Sudden cardiac arrest is the abrupt loss of heart function, breathing and consciousness. The condition usually results from a problem with your heart's electrical system, which disrupts your heart's pumping action and stops blood flow to your body.

Sudden cardiac arrest isn't the same as a heart attack, when blood flow to a part of the heart is blocked. However, a heart attack can sometimes trigger an electrical disturbance that leads to sudden cardiac arrest.

If not treated immediately, sudden cardiac arrest can lead to death. Survival is possible with fast, appropriate medical care. Cardiopulmonary resuscitation (CPR), using a defibrillator — or even just giving compressions to the chest — can improve the chances of survival until emergency workers arrive.

Signs of sudden cardiac arrest are immediate and drastic and include:

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

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

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

But sudden cardiac arrest often occurs with no warning.

When to see a doctor

Call 911 or emergency medical help if you experience any of these signs and symptoms:

• Chest pain or discomfort
• Heart palpitations
• Rapid or irregular heartbeats
• Unexplained wheezing
• Shortness of breath
• Fainting or near fainting
• Lightheadedness or dizziness

When the heart stops, the lack of oxygen-rich blood can cause death or permanent brain damage within minutes. Time is critical when you're helping an unconscious person who isn't breathing.

If you see someone who's unconscious and not breathing normally, do the following:

• Call 911 or emergency medical help. f you have immediate access to a telephone, call before beginning CPR.

• Perform CPR. Quickly check the person's breathing. If the person isn't breathing normally, begin CPR. Push hard and fast on the person's chest — at the rate of 100 to 120 compressions a minute. If you've been trained in CPR, check the person's airway and 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 a portable defibrillator is available or emergency workers arrive.

• Use a portable defibrillator, if one is available. It will give you step-by-step voice instructions. Continue chest compressions while the defibrillator is charging. When it's charged, the defibrillator will check the person's heart rhythm and recommend a shock if needed. Deliver one shock if advised by the device and then immediately resume CPR, starting with chest compressions, or give chest compressions only, for about two minutes.

  Using the defibrillator, check the person's heart rhythm. If necessary, the defibrillator will give another shock. Repeat this cycle until the person recovers consciousness or emergency workers take over.

Portable automated external defibrillators (AEDs) are available in many places, including airports, casinos and shopping malls. You can also purchase one for your home. AEDs come with built-in instructions for their use. They're programmed to allow a shock only when appropriate.

The usual cause of sudden cardiac arrest is an abnormal heart rhythm (arrhythmia), which happens when your heart's electrical system isn't working correctly.

The heart's electrical system controls the rate and rhythm of your heartbeat. If something goes wrong, your heart can beat too fast, too slowly or irregularly (arrhythmia). Often these arrhythmias are brief and harmless, but some types can lead to sudden cardiac arrest.

The most common heart rhythm at the time of cardiac arrest is an arrhythmia in a lower chamber of your heart (ventricle). Rapid, erratic electrical impulses cause your ventricles to quiver uselessly instead of pumping blood (ventricle fibrillation).

Heart conditions that can lead to sudden cardiac arrest

Sudden cardiac arrest can happen in people who have no known heart disease. However, a life-threatening arrhythmia usually develops in a person with a preexisting, possibly undiagnosed heart condition. Conditions include:

• Coronary artery disease. Most cases of sudden cardiac arrest occur in people who have coronary artery disease, in which the 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 your heart. Electrical short circuits around the scar tissue can lead to abnormalities in your heart rhythm.
• Enlarged heart (cardiomyopathy). This occurs primarily when your heart's muscular walls stretch and enlarge or thicken. Then your heart's muscle is abnormal, a condition that often leads to arrhythmias.
• Valvular heart disease. Leaking or narrowing of your heart valves can lead to stretching or thickening of your 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 arrhythmia.
• Heart defect present at birth (congenital heart disease). When sudden cardiac arrest occurs in children or adolescents, it can be due to congenital heart disease. Adults who've had corrective surgery for a congenital heart defect still have a higher risk of sudden cardiac arrest.
• Electrical problems in the heart. In some people, the problem is in the heart's electrical system itself instead of a problem with the heart muscle or valves. These are called primary heart rhythm abnormalities and include conditions such as Brugada syndrome and long QT syndrome.

Because sudden cardiac arrest is so often linked with coronary artery disease, the same factors that put you at risk of coronary artery disease can also put you at 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 factors that might increase your risk of sudden cardiac arrest include:

• A previous episode of cardiac arrest or a family history of cardiac arrest
• A previous heart attack
• A personal or family history of other forms of heart disease, such as heart rhythm disorders, congenital heart defects, heart failure and cardiomyopathy
• Growing older — the risk of sudden cardiac arrest increases with age
• Being male
• Using illegal drugs, such as cocaine or amphetamines
• Nutritional imbalance, such as low potassium or magnesium levels
• Obstructive sleep apnea
• Chronic kidney disease

When sudden cardiac arrest occurs, reduced blood flow to your brain causes unconsciousness. If your heart rhythm doesn't rapidly return to normal, brain damage occurs and death results. Survivors of cardiac arrest might show signs of brain damage.

Reduce your risk of sudden cardiac arrest by getting regular checkups, being screened for heart disease and living a heart-healthy lifestyle.

If you survive sudden cardiac arrest, your doctor will try to learn what caused it to help prevent future episodes. Tests your doctor may recommend include:

Electrocardiogram (ECG)

During an ECG, sensors (electrodes) that can detect the electrical activity of your heart are attached to your chest and sometimes to your limbs. An ECG can reveal disturbances in heart rhythm or detect abnormal electrical patterns, such as a prolonged QT interval, that increase your risk of sudden death.

Blood tests

A sample of your blood might be tested to check the levels of potassium, magnesium, hormones and other chemicals that can affect your heart's ability to function. Other blood tests can detect recent heart injury and heart attacks.

Imaging tests

These might include:

• Chest X-ray. This allows your doctor to check the size and shape of your heart and its blood vessels. It might also show whether you have heart failure.

• Echocardiogram. This test uses sound waves to produce an image of your heart. It can help identify whether an area of your heart has been damaged by a heart attack and isn't pumping hard enough or whether there are problems with your heart valves.

  This test and others, including a nuclear scan, MRI, CT scan and cardiac catheterization, can all determine your heart's pumping capacity by measuring what's called the ejection fraction, one of the most important predictors of your risk of sudden cardiac arrest. Ejection fraction refers to the percentage of blood that's pumped out of a filled ventricle with each heartbeat.

  A normal ejection fraction is 50% to 70%. An ejection fraction of less than 40% increases your risk of sudden cardiac arrest.

• Nuclear scan. This test, usually done with a stress test, helps identify blood flow problems to your heart. Tiny amounts of radioactive material, such as thallium, are injected into your bloodstream. Special cameras can detect the radioactive material as it flows through your heart and lungs.

• Coronary catheterization. During this procedure, a liquid dye is injected into the arteries of your heart through a long, thin tube (catheter) that's advanced through an artery, usually in your arm, to arteries in your heart. As the dye fills your arteries, the arteries become visible on X-ray and videotape, revealing areas of blockage.

  While the catheter is in position, your doctor may treat a blockage by opening the artery (angioplasty) and inserting a stent to hold the artery open.

Sudden cardiac arrest requires immediate action for survival.

CPR

Immediate CPR is crucial for treating sudden cardiac arrest. By maintaining a flow of oxygen-rich blood to the body's vital organs, CPR can provide a vital link until more-advanced emergency care is available.

If you don't know CPR and someone collapses unconscious near you, call 911 or emergency medical help. Then, if the person isn't breathing normally, begin pushing hard and fast on the person's chest — at a rate of 100 to 120 compressions a minute, allowing the chest to fully rise between compressions. Do this until an automated external defibrillator (AED) becomes available or emergency personnel arrive.

Defibrillation

Advanced care for ventricular fibrillation, a type of arrhythmia that can cause sudden cardiac arrest, generally includes delivery of an electrical shock through the chest wall to the heart. The procedure, called defibrillation, momentarily stops the heart and the chaotic rhythm. This often allows the normal heart rhythm to resume.

Defibrillators are programmed to recognize ventricular fibrillation and send a shock only when it's appropriate. These portable defibrillators, such as AEDs, are increasingly available in public places, including airports, shopping malls, casinos, health clubs, and community and senior citizen centers.

At the emergency room

Once you arrive in the emergency room, the medical staff will work to stabilize your condition and treat a possible heart attack, heart failure or electrolyte imbalances. You might be given medications to stabilize your heart rhythm.

Long-term treatment

After you recover, your doctor will discuss with you or your family what other tests might help determine the cause of the cardiac arrest. Your doctor will also discuss preventive treatment options with you to reduce your risk of another cardiac arrest.

Treatments might include:

• Drugs. Doctors use various anti-arrhythmic drugs for emergency or long-term treatment of arrhythmias or potential arrhythmia complications. A class of medications called beta blockers is commonly used in people at risk of sudden cardiac arrest.

  Other possible drugs that can be used to treat the condition that led to the arrhythmia include angiotensin-converting enzyme (ACE) inhibitors and calcium channel blockers.

• Implantable cardioverter-defibrillator (ICD). After your condition stabilizes, your doctor is likely to recommend an ICD, a battery-powered unit that's put into your body near your left collarbone. One or more electrode-tipped wires from the ICD run through veins to your heart.

  The ICD constantly monitors your heart rhythm. If it detects a rhythm that's too slow, it paces your heart as a pacemaker would. If it detects a dangerous heart rhythm change, it sends out low- or high-energy shocks to reset your heart to a normal rhythm.

• Coronary angioplasty. This procedure opens blocked coronary arteries, letting blood flow more freely to your heart, which might reduce your risk of serious arrhythmia. A long, thin tube is passed through an artery, usually in your leg, to a blocked artery in your heart. This catheter is equipped with a special balloon tip that briefly inflates to open the blocked artery.

  At the same time, a metal mesh stent might be inserted into the artery to keep it open long term, restoring blood flow to your heart. Coronary angioplasty can be done at the same time as a coronary catheterization, a procedure that doctors do to locate narrowed arteries to the heart.

• Coronary bypass surgery. Also called coronary artery bypass grafting, bypass surgery involves sewing veins or arteries in place at a site beyond a blocked or narrowed coronary artery, restoring blood flow to your heart. This can improve the blood supply to your heart and reduce the frequency of racing heartbeats.

• Radiofrequency catheter ablation. This procedure can be used to block a single abnormal electrical pathway. One or more catheters are threaded through your blood vessels to inside your heart. They're positioned along electrical pathways identified by your doctor as causing your arrhythmia.

  Electrodes at the catheter tips are heated with radiofrequency energy. This destroys a small spot of heart tissue and creates an electrical block along the pathway that's causing your arrhythmia to stop your arrhythmia.

• Corrective heart surgery. If you have a congenital heart deformity, a faulty valve or diseased heart muscle tissue due to cardiomyopathy, surgery to correct the abnormality might improve your heart rate and blood flow, reducing your risk of fatal arrhythmias.

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.
• Stay physically active.
• Manage stress.

Medication

If you already have heart disease or conditions that make you more vulnerable to heart disease, your doctor might recommend that you take steps to improve your health, such as taking medications for high cholesterol or managing diabetes.

If you have a certain heart conditions that put you at risk of sudden cardiac arrest, your doctor might recommend anti-arrhythmic drugs.

Devices

If you have a known risk of cardiac arrest, your doctor might recommend an implantable cardioverter-defibrillator. You might consider purchasing an automated external defibrillator for home use. Discuss this with your doctor. AEDs can be expensive and aren't always covered by health insurance.

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 cardiac emergency, the greater the survival rate for sudden cardiac arrest is likely to be.