Sudden Cardiac Arrest

Electrical signals moving through the heart and the electrocardiographic tracing of those signals. Source: Wikimedia Commons, GNU FDL.‎

Sudden cardiac arrest (SCA), also known as sudden cardiac death, occurs when the heart suddenly and unexpectedly stops beating.It is also defined as an unexpected death due to cardiac causes occurring in a short time period (generally within 1 h of symptom onset) in a person with known or unknown cardiac disease in whom no previously diagnosed fatal condition was apparent. As a consequence, blood stops flowing to the brain and other vital organs. SCA usually causes death if not treated within minutes. 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.

Other Names

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 SCA occurrence.

Cardiac arrests are sometimes referred to as cardiopulmonary arrest, cardiorespiratory arrest, or circulatory arrest.

Symptoms

Usually, the first sign of SCA 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.

Causes

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. There are many types of arrhythmia. During an arrhythmia, the heart can beat too fast, too slow, or stop beating altogether.

Most cases of 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:

• coronary artery disease (CAD)
• severe physical stress
• inherited disorders
• structural changes in the heart

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 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:

• 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.

Other Names

Diagnosis

SCA occurs 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.

Cardiologists can suggest preventative measures for people at high risk of SCA. Some cardiologists specialize in recognizing and treating problems with the electrical system of the heart. These specialists are called electrophysiologists.

Diagnostic tests and procedures

Doctors use several tests to help detect the factors that put people at risk for SCA:

• 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 can also detect evidence of a heart attack.
• Echocardiogram. This test uses sound waves to create a moving picture of the heart and provides information about heart shape, function, and size. 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 the heart is stressed either by exercise or by injecting a medicine into the bloodstream that makes the heart beat faster and work harder. A stress echocardiogram is usually done to find out if blood flow to the heart is low.
• 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. This procedure is used 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|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.

Treatment

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 SCA. 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) can 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 Cad 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) is 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.

Prevention

Ways to prevent death due to SCA depends 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.

Living With Sudden Cardiac Arrest

People who have already had SCA are at high risk of having it again. For these people, research shows that an ICD reduces the chances of dying from a second SCA.

The illustration shows the location of an implantable cardioverter defibrillator in the upper chest. Source: NIH

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.

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 reduce the chances of CAD, SCA, and other heart problems. These lifestyle choices include the following:

• a diet low in cholesterol and saturated fats and high in omega-3 fatty acids
• physical activity
• not smoking
• a healthy weight

Treatments for high blood pressure, diabetes, and high blood cholesterol also help lower the risk for SCA.

Chances of Developing Sudden Cardiac Arrest

Each year, between 250,000 and 450,000 Americans have 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 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 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.

In many people, a silent heart attack precedes SCA. 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 six months after a heart attack.

Other risk factors

Other risk factors for SCA include the following:

• personal or family history of SCA
• arrhythmias
• birth defects of the heart or blood vessels, or an enlarged heart
• heart failure
• recreational drug abuse

Expected Outcome

Over 90% of people who experience SCA die from it, most within minutes. Rapid treatment of SCA with a defibrillator can be lifesaving.

Clinical Trials

The U.S. National Institutes of Health is supporting clinical trials on SCA.

Research

Treatments to date for SCA have had limited success. In April of 2008, the New England Journal of Medicine published a study of the effectiveness of AEDs used at home.^[1] The study compared the effectiveness of AEDs followed by calling emergency medical personnel and performing CPR to CPR followed by contacting emergency medical personnel in 7,001 people at risk for a SCA following a heart attack. The number of deaths from any cause did not differ in the two treatment groups (approximately 6% of people died In each group). AEDs were used in 32 people and 4 had survived long enough to be discharged from a hospital.

Some researchers are examining the usefulness of clot-busting drugs for the treatment of SCA, but results to date have been discouraging. A small trial of 50 people with SCA found that administration of the clot-busting drug tenecteplase in the emergency room restored circulation in 26% of patients; circulation was restored in 12% of patients given standard care.^[2] Fewer than 5% of the patients treated with either standard care or tenecteplase survived to be discharged from the hospital. Results of the Thrombolysis in Cardiac Arrest (TROICA) trial reported in 2006 showed no benefit of using tenecteplase on survival or any other outcomes when administered out-of-hospital.^[3]

References

1. ↑ Bardy GH, Lee KL, Mark DB, et al. Home use of automated external defibrillators for sudden cardiac arrest. N Engl J Med. 2008 Apr 24;358(17):1793-804. Abstract | Press Release
2. ↑ Bozeman WP, Kleiner DM, Ferguson KL. Empiric tenecteplase is associated with increased return of spontaneous circulation and short term survival in cardiac arrest patients unresponsive to standard interventions. Resuscitation. 2006 Jun;69(3):399-406. Abstract | Press Release
3. ↑ theheart.org TROICA: No benefit of thrombolysis in cardiac arrest.

External Links

Sudden Cardiac Arrest Association

Sudden Cardiac Arrest Foundation