Sudden Cardiac Arrest

What happens in cardiac arrest

The heart's pumping is controlled by electrical signals. In most cardiac arrests, these signals become chaotic:

• Ventricular fibrillation (VF): the lower chambers quiver rapidly and uselessly. No blood is pumped. VF is the rhythm a defibrillator can correct.
• Pulseless ventricular tachycardia: the ventricles beat so fast that they cannot fill, so no effective pulse is produced. It is also shockable.
• Asystole ("flatline") and pulseless electrical activity: no effective electrical or mechanical activity. These do not respond to shocks and are usually caused by another problem, such as massive blood loss, low oxygen or a large blood clot.

Within seconds, the person loses consciousness. Brain injury starts after about 4 to 6 minutes without blood flow.

Cardiac arrest vs heart attack

These terms are often confused. A heart attack is a circulation problem: a blocked coronary artery starves part of the heart muscle of oxygen. The person is usually awake and has chest pain. Cardiac arrest is an electrical problem: the heart stops pumping altogether. A heart attack is one of the most common triggers of cardiac arrest, especially in the first hours.

Causes

Heart conditions in adults

• Coronary artery disease: responsible for most cardiac arrests in adults over 35. A heart attack or scar from an old one can trigger VF.
• Heart failure and cardiomyopathy: a weakened, enlarged heart, especially when the pumping fraction (ejection fraction) is 35% or less.
• Heart valve disease: particularly severe aortic stenosis.
• Myocarditis: inflammation of the heart muscle, often after a viral infection.

Inherited and structural conditions in young people

• Hypertrophic cardiomyopathy: abnormally thick heart muscle; a leading cause in young athletes.
• Long QT syndrome: arrhythmias triggered by exercise, swimming, loud noises or some medicines.
• Brugada syndrome: arrhythmias often during sleep or fever.
• Arrhythmogenic cardiomyopathy, catecholaminergic polymorphic VT and Wolff-Parkinson-White syndrome.
• Congenital coronary artery anomalies.
• Commotio cordis: a blow to the chest at a precise moment of the heartbeat, for example from a baseball.

Non-cardiac causes

• breathing problems: drowning, choking, severe asthma
• drug overdose, especially opioids; cocaine and stimulants
• severe bleeding or shock
• large pulmonary embolism
• very high or low blood potassium, often in kidney disease
• hypothermia, electrocution and severe trauma

Risk factors

• previous heart attack or known coronary artery disease
• reduced ejection fraction or heart failure
• previous cardiac arrest or episodes of VT
• family history of sudden cardiac death or inherited heart conditions
• unexplained fainting, particularly during exercise
• smoking, high blood pressure, high cholesterol, diabetes and obesity
• obstructive sleep apnea and chronic kidney disease
• illicit drug use, and certain medicines that prolong the QT interval

Emergency treatment

The "chain of survival":

1. Early recognition and calling 911.
2. Immediate CPR: chest compressions keep some blood flowing to the brain.
3. Rapid defibrillation: an AED shock within 3 to 5 minutes gives the best chance. Public-access AED programs and trained bystanders save lives.
4. Advanced life support by paramedics: airway management, medicines such as epinephrine and amiodarone.
5. Post-cardiac arrest care in hospital.

For a step-by-step guide to helping someone who has collapsed, see signs of cardiac arrest and what to do.

Hospital care after cardiac arrest

• Coronary angiography to find and open blocked arteries if a heart attack is the likely cause.
• Temperature control: preventing fever for at least 72 hours protects the brain; some patients are cooled.
• Ventilator and blood pressure support in intensive care.
• Tests to find the cause: ECG, echocardiogram, cardiac MRI, blood tests, and sometimes genetic testing.
• Neurological assessment: waiting at least 72 hours before judging the likely brain outcome, because recovery can be slow.

Preventing a second arrest

• Implantable cardioverter-defibrillator (ICD): a small device placed under the skin that detects dangerous rhythms and delivers a shock within seconds. Most survivors whose arrest did not have a reversible cause receive one.
• Medicines: beta-blockers, antiarrhythmic drugs and heart failure medicines.
• Catheter ablation: to destroy tissue causing recurrent VT.
• Treating the cause: stents or bypass surgery for blocked arteries, valve replacement, correcting electrolyte problems.

Outlook

Survival depends most on how quickly CPR and defibrillation are given. Survival from out-of-hospital arrest is roughly 1 in 10, but it can exceed 40 to 50% when a witnessed VF arrest receives bystander CPR and an AED shock within a few minutes. Survivors may have memory problems, fatigue, anxiety, depression or post-traumatic stress. Cardiac rehabilitation and psychological support help recovery.

Prevention

• Know and treat risk factors: blood pressure, cholesterol, diabetes, smoking.
• Report fainting during exercise, chest pain or palpitations promptly.
• Relatives of anyone who died suddenly and young should have heart screening (ECG, echocardiogram, and genetic counseling when relevant).
• Learn CPR and where your nearest AED is.

Frequently asked questions

What is the main cause of cardiac arrest?

In adults, the most common cause is coronary artery disease, which can trigger ventricular fibrillation, a chaotic heart rhythm that stops the heart pumping. In people under 35, inherited conditions such as hypertrophic cardiomyopathy and long QT syndrome are more common causes.

What is the difference between cardiac arrest and a heart attack?

A heart attack happens when a blocked artery cuts blood supply to part of the heart; the person is usually conscious with chest pain. Cardiac arrest is when the heart stops pumping entirely and the person collapses. A heart attack can lead to cardiac arrest.

What is the survival rate for sudden cardiac arrest?

Outside hospital, roughly 1 in 10 people survive to leave hospital in the US. Survival rises sharply with bystander CPR and rapid use of an AED, reaching 40% or more in witnessed arrests with a shockable rhythm and a quick shock.

Why do young athletes have cardiac arrest?

Sudden cardiac arrest in young athletes is usually caused by an undiagnosed inherited or structural heart problem, such as hypertrophic cardiomyopathy, an abnormal coronary artery or an electrical disorder. Fainting or chest pain during exercise needs prompt evaluation.

Can you recover fully after cardiac arrest?

Many people do, especially when CPR and defibrillation were immediate. Some survivors have lasting memory, concentration or mood problems. Rehabilitation, an ICD when needed, and treatment of the underlying heart disease support recovery and reduce the risk of another arrest.