Sudden Cardiac Death (Cardiac Arrest)
Common Questions

SCD is caused by a deadly heart rhythm disorder called ventricular fibrillation, a condition in which the electrical signals that coordinate the heart muscle become rapid and chaotic. The lower chambers of the heart - the ventricles - begin to quiver and can no longer pump blood to the brain, lungs and other parts of the body. Unless an immediate emergency shock is delivered to the heart, death occurs within minutes.

1. What is sudden cardiac death (SCD)? SCD is an abrupt, unexpected loss of heart function (cardiac arrest), that frequently occurs in active, outwardly healthy people with no known heart disease or other health problems. Unless emergency treatment with a device called a "defibrillator" is immediately available to deliver an electric shock that will restore the rhythm of the heart, death occurs within minutes of the event.
   
   
2. Is sudden cardiac death the same thing as a heart attack? No. Heart attack, or myocardial infarction, refers to a condition in which a part of the muscle of the heart dies or is damaged from a sudden lack of blood flow - the dead area of heart muscle is called an "infarct." Heart attack has been compared to a "plumbing problem" because it's most often caused by a blockage in a blood vessel - like a clogged plumbing pipe - that cuts off the supply of blood to the heart. Sudden Cardiac Death, on the other hand, is an "electrical problem" in the heart. Without warning, the electrical signals that regulate the pumping action of the lower chambers of the heart (ventricles) become rapid and chaotic. The normal rhythmic contractions of the ventricles stop, and the heart can't pump blood to the rest of the body. The brain is starved of oxygen, and the individual loses consciousness in seconds. Without immediate emergency help, death follows within minutes. SCD may occur in association with a heart attack, however.
   
   
3. Who is at greatest risk for SCD? The underlying causes of SCD are often the same as those that cause a heart attack, and people who have had a prior MI are at greater risk for SCD. Like MI, the most common underlying problem seen in victims of SCD is coronary artery disease. This is a condition in which the arteries that supply blood to the heart are narrowed or blocked, usually due to arteriosclerosis (sometimes called "hardening of the arteries"). In this disease, a fatty substance called "plaque" builds up in the blood vessels.
   
   
4. How do I find out if I am at high risk for SCD? There are a number of tests that can be performed by electrophysiologists and other experts to determine if an individual is in a group at high risk for cardiac arrest or other cardiovascular disease. These may include:
   
   
   • electrocardiogram (ECG) - a test in which electrodes are pasted on the patient's skin to record the electrical activity of the heart.
   • echocardiogram - in this test, a device called a transducer is placed on the chest and sound waves are bounced off the heart. This provide a moving picture of the heart and a measure of heart function.
   • Holter monitors and event recorders - these are external devices that are worn by the patient for a few days or more to record irregular heart rhythms.
   • An electrophysiology (EP) study. This test can predict if an individual is at high risk for sudden cardiac death. Electrical signals are administered to the heart muscle in patterns to see if they will stimulate VT. In an EP study, local anesthetics are used to numb areas in the groin or near the neck, and small catheters are passed into the heart to record its electrical signals. The study is performed in a safe and controlled hospital environment, under light sedation and is supervised by a trained electrophysiologist.
     
     
5. How can SCD be prevented? There is much that patients and physicians can do to prevent or reduce the risk of diseases that may lead to SCD, or to stop dangerous heart rhythms in patients who already are at high risk for cardiac arrest. These include:
   
   
   • Primary prevention to control risk factors that contribute to cardiovascular disease, such as lifestyle modifications (e.g., stopping smoking, exercise, weight control and eating a heart healthy diet).
   • Secondary prevention to treat existing heart disease, heart rhythm disorders or other conditions that put people at risk for SCD. These treatments may include implantable cardioverter defibrillators (ICDs) - devices that are implanted under the skin to detect and correct life-threatening heart rhythms; medications called anti-arrhythmias; and catheter ablation - a technique in which a thin tube is threaded into the heart and heat is used to destroy small areas of heart tissue that gives rise to abnormal heart rhythms.
     
     
6. Are medications available that can prevent SCD? There have been many clinical trials and other studies of medications currently available to prevent cardiac arrest. The results of drug therapy alone have been disappointing and ICD implantation remains the most effective way to prevent SCD in high-risk patients. In some cases, medications have actually increased patients' risk of SCD. Medications often are helpful in treating other symptoms of cardiovascular disease. Sometimes, more than one medication is prescribed at the same time. These medications also often are prescribed for patients who have an ICD to reduce the number of shocks patients receive.
   
   
7. What is an implantable cardioverter defibrillator (ICD)? An ICD is a small device that is implanted under the skin, like a pacemaker. Special wires, or "leads" connected to the ICD are placed in the heart to record its electrical activity. The system automatically monitors the heart rate to detect and correct abnormal rhythms. The device can act as a pacemaker when it detects a too-slow heart beat (bradycardia).
   
   
8. How does an ICD prevent cardiac arrest and Sudden Cardiac Death? When a life-threatening ventricular tachycardia of fibrillation is detected, the ICD delivers a controlled electrical shock to restore the heart's normal rhythm and prevent sudden cardiac death. In clinical trials, ICDs have been shown to be 99 percent effective in stopping life-threatening heart rhythms.
   
   
9. How do I know if an ICD is the right treatment for me? The American College of Cardiology and the American Heart Association, along with representatives of the the Heart Rhythm Society, have developed guidelines to help physicians and patients decide whether an ICD is the best treatment for an individual at risk for SCD. For example, it is agreed that ICD therapy will benefit:
   
   
   • Individuals who have suffered a prior cardiac arrest or who experience spontaneous, sustained episodes of ventricular tachycardia (VT that is not self-correcting), especially if they also have episodes of unexplained fainting
   • Certain patients with an ejection fraction (a measure of the heart's pumping ability) of less than 35-40 percent and documented episodes of ventricular tachycardia that are self-correcting and cause no adverse symptoms
   • Heart attack survivors with an ejection fraction of 30% or below, even if they have not had documented episodes of ventricular tachycardia