Symptoms of sudden cardiac arrest are immediate and severe and include:

• Sudden collapse.
• No pulse.
• No breathing.
• Loss of consciousness.

Sometimes other symptoms occur before sudden cardiac arrest. These might include:

• Chest discomfort.
• Shortness of breath.
• Weakness.
• Fast-beating, fluttering or pounding heart called palpitations.

But sudden cardiac arrest often occurs with no warning.

When to see a doctor

When the heart stops, the lack of oxygen-rich blood can quickly cause death or permanent brain damage.

Call 911 or emergency medical services for these symptoms:

• Chest pain or discomfort.
• Feeling of a pounding heartbeat.
• Rapid or irregular heartbeats.
• Unexplained wheezing.
• Shortness of breath.
• Fainting or near fainting.
• Lightheadedness or dizziness.

If you see someone who's unconscious and not breathing, call 911 or local emergency services. Then start CPR. The American Heart Association recommends doing CPR with hard and fast chest compressions. Use an automated external defibrillator, called an AED, if one is available.

How to do CPR

Do CPR if the person isn't breathing. Push hard and fast on the person's chest — about 100 to 120 pushes a minute. If you've been trained in CPR, check the person's airway. Then deliver rescue breaths after every 30 compressions.

If you haven't been trained, just continue chest compressions. Allow the chest to rise completely between compressions. Keep doing this until an AED is available or emergency workers arrive.

Portable automated external defibrillators, called AEDs, are available in many public places, including airports and shopping malls. You can also buy one for home use. AEDs come with step-by-step voice instructions for their use. They're programmed to allow a shock only when appropriate.

A change in the heart's electrical activity causes sudden cardiac arrest. The change makes the heart stop pumping blood. No blood flow goes to the body.

How the heart beats

To understand sudden cardiac arrest, it may help to know more about the heart's signaling system.

Electric signals in the heart control the rate and rhythm of the heartbeat. Faulty or extra electrical signals can make the heart beat too fast, too slowly or in an uncoordinated way. Changes in the heartbeat are called arrhythmias. Some arrhythmias are brief and harmless. Others can lead to sudden cardiac arrest.

Heart conditions that can lead to sudden cardiac arrest

The most common cause of sudden cardiac arrest is an irregular heart rhythm called ventricular fibrillation. Rapid, erratic heart signals cause the lower heart chambers to quiver uselessly instead of pumping blood. Certain heart conditions can make you more likely to have this type of heartbeat problem.

However, sudden cardiac arrest can happen in people who have no known heart disease.

Heart conditions that can cause sudden cardiac arrest include:

• Coronary artery disease. Sudden cardiac arrest may occur if the heart arteries become clogged with cholesterol and other deposits, reducing blood flow to the heart.
• Heart attack. If a heart attack occurs, often as a result of severe coronary artery disease, it can trigger ventricular fibrillation and sudden cardiac arrest. Also, a heart attack can leave scar tissue in the heart. The scar tissue can cause changes in the heartbeat.
• Enlarged heart called cardiomyopathy. This condition usually happens when the walls in the heart muscle stretch. The heart muscle gets bigger or thicker.
• Heart valve disease. Leaking or narrowing of the heart valves can lead to stretching or thickening of the heart muscle. When the chambers become enlarged or weakened because of stress caused by a tight or leaking valve, there's an increased risk of developing a heart rhythm problem.
• Heart problem present at birth, called a congenital heart defect. Sudden cardiac arrest in children or adolescents is often due to a heart problem that they're born with. Adults who've had repair surgery for a congenital heart defect also have an increased risk of sudden cardiac arrest.
• Long QT syndrome (LQTS) and other heart signaling problems. Conditions such as long QT syndrome and Brugada syndrome cause the heart to beat in an unorganized way. If the heart rhythm isn't quickly restored, sudden death can occur. Young people with LQTS are especially at risk of sudden death.

The same things that increase the risk of heart disease can raise the risk of sudden cardiac arrest. These include:

• A family history of coronary artery disease.
• Smoking.
• High blood pressure.
• High blood cholesterol.
• Obesity.
• Diabetes.
• An inactive lifestyle.

Other things that might increase the risk of sudden cardiac arrest include:

• A previous episode of sudden cardiac arrest or a family history of it.
• A previous heart attack.
• A personal or family history of other forms of heart disease such as heart rhythm problems, heart failure and heart problems present at birth.
• Growing older — the risk of sudden cardiac arrest increases with age.
• Being male.
• Using illegal drugs such as cocaine or amphetamines.
• Low potassium or magnesium levels.
• A sleep disorder called obstructive sleep apnea.
• Chronic kidney disease.

When sudden cardiac arrest occurs, less blood flows to the brain. If the heart rhythm isn't rapidly restored, complications may include brain damage and death.

Keeping the heart healthy may help prevent sudden cardiac arrest. You can do this by:

• Eating healthy.
• Getting regular checkups.
• Not smoking or using tobacco.
• Being screened for heart disease.
• Controlling blood pressure and cholesterol.

Genetic tests can be done to see if you have long QT syndrome, a common cause of sudden cardiac death. Check with your insurer to see if it is covered. If you have the long QT gene, your health care provider may recommend that other family members also be tested.

If you have a known risk of cardiac arrest, your health care provider might recommend a heart device called an implantable cardioverter-defibrillator (ICD). The device is placed under your collarbone.

You also might consider purchasing an automated external defibrillator (AED) for home use. Discuss this with your health care provider. AEDs help reset the heart's rhythm when a person has sudden cardiac arrest. But they can be expensive and aren't always covered by health insurance.

Sudden cardiac arrest happens suddenly and requires emergency medical care at a hospital. If the heart is quickly restored, survival is possible. When you are stable, health care providers at the hospital run tests to determine the cause.

Tests

Tests are done to help determine how well the heart pumps blood and to look for diseases that affect the heart.

Tests for sudden cardiac arrest often include:

• Blood tests. Certain heart proteins slowly leak into the blood after heart damage from a heart attack. Blood tests can be done to check for these proteins. Other blood tests are done to check levels of potassium, magnesium, hormones and other body chemicals that affect the heart's ability to work.
• Electrocardiogram (ECG or EKG). This quick and painless test checks the electrical activity of the heart. Sensors, called electrodes, are attached to the chest and sometimes the arms and legs. An ECG can tell how fast or how slowly the heart is beating. The test can show changes in the heartbeat that increase the risk of sudden death.
• Echocardiogram. Sound waves create images of the heart in motion. This test can show how blood flows through the heart and heart valves. It can show heart valve problems and heart muscle damage.
• Ejection fraction. This test is done during an echocardiogram. It's a measurement of the percentage of blood leaving the heart each time it squeezes. A typical ejection fraction is 50% to 70%. An ejection fraction of less than 40% increases the risk of sudden cardiac arrest.
• Chest X-ray. This test shows the size and shape of the heart and lungs. It might also show whether you have heart failure.
• Nuclear scan. This test is usually done with a stress test. It helps see blood flow problems to the heart. Tiny amounts of radioactive material, called a tracer, are given by IV. Special cameras can see the radioactive material as it flows through the heart and lungs.

• Cardiac catheterization. This test helps health care providers see blockages in the heart arteries. A long, thin flexible tube called a catheter is inserted in a blood vessel, usually in the groin or wrist, and guided to the heart. Dye flows through the catheter to arteries in the heart. The dye helps the arteries show up more clearly on X-ray images and video.

  A treatment called balloon angioplasty can be done during this test to treat a blockage. If a blockage is found, the health care provider may treat place a tube called a stent to hold the artery open.

Treatment for sudden cardiac death includes:

• CPR. Immediate CPR is needed to treat sudden cardiac arrest and prevent death.
• Resetting the heart rhythm. This is called defibrillation. You can do this by using an automated external defibrillator, called an AED, if one is available. They are found in many public places.
• Medicines to treat irregular heartbeats and to manage symptoms.
• Heart procedure or surgery to place heart devices or to treat a blockage.

At the emergency room, health care providers run tests to check for the cause, such as a possible heart attack, heart failure or changes in electrolyte levels. Treatments depend on the causes.

Medications

Medicines may be used to help restore the heart rhythm. These medicines are called anti-arrhythmic drugs.

Other medicines that might be used to treat causes of sudden cardiac death or lower the risk of it include:

• Beta blockers.
• Angiotensin-converting enzyme (ACE) inhibitors.
• Calcium channel blockers.

Surgery or other procedures

Surgeries and other treatments may be needed to correct a heart rhythm problem, open a blockage, or place a device to help the heart work better. They may include:

• Implantable cardioverter-defibrillator (ICD). An ICD is a battery-powered unit that's implanted under the skin near the collarbone — similar to a pacemaker. The ICD continuously monitors the heart rhythm. If the device finds an irregular heartbeat, it sends out shocks to reset the heart's rhythm. It can stop a potentially life-threatening change in the heartbeat.

• Coronary angioplasty. Also called percutaneous coronary intervention, this treatment opens blocked or clogged heart arteries. It can be done at the same time as a coronary catheterization, a test that doctors do to find narrowed arteries to the heart.

  The health care provider inserts a thin, flexible tube into a blood vessel, usually in the groin, and moves it to the area of the blockage. A tiny balloon on the tip of the tube is widened. This opens the artery and improves blood flow to the heart.

  A metal mesh tube called a stent may be passed through the tube. The stent stays in the artery and helps keep it open.

• Coronary artery bypass surgery. Also called coronary artery bypass grafting or CABG, this surgery creates a new pathway for blood to flow around a blocked artery to the heart. This restores blood flow to the heart.
• Radiofrequency catheter ablation. This treatment is done to block a faulty heart signaling pathway. A problem with heart signaling can cause an irregular heartbeat. One or more flexible tubes called catheters are threaded through the blood vessels to inside the heart. Heat, called radiofrequency energy, on the end of the catheter is used to create small scars in the heart. This blocks the irregular heart signals.
• Corrective heart surgery. Surgery may be done to correct heart problems present at birth, heart valve disease or diseased heart muscle.

Preventing sudden cardiac arrest starts with keeping the heart and blood vessels in good shape. To live a heart-healthy lifestyle:

• Don't smoke.
• Achieve and maintain a healthy weight.
• If you drink alcohol, do so in moderation — no more than one drink a day for women and men older than 65 and no more than two drinks a day for younger men.
• Eat a heart-healthy diet.
• Get regular exercise.
• Manage stress.

Training

If you live with someone who is at risk of sudden cardiac arrest, it's important that you be trained in CPR. The American Red Cross and other organizations offer courses in CPR and defibrillator use.

Being trained will help not only your loved one, but your training might help others. The more people know how to respond to a heart emergency, the greater the survival rate for sudden cardiac arrest is likely to be.