Sudden cardiac arrest (SCA) is a serious medical emergency that occurs when the heart suddenly stops beating, causing a loss of blood flow to the brain and other vital organs. It is different from a heart attack, which occurs when blood flow to the heart is blocked, and can sometimes lead to SCA.

SCA can occur in people of all ages, including those who appear healthy and have no history of heart problems. It is often caused by an electrical malfunction in the heart, which can be triggered by a number of factors including underlying heart disease, heart muscle damage, genetic conditions, or certain medications or substances.

Symptoms of SCA can include sudden loss of consciousness, no pulse, and no breathing. If someone appears to be experiencing SCA, it is important to call 911 or your local emergency number immediately and begin CPR (cardiopulmonary resuscitation) until medical help arrives.

Early treatment is crucial for improving the chances of survival and minimizing the risk of long-term complications. Treatment for SCA may include defibrillation, which delivers an electric shock to the heart to restore its normal rhythm, or medications to stabilize the heart. In some cases, surgery or other medical procedures may be necessary to treat underlying heart conditions that can lead to SCA.

To reduce the risk of SCA, it is important to maintain a healthy lifestyle by eating a balanced diet, staying physically active, avoiding tobacco and excessive alcohol use, and managing any underlying medical conditions such as high blood pressure or diabetes. Additionally, those who are at high risk for SCA may benefit from preventive measures such as implantable cardioverter-defibrillators (ICDs) or medications.

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.

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

Sudden cardiac arrest requires immediate action for survival.

CPR

Immediate CPR is crucial for treating sudden cardiac arrest. By maintaining a flow of oxygen-rich blood to the body's vital organs, CPR can provide a vital link until more-advanced emergency care is available.

If you don't know CPR and someone collapses unconscious near you, call 911 or emergency medical help. Then, if the person isn't breathing normally, begin pushing hard and fast on the person's chest — at a rate of 100 to 120 compressions a minute, allowing the chest to fully rise between compressions. Do this until an automated external defibrillator (AED) becomes available or emergency personnel arrive.

Defibrillation

Advanced care for ventricular fibrillation, a type of arrhythmia that can cause sudden cardiac arrest, generally includes delivery of an electrical shock through the chest wall to the heart. The procedure, called defibrillation, momentarily stops the heart and the chaotic rhythm. This often allows the normal heart rhythm to resume.

Defibrillators are programmed to recognize ventricular fibrillation and send a shock only when it's appropriate. These portable defibrillators, such as AEDs, are increasingly available in public places, including airports, shopping malls, casinos, health clubs, and community and senior citizen centers.

At the emergency room

Once you arrive in the emergency room, the medical staff will work to stabilize your condition and treat a possible heart attack, heart failure or electrolyte imbalances. You might be given medications to stabilize your heart rhythm.

Long-term treatment

After you recover, your doctor will discuss with you or your family what other tests might help determine the cause of the cardiac arrest. Your doctor will also discuss preventive treatment options with you to reduce your risk of another cardiac arrest.

Treatments might include:

• Drugs. Doctors use various anti-arrhythmic drugs for emergency or long-term treatment of arrhythmias or potential arrhythmia complications. A class of medications called beta blockers is commonly used in people at risk of sudden cardiac arrest.
• Other possible drugs that can be used to treat the condition that led to the arrhythmia include angiotensin-converting enzyme (ACE) inhibitors and calcium channel blockers.
• Implantable cardioverter-defibrillator (ICD). After your condition stabilizes, your doctor is likely to recommend an ICD, a battery-powered unit that's put into your body near your left collarbone. One or more electrode-tipped wires from the ICD run through veins to your heart.
• The ICD constantly monitors your heart rhythm. If it detects a rhythm that's too slow, it paces your heart as a pacemaker would. If it detects a dangerous heart rhythm change, it sends out low- or high-energy shocks to reset your heart to a normal rhythm.
• Coronary angioplasty. This procedure opens blocked coronary arteries, letting blood flow more freely to your heart, which might reduce your risk of serious arrhythmia. A long, thin tube is passed through an artery, usually in your leg, to a blocked artery in your heart. This catheter is equipped with a special balloon tip that briefly inflates to open the blocked artery.
• At the same time, a metal mesh stent might be inserted into the artery to keep it open long term, restoring blood flow to your heart. Coronary angioplasty can be done at the same time as a coronary catheterization, a procedure that doctors do to locate narrowed arteries to the heart.
• Coronary bypass surgery. Also called coronary artery bypass grafting, bypass surgery involves sewing veins or arteries in place at a site beyond a blocked or narrowed coronary artery, restoring blood flow to your heart. This can improve the blood supply to your heart and reduce the frequency of racing heartbeats.
• Radiofrequency catheter ablation. This procedure can be used to block a single abnormal electrical pathway. One or more catheters are threaded through your blood vessels to inside your heart. They're positioned along electrical pathways identified by your doctor as causing your arrhythmia.
• Electrodes at the catheter tips are heated with radiofrequency energy. This destroys a small spot of heart tissue and creates an electrical block along the pathway that's causing your arrhythmia to stop your arrhythmia.
• Corrective heart surgery. If you have a congenital heart deformity, a faulty valve or diseased heart muscle tissue due to cardiomyopathy, surgery to correct the abnormality might improve your heart rate and blood flow, reducing your risk of fatal arrhythmias.