Sudden Cardiac Death

What to do if someone collapses

1. Check responsiveness and breathing. Gasping is not normal breathing.
2. Call 911 or your local emergency number and put the phone on speaker.
3. Start chest compressions: push hard and fast in the center of the chest, at least 5 cm (2 inches) deep, 100 to 120 times per minute.
4. Use an AED as soon as one arrives. Turn it on and follow the voice prompts.
5. Continue CPR until help arrives or the person starts breathing normally.

Hands-only CPR is recommended for untrained bystanders. Every minute without CPR and defibrillation reduces survival by roughly 7% to 10%.

Cardiac arrest vs heart attack

See cardiac arrest.

Causes

Adults over 35

• coronary artery disease: heart attack or scarring from a previous one is the leading cause
• heart failure and weakened heart muscle (low ejection fraction)
• valve disease, such as severe aortic stenosis

Young people and athletes

• hypertrophic cardiomyopathy: thickened heart muscle
• arrhythmogenic cardiomyopathy
• inherited rhythm disorders (channelopathies): long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia
• Wolff-Parkinson-White syndrome with atrial fibrillation
• coronary artery anomalies present from birth
• myocarditis (heart muscle inflammation, often after a viral infection)
• commotio cordis: a blow to the chest at a vulnerable moment in the heartbeat
• drugs: cocaine, stimulants, some medicines that prolong the QT interval

Other triggers

• electrolyte imbalances (low potassium or magnesium)
• severe dehydration or heat
• drowning, electrocution

Warning signs

Many victims have no warning, but some have:

• fainting, especially during exercise
• chest pain or pressure
• palpitations or a racing heartbeat
• breathlessness out of proportion to effort
• unusual tiredness in the days or weeks before

Who is at higher risk

• previous heart attack or heart failure
• ejection fraction 35% or lower
• previous cardiac arrest or ventricular arrhythmia
• inherited heart conditions or a family history of sudden death
• smoking, high blood pressure, diabetes, high cholesterol, obesity
• drug use

Diagnosis in survivors and relatives

• ECG and Holter or longer-term rhythm monitoring
• echocardiogram and cardiac MRI
• coronary angiography
• exercise testing
• genetic testing and screening of family members after an unexplained sudden death, including a molecular autopsy

Prevention

For people at high risk

• implantable cardioverter-defibrillator (ICD): a device that detects dangerous rhythms and shocks the heart back to normal. Recommended for survivors of cardiac arrest and for selected people with weak hearts or high-risk inherited conditions
• medicines: beta blockers, other antiarrhythmics
• ablation of abnormal electrical pathways or scar
• treating coronary disease with stents or bypass surgery

For everyone

• control blood pressure, cholesterol and diabetes
• do not smoke
• stay active and maintain a healthy weight
• learn CPR and support public access to AEDs
• report fainting with exertion or a family history of sudden death

Outlook

Out-of-hospital cardiac arrest survival in the US is roughly 1 in 10, but much higher when bystanders give immediate CPR and use an AED, especially in public places.

Frequently asked questions

What is sudden cardiac death?

It is an unexpected death caused by a sudden loss of heart function, usually from a dangerous heart rhythm such as ventricular fibrillation. It often occurs within an hour of symptoms, or without warning.

What causes sudden cardiac death in young people?

In people under 35, common causes are inherited heart muscle diseases such as hypertrophic cardiomyopathy, inherited rhythm disorders such as long QT and Brugada syndrome, coronary artery anomalies, myocarditis and drug use.

Are there warning signs before sudden cardiac arrest?

Some people have warning signs such as fainting during exercise, chest pain, palpitations or unusual breathlessness. Many have none, which is why family history and screening matter for people at risk.

Is cardiac arrest the same as a heart attack?

No. A heart attack is a blockage of blood flow to the heart muscle. Cardiac arrest is an electrical failure that stops the heart pumping. A heart attack can trigger cardiac arrest, and both are emergencies.

Can sudden cardiac death be prevented?

Risk can be reduced by treating heart disease, controlling risk factors, and implanting a defibrillator (ICD) in high-risk people. Bystander CPR and rapid AED use save many lives when cardiac arrest occurs.