Sudden cardiac death (SCD) is a sudden, unexpected death caused by a change in heart rhythm (sudden cardiac arrest). It is the largest cause of natural death in the U.S., causing about 325,000 adult deaths in the U.S. each year. SCD is responsible for half of all heart disease deaths.
How Is Sudden Cardiac Arrest Different from a Heart Attack?
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 care providers use portable defibrillators and frequently there are public access defibrillators (AEDs, automated external defibrillators) in public locations that are intended to be available for use by citizens who observe cardiac arrest.
What Are the Symptoms of Sudden Cardiac Arrest?
Some people may experience symptoms of sudden cardiac arrest, such as a racing heartbeat or feeling 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.
What Causes Sudden Cardiac Death?
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.
What Are the Risk Factors of Sudden Cardiac Arrest?
There are many risk 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% of SCD cases are linked to a previous heart attack.)
- A person's risk of SCD is higher during the first 6 months after a heart attack.
- Coronary artery disease (80% of SCD cases are linked with this disease.)
- Risk factors for coronary artery disease include smoking, hypertension, family history of heart disease, and high cholesterol.
Other risk factors of sudden cardiac arrest include:
- Ejection fraction -- a measure of how much blood the left ventricle pumps out with each contraction -- of under 40%, particularly in combination 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
- 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
- Recreational drug abuse
- Taking drugs that are "pro-arrhythmic" may increase the risk for life-threatening arrhythmias
Can Sudden Cardiac Death Be Prevented?
If you have any of the risk factors for sudden cardiac death (listed above), 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 (fraction) of blood pumped (ejected) 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 75%. 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 heart-healthy diet
- Managing diabetes
- Managing other health conditions including high blood pressure and cholesterol
If you have questions or are unsure how to 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 drugs may include ACE inhibitors, beta-blockers, calcium channel blockers, and other antiarrhythmics. For patients with high cholesterol and coronary artery disease, statin drugs 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 using a special machine 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. Classes to teach this are available in most communities.
Can Sudden Cardiac Arrest Be Treated?
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 better long-term outlook.
What Should I Do if I Witness Sudden Cardiac Arrest?
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.
Sudden Cardiac Death and Athletes
SCD occurs rarely in athletes, but when it does happen, it often affects us with shock and disbelief.
Cause: Many cases of SCD are related to undetected heart disease. In the younger population, SCD is often caused by congenital heart defects, while in older athletes (ages 35 and older), the cause is more often related to coronary artery disease.
Prevalence: In the younger population, most SCD occurs while playing team sports. It occurs in about one in 50,000 athletes, and more often in males. In older athletes (ages 35 and older), SCD occurs more often while running or jogging.
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. An electrocardiogram may detect asymptomatic heart disease in some young people. Men ages 40 and older and women ages 50 and older should also have a thorough examination and receive education about heart disease risk factors and symptoms. They may also need an exercise stress test based on their doctor’s evaluation. 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.
For More Information:
Sudden Arrhythmia Death Syndromes Foundation
4527 S 2300 E, Suite 104
Salt Lake City, UT 84117-4448
Heart Rhythm Society
1325 G Street NW, Suite 400
Washington, DC 20005
CPR Information: For more information about CPR, please contact your local chapter of the American Red Cross or the American Heart Association (www.heart.org). Or ask your doctor for more information.