your leg, arm or chest and connects it below and above the blocked arteries in your heart. This creates a new pathway for blood to flow through.

Lifestyle changes that help keep your heart as healthy as possible include the following:

• Eat a healthy diet. Heart-healthy foods include fruits, vegetables and whole grains, as well as lean protein sources such as soy, beans, nuts, fish, skinless poultry and low-fat dairy products. Avoid added salt (sodium), added sugars and saturated fats.
• Exercise regularly. Get at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous aerobic activity a week, or a combination of moderate and vigorous activity. The guidelines suggest that you spread out this exercise during the course of a week.
• Don't smoke. If you need help quitting, talk with your doctor about strategies to help.
• Keep your blood pressure and cholesterol levels in a healthy range. Maintaining a healthy body weight can help control blood pressure and cholesterol. Take medications as prescribed to manage high blood pressure or high cholesterol.
• Limit alcohol. Too much alcohol can damage your heart. If you choose to drink alcohol, do so in moderation. For healthy adults, that means up to one drink a day for women and up to two drinks a day for men.
• Get regular checkups. Take your medications as prescribed and have regular follow-up appointments with your doctor. Tell your doctor if your symptoms worsen.

Some abnormal heart rhythms can be triggered by emotional stress. Taking steps to ease stress and anxiety can help keep your heart healthy.

Some types of complementary and alternative therapies may help reduce stress, such as:

• Yoga
• Meditation
• Relaxation or mindfulness techniques

Getting support from your loved ones also is key to managing stress.