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. 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.

Symptoms

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.

Diagnosis

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.

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.
• 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.
• 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.

Causes

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)
• Severe physical stress
• Inherited disorders
• Structural changes in the heart

Treatment

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 9?? 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.

Reference:

National Heart, Lung, and Blood Institute, USA.