Sudden cardiac arrest symptoms are sudden and drastic:

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

Sometimes, other signs and symptoms precede sudden cardiac arrest. These may include fatigue, fainting, blackouts, dizziness, chest pain, shortness of breath, palpitations or vomiting. But sudden cardiac arrest often occurs with no warning.

When to see a doctor
If you have frequent episodes of chest pain or discomfort, heart palpitations, irregular or rapid heartbeats, unexplained wheezing or shortness of breath, fainting or near fainting, or you're feeling lightheaded or dizzy, see your doctor promptly. If these symptoms are ongoing, you should call 911 or emergency medical help.

When the heart stops, the absence of oxygenated blood can cause brain damage in only a few minutes. Death will occur within eight to 10 minutes. Time is critical when you're helping an unconscious person who isn't breathing. Take immediate action:

• Call 911, or the emergency number in your area, if you encounter someone who has collapsed or is found unresponsive. If the unconscious person is a child and you're alone, administer CPR or chest compressions only for two minutes before calling 911 or emergency medical help or before using a portable defibrillator.
• Administer CPR. Quickly check the unconscious person's breathing. If he or she isn't breathing normally, begin CPR. If you don't know CPR, just push hard and fast on the person's chest — about two compressions per second or 100 per minute. Allow the chest to rise completely between compressions. Don't worry about breathing into the person's mouth. Keep doing this until a portable defibrillator is available or emergency personnel arrive.
• Use a portable defibrillator, if one is available. If you're not trained to use a portable defibrillator, a 911 or emergency medical help operator may be able to guide you in its use. Deliver one shock if advised by the device, then immediately begin 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 administer a shock. Repeat this cycle until the person recovers consciousness or emergency personnel take over.

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

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

The immediate cause of sudden cardiac arrest is usually an abnormality in your heart rhythm (arrhythmia), the result of a malfunction in your heart's electrical system.

Unlike other muscles in your body, which rely on nerve connections to receive the electrical stimulation they need to function, your heart has its own electrical stimulator — a specialized group of cells called the sinus node, located in the upper right chamber (right atrium) of your heart. The sinus node generates electrical impulses that flow in an orderly manner through your heart to synchronize heart rate and coordinate the pumping of blood from your heart to the rest of your body.

If something goes wrong with the sinus node or the flow of electric impulses through your heart, an arrhythmia can result, causing your heart to beat too fast, too slow or in an irregular fashion. Often, these interruptions in rhythm are momentary and harmless. But some types of arrhythmia can be serious and lead to a sudden stop in heart function (sudden cardiac arrest).

The most common cause of cardiac arrest is an arrhythmia called ventricular fibrillation — when rapid, erratic electrical impulses cause your ventricles to quiver uselessly instead of pumping blood. Without an effective heartbeat, your blood pressure plummets, cutting off blood supply to your vital organs.

Most of the time, cardiac-arrest-inducing arrhythmias don't occur on their own. In a person with a normal, healthy heart, a sustained arrhythmia is unlikely to develop without some outside trigger, such as an electrical shock, the use of illegal drugs, or trauma to the chest at just the wrong time of the heart's cycle (commotio cordis).

Heart conditions that can lead to sudden cardiac arrest
More often, a life-threatening arrhythmia develops in a person with a pre-existing heart condition, such as:

• Coronary artery disease. More than 80 percent of cases of sudden cardiac arrest occur in people who have coronary artery disease. In coronary artery disease, your arteries become clogged with cholesterol and other deposits, reducing blood flow to your heart. This can alter the ability of your heart to conduct electrical impulses smoothly.
• 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. In addition, a heart attack can leave behind areas of dead scar tissue. 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. In both cases, your heart's muscle is abnormal, a condition that often leads to heart tissue damage and potential arrhythmias.
• Valvular heart disease. Leaking or narrowing of your heart valves can lead to stretching or thickening of your heart muscle, or both. 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.
• Congenital heart disease. When sudden cardiac arrest occurs in children or adolescents, it's more often due to a heart condition that was present at birth (congenital heart disease). Hypertrophic cardiomyopathy is a genetic disorder and is the most common cause of sudden cardiac arrest in young athletes, triggered perhaps by vigorous exertion, although the process isn't completely understood. Even adults who've had corrective surgery for a congenital heart defect remain at increased risk of sudden cardiac arrest.
• Electrophysiological abnormalities. 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. For example, some people have primary ventricular fibrillation, unrelated to another heart condition. Other examples include long QT syndrome, Wolff-Parkinson-White syndrome and Brugada syndrome.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

Because sudden cardiac arrest is so often linked with coronary artery disease, the same factors that put you at risk of coronary artery disease may 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
• A sedentary lifestyle

Other factors that may increase your risk of sudden cardiac arrest include:

• Previous episode of cardiac arrest or a family history of cardiac arrest
• 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
• Age; the incidence of sudden cardiac arrest increases with age, especially after age 45 for men and age 55 for women 
• Being male; men are two to three times more likely to experience sudden cardiac arrest
• Using illegal drugs, such as cocaine or amphetamines
• Lightning strike or another electrical shock
• Immersion in cold water

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

When sudden cardiac arrest occurs, your brain is the first part of your body to suffer because, unlike other organs, it doesn't have a reserve of oxygen-rich blood. It's completely dependent on an uninterrupted supply of blood. Reduced blood flow to your brain causes unconsciousness.

If your heart rhythm doesn't rapidly return to its normal rhythm, brain damage occurs and death results. If sudden cardiac arrest lasts more than 10 minutes, the survival rate is less than 5 percent. Survivors of cardiac arrest may show signs of brain damage.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

If you experience an episode of sudden cardiac arrest without warning and survive, your doctor will want to investigate what caused the cardiac arrest. Identifying the underlying problem may help prevent future episodes of cardiac arrest.

Tests your doctor may recommend include:

Electrocardiogram
A test commonly given after cardiac arrest is an 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 measures the timing and duration of each electrical phase in your heartbeat and can reveal disturbances in heart rhythm. Because injured heart muscle doesn't conduct electrical impulses normally, the ECG may show that a heart attack has occurred.

Blood tests
Blood tests may include:

• Cardiac enzyme test. Certain heart enzymes leak into your blood if your heart has been damaged by a heart attack. Because a heart attack can trigger sudden cardiac arrest, it's important to know whether you've had a heart attack. Testing a blood sample for these enzymes may help indicate whether a heart attack has indeed occurred.
• Electrolyte test. A sample of your blood may also be tested for levels of electrolytes, such as potassium, calcium and magnesium. Electrolytes are minerals in your blood and body fluids that participate in the creation of electrical impulses. An imbalance in the levels of these substances can increase your risk of arrhythmia and sudden cardiac arrest.
• Drug test. Your doctor may check your blood for evidence of drugs that have the potential to induce arrhythmia, including certain prescription and over-the-counter drugs and illegal drugs.
• Hormone test. Testing for hyperthyroidism may indicate this condition as the trigger for your cardiac arrest.

Imaging tests
These may include:

• 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. It may also indicate whether you have congestive heart failure.
• Nuclear scan. This test, usually done along with a stress test, helps identify blood flow problems to your heart. Trace 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.
• Echocardiogram. This test uses sound waves to produce an image of your heart. An echocardiogram can help identify whether an area of your heart has been damaged by a heart attack and isn't pumping normally or at peak capacity (ejection fraction), or whether there are valvular abnormalities.

Other tests
Other tests that are often done include:

• Electrophysiological testing and mapping. This test, if needed, is usually done later, after you've recovered and if an underlying explanation for your cardiac arrest hasn't been identified. With this type of test, your doctor may try to cause an arrhythmia while closely monitoring your heart. The test can help locate where in the heart the arrhythmia originates.

  During the test, thin, flexible tubes (catheters) tipped with electrodes are threaded through your blood vessels to a variety of spots within your heart. Once in place, the electrodes can precisely map the spread of electrical impulses through your heart. In addition, your cardiologist can use the electrodes to stimulate your heart to beat at rates that may trigger — or halt — an arrhythmia. This allows your doctor to observe the location of the arrhythmia.

• Ejection fraction testing. One of the most important predictors of your risk of sudden cardiac arrest is how well your heart is able to pump blood. Your doctor can determine your heart's pumping capacity by measuring what's called the ejection fraction. This refers to the percentage of blood that's pumped out of a filled ventricle with each heartbeat. A normal ejection fraction is 55 to 70 percent. An ejection fraction of less than 35 percent increases your risk of sudden cardiac arrest.

  Your doctor can measure ejection fraction in several ways, such as with an echocardiogram, magnetic resonance imaging (MRI) of your heart, a nuclear medicine scan (multiple gated acquisition, or MUGA) of your heart or a computerized tomography (CT) scan of your heart.

• Coronary catheterization (angiogram). This test can show if your coronary arteries are narrowed or blocked. Along with ejection fraction, the number of obstructed blood vessels is another important predictor of sudden cardiac arrest.

  During the 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 leg, to arteries in your heart. As the dye fills your arteries, the arteries become visible on X-ray and videotape, revealing areas of blockage.

  Also, while the catheter is in position, your doctor may treat a blockage by performing angioplasty and inserting a stent to hold the artery open.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

Sudden cardiac arrest requires immediate action for survival.

CPR
Immediate cardiopulmonary resuscitation (CPR) is critical to 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. A quick primer on CPR follows below.

If you don't know CPR but someone collapses unconscious near you, call 911 or emergency medical help. Then, if the person isn't breathing normally, immediately begin pushing hard and fast on the person's chest — two compressions per second, allowing the chest to fully rise between compressions. Do this until an automatic external defibrillator becomes available or emergency personnel arrive.

To perform CPR:

• Is the person conscious or unconscious?
• If the person appears unconscious, tap or shake his or her shoulder and ask loudly, "Are you OK?"
• If the person doesn't respond and two people are available, one should call 911 or the local emergency number and one should begin CPR.
• If you're alone and have immediate access to a telephone, call 911 or the local emergency number before beginning CPR — unless you think the person has become unresponsive because of suffocation (such as from drowning); in this special case, begin CPR for one minute and then call 911 or emergency medical help. If you're alone and rescuing a child, perform CPR for two minutes before calling 911 or emergency help or using an AED.
• If an AED is immediately available, deliver one shock if advised by the device, then begin CPR.
• Gently tilt the head back and lift the chin up to open the airway.
• Quickly check for normal breathing, taking no more than five or 10 seconds.
• Pinch the nostrils shut and give the first rescue breath — lasting one second — and watch to see if the chest rises. If it does rise, give the second breath. If the chest doesn't rise, repeat the head-tilt, chin-lift maneuver and then give the second breath.
• Start chest compressions by putting the heel of one hand in the center of the person's chest and covering the first hand with the other hand. Keeping your elbows straight, use your upper body weight to push down hard and fast on the person's chest, about two compressions per second. For a child, you may need to use only one hand.
• After 30 compressions, give two more rescue breaths, making sure the chest rises after a breath.
• If the person has not begun moving after five cycles (about two minutes) and an automatic external defibrillator (AED) is available, apply it and follow the prompts. Administer one shock, then resume CPR — starting with chest compressions — for two more minutes before administering a second shock. If you're not trained to use an AED, a 911 or emergency medical help operator may be able to guide you in its use.
• Continue CPR until the person recovers consciousness and is breathing normally or until emergency medical personnel take over.

Defibrillation
Advanced care for ventricular fibrillation, a type of arrhythmia that can cause sudden cardiac arrest, typically 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.

The shock may be administered by emergency personnel or by a trained citizen if a public-use defibrillator, the device used to administer the shock, is available. If you're not trained to use an AED, a 911 or emergency medical help operator may be able to guide you in its use. Trained staff members at many public places are able to provide and use an AED.

Defibrillators are available in a small, portable form and come with built-in automated instructions to ensure proper use. They're programmed to recognize ventricular fibrillation and send a shock only when it's appropriate. These portable defibrillators are available in an increasing number of 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 possible heart attack, heart failure or electrolyte imbalances. You may be given medications to stabilize your heart rhythm.

The prognosis after sudden cardiac arrest varies. Some people may be in a coma for days, weeks or indefinitely. Others may recover only partial function. After you recover, your doctor will discuss with you or your family what additional tests you may need to 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.

Therapies may 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 include angiotensin-converting enzyme (ACE) inhibitors, calcium channel blockers or a drug called amiodarone (Cordarone).

  Anti-arrhythmic drugs may have certain potential side effects. For example, an anti-arrhythmic drug may cause your particular arrhythmia to occur more frequently — or even cause a new arrhythmia to appear that's as bad as or worse than your pre-existing condition. Side effects not related to your heart also may occur.

• Implantable cardioverter-defibrillator (ICD). After your condition stabilizes, your doctor is likely to recommend implantation of an ICD. An ICD is a battery-powered unit that's implanted 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 ventricular tachycardia or ventricular fibrillation, it sends out low- or high-energy shocks to reset your heart to a normal rhythm. An ICD may be more effective than is preventive drug treatment at reducing your chance of having a fatal arrhythmia.

• Coronary angioplasty. This procedure is for the treatment of severe coronary artery disease. It opens blocked coronary arteries, letting blood flow more freely to your heart, which may reduce your risk of serious arrhythmia. Doctors insert a long, thin tube (catheter) that's 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 up a blocked coronary artery. At the same time, a metal mesh stent may be inserted into the artery to keep it open long term, restoring blood flow to your heart. Coronary angioplasty may be done at the same time as a coronary catheterization (angiogram), a procedure that doctors do first to locate narrowed arteries to the heart.
• Coronary bypass surgery. Another procedure to improve blood flow is coronary bypass surgery. Bypass surgery involves sewing veins or arteries in place at a site beyond a blocked or narrowed coronary artery (bypassing the narrowed section), restoring blood flow to your heart. This may improve the blood supply to your heart and reduce the frequency of ventricular tachycardia, similar to angioplasty.
• Radiofrequency catheter ablation. This procedure works best to block a single abnormal electrical pathway, which is the cause of arrhythmias such as Wolff-Parkinson-White syndrome. In this procedure, one or more catheters are threaded through your blood vessels to your inner 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 (ablates) a small spot of heart tissue and creates an electrical block along the pathway that's causing your arrhythmia. Usually, this stops 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 may improve your heart rate and blood flow, reducing your risk of fatal arrhythmias.
• Heart transplantation. Some people with severe congestive heart failure who've experienced cardiac arrest may be eligible for a heart transplant. But given the limited number of donor hearts, this may be available to few people.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

There's no sure way to know your risk of sudden cardiac arrest, so primary prevention — methods to stop first-time development of a condition — consists mostly of regular checkups, including screening for heart disease, and living a heart-healthy lifestyle with the following approaches:

• Don't smoke.
• Eat a nutritious, balanced diet.
• Stay physically active.

If you know you have heart disease or conditions that make you more vulnerable to an unhealthy heart, your doctor may recommend that you take appropriate steps to improve your health, such as taking medications for high cholesterol or carefully managing diabetes.

In some people with a known high risk of sudden cardiac arrest — such as those with a heart condition — doctors may recommend anti-arrhythmic drugs or an implantable cardioverter-defibrillator (ICD) as primary prevention.

If you have a high risk of sudden cardiac arrest, you may also wish to consider purchasing an automatic external defibrillator (AED) for home use. Before purchasing one, discuss the decision with your doctor; the devices can be expensive and aren't always covered by health insurance.

If you live with someone who is vulnerable to sudden cardiac arrest, it's important that you be trained in CPR. The American Red Cross offers courses in CPR and defibrillator use to the public. Being trained will help not only your loved one but also those in your community. The more people who know how to respond to a cardiac emergency, the more the survival rate for sudden cardiac arrest can be improved.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.