Heart Disease: Sudden Cardiac Death

Sudden cardiac death is an unexpected, sudden death caused by sudden cardiac arrest (loss of heart function). Causes and risk factors of sudden cardiac death include (not inclusive): abnormal heart rhythms (arrhythmias), previous heart attack, coronary artery disease, smoking, high cholesterol, Wolff-Parkinson-White Syndrome, ventricular tachycardia or ventricular fibrillation after a heart attack, congenital heart defects, history of fainting, and heart failure, obesity, diabetes, and drug abuse. Treatment of sudden cardiac arrest is an emergency, and action must be taken immediately.

Sudden cardiac death (SCD) is a sudden, unexpected death caused by loss of heart function (sudden cardiac arrest). It is the largest cause of natural death in the U.S., causing about 325,000 adult deaths in the United States each year. SCD is responsible for half of all heart disease deaths.

SCD occurs most frequently in adults in their mid-30s to mid-40s, and affects men twice as often as it does women. SCD is rare in children, affecting only 1 to 2 per 100,000 children each year.

Sudden cardiac arrest is not a heart attack (myocardial infarction) but can occur during a heart attack. Heart attacks occur when there is a blockage in one or more of the arteries to the heart, preventing the heart from receiving enough oxygen-rich blood. If the oxygen in the blood cannot reach the heart muscle, the heart becomes damaged.

In contrast, sudden cardiac arrest occurs when the electrical system to the heart malfunctions and suddenly becomes very irregular. The heart beats dangerously fast. The ventricles may flutter or quiver (ventricular fibrillation), and blood is not delivered to the body. In the first few minutes, the greatest concern is that blood flow to the brain will be reduced so drastically that a person will lose consciousness. Death follows unless emergency treatment is begun immediately.

Emergency treatment includes cardiopulmonary resuscitation (CPR) and defibrillation. CPR is a manual technique using repetitive pressing to the chest and breathing into the person's airways that keeps enough oxygen and blood flowing to the brain until the normal heart rhythm is restored with an electric shock to the chest, a procedure called defibrillation. Emergency squads use portable defibrillators and frequently there are public access defibrillators (AEDs, ambulatory external defibrillators) in public locations that are intended to be available for use by citizens who observe cardiac arrest.

Some people may experience a racing heartbeat or they may feel dizzy, alerting them that a potentially dangerous heart rhythm problem has started. In over half of the cases, however, sudden cardiac arrest occurs without prior symptoms.

Most sudden cardiac deaths are caused by abnormal heart rhythms called arrhythmias. The most common life-threatening arrhythmia is ventricular fibrillation, which is an erratic, disorganized firing of impulses from the ventricles (the heart's lower chambers). When this occurs, the heart is unable to pump blood and death will occur within minutes, if left untreated.

There are many factors that can increase a person's risk of sudden cardiac arrest and sudden cardiac death, including the following:

• Previous heart attack with a large area of the heart damaged (75 percent of SCD cases are linked to a previous heart attack).
  
  
• A person's risk of SCD is higher during the first six months after a heart attack.
  
  
• Coronary artery disease (80 percent of SCD cases are linked with this disease).
  
  
• Risk factors for coronary artery disease include smoking, family history of cardiovascular disease and high cholesterol.

Other risk factors include:

• Ejection fraction of less than 40 percent, combined with ventricular tachycardia.
  
  
• Prior episode of sudden cardiac arrest.
  
  
• Family history of sudden cardiac arrest or SCD.
  
  
• Personal or family history of certain abnormal heart rhythms, including long or short QT syndrome, Wolff-Parkinson-White syndrome, extremely low heart rates, or heart block.
  
  
• Ventricular tachycardia or ventricular fibrillation after a heart attack.
  
  
• History of congenital heart defects or blood vessel abnormalities.
  
  
• History of syncope (fainting episodes of unknown cause).
  
  
• Heart failure: a condition in which the heart's pumping power is weaker than normal. Patients with heart failure are 6 to 9 times more likely than the general population to experience ventricular arrhythmias that can lead to sudden cardiac arrest.
  
  
• Dilated cardiomyopathy (cause of SCD in about 10 percent of the cases): a decrease in the heart's ability to pump
  
  
• Hypertrophic cardiomyopathy: a thickened heart muscle that especially affects the ventricles.
  
  
• Significant changes in blood levels of potassium and magnesium (from using diuretics, for example), even if there is not underlying heart disease.
  
  
• Obesity.
  
  
• Diabetes.
  
  
• Recreational drug abuse.
  
  
• Taking drugs that are "pro-arrhythmic" may increase the risk for life-threatening arrhythmias.

SLIDESHOW

Heart Disease: Causes of a Heart Attack See Slideshow

If you have any of the above listed risk factors for SCD, it is important that you speak with your doctor about possible steps to reduce your risk.

Keeping regular follow-up appointments with your doctor, making certain lifestyle changes, taking medications as prescribed, and having interventional procedures or surgery (as recommended) are ways you can reduce your risk.

Follow-up Care with Your Doctor: Your doctor will tell you how often you need to have follow-up visits. To prevent future episodes of sudden cardiac arrest, your doctor will want to perform diagnostic tests to determine what caused the cardiac event. Tests may include electrocardiogram (ECG or EKG), ambulatory monitoring, echocardiogram, cardiac catheterization and electrophysiology studies.

Ejection Fraction (EF): EF is a measurement of the percentage of blood pumped out of the heart with each beat. EF can be measured in your doctor's office during an echocardiogram (echo) or during other tests such as a MUGA (multiple gated acquisition) scan, cardiac catheterization, nuclear stress test, or magnetic resonance imaging (MRI) scan of the heart. The EF of a healthy heart ranges from 55 to 65 percent. Your EF can go up and down, based on your heart condition and the effectiveness of the therapies that have been prescribed. If you have heart disease, it is important to have your EF measured initially, and then as needed, based on changes in your condition. Ask your doctor how often you should have your EF checked.

Reducing your risk factors: If you have coronary artery disease -- and even if you do not -- there are certain lifestyle changes you can make to reduce your risk of sudden cardiac arrest.

These lifestyle changes include:

• Quitting smoking
  
  
• Losing weight
  
  
• Exercising regularly
  
  
• Following a low-fat diet
  
  
• Managing diabetes
  
  
• Managing other health conditions including high blood pressure and cholesterol

If you have questions or are unsure how make these changes, talk to your doctor. Patients and families should know the signs and symptoms of coronary artery disease and the steps to take if symptoms occur.

Medications: To help reduce the risk of sudden cardiac arrest, doctors may prescribe medications to people who have had heart attacks or who have heart failure or arrhythmias such as irregular heart rhythms. These medications may include ACE inhibitors, beta blockers, calcium channel blockers, and other antiarrhythmics. For patients with high cholesterol and coronary artery disease, statin medications may be prescribed.

If medication is prescribed, your doctor will give you more specific instructions. It is important that you know the names of your medications and any directions that you need to follow when taking them. If you have any questions, be sure to ask your doctor or pharmacist.

Implantable cardioverter-defibrillator (ICD): For people whose risk factors put them at great risk for sudden cardiac death, an ICD may be inserted as a preventive treatment. An ICD is a small machine similar to a pacemaker that is designed to correct arrhythmias. It detects and then corrects a fast heart rate. The ICD constantly monitors the heart rhythm. When it detects a very fast or slow heart rhythm, it delivers energy (a small, but powerful shock) to the heart muscle to cause the heart to beat in a normal rhythm again. The ICD also records the data of each abnormal heartbeat, which can be viewed by the doctor through a third part of the system kept at the hospital.

The ICD may be used in patients who have survived sudden cardiac arrest and need their heart rhythms constantly monitored. It may also be combined with a pacemaker to treat other underlying irregular heart rhythms.

Interventional procedures or surgery: For patients with coronary artery disease, an interventional procedure such as angioplasty (blood vessel repair) or bypass surgery may be needed to improve blood flow to the heart muscle and reduce the risk of SCD. For patients with other conditions, such as hypertrophic cardiomyopathy or congenital heart defects, an interventional procedure or surgery may be needed to correct the problem. Other procedures may be used to treat abnormal heart rhythms, including electrical cardioversion and catheter ablation.

When a heart attack occurs in the left ventricle (left lower pumping chamber of the heart), a scar forms. The scarred tissue may increase the risk of ventricular tachycardia. The electrophysiologist (doctor specializing in electrical disorders of the heart) can determine the exact area causing the arrhythmia. The electrophysiologist, working with your surgeon, may combine ablation (the use of high-energy electrical energy to "disconnect" abnormal electrical pathways within the heart) with left ventricular reconstruction surgery (surgical removal of the infarcted or dead area of heart tissue).

Educate your family members: If you are at risk for SCD, talk to your family members so they understand your condition and the importance of seeking immediate care in the event of an emergency. Family members and friends of those at risk for SCD should know how to perform CPR.

Yes, sudden cardiac arrest can be treated and reversed, but emergency action must take place immediately. Survival can be as high as 90% if treatment is initiated within the first minutes after sudden cardiac arrest. The rate decreases by about 10% each minute longer it takes to initiate therapy. Those who survive have a good long-term outlook.

If you witness someone experiencing sudden cardiac arrest, dial 911 or your local emergency personnel immediately and initiate CPR. If done properly, CPR can save a person's life, as the procedure keeps blood and oxygen circulating through the body until help arrives.

If there is an AED available, the best chance of rescuing the person includes defibrillation with that device. The shorter the time until defibrillation, the greater the chance the person will survive. It is CPR plus defibrillation that saves a person.

After successful defibrillation, most people require hospital care to treat and prevent future cardiac problems.

SCD occurs rarely in athletes, but when it does happen, it often affects us with shock and disbelief.

Cause: Most cases of SCD are related to undetected cardiovascular disease. In the younger population, SCD is often due to congenital heart defects, while in older athletes (35 years and older), the cause is more often related to coronary artery disease.

Prevalence: SCD in athletes is rare, but media coverage often makes it seem like it is more prevalent. In the younger population, most SCD occurs while playing team sports. It occurs in about one in 100,000 to one in 300,000 athletes, and more often in males. In older athletes (35 years and older), SCD occurs more often while running or jogging, and in about one in 15,000 joggers and one in 50,000 marathon runners.

Screening: The American Heart Association recommends cardiovascular screening for high school and collegiate athletes and should include a complete and careful evaluation of the athlete's personal and family history and a physical exam. Screening should be repeated every two years, with a history obtained every year. Men aged 40 and older and women aged 50 and older should also have a thorough examination and an exercise stress test and receive education about cardiac risk factors and symptoms. If heart problems are identified or suspected, the individual should be referred to a cardiologist for further evaluation and treatment guidelines before participating in sports.

Sudden Arrhythmia Death Syndromes Foundation
A nonprofit organization, established to help prevent sudden and unexpected cardiac death in children and young adults.
508 E South Temple Ste. 20,
Salt Lake City, UT 84102
1-800-786-7723
www.sads.org

Heart Rhythm Society
1400 K St., NW, Suite 500,
Washington D.C. 20005
(202) 464-3400
www.HRSpatients.org

CPR Information: For more information about CPR, please contact your local chapter of the American Red Cross or the American Heart Association. Or ask your doctor for more information.

Reviewed by The Cleveland Clinic Heart Center (2005).
SOURCE: The American Heart Association
Reviewed by David W. Stein, MD on December 01, 2006 and Edited by Tracy C. Shuman, MD on October 01, 2005

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