Sudden cardiac arrest is the abrupt loss of heart function, breathing and consciousness. The condition usually results from a problem with your heart’s electrical system, which disrupts your heart’s pumping action and stops blood flow to your body.

Sudden cardiac arrest isn’t the same as a heart attack, when blood flow to a part of the heart is blocked. However, a heart attack can sometimes trigger an electrical disturbance that leads to sudden cardiac arrest.

If not treated immediately, sudden cardiac arrest can lead to death. Survival is possible with fast, appropriate medical care. Cardiopulmonary resuscitation (CPR), using a defibrillator — or even just giving compressions to the chest — can improve the chances of survival until emergency workers arrive.

Symptoms

Signs of sudden cardiac arrest are immediate and drastic and include:
Sudden collapse
No pulse
No breathing
Loss of consciousness
Sometimes other signs and symptoms occur before sudden cardiac arrest. These might include:
Chest discomfort
Shortness of breath
Weakness
Fast-beating, fluttering or pounding heart (palpitations)
But sudden cardiac arrest often occurs with no warning.

Causes
The usual cause of sudden cardiac arrest is an abnormal heart rhythm (arrhythmia), which happens when your heart’s electrical system isn’t working correctly.
The heart’s electrical system controls the rate and rhythm of your heartbeat. If something goes wrong, your heart can beat too fast, too slowly or irregularly (arrhythmia). Often these arrhythmias are brief and harmless, but some types can lead to sudden cardiac arrest.
The most common heart rhythm at the time of cardiac arrest is an arrhythmia in a lower chamber of your heart (ventricle). Rapid, erratic electrical impulses cause your ventricles to quiver uselessly instead of pumping blood (ventricle fibrillation).
Heart conditions that can lead to sudden cardiac arrest
Sudden cardiac arrest can happen in people who have no known heart disease. However, a life-threatening arrhythmia usually develops in a person with a preexisting, possibly undiagnosed heart condition. Conditions include:
Coronary artery disease. Most cases of sudden cardiac arrest occur in people who have coronary artery disease, in which the arteries become clogged with cholesterol and other deposits, reducing blood flow to the heart.
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. Also, a heart attack can leave scar tissue in your heart. 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. Then your heart’s muscle is abnormal, a condition that often leads to arrhythmias.
Valvular heart disease. Leaking or narrowing of your heart valves can lead to stretching or thickening of your heart muscle. 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.
Heart defect present at birth (congenital heart disease). When sudden cardiac arrest occurs in children or adolescents, it can be due to congenital heart disease. 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 syndrome and long QT syndrome.
Risk factors
A family history of coronary artery disease
Smoking
High blood pressure
High blood cholesterol
Obesity
Diabetes
An inactive lifestyle
Other factors that might increase your risk of sudden cardiac arrest include:
A previous episode of cardiac arrest or a family history of cardiac arrest
A previous heart attack
A personal or family history of other forms of heart disease, such as heart rhythm disorders, congenital heart defects, heart failure and cardiomyopathy
Growing older — the risk of sudden cardiac arrest increases with age
Being male
Using illegal drugs, such as cocaine or amphetamines
Nutritional imbalance, such as low potassium or magnesium levels
Obstructive sleep apnea
Chronic kidney disease
Complications

When sudden cardiac arrest occurs, reduced blood flow to your brain causes unconsciousness. If your heart rhythm doesn’t rapidly return to normal, brain damage occurs and death results. Survivors of cardiac arrest might show signs of brain damage.
Prevention

Reduce your risk of sudden cardiac arrest by getting regular checkups, being screened for heart disease and living a heart-healthy lifestyle.
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