Sudden Cardiac Arrest

Overview

Sudden cardiac arrest is the abrupt and unexpected loss of heart function. Due to a sudden disruption in the heart's electrical system, the heart either begins to quiver chaotically or stops beating altogether. When this happens, no blood is pumped to the brain or the rest of the body. Without intervention within minutes, it is fatal.

Sudden cardiac arrest is frequently confused with a heart attack, but the two are distinct events. In a heart attack, a blocked artery cuts off blood supply to part of the heart muscle, which begins to die — but the heart continues to beat. In sudden cardiac arrest, the electrical system collapses and the heart stops pumping effectively. That said, a heart attack is one of the most important triggers of sudden cardiac arrest and the two can occur together.

Sudden cardiac arrest is one of the leading causes of cardiovascular death worldwide. However, the chances of survival improve dramatically with a rapid response. Starting chest compressions and using a defibrillator within the first few minutes saves lives.

Symptoms

Sudden cardiac arrest most often occurs without warning. In some people, symptoms appear in the hours or minutes before the event, but these may go unnoticed or not be taken seriously.

• Sudden loss of consciousness. The person collapses abruptly and becomes unresponsive. This is the most recognizable sign of sudden cardiac arrest.
• No breathing or abnormal breathing. The person may not be breathing, or may appear to be breathing in a very shallow and irregular way. Gasping sounds may sometimes be heard. This is not normal breathing.
• No detectable pulse. Because the heart is not pumping effectively, a pulse cannot be felt or is extremely faint.

In some people, the following symptoms may occur in the period leading up to sudden cardiac arrest.

• Sudden, severe chest pain or pressure
• Shortness of breath
• Palpitations or a very rapid heartbeat
• Dizziness or a feeling of nearly fainting
• Nausea and sweating

What to Do: Act Immediately

Every action and every second matters in sudden cardiac arrest.

If someone nearby suddenly collapses and becomes unresponsive, do the following.

• Call emergency services immediately, or ask someone nearby to call.
• Check whether the person is breathing. If they are not breathing or are breathing abnormally, begin chest compressions immediately.
• Place both hands on the center of the person's chest and push down hard and fast. Aim for at least 100 compressions per minute, pressing the chest down by approximately five centimeters. Do not stop.
• If an automated external defibrillator is nearby, have someone retrieve it and follow its spoken instructions. Do not hesitate to pause compressions briefly to use it — the device will tell you exactly what to do.
• Continue until professional help arrives.

If you do not know how to perform CPR, the emergency services dispatcher can guide you step by step. It does not need to be perfect. Doing something is always better than doing nothing.

Causes

The great majority of sudden cardiac arrests result from a sudden disruption in the heart's electrical system. In most cases, an underlying heart condition is present, though for some people sudden cardiac arrest is the first sign of a problem they were not aware of.

• Ventricular fibrillation. This is the most common cause. Instead of contracting in a coordinated way, the lower chambers of the heart quiver chaotically. No meaningful blood is pumped. Ventricular fibrillation usually develops on the background of coronary artery disease or a heart attack.
• Ventricular tachycardia. The heart beats very rapidly and may no longer pump blood effectively. Ventricular tachycardia can deteriorate into ventricular fibrillation, leading to sudden cardiac arrest.
• Heart attack. A blocked coronary artery deprives part of the heart muscle of oxygen. This can trigger dangerous rhythm disturbances and precipitate sudden cardiac arrest.
• Coronary artery disease. The buildup of fatty plaques inside the coronary arteries over many years creates conditions for both heart attack and sudden cardiac arrest. A significant proportion of people who experience sudden cardiac arrest have undiagnosed coronary artery disease.
• Heart muscle diseases. Dilated cardiomyopathy, hypertrophic cardiomyopathy, and arrhythmogenic cardiomyopathy are among the most important conditions that raise the risk of sudden cardiac arrest. Hypertrophic cardiomyopathy is one of the leading causes of sudden cardiac death in young athletes.
• Heart failure. A weakened heart muscle is more electrically vulnerable. Patients with a significantly reduced ejection fraction carry a substantially higher risk of sudden cardiac arrest.
• Heart valve disease. Severe aortic stenosis and other valve conditions can affect the heart both mechanically and electrically.
• Congenital heart defects. Some structural heart defects, even when surgically repaired, can increase the risk of sudden cardiac arrest in later life.
• Inherited electrical disorders. Conditions such as Brugada syndrome, long QT syndrome, and catecholaminergic polymorphic ventricular tachycardia can cause sudden cardiac arrest in young and apparently healthy people without any structural heart abnormality. Unexplained sudden death in a young person should prompt investigation for these conditions in surviving family members.
• Commotio cordis. A sudden, sharp blow to the chest wall, timed to coincide with a specific phase of the heart's electrical cycle, can trigger ventricular fibrillation. This is most commonly seen in sports injuries involving a ball striking the chest.

Risk Factors

• A prior sudden cardiac arrest. This is the strongest single risk factor. People who survive a sudden cardiac arrest have a high risk of recurrence and almost always require an ICD.
• Known coronary artery disease or prior heart attack. The majority of sudden cardiac arrest cases occur in people with underlying coronary artery disease.
• Reduced ejection fraction. An ejection fraction at or below 35 percent substantially raises the risk of sudden cardiac arrest.
• Family history of sudden cardiac death. Unexplained sudden cardiac death in a first-degree relative at a young age may indicate an inherited cardiac condition.
• Heart muscle disease. Hypertrophic cardiomyopathy, arrhythmogenic cardiomyopathy, and dilated cardiomyopathy are all important risk conditions.
• Inherited electrical disorders. Long QT syndrome, Brugada syndrome, and related conditions increase sudden cardiac arrest risk, particularly in young and otherwise healthy people.
• Male sex. Sudden cardiac arrest is considerably more common in men than in women.
• Older age. Risk increases with age, though young people can also be affected.
• Smoking, obesity, and diabetes. These factors increase the risk of coronary artery disease and thereby indirectly raise the risk of sudden cardiac arrest.

Diagnosis

Sudden cardiac arrest is a clinical diagnosis. A person who collapses suddenly, becomes unresponsive, and is not breathing normally is in cardiac arrest. Intervention begins immediately — the diagnosis does not wait for testing.

After survival has been achieved, identifying the underlying cause of the arrest is essential for reducing the risk of recurrence and planning appropriate long-term treatment.

• Electrocardiogram (ECG). Performed after resuscitation, the ECG can identify a heart attack, conduction abnormalities, and genetic electrical disorders such as long QT syndrome and Brugada syndrome. It also helps document the type of rhythm disturbance that caused the arrest.
• Blood tests. Troponin elevation suggests a heart attack. Electrolytes, kidney function, and thyroid tests are used to identify contributing causes. Blood gas analysis and lactate levels assess the metabolic state following resuscitation.
• Coronary angiography. When a heart attack is thought to have triggered the arrest, emergency coronary angiography identifies the blocked artery and allows it to be opened immediately. This is typically performed within the first hours after resuscitation in patients monitored in an intensive care setting.
• Echocardiogram (heart ultrasound). Evaluates the structure and function of the heart, including ejection fraction, wall motion, valve function, and evidence of a heart muscle disease.
• Cardiac MRI. Provides detailed images of the heart muscle including areas of fibrosis, structural abnormalities, and changes associated with cardiomyopathy. Valuable for identifying the underlying cause when initial tests do not provide a clear answer.
• Genetic testing and family screening. In young patients and in those with no identifiable structural cause, genetic testing for inherited electrical disorders is recommended. When a hereditary condition such as long QT syndrome, Brugada syndrome, or arrhythmogenic cardiomyopathy is identified, screening of first-degree family members can be life-saving.
• Electrophysiology study. The electrical pathways of the heart are mapped in detail to identify the origin of dangerous rhythm disturbances. This information guides both ICD programming and decisions about catheter ablation.

Treatment

Treatment of sudden cardiac arrest is addressed in two phases: immediate survival and preventing recurrence.

Emergency Response: The Chain of Survival

• Early recognition and calling emergency services. Rapidly recognizing that someone is in cardiac arrest and summoning professional help is the first link in the chain of survival. Every minute without intervention reduces the chance of survival.
• CPR (cardiopulmonary resuscitation). Chest compressions maintain blood flow to the brain and other organs until the heart can be restarted. Compressions must be strong, fast, and uninterrupted. Hands-only CPR — without mouth-to-mouth breathing — is effective and is the recommended approach for bystanders who are hesitant about rescue breathing.
• Early defibrillation. Ventricular fibrillation requires an electrical shock to restore a normal rhythm. Automated external defibrillators are increasingly available in public spaces. They provide spoken instructions, are designed for use by non-medical bystanders, and require no formal training. The sooner a shock is delivered, the higher the chance of survival.
• Advanced life support. Emergency medical teams provide medications, advanced airway management, and further defibrillation as needed, both before and after hospital arrival.
• Post-resuscitation intensive care. After resuscitation, targeted temperature management, brain-protective measures, and organ support may be provided. Simultaneous investigation into the cause of the arrest proceeds in parallel.

Preventing Recurrence

• Implantable cardioverter-defibrillator (ICD). The risk of a further arrest is very high in survivors of sudden cardiac arrest. An ICD is the most effective preventive treatment. This small device implanted under the chest skin continuously monitors the heart rhythm. When it detects a life-threatening arrhythmia, it delivers an electrical shock to restore a normal rhythm. An ICD substantially reduces the risk of dying from a recurrent event.
• Treating the underlying cause. The cause of the arrest is addressed specifically. A blocked coronary artery is opened with stenting or bypass surgery. Heart muscle disease is managed with appropriate medications. When an inherited electrical disorder is identified, condition-specific treatments are planned. Some medications may need to be stopped or changed.
• Catheter ablation. In patients with recurrent ventricular tachycardia or frequent ICD shocks, catheter ablation may be performed. The electrical pathways of the heart are mapped and the source of the arrhythmia is selectively destroyed using radiofrequency energy. Catheter ablation does not replace an ICD and the two are often used together.
• Antiarrhythmic medications. Medications such as amiodarone or sotalol can reduce the frequency of dangerous rhythm disturbances and may help decrease the number of ICD shocks. They do not provide sufficient protection against sudden cardiac arrest on their own.
• Cardiac resynchronization therapy. In patients with a reduced ejection fraction and left bundle branch block, a CRT-D device both supports heart failure and provides protection against sudden cardiac arrest.

Complications

In people who survive sudden cardiac arrest, long-term outcomes are largely determined by how quickly intervention began and how effectively resuscitation was performed.

• Brain injury. The duration of time without blood flow to the brain is the most important determinant of neurological outcome. Effects can range from mild cognitive difficulties to severe permanent brain damage. Early and effective CPR substantially reduces this risk.
• Rib fractures and chest wall bruising. Vigorous chest compressions can cause rib fractures. This is an expected consequence of effective CPR and should not discourage bystanders from compressing firmly.
• Reduced heart function. A temporary decline in cardiac function known as post-resuscitation myocardial stunning can occur after cardiac arrest. The heart may recover partially or fully over days to weeks.
• Psychological impact. Post-traumatic stress disorder, anxiety, and depression are common both in survivors of sudden cardiac arrest and in family members who witnessed the event. These experiences deserve serious attention and professional support.

Lifestyle

Recovery after sudden cardiac arrest involves both physical and emotional dimensions, and both require genuine attention.

Living with an ICD

Most people who receive an ICD can return to a normal and active life. When the device delivers a shock, a sudden thumping or jolting sensation in the chest is felt. A single shock after which you feel well should be reported to your doctor. Multiple shocks within a short period require emergency care immediately. Regular device check appointments must not be missed.

Managing the Underlying Condition

Long-term treatment for the condition that caused the arrest may be necessary for life. Consistently taking medications for coronary artery disease, heart failure, or a heart muscle condition is critical for preventing another event. Do not stop any medication without medical guidance.

Managing Risk Factors

Smoking should be stopped entirely. High blood pressure, diabetes, and high cholesterol need regular monitoring and active management. A heart-healthy diet and maintaining an appropriate weight support both heart function and long-term cardiovascular health. These changes reduce the strain on the heart and lower the risk of future events.

Physical Activity

The type and amount of physical activity that is safe after sudden cardiac arrest depends on the underlying cause, the treatment received, and the current state of heart function. This decision must be made by a cardiologist. Many survivors benefit from a supervised cardiac rehabilitation program, which provides a structured and medically safe pathway back to physical activity.

Informing Family Members

When sudden cardiac arrest has a hereditary cause, first-degree relatives should be referred for cardiac evaluation. Additionally, having family members trained in basic life support — CPR and defibrillator use — is both practically and psychologically valuable. Knowing how to respond in an emergency can give families a meaningful sense of preparedness.

Emotional Recovery

Surviving sudden cardiac arrest is a profound experience. Anxiety about recurrence, fear of ICD shocks, and depression are common in survivors. Family members who witnessed the event may also experience significant psychological effects. Sharing these feelings openly with your care team is important. Professional psychological support and peer support groups can make a meaningful difference in the recovery process.

Regular Follow-up

Ongoing cardiology monitoring is essential after sudden cardiac arrest. Echocardiography, ECG, blood tests, and ICD device checks are performed at regular intervals. Seek emergency care immediately in any of the following situations.

• You receive a shock from your ICD
• You receive multiple ICD shocks within a short period
• You faint or nearly faint
• You develop chest pain or severe shortness of breath
• You experience palpitations or a very rapid heartbeat

Preparing for Your Appointment

Coming prepared to an appointment for sudden cardiac arrest helps your doctor make a more accurate assessment and choose the most appropriate treatment for you.

What You Can Do

• Describe how the event occurred and how quickly intervention began.
• Share any prior history of heart disease, rhythm disturbances, or unexplained fainting.
• Mention any family history of unexplained sudden cardiac death at a young age.
• List all medications, supplements, and herbal products you are currently taking.
• If you have an ICD, bring your device card and most recent device check information.
• Write your questions down before the appointment.

Questions You May Wish to Ask Your Doctor

• What caused my sudden cardiac arrest?
• Do I need an ICD and if one has been implanted, when will it need to be replaced?
• What can I do to reduce the risk of this happening again?
• Could catheter ablation be an option for me?
• Should my family members be screened?
• Can I exercise and should I join a cardiac rehabilitation program?
• What should I do if I receive a shock from my ICD?
• How often do I need follow-up appointments?

Questions Your Doctor May Ask You

• How did the event occur and how quickly did help arrive?
• Did you have any prior diagnosis of heart disease or a rhythm disturbance?
• Is there a family history of unexplained sudden cardiac death at a young age?
• What medications were you taking at the time?
• Had you experienced fainting or palpitations before the event?
• Do you smoke or use recreational drugs?