Sudden Cardiac Arrest: Causes, Risks, Warning Signs and What to Do

Sudden cardiac arrest (SCA) is when the heart suddenly stops beating. Blood stops flowing to the brain and other vital organs, and without treatment SCA usually kills within minutes. Quick treatment with cardiopulmonary resuscitation (CPR) and a defibrillator can save a life.

Not the same as a heart attack

A heart attack happens when blood flow to the heart is blocked; the heart usually keeps beating. In SCA, the heart stops. SCA can sometimes happen during or after recovery from a heart attack.

Causes

The heart's electrical system controls the rate and rhythm of the heartbeat. SCA happens when that system malfunctions and causes arrhythmias — irregular heartbeats that can make the heart beat too fast, too slow or erratically. Some stop the heart pumping blood altogether; that kind causes SCA. Conditions that can lead to it include:

• ventricular fibrillation, in which the heart's lower chambers (ventricles) beat very fast and irregularly and cannot pump blood — the cause of most SCAs;
• coronary artery disease (CAD), or ischemic heart disease, in which the heart's arteries can't deliver enough oxygen-rich blood, often because plaque, a waxy substance, builds up inside the larger coronary arteries;
• certain physical stresses — intense activity, when the body releases adrenaline, which can trigger SCA in people with heart problems; very low blood potassium or magnesium, minerals important to the heart's electrical system; major blood loss; or severe lack of oxygen;
• inherited disorders that cause arrhythmias or structural heart problems;
• structural changes to the heart, such as enlargement from high blood pressure or advanced heart disease, or damage from heart infections.

Who is at higher risk

• People with coronary artery disease — most people who have SCA have it, often without knowing, since it usually causes no symptoms.
• Older people; risk rises with age.
• Men, in whom SCA is more common.
• Black or African American people, especially with diabetes, high blood pressure, heart failure or chronic kidney disease.
• People with a personal history of arrhythmia, a personal or family history of SCA or of inherited disorders that cause arrhythmia, drug or alcohol use problems, a past heart attack, or heart failure.

Warning signs

The first sign is usually fainting, when the heart stops. Some people feel a racing heartbeat, dizziness or light-headedness just before, and some have chest pain, shortness of breath, nausea or vomiting in the hour beforehand.

What to do

SCA is an emergency. Call 911 right away — the sooner help comes, the sooner lifesaving treatment can start.

• Start CPR and keep going until a defibrillator is ready. CPR keeps blood moving to the brain and other organs. If you aren't trained, you can still do hands-only CPR: push hard and fast on the center of the chest.
• Use a defibrillator within minutes. It sends an electric shock that can restore a normal rhythm. Many schools, businesses and airports have automated external defibrillators (AEDs), which untrained people can use: they give spoken step-by-step instructions and only deliver a shock if they detect a dangerous arrhythmia, so they won't shock someone who has simply fainted. Most police officers, emergency medical technicians and other first responders are trained and equipped to use defibrillators.
• People at risk may want an AED at home; ask a cardiologist.

Diagnosis and aftercare

SCA strikes without warning, so it is rarely diagnosed with tests as it happens; it is usually diagnosed afterward, by ruling out other causes of the collapse. People at high risk may be referred to a cardiologist for heart tests and to decide whether preventive treatment is needed.

Survivors are usually hospitalized so their heart can be watched closely. Doctors may give medicine to lower the risk of another SCA and look for its cause. People with coronary artery disease may have angioplasty or bypass surgery to restore blood flow. Many receive an implantable cardioverter defibrillator (ICD), a small device placed under the skin of the chest or abdomen that uses electrical pulses or shocks to control dangerous arrhythmias.

Prevention

A heart-healthy lifestyle may lower the risk. Treating coronary artery disease or other heart disease also helps, and for someone who has had SCA, an ICD lowers the chance of another.

Sources

Based on "Sudden Cardiac Arrest", MedlinePlus, U.S. National Library of Medicine, drawing on the National Heart, Lung, and Blood Institute; a work of the United States government in the public domain.