Sudden Cardiac Death

Cardiac arrest, or sudden cardiac death (SCD), happens when a heart rhythm disturbance prevents the heart from operating properly and delivering blood to the brain and other vital organs.

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A heart attack occurs when a partial or complete vessel blockage interferes with the ability of blood to flow to the heart, and heart muscle dies.

Cardiac arrest, or sudden cardiac death (SCD), is NOT a heart attack, but a prior heart attack can put someone at risk for SCD.

SCD is the result of an “electrical problem” in the conduction system that regulates the normal, rhythmic contractions of the heart muscle that pumps blood throughout the body. In SCD, the electrical signals that regulate the pumping action of the lower chambers of the heart (ventricles) suddenly and without warning become rapid and chaotic. When the rhythmic contractions of the ventricles stop, the heart can’t pump blood. The brain is starved of oxygen, and the individual loses consciousness in seconds. The heart cannot recover on its own from VF. Unless immediate emergency help is available, death follows in minutes.



Ways to prevent death due to sudden cardiac arrest (SCD) differ depending on whether:

  • You’ve already had SCD
  • You’ve never had SCD but are at high risk for the condition
  • You’ve never had SCD and have no known risk factors for the condition


If you’ve already had SCD, you’re at high risk of having it again. Research shows that an implantable cardioverter defibrillator (ICD) reduces the chances of dying from a second SCD. An ICD is surgically placed under the skin in your chest or abdomen. The device has wires with electrodes on the ends that connect to your heart’s chambers. The ICD monitors your heartbeat.

If the ICD detects a dangerous heart rhythm, it gives an electric shock to restore the heart’s normal rhythm. Your doctor may give you medicine to limit irregular heartbeats that can trigger the ICD.


If you have severe coronary heart disease (CHD), you’re at increased risk for SCD. This is especially true if you’ve recently had a heart attack.

Your doctor may prescribe a type of medicine called a beta blocker to help lower your risk for SCD. Your doctor also may discuss beginning statin treatment if you have an elevated risk for developing heart disease or having a stroke.

Doctors usually prescribe statins for people who have:
  • Diabetes
  • Heart disease or had a prior stroke
  • High LDL cholesterol levels
Your doctor also may prescribe other medications to:
  • Decrease your chance of having a heart attack or dying suddenly.
  • Lower blood pressure.
  • Prevent blood clots, which can lead to heart attack or stroke.
  • Prevent or delay the need for a procedure or surgery, such as angioplasty or coronary artery bypass grafting.
  • Reduce your heart’s workload and relieve coronary heart disease symptoms.

Take all medicines regularly, as your doctor prescribes. Don’t change the amount of your medicine or skip a dose unless your doctor tells you to. You should still follow a heart-healthy lifestyle, even if you take medicines to treat your coronary heart disease.

Other treatments for coronary heart disease—such as percutaneous coronary intervention, also known as coronary angioplasty, orcoronary artery bypass grafting—also may lower your risk for SCD. Your doctor also may recommend an ICD if you’re at high risk for SCD.

CHD seems to be the cause of most SCDs in adults. CHD also is a major risk factor for angina (chest pain or discomfort) and heart attack, and it contributes to other heart problems.

Following a healthy lifestyle can help you lower your risk for CHD, SCD, and other heart problems. A heart-healthy lifestyle includes:
  • Heart-healthy eating
  • Maintaining a healthy weight
  • Managing stress
  • Physical activity
  • Quitting smoking


Risk Factors

The risk of sudden cardiac arrest (SCD) increases:

  • With age
  • If you are a man. Men are more likely than women to have SCD.
  • Some studies show that blacks—particularly those with underlying conditions such as diabetes, high blood pressure, heart failure, and chronic kidney disease or certain cardiac findings on tests such as an electrocardiogram—have a higher risk for SCD.


The major risk factor for SCD is coronary heart disease. Most people who have SCD have some degree of coronary heart disease; however, many people may not know that they have coronary heart disease until SCD occurs. Usually their coronary heart disease is “silent”—that is, it has no signs or symptoms. Because of this, doctors and nurses have not detected it.

Many people who have SCD also have silent, or undiagnosed, heart attacks before sudden cardiac arrest happens. These people have no clear signs of heart attack, and they don’t even realize that they’ve had one.


Other risk factors for SCD include:
  • A personal history of arrhythmias
  • A personal or family history of SCD or inherited disorders that make you prone to arrhythmias
  • Drug or alcohol abuse
  • Heart attack
  • Heart failure



Ventricular fibrillation (v-fib) causes most sudden cardiac death (SCDs). V-fib is a type of arrhythmia.

During v-fib, the ventricles (the heart’s lower chambers) don’t beat normally. Instead, they quiver very rapidly and irregularly. When this happens, the heart pumps little or no blood to the body. V-fib is fatal if not treated within a few minutes.

Other problems with the heart’s electrical system also can cause SCD. For example, SCD can occur if the rate of the heart’s electrical signals becomes very slow and stops. SCD also can occur if the heart muscle doesn’t respond to the heart’s electrical signals.

Certain diseases and conditions can cause the electrical problems that lead to SCD. Examples include coronary heart disease (CHD), also called coronary artery disease; severe physical stress; certain inherited disorders; and structural changes in the heart.

Several research studies are under way to try to find the exact causes of SCD and how to prevent them.


CHD is a disease in which a waxy substance called plaque builds up in the coronary arteries. These arteries supply oxygen-rich blood to your heart muscle.

Plaque narrows the arteries and reduces blood flow to your heart muscle. Eventually, an area of plaque can rupture (break open). This may cause a blood clot to form on the plaque’s surface.

A blood clot can partly or fully block the flow of oxygen-rich blood to the portion of heart muscle fed by the artery. This causes aheart attack.

During a heart attack, some heart muscle cells die and are replaced with scar tissue. The scar tissue damages the heart’s electrical system. As a result, electrical signals may spread abnormally throughout the heart. These changes to the heart increase the risk of dangerous arrhythmias and SCD.

CHD seems to cause most cases of SCD in adults. Many of these adults, however, have no signs or symptoms of CHD before having SCD.


Certain types of physical stress can cause your heart’s electrical system to fail.

Examples include:
  • Intense physical activity. The hormone adrenaline is released during intense physical activity. This hormone can trigger SCD in people who have heart problems.
  • Very low blood levels of potassium or magnesium. These minerals play an important role in your heart’s electrical signaling.
  • Major blood loss.
  • Severe lack of oxygen.


A tendency to have arrhythmias runs in some families. This tendency is inherited, which means it’s passed from parents to children through the genes. Members of these families may be at higher risk for SCD.

An example of an inherited disorder that makes you more likely to have arrhythmias is long QT syndrome (LQTS). LQTS is a disorder of the heart’s electrical activity. Problems with tiny pores on the surface of heart muscle cells cause the disorder. LQTS can cause sudden, uncontrollable, dangerous heart rhythms.

People who inherit structural heart problems also may be at higher risk for SCD. These types of problems often are the cause of SCD in children.


Changes in the heart’s normal size or structure may affect its electrical system. Examples of such changes include an enlarged heart due to high blood pressure or advanced heart disease. Heart infections also may cause structural changes in the heart.



Usually, the first sign of sudden cardiac death (SCD) is loss of consciousness (fainting). At the same time, no heartbeat (or pulse) can be felt.

Some people may have a racing heartbeat or feel dizzy or light-headed just before they faint. Within an hour before SCD, some people have chest pain, shortness of breath, nausea, or vomiting.



Sudden cardiac death (SCA) happens without warning and requires emergency treatment. Doctors rarely diagnose SCD with medical tests as it’s happening. Instead, SCD often is diagnosed after it happens. Doctors do this by ruling out other causes of a person’s sudden collapse.


Doctors use several tests to help detect the factors that put people at risk for SCD.

EKG (Electrocardiogram)

An EKG is a simple, painless test that detects and records the heart’s electrical activity. The test shows how fast the heart is beating and its rhythm (steady or irregular). An EKG also records the strength and timing of electrical signals as they pass through each part of the heart.


Echocardiography, or echo, is a painless test that uses sound waves to create pictures of your heart. The test shows the size and shape of your heart and how well your heart chambers and valves are working.

Echo also can identify areas of poor blood flow to the heart, areas of heart muscle that aren’t contracting normally, and previous injury to the heart muscle caused by poor blood flow.

MUGA Test or Cardiac MRI

A MUGA (multiple gated acquisition) test shows how well your heart is pumping blood.

Cardiac MRI (magnetic resonance imaging) is a safe procedure that uses radio waves and magnets to create detailed pictures of your heart. The test creates still and moving pictures of your heart and major blood vessels.

Doctors use cardiac MRI to get pictures of the beating heart and to look at the structure and function of the heart.

Cardiac Catheterization

Cardiac catheterization is a procedure used to diagnose and treat certain heart conditions. A long, thin, flexible tube called a catheter is put into a blood vessel in your arm, groin, or neck and threaded to your heart. Through the catheter, your doctor can do diagnostic tests and treatments on your heart.

Electrophysiology Study

For an electrophysiology study, doctors use cardiac catheterization to record how your heart’s electrical system responds to certain medicines and electrical stimulation. This helps your doctor find where the heart’s electrical system is damaged.

Blood Tests

Your doctor may recommend blood tests to check the levels of potassium, magnesium, and other chemicals in your blood. These chemicals play an important role in your heart’s electrical signaling.




Sudden cardiac death (SCD) is an emergency. A person having SCD needs to be treated with a defibrillator right away. This device sends an electric shock to the heart. The electric shock can restore a normal rhythm to a heart that’s stopped beating.

To work well, defibrillation must be done within minutes of SCD. With every minute that passes, the chances of surviving SCD drop rapidly.

Police, emergency medical technicians, and other first responders usually are trained and equipped to use a defibrillator. Call 9–1–1 right away if someone has signs or symptoms of SCD. The sooner you call for help, the sooner lifesaving treatment can begin.

Automated External Defibrillators

Automated external defibrillators (AEDs) are special defibrillators that untrained bystanders can use. These portable devices often are found in public places, such as shopping malls, golf courses, businesses, airports, airplanes, casinos, convention centers, hotels, sports venues, and schools.

AEDs are programmed to give an electric shock if they detect a dangerous arrhythmia, such as ventricular fibrillation. This prevents giving a shock to someone who may have fainted but isn’t having SCD.

You should give cardiopulmonary resuscitation (CPR) to a person having SCD until defibrillation can be done.

People who are at risk for SCD may want to consider having an AED at home. A 2008 study by the National Heart, Lung, and Blood Institute and the National Institutes of Health found that AEDs in the home are safe and effective.

Some people feel that placing these devices in homes will save many lives because many SCs occur at home. Others note that no evidence supports the idea that home-use AEDs save more lives. These people fear that people who have AEDs in their homes will delay calling for help during an emergency. They’re also concerned that people who have home-use AEDs will not properly maintain the devices or forget where they are.

When considering a home-use AED, talk with your doctor. He or she can help you decide whether having an AED in your home will benefit you.


If you survive SCD, you’ll likely be admitted to a hospital for ongoing care and treatment. In the hospital, your medical team will closely watch your heart. They may give you medicines to try to reduce the risk of another SCD.

While in the hospital, your medical team will try to find out what caused your SCD. If you’re diagnosed with coronary heart disease, you may have percutaneous coronary intervention, also known as coronary angioplasty, or coronary artery bypass grafting. These procedures help restore blood flow through narrowed or blocked coronary arteries.

Often, people who have SCD get a device called an implantable cardioverter defibrillator (ICD). This small device is surgically placed under the skin in your chest or abdomen. An ICD uses electric pulses or shocks to help control dangerous arrhythmias.


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