Heart Attack & SCA

A new scientific study shows that certain people who have had heart attacks might be susceptible to sudden cardiac arrest.¹ Find out more about the heart and the results of this study. Select a link below to jump down the page:

• Your heart has a plumbing & electrical system
• Your heart's rhythm shouldn't be too slow or too fast
• Sudden cardiac arrest (SCA) is an electrical accident
• SCA is leading cause of cardiac-related deaths
• Are you, as a heart attack survivor, at risk for SCA?
• Knowing your ejection fraction (EF) could save your life
• Warning signs that you might be at risk
• New research shows an ICD may reduce the risk of death in heart attack survivors by up to 31%
• ICDs are changing people's lives

Your Heart Has a Plumbing & Electrical System

Your heart has two main systems that help it run efficiently. First, your heart is a pump. It has a network of pipes (blood vessels) along with some valves and pumping chambers. A heart attack is a problem with the heart's plumbing system, in that some arteries get clogged and that damages the main muscle, or main pump.

The heart also has a complicated electrical system. The heart generates its own electricity and uses this electricity to run the pumps (upper and lower chambers, also called the atria and ventricles) causing them to contract and relax in the proper timing sequence. For many years, scientists have known much about the heart's plumbing system, but not as much about its electrical system. In the past 20 years or so, a new specialty in medicine has developed called electrophysiology. Electrophysiology is the medical study of how the heart's electrical system works.

Your Heart's Rhythm Shouldn't Be Too Slow or Too Fast

Just as your heart can experience a plumbing problem, it also can experience different electrical problems. One electrical problem occurs when the heart's electrical system is too slow, or when electrical signals get blocked or delayed. Doctors call this bradyarrhythmia. Some patients with bradycardia benefit from getting a pacemaker. A pacemaker is a small implanted device that helps pace the heart by providing electrical signals that make the heart beat in the proper timing sequence.

Another electrical problem occurs when the heart beats too quickly. This is called tachyarrhythmia. In an adult, a normal healthy heart might beat 60 or 70 beats a minute. When a heart has an electrical disorder that causes it to beat too rapidly, it may beat as much as 200 or even 300 or more times a minute. The heart cannot beat effectively at that rate. It tries to beat very rapidly, but ends up quivering. It no longer pumps. As a result the blood flow is greatly impaired and may even stop. This condition is extremely serious.

The dangerous electrical condition that causes the heart to beat too rapidly is called ventricular tachyarrhythmia or ventricular tachycardia. A very dangerous form of ventricular tachyarrhythmia is ventricular fibrillation. Most doctors define ventricular fibrillation as an occasion when your heart tries to beat 300 or more beats a minute. The quivering heart muscle can no longer pump blood, and you can die in minutes if the condition is not resolved.

Sudden Cardiac Arrest (SCA) is an Electrical Accident

SCA is an electrical accident in the heart that results in ventricular fibrillation. Often, this condition is deadly. (Sometimes SCA is called sudden cardiac death.) If immediate therapy is given, some people do survive.

People who are prone to SCA may receive an implantable cardioverter defibrillator (ICD). The great benefit of an ICD is that it's implanted: always with you, always on, and always monitoring your heart. When ventricular fibrillation occurs, the ICD can send electrical energy to the heart muscle to defibrillate or stop the cycle of rapid twitching. Having an ICD is like having a paramedic with you at all times.

One famous person with an ICD is United States Vice President, Dick Cheney. You might wonder how people know they need an ICD. In many cases, specialists such as electrophysiologists may notice from examinations (which may or may not include an electrophysiology study) that certain people have hearts which may be prone to SCA, even before it occurs.

SCA is Leading Cause of Cardiac-Related Deaths

According to the European Society of Cardiology, SCA is the single most important cause of death among adults of the industrialized world. The American Heart Association states that everyday in the United States; more than 680 people experience sudden cardiac arrest-over 250,000 a year-and most of these are from coronary heart disease. If you are not treated within four to six minutes from the onset of SCA, the results can be fatal. It takes an electric shock delivered by an external defibrillator or an implanted cardioverter defibrillator (ICD) to restore a normal heartbeat.

Are You, as a Heart Attack Survivor, at Risk for SCA?

As important as this question is, there are no easy answers. In general, heart attack survivors are more at risk for SCA than the general population. But how does a specific heart attack survivor know if he or she is at risk for SCA, or would benefit from an ICD?

Ask your doctor. Your doctor knows your medical history better than anyone. Ask him or her about the MADIT II trial, which showed that heart attack survivors with a low ejection fraction do better with an ICD than without one.¹

Knowing Your Ejection Fraction (EF) Could Save Your Life

Your EF or ejection fraction refers to the amount of blood that is pumped out of the heart with each heartbeat. A normal, healthy heart pumps 55-75% of its blood per beat (an EF of 55-75%). But when a heart pumps only 40-54% of its blood per beat (an EF of 40-54%) it could indicate a damaged heart muscle, possibly from a heart attack, and require medical care. When your EF drops below 40% it may indicate some degree of heart failure.

How do you know your EF? Your doctor can measure it in a variety of ways, the most common being an echocardiogram. An echocardiogram is a painless test that uses sound waves to show how well your heart is functioning.

Warning Signs That You Might Be At Risk

• Is your EF 30% or less?
• Has it been 6 to 18 months since your heart attack?
• Do you have coronary artery disease?
• Do you have a family history of sudden cardiac arrest?
• Have you survived a previous incident of sudden cardiac arrest?

New Research Shows an ICD May Reduce the Risk of Death in Heart Attack Survivors By Up to 31%

A recent scientific study has discovered that people who have an EF of less than 30% and who have had a heart attack may benefit from receiving an implantable cardioverter defibrillator (ICD). The MADIT II study compared heart attack survivors with significant muscle damage who received traditional therapies to similar individuals treated with an ICD.¹

Over four years, 1,232 patients were enrolled in the study, which actually had to be ended before it was completed because it became obvious that the heart attack survivors with an ICD did so much better.

As published in the New England Journal of Medicine, the study showed a 31% reduction in the risk of death from sudden cardiac arrest in those patients who received ICDs compared to those patients who did not.

ICDs are Changing People's Lives

Today, ICDs are not much bigger than pacemakers. They are implanted in the upper chest in a fairly simple procedure. After that, most ICD patients almost forget about the device as it monitors their heartbeat 24 hours a day, 7 days a week. But they know it's there to deliver life-saving treatment if and exactly when they need it.

Talk to your doctor today! Right now we know more about matters of the heart than ever before. For your sake, for your family's sake, take advantage of this by asking your doctor whether or not an ICD is appropriate for you.

Reference

¹ Moss AJ, Zareba W, Hall WJ, et al, for the Multicenter Automatic Defibrillator Implantation Trial II Investigators. Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction. N Engl J Med. 2002;346:877-883.

Related Web Sites

Inside Cardiac Arrest

This site — created by St. Jude Medical — is an educational resource providing information about sudden cardiac arrest and a review of the heart's anatomy. Watch the “Am I at Risk?” video and commentary provided by Charles Machell, MD.

[ www.insidecardiacarrest.com

]

Sudden Cardiac Arrest Foundation

The SCA Foundation, a nonprofit organization, has been established to help increase awareness about this public health crisis and reduce death and disability from SCA, through their Web site and other initiatives. St. Jude Medical supports the SCA Foundation.

[ www.sca-aware.org ]