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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.
Most of the time, cardiac-arrest-inducing arrhythmias don't occur on their own. In a person with a normal, healthy heart, a lasting irregular heart rhythm isn't likely to develop without an 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. Most 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 make it harder for 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 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 may be due to a heart condition that was present at birth (congenital heart disease). Even adults who've had corrective surgery for a congenital heart defect still have a higher risk of sudden cardiac arrest.
- Electrical problems in the heart. 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 and include conditions such as Brugada's syndrome and long QT syndrome.
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- What is sudden cardiac arrest? National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/scda/scda_all.html. Accessed April 26, 2010.
- 2005 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2005;112(Suppl):IV-12.
- Myerburg RJ, et al. Cardiovascular collapse, cardiac arrest, and sudden cardiac death. In: Fauci AS, et al. Harrison's Principles of Internal Medicine. 17th ed. New York, N.Y.: McGraw Hill; 2007. http://www.accessmedicine.com/content.aspx?aID=2869694. Accessed April 27, 2010.
- Sudden cardiac death. American Heart Association. http://www.americanheart.org/print_presenter.jhtml?identifier=4741. Accessed April 26, 2010.
- Ejection fraction and heart failure. American Heart Association. http://www.americanheart.org/presenter.jhtml?identifier=3065321. Accessed April 27, 2010.
- Sayre MR, et al. Hands-only (compression-only) cardiopulmonary resuscitation: A call to action for bystander response to adults who experience out-of-hospital sudden cardiac arrest. Circulation. 2008;117:2162.
- Prevention and treatment. Heart Rhythm Society. http://www.hrsonline.org/PatientInfo/HeartRhythmDisorders/SCA/Prevention/index.cfm. Accessed April 27, 2010.
- Bollmann A, et al. Antiarrhythmic drugs in patients with implantable cardioverter-defibrillators. American Journal of Cardiovascular Drugs. 2005;5:371.
- Grogan M (expert opinion). Mayo Clinic, Rochester, Minn. May 7, 2010.
- Field JM, et al. Part 1: Executive summary — 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122(suppl):S640.
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