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sudden cardiac arrest: it's not a heart attack
Sudden cardiac arrest (SCA), also called cardiac arrest,
is not the same as a heart attack. Often confused, the two problems have different origins, causes and outcomes.
Sudden cardiac arrest happens when the heart abruptly and without warning starts beating very rapidly and erratically. It is a leading cause of death in the United States, responsible for half of all heart disease deaths.
Sudden cardiac arrest occurs when the heart's electrical system malfunctions. It is not a heart attack, which also is known as a myocardial infarction, or MI, but can occur in association with a heart attack. A heart attack happens when a blockage in a blood vessel interrupts the flow of oxygen-rich blood to the heart, causing heart muscle to die. So, if the heart can be compared to a house, SCA occurs when there is an electrical problem and a heart attack happens when the problem is the plumbing.
The most common cause of cardiac arrest is a heart rhythm disorder, or arrhythmia, called ventricular fibrillation (VF). The heart has a built-in electrical system. In a healthy heart, a "pacemaker" triggers the heartbeat, then electrical impulses run along pathways in the heart, causing it to contract in a regular, rhythmic way. When a contraction happens, blood is pumped.
But in ventricular fibrillation, the electrical signals that control the pumping of the heart suddenly become rapid and chaotic. As a result, the lower chambers of the heart, the ventricles, begin to quiver (fibrillate) instead of contract, and no longer effectively pump blood from the heart to the rest of the body. Without the flow of blood, the brain becomes starved of oxygen, and the victim loses consciousness in seconds. Unless the heart's regular rhythm is restored by an emergency shock, using a machine called a defibrillator, death occurs within minutes. The majority of ventricular fibrillation victims die before reaching the hospital.
Who Is At Risk?
SCA often occurs in active, outwardly healthy people with no known heart disease or other health problems. But in actuality, sudden cardiac arrest is not a random event. Most victims do have heart diseases or other health problems, although they may not know it.
A number of problems increase the risk of having a cardiac arrest. The most important ones are:
- having suffered a previous heart attack— Seventy-five percent of people who die of SCA show signs of a previous heart attack.
- coronary artery disease — Eighty percent of SCA victims have signs of coronary artery disease, a condition in which the arteries that supply blood to the heart are narrowed or blocked.
- heart failure from other causes
A number of signs and symptoms may indicate that a person is at increased risk for SCA. These include:
- an abnormal heart rate or rhythm (arrhythmia) of unknown cause
- episodes of fainting (called syncope) of unknown cause
- a low ejection fraction (EF) — The ejection fraction is a measurement of how much blood is pumped by the ventricles with each heart beat. A healthy heart pumps 55 percent or more of its blood with each beat. People at highest risk for SCA have ejection fractions of less than 40 percent, combined with ventricular tachycardia, an abnormally fast heart rate in the lower chambers of the heart.
Do you know your EF?
If you don't, ask your doctor.
It could save your life.
To identify people at high risk for SCA, some undergo specialized tests performed by an electrophysiologist, a cardiologist with training in heart rhythm disorders. Tests include echocardiograms, electrocardiogram, holter monitoring, event recorders, and electrophysiology studies (EPS).
Prevention
Since a heart attack can damage the heart's electrical system, decreasing the risk of heart attacks also decreases the risk of SCA. So, living a "heart healthy" life can help reduce the chances of dying of cardiac arrest or other heart conditions. This includes exercising regularly, eating healthful foods, maintaining a reasonable weight and avoiding smoking.
Treating and monitoring diseases and conditions that can contribute to heart problems, including high blood pressure, high cholesterol and diabetes, is also important.
Finally, for some patients, preventing sudden cardiac arrest means controlling or stopping the abnormal heart rhythms that may trigger ventricular fibrillation. Treating arrhythmias is done in three ways:
- Implantable cardioverter defibrillators (ICDs)
These devices are very successful in preventing sudden cardiac arrest in certain high-risk patients. ICDs are implanted in the chest, under the skin. Wires, called leads, run from the ICD to the heart, and the device monitors the heart to detect any abnormal rhythms. If the ICD detects a dangerous arrhythmia, it delivers an electrical shock to restore the heart's normal rhythm and prevent sudden cardiac arrest. The ICD also can act like a pacemaker and jolt a heart that is beating too slowly.
- Medications
Medications, including ACE inhibitors, beta blockers and calcium channel blockers, can control abnormal heart rhythms or treat other conditions that may contribute to heart disease or SCA. But taking medication alone has not proved to be very effective in reducing SCA. Often, medications are used in concert with ICDs, to reduce how often the device fires.
- Catheter Ablation
In this technique, radiofrequency energy (heat) or other energy forms destroy the small areas of heart muscle that give rise to abnormal electrical signals that cause rapid or irregular heart rhythms. The heat is delivered through catheters that are snaked through the veins or arteries to the heart. Catheter ablation is sometimes performed on patients who also have an ICD. Ablation can decrease the frequency of abnormal heart rhythms, and as with medications, may reduce how often the device fires.
Since treating SCA once it occurs may be ineffective, the best way to prevent SCA deaths is to preemptively treat those at high risk. People at high risk for heart disease, those who experience rapid heartbeats and those who have suffered a heart attack should meet with a cardiologist to evaluate their risk of SCA.
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