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Causes
By Mayo Clinic staff
The immediate cause of sudden cardiac arrest is usually an abnormality in your heart rhythm (arrhythmia), the result of a malfunction in your heart's electrical system.
Unlike other muscles in your body, which rely on nerve connections to receive the electrical stimulation they need to function, your heart has its own electrical stimulator — a specialized group of cells called the sinus node, located in the upper right chamber (right atrium) of your heart. The sinus node generates electrical impulses that flow in an orderly manner through your heart to synchronize heart rate and coordinate the pumping of blood from your heart to the rest of your body.
If something goes wrong with the sinus node or the flow of electric impulses through your heart, an arrhythmia can result, causing your heart to beat too fast, too slow or in an irregular fashion. Often, these interruptions in rhythm are momentary and harmless. But some types of arrhythmia can be serious and lead to a sudden stop in heart function (sudden cardiac arrest).
The most common cause of cardiac arrest is an arrhythmia called ventricular fibrillation — when rapid, erratic electrical impulses cause your ventricles to quiver uselessly instead of pumping blood. Without an effective heartbeat, your blood pressure plummets, cutting off blood supply to your vital organs.
Most of the time, cardiac-arrest-inducing arrhythmias don't occur on their own. In a person with a normal, healthy heart, a sustained arrhythmia is unlikely to develop without some outside trigger, such as an electrical shock, the use of illegal drugs, or trauma to the chest at just the wrong time of the heart's cycle (commotio cordis).
Heart conditions that can lead to sudden cardiac arrest
More often, a life-threatening arrhythmia develops in a person with a pre-existing heart condition, such as:
- Coronary artery disease. More than 80 percent of cases of sudden cardiac arrest occur in people who have coronary artery disease. In coronary artery disease, your arteries become clogged with cholesterol and other deposits, reducing blood flow to your heart. This can alter the ability of your heart to conduct electrical impulses smoothly.
- Heart attack. If a heart attack occurs, often as a result of severe coronary artery disease, it can trigger ventricular fibrillation and sudden cardiac arrest. In addition, a heart attack can leave behind areas of dead scar tissue. Electrical short circuits around the scar tissue can lead to abnormalities in your heart rhythm.
- Enlarged heart (cardiomyopathy). This occurs primarily when your heart's muscular walls stretch and enlarge or thicken. In both cases, your heart's muscle is abnormal, a condition that often leads to heart tissue damage and potential arrhythmias.
- Valvular heart disease. Leaking or narrowing of your heart valves can lead to stretching or thickening of your heart muscle, or both. When the chambers become enlarged or weakened because of stress caused by a tight or leaking valve, there's an increased risk of developing arrhythmia.
- Congenital heart disease. When sudden cardiac arrest occurs in children or adolescents, it's more often due to a heart condition that was present at birth (congenital heart disease). Hypertrophic cardiomyopathy is a genetic disorder and is the most common cause of sudden cardiac arrest in young athletes, triggered perhaps by vigorous exertion, although the process isn't completely understood. Even adults who've had corrective surgery for a congenital heart defect remain at increased risk of sudden cardiac arrest.
- Electrophysiological abnormalities. In some people, the problem is in the heart's electrical system itself, instead of a problem with the heart muscle or valves. These are called primary heart rhythm abnormalities. For example, some people have primary ventricular fibrillation, unrelated to another heart condition. Other examples include long QT syndrome, Wolff-Parkinson-White syndrome and Brugada syndrome.
