Diagnosis

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.