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Sudden Cardiac Death

What causes sudden cardiac death?

Sudden cardiac death can be caused by ventricular fibrillation. The heart fibrillates (quivers) and stops pumping blood to the body. Although there are other causes of sudden cardiac death, the majority are due to ventricular fibrillation.

Who is at risk for Sudden Cardiac Death?

Patients with a previous heart attack or those with heart failure are the highest risk of sudden cardiac death. However, certain patients with heart surgeries as children, those with syncope (fainting), those with premature ventricular complexes all may be at risk. Also, patients may have genetic conditions that may predispose them to having sudden cardiac death. Ask your doctor if you think you are at risk.

Is sudden cardiac death the same as a heart attack?

No. While most people think they're the same, they're two separate problems. Sudden cardiac death is a disorder of the heart's electrical system. Heart attacks, however, are caused by plaque buildup in the heart's arteries. This prevents blood flow to the heart tissue and causes a scar.

Some people who are said to have died from a "massive heart attack" may instead have died from sudden cardiac death.

Why do heart attack survivors experience sudden cardiac death?

Some heart attack survivors are at increased risk due to the extent of the scar from their attack. The scar impairs the heart's ability to pump blood. It also disrupts the heart's normal electrical conduction and can do so without warning. When this occurs, it creates a fatal heart rhythm called ventricular fibrillation.

Sudden cardiac death can also occur, without warning, to those with no prior signs of heart disease. However, some heart attack survivors are at increased risk depending on the severity of their heart attack(s). It's estimated that 1.1 million1 Americans survive a heart attack each year. Many of these heart attack survivors may be at increased risk for sudden cardiac death.

I'm a heart attack survivor. How can I determine my risk for sudden cardiac death?

The key to measuring your risk is to know your ejection fraction.

What is the ejection fraction?

The ejection fraction is the amount of blood pumped (ejected) from the heart with each beat. It measures how much damage a heart attack caused. The heart normally ejects at least one-half of the blood it holds with each beat. One or more heart attacks can cause a decrease in the ejection fraction. When less than one-third of the blood is ejected, the risk for sudden cardiac death increases.

How is the ejection fraction measured?

The ejection fraction can be measured using a painless heart ultrasound called an echocardiogram ("echo"). An echo can be performed in a physician's office in just a few minutes.

How does an implantable cardioverter defibrillator (ICD) prevent sudden cardiac death?

An implantable cardioverter defibrillator (ICD) is a pacemaker-like device. It's about the size of three silver dollars. It's placed under the skin just below the collarbone. The device uses leads (wires threaded into the heart's chambers) to monitor every single heartbeat. If a lethal rhythm appears, the defibrillator shocks the heart back to a normal rhythm.

Should every heart attack survivor have a defibrillator to protect against sudden cardiac death? Patients with a normal or nearly normal ejection fraction are not at high risk for sudden cardiac death. For them, a defibrillator may not be necessary. Heart attack survivors should be selected for defibrillators based on their ejection fraction.

What Every Heart Attack Survivor Should Know


More people die of SCD than AIDS A recent study (MADIT II) is changing how doctors treat heart attack survivors. Here are three things you should know:

  • Heart attack survivors are at risk for sudden cardiac death (SCD)
  • A simple test can help determine your risk for SCD
  • SCD can be prevented

Heart Attack Survivors Are at Risk for SCD

A heart attack can damage your heart and create an area of scar tissue. If large enough, this scar tissue may put you at risk for SCD.

The scar can unexpectedly create a fast, dangerous heart rhythm. Without immediate treatment, this condition may be lethal.

SCD can strike without warning. Often, those who experience it felt fine moments before. Knowing that a heart attack puts you at risk is your first step in learning about SCD.

A Simple Test Can Help Determine Your Risk for SCD

Your doctor can determine your risk by measuring the fraction of blood pumped (ejected) by your heart with each heartbeat. Doctors call this measurement the ejection fraction, or EF.

A healthy heart pumps at least one-half of the blood it holds with each beat. But after a heart attack, the damaged heart has a reduced ejection fraction. A level of less than one-third dramatically raises the risk for SCD.
Risk for Sudden Cardiac Death

The ejection fraction is measured using a simple and painless heart ultrasound called an echocardiogram, or "echo." An echo can be performed easily in your doctor's office in just a few minutes.

SCD Can Be Prevented

If you have a low ejection fraction, your doctor may recommend that you visit a heart rhythm specialist. Your heart rhythm specialist may recommend that you receive a pacemaker-like device that can prevent SCD.

This device is called an implantable cardioverter defibrillator (ICD). U.S. Vice President Dick Cheney received a defibrillator in 2001. The defibrillator is typically placed beneath the skin near the collarbone and monitors every heartbeat for dangerous heart rhythms. If one is detected, the defibrillator can prevent SCD by delivering a life-saving shock.

Defibrillators can be true life savers. Many scientific studies prove that defibrillators dramatically reduce the risk for SCD.