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:


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

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 heart failure.
  • 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.
  • Nuclear scan. This test, usually done along 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.

Other tests

Other tests that are often done include:

  • Electrical system (electrophysiological) testing and mapping. 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 starts.

    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.

  • Coronary catheterization (angiogram). 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 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.

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

  • 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 40 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), a nuclear medicine scan (multiple gated acquisition, or MUGA), a computerized tomography (CT) scan or a cardiac catheterization.


Sudden cardiac arrest requires immediate action for survival.


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.

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 — 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.

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, have one person call 911 or the local emergency number and one 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.
  • 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 at a rate of 100 to 120 compressions a minute. For a child, you may need to use only one hand.
  • If you haven't been trained in CPR, continue chest compressions until emergency medical help arrives.
  • If you have been trained in CPR, after every 30 compressions, gently tilt the head back and lift the chin up to open the airway. Quickly check for normal breathing, taking no more than 10 seconds. If the person isn't breathing, give two rescue breaths, making sure the chest rises after a breath. 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.
  • If a child has not begun moving after five cycles (about two minutes) and an AED is available, apply it and follow the prompts. Administer one shock if so advised, 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 or chest compressions until the person recovers consciousness and is breathing normally or until emergency medical personnel take over.


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.

The shock may be administered by emergency personnel or by a citizen if a public-use defibrillator, the device used to administer the shock, is available.

Defibrillators are 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 a possible heart attack, heart failure or electrolyte imbalances. You may be given medications to stabilize your heart rhythm.

Long-term treatment

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.

Treatments 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, Pacerone).

    As with any medication, anti-arrhythmic drugs may have 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.

  • 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 a dangerous heart rhythm change, it sends out low- or high-energy shocks to reset your heart to a normal rhythm. An ICD may be more effective than preventive drug treatment at reducing your chance of having a fatal arrhythmia.

  • Coronary angioplasty. This procedure 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. 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 (bypassing the narrowed section), restoring blood flow to your heart. This may improve the blood supply to your heart and reduce the frequency of racing heartbeats.
  • Radiofrequency catheter ablation. This procedure may be used to block a single abnormal electrical pathway. 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.

Clinical trials

Explore Mayo Clinic studies testing new treatments, interventions and tests as a means to prevent, detect, treat or manage this disease.

Sudden cardiac arrest care at Mayo Clinic

June 20, 2018
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