What Is Sudden Cardiac Arrest?
Sudden cardiac arrest (SCA), also known as sudden
cardiac death, is when the heart suddenly and unexpectedly stops beating. When
this occurs, blood stops flowing to the brain and other vital organs. SCA
usually causes death if not treated in minutes.
The heart has an internal electrical system that
controls the rhythm of the heartbeat. Problems with the electrical system can
cause abnormal heart rhythms, called
arrhythmias (ah-RITH-me-ahs). There are many types of
arrhythmia. During an arrhythmia, the heart can beat too fast, too slow, or it
can stop beating. SCA occurs when the heart develops an arrhythmia that causes
it to stop beating.
SCA is not the same thing as a
heart
attack. A heart attack is a problem with blocked blood flow to a part of
the heart muscle. In a heart attack, the heart usually does not suddenly stop
beating. SCA, however, may happen during recovery from a heart attack.
People with heart disease have a higher chance of
having SCA. But most SCAs happen in people who appear healthy and have no known
heart disease or other risk factors for SCA.
Outlook
Ninety-five percent of people who have SCA die from
it, most within minutes. Rapid treatment of SCA with a device that sends an
electrical shock to the heart (called a defibrillator) can be lifesaving.
Automated external defibrillators (AEDs), which are often found in public
places like airports and office buildings, can be used to save the lives of
people having SCAs.
Other Names for Sudden Cardiac Arrest
The term "sudden cardiac death" is sometimes used to
describe the sudden loss of heart function, even if the person is resuscitated
and survives. This is the term that doctors most often use when gathering
information on the number of people who have suffered sudden cardiac arrest.
What Causes Sudden Cardiac Arrest?
Most cases of sudden cardiac arrest (SCA) are due to
an
arrhythmia called ventricular fibrillation (v-fib). In v-fib,
the ventricles (the large pumping chambers of the heart) quiver very rapidly
and irregularly instead of beating normally. When this happens, the heart pumps
little or no blood to the body. Death results if the arrhythmia is not treated
within a few minutes.
Other electrical problems that can cause SCA are
extreme slowing of the rate of the heart's electrical signals or when heart
muscle stops responding to the electrical signals.
Several factors can cause the electrical problems
that lead to SCA. These factors include:
Coronary Artery Disease
CAD occurs when the arteries that supply blood to
the heart muscle (the coronary arteries) become hardened and narrowed, causing
less blood to flow to the muscle. The arteries harden and narrow because a
material called plaque (plak) builds up on their inner walls. As the plaque
increases in size, the insides of the coronary arteries narrow, and less blood
flows through them to the heart muscle. Eventually, the heart muscle is not
able to receive the amount of blood and oxygen that it needs. Reduced blood
flow or no blood flow to the heart muscle can result in a
heart
attack. During a heart attack, some heart tissue dies and turns into scar
tissue. This can damage the heart's electrical system, increasing the risk for
dangerous arrhythmias and SCA.
Physical Stress
Certain physical stresses can cause the heart's
electrical system to fail. The physical stresses that cause this to happen
include:
- Major blood loss.
- Severe lack of oxygen.
- Very low blood levels of potassium or
magnesium.
- Intense exercise. The hormone adrenaline
released during intense exercise can trigger SCA in people who have other heart
problems.
Inherited Disorders
A tendency to develop arrhythmias runs in some
families. This tendency is inherited, which means it is passed from parents to
children. Members of these families might have an increased chance of having
SCA. Other people are born with inherited structural defects in their hearts
that may increase their chance of having SCA.
Structural Changes in the Heart
Changes in the heart's normal size or structure can
affect its electrical system. Such changes include a heart enlarged by blood
pressure or advanced heart disease. Heart infections also can cause structural
changes in the heart.
Several research studies are under way to try to
understand these possible causes of SCA and to find other causes.
Who Is At Risk for Sudden Cardiac Arrest?
Populations Affected
Each year, between 250,000 and 450,000 Americans
have sudden cardiac arrest (SCA). Ninety-five percent of these people die
within minutes.
SCA occurs most often in adults in their
mid-thirties to mid-forties. It affects men twice as often as women. SCA rarely
occurs in children unless they have inherited problems that make them likely to
have SCA. Only 1 to 2 out of every 100,000 children experiences SCA each year.
Major Risk Factors
The major risk factor for SCA is having
coronary
artery disease (CAD). Most people who have SCA have some degree of CAD. But
most of these people don't know they have CAD until SCA occurs. Their CAD is
"silent" (that is, it has no symptoms), and doctors and nurses have not
previously found it. Because of this, most cases of SCA happen in people with
silent CAD who have no known heart disease at the time of the event.
Many people with SCA had a silent
heart
attack before the SCA happened. These people have no obvious signs of
having a heart attack, and they don't even realize that they've had one. The
chances for having SCA are higher during the first 6 months after a heart
attack.
The risk factors for developing CAD include:
- Smoking
- A family history of early cardiovascular disease
(that is, heart disease diagnosed before age 55 in your father or a brother, or
heart disease diagnosed before age 65 in your mother or a sister)
- High
blood cholesterol
- Diabetes
- Increasing age (risk increases for men after age
45 and for women after age 55)
- High blood pressure
- Overweight and obesity
- Lack of physical activity
Other Risk Factors
Other risk factors for SCA include:
- A personal or family history of SCA
- Abnormal heart rhythms (arrhythmias)
- Birth defects of the heart or blood vessels, or
an enlarged heart
- Heart
failure
- Recreational drug abuse
What Are the Signs and Symptoms of Sudden Cardiac
Arrest?
Usually, the first sign of sudden cardiac arrest is
loss of consciousness, which is similar to fainting. At the same time,
breathing often stops and no heartbeat (or pulse) can be felt. Some people may
first notice that they have a racing heartbeat or feel dizzy or lightheaded
just before they faint.
How Is Sudden Cardiac Arrest Diagnosed?
Sudden cardiac arrest (SCA) happens without warning
and requires immediate treatment. Rarely is there a chance to diagnose it with
medical tests as it is happening. Instead, SCA is often diagnosed after it
happens, by ruling out other causes of the patient's sudden collapse.
Specialists Involved
People who may be at high risk for SCA can see a
cardiologist (heart specialist) who can decide whether they need preventive
treatments. Some cardiologists specialize in recognizing and treating problems
with the electrical system of the heart. These specialists are called
electrophysiologists (e-LEK-tro-FIH-ze-ah-low-jists).
Diagnostic Tests and Procedures
Doctors use several tests to help detect the
factors that put people at risk for SCA. These tests include:
- EKG
(electrocardiogram). This is a simple test that records the electrical activity
of the heart from the body's surface. It's used to detect and locate the source
of
arrhythmias and other heart problems. It may show whether you
have had a
heart
attack.
- Echocardiogram. This test uses sound waves to create a
moving picture of your heart. Echocardiogram provides information about the
size and shape of your heart and how well your heart chambers and valves are
functioning. The test also can identify areas of poor blood flow to the heart,
areas of heart muscle that are not contracting normally, and previous injury to
the heart muscle caused by poor blood flow.
- There are several different
types of echocardiograms, including a stress echocardiogram. During this test,
an echocardiogram is done both before and after your heart is stressed either
by having you exercise or by injecting a medicine into your bloodstream that
makes your heart beat faster and work harder. A stress echocardiogram is
usually done to find out if you have decreased blood flow to your heart (coronary
artery disease).
- MUGA test or
magnetic resonance imaging (MRI) heart scans. These scans can
detect whether the heart has a reduced ability to pump blood.
- Cardiac
catheterization. In this procedure, a thin, flexible tube (called a
catheter) is passed through an artery in the groin (upper thigh) or arm to
reach the coronary arteries in the heart. Your doctor can use the catheter to
determine pressure and blood flow in the heart's chambers, collect blood
samples from the heart, and examine the coronary arteries by x ray.
- Electrophysiology study. For this study, doctors also use
cardiac catheterization to see how the heart's electrical system responds to
certain medicines and electrical stimulation. The electrical stimulation helps
to find where the heart's electrical system is damaged.
How Is Sudden Cardiac Arrest Treated?
Sudden cardiac arrest (SCA) requires immediate
treatment with a defibrillator, a device that sends an electrical shock to the
heart. Defibrillation can restore a normal rhythm to a heart that is beating
irregularly. To be effective, defibrillation must be provided within minutes of
cardiac arrest. With every minute of delay in providing defibrillation, the
chances of surviving SCA drop rapidly.
Police, emergency medical technicians, and other
first responders are usually trained and equipped to use a defibrillator. The
sooner 911 is called after a person experiences SCA, the sooner
potentially lifesaving defibrillation can be provided.
Special defibrillators that untrained bystanders can
use in an emergency are becoming more available in some public places, like
airports, office buildings, and shopping centers. These devices are called
automated external defibrillators (AEDs). To prevent delivering a shock to
someone who may have fainted but is not having a SCA, AEDs are programmed to
deliver a shock only if the computer detects a dangerously abnormal heart
rhythm, such as ventricular fibrillation.
Cardiopulmonary resuscitation (CPR) should be given to a
person having SCA until defibrillation can be provided.
A person who survives SCA is usually admitted to the
hospital for observation and treatment. In the hospital, the heart is monitored
closely, medicines may be given to try to reduce the chance of another SCA, and
tests are performed to identify the cause of the SCA. If
coronary
artery disease is detected, the person may undergo a procedure called
angioplasty
to restore blood flow through blocked coronary arteries.
Often, a device called an implantable cardioverter
defibrillator (ICD) will be surgically placed under the skin. An ICD
continuously monitors the heart for dangerous rhythms. If SCA or another
dangerous rhythm is detected, the ICD immediately delivers an electric shock to
restore a normal rhythm.
How Can Death Due to Sudden Cardiac Arrest Be
Prevented?
Ways to prevent death due to sudden cardiac arrest
(SCA) differ depending on whether a person has already had SCA; has never had
SCA but is at high risk; or has never had SCA and has no known risk factors for
it.
For People Who Have Survived Sudden Cardiac
Arrest
People who have already had SCA are at high risk of
having it again. For these people, research shows that an implantable
cardioverter defibrillator (ICD) reduces the chances of dying from a second
SCA. An ICD is surgically implanted under the skin. It continually monitors the
heartbeat and delivers a shock to the heart when it detects a dangerous rhythm.
The shocks can be painful, like a kick in the chest. Medicines can be given to
try to reduce how often the person experiences the irregular heartbeats that
trigger the device to deliver a shock.
The illustration shows the location
of an implantable cardioverter defibrillator in the upper chest. The electrodes
are inserted into the heart through a vein.
An ICD is not the same as a pacemaker. Doctors
mainly use pacemakers to treat hearts that beat too slowly. However, some ICDs
also can function as pacemakers.
For People at Increased Risk of a First Sudden
Cardiac Arrest
People with severe
coronary
artery disease (CAD) are at increased risk for SCA. This is especially true
if they have recently had a
heart
attack. For these people, a type of medicine called a beta blocker can help
reduce the chances of dying from SCA.
For People With No Known Risk Factors for Sudden
Cardiac Arrest
The underlying cause of most SCAs seems to be CAD.
CAD also is a major risk factor for
angina
and heart attack, and it contributes to other heart problems. Heart-healthy
lifestyle choices can help you reduce your chances of CAD, SCA, and other heart
problems. These lifestyle choices include:
- Eating a diet low in cholesterol and saturated
fats and high in omega-3 fatty acids (see the National Heart, Lung, and Blood
Institute's
Aim for a Healthy Weight Web site).
- Participating in physical activity
- Not smoking
- Maintaining a healthy weight
Treatments for
high
blood pressure,
diabetes, and
high
blood cholesterol also help lower the risk for SCA.
Key Points
- Sudden cardiac arrest (SCA) is when the heart
suddenly and unexpectedly stops beating. This is often because of a problem
with the heart's electrical system.
- SCA is not the same thing as a
heart
attack, although it may happen during recovery from a heart attack.
- The first sign of SCA is usually sudden loss of
consciousness.
- Ninety-five percent of people who have SCA die
from it, most within minutes.
- Several factors can cause electrical problems
that trigger SCA, including
coronary
artery disease, physical stress, inherited disorders, and structural
changes in the heart.
- People with heart disease have a greater chance
of having SCA. But most cases occur in people who appear healthy and have no
known heart disease or other risk factors for SCA.
- SCA occurs most often in adults in their
mid-thirties to mid-forties. It affects men twice as often as women. SCA rarely
occurs in children (although children with certain inherited heart conditions
are at increased risk).
- Several tests can help show if people have a
greater chance for having SCA. These tests are
EKG,
echocardiogram,
MUGA test,
magnetic resonance imaging (MRI) heart scan,
cardiac
catheterization, and
electrophysiology study.
- SCA requires immediate treatment with a device
called a defibrillator, which delivers an electrical shock to the heart.
Successful defibrillation restores normal rhythm to the heart.
- Defibrillation must be provided within minutes
after SCA to avoid permanent damage to the body and brain and to prevent death.
With every minute of delay in providing defibrillation, the chances of
surviving SCA drop rapidly.
- People experiencing SCA should be given
cardiopulmonary resuscitation (CPR) until they can be treated with a
defibrillator.
- Special defibrillators called automated external
defibrillators (AEDs) can be used by untrained bystanders in an emergency. AEDs
are becoming increasingly available at public places, such as airports, office
building, and shopping centers.
- People who survive SCA may need an implantable
cardioverter defibrillator to help prevent death if another SCA happens.
- Beta blocker drugs also help reduce the chance of
death from SCA in people with known heart disease.
- Heart healthy lifestyle choices may lower
people's chances for SCA.
Links to Other Information About Sudden Cardiac
Arrest
NHLBI Resources
Clinical Trials
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