Understanding cardiac arrest

Cardiac arrest is a sudden and life-threatening condition where the heart abruptly stops beating. When this happens, the heart is no longer able to pump blood to the brain, lungs, and other vital organs, resulting in loss of consciousness and death within minutes if not treated immediately.

Unlike a heart attack, which is caused by a blockage in blood flow to the heart, cardiac arrest is primarily an electrical problem. The electrical system controlling the heart’s rhythm becomes chaotic, leading to an arrhythmia — or an abnormal heartbeat — that prevents effective pumping.

Without rapid intervention such as cardiopulmonary resuscitation (CPR) or defibrillation, cardiac arrest is almost always fatal. Therefore, understanding what causes this sudden failure of the heart is essential to prevention and treatment.

Sudden arrhythmias

The most common cause of cardiac arrest is an arrhythmia called ventricular fibrillation (VF). In VF, the heart’s electrical impulses become erratic, causing the ventricles to quiver instead of contracting normally. This prevents the heart from pumping blood, leading quickly to collapse and death.

Other dangerous arrhythmias include:

  • Ventricular tachycardia (VT): A rapid heartbeat originating in the lower chambers of the heart.

  • Asystole: A total absence of electrical activity in the heart (also known as flatline).

  • Pulseless electrical activity (PEA): Electrical signals may be present, but the heart fails to contract and circulate blood.

These irregular rhythms often result from underlying heart conditions or other physiological disturbances.

Coronary artery disease

Coronary artery disease (CAD) is the leading cause of cardiac arrest in adults. It occurs when the coronary arteries that supply blood to the heart muscle become narrowed or blocked due to plaque buildup (atherosclerosis).

A complete blockage can trigger a heart attack, which may destabilize the heart's electrical system and lead to ventricular fibrillation — and ultimately, cardiac arrest.

Often, CAD develops silently over time, and cardiac arrest may be the first sign of any heart trouble in some individuals.

Heart attack

While a heart attack and cardiac arrest are different conditions, a heart attack can often lead to cardiac arrest. During a heart attack, blood flow to part of the heart muscle is blocked, causing tissue damage and increasing the risk of fatal arrhythmias.

The more extensive the heart damage, the greater the chance of electrical instability. In some cases, cardiac arrest can occur during or shortly after a heart attack, particularly if there is scar tissue in the heart muscle that interferes with normal electrical signals.

Heart failure

Heart failure doesn’t mean the heart stops beating, but it refers to a weakened heart muscle that can’t pump blood efficiently. Over time, the strain on the heart can lead to changes in electrical signaling and an increased risk of sudden cardiac arrest.

Patients with advanced heart failure often have implanted cardioverter defibrillators (ICDs) to monitor and correct dangerous rhythms before they become fatal.

Cardiomyopathy

Cardiomyopathy refers to diseases of the heart muscle that make it enlarged, thick, or rigid. These changes can impair the heart’s ability to pump and increase the risk of arrhythmias.

There are several types of cardiomyopathy:

  • Dilated cardiomyopathy

  • Hypertrophic cardiomyopathy

  • Restrictive cardiomyopathy

  • Arrhythmogenic right ventricular cardiomyopathy

Hypertrophic cardiomyopathy, often inherited, is a leading cause of sudden cardiac death in young athletes. It can go undetected until a fatal arrhythmia occurs during physical exertion.

Congenital heart defects

Some people are born with structural heart abnormalities that disrupt blood flow or electrical activity. Even after surgical repair, individuals with congenital heart disease remain at higher risk for cardiac arrest.

Pediatric cardiac arrest is often linked to undiagnosed congenital issues, emphasizing the importance of early screening and regular follow-up for children with known heart anomalies.

Electrical disorders

Certain genetic or acquired electrical abnormalities in the heart can lead to cardiac arrest, even in the absence of structural damage. These include:

  • Long QT syndrome: Delayed repolarization of the heart after a heartbeat, increasing risk of arrhythmias.

  • Brugada syndrome: A genetic condition causing dangerous arrhythmias, often during sleep or rest.

  • Wolff-Parkinson-White syndrome: An extra electrical pathway in the heart that can cause rapid heart rate.

These syndromes are often inherited and may require medication, lifestyle adjustments, or an implantable defibrillator.

Drug and substance use

The use of certain drugs — both legal and illicit — can trigger cardiac arrest. Substances that may contribute include:

  • Cocaine and methamphetamine: These stimulate the heart and can cause fatal arrhythmias.

  • Opioids: Overdose can depress breathing and oxygen supply, triggering cardiac arrest.

  • Alcohol: Excessive consumption over time can damage the heart muscle and electrical system.

  • Prescription medications: Certain drugs like antiarrhythmics, antidepressants, and antipsychotics can prolong the QT interval or cause other disturbances that increase risk.

Mixing medications or using them without medical supervision can heighten the danger.

Severe blood loss or trauma

Trauma resulting in massive bleeding can reduce blood flow to vital organs, leading to shock and cardiac arrest. This is common in:

  • Major car accidents

  • Severe internal bleeding

  • Gunshot or stab wounds

  • Surgery complications

Loss of oxygenated blood starves the heart and brain, leading to multi-organ failure and cardiac arrest.

Electrolyte imbalances

Electrolytes like potassium, calcium, and magnesium are essential for proper heart function. Imbalances can disrupt the heart’s rhythm and cause sudden cardiac arrest.

Common causes of imbalance include:

  • Dehydration

  • Chronic kidney disease

  • Diuretics

  • Eating disorders (e.g., anorexia or bulimia)

Maintaining proper hydration and electrolyte levels is especially important for athletes and individuals with underlying health conditions.

Respiratory issues and oxygen deprivation

Cardiac arrest can also result from conditions that impair breathing and oxygen delivery, such as:

  • Asthma attacks

  • Severe pneumonia

  • Choking

  • Drowning

  • Sleep apnea (in chronic or untreated cases)

Without enough oxygen, the heart struggles to function and may eventually stop beating.

Sepsis and systemic infections

Sepsis is a life-threatening immune response to infection that can cause dangerously low blood pressure, inflammation, and multi-organ failure. In severe cases, it can lead to cardiac arrest due to impaired oxygen delivery and heart overload.

Sepsis-related cardiac arrest is more common in older adults and those with chronic conditions.

Hypothermia

Prolonged exposure to extreme cold can slow the heart’s electrical signals, causing bradycardia (a very slow heartbeat) or ventricular fibrillation.

Once the core body temperature drops significantly, the risk of cardiac arrest increases dramatically. Proper insulation, heated environments, and prompt rewarming are key for prevention.

Physical exertion and emotional stress

Sudden cardiac arrest can also be triggered by intense physical activity or emotional shock, especially in individuals with undiagnosed heart issues.

Examples include:

  • Strenuous exercise in extreme heat

  • Sudden fright or grief (e.g., “broken heart syndrome” or stress cardiomyopathy)

  • Sports-related impacts to the chest (commotio cordis)

These cases highlight the importance of cardiac screening in athletes and people with family history of heart disease.

The role of underlying risk factors

Many causes of cardiac arrest are linked to long-term risk factors, including:

  • High blood pressure

  • High cholesterol

  • Diabetes

  • Obesity

  • Smoking

  • Sedentary lifestyle

  • Family history of heart disease

Addressing these risk factors through lifestyle changes and medical care significantly reduces the likelihood of a cardiac event.

How to reduce your risk

While not all cardiac arrests are preventable, steps can be taken to lower your risk:

  • Maintain a healthy diet and exercise regularly.

  • Manage blood pressure, cholesterol, and diabetes.

  • Avoid smoking and limit alcohol use.

  • Get regular heart screenings if you have risk factors or a family history.

  • Be alert to symptoms like chest pain, palpitations, or shortness of breath.

In some cases, doctors may recommend implantable devices or medications to control arrhythmias or support weak heart muscles.

When to seek emergency help

If you or someone around you experiences the following signs, seek emergency help immediately:

  • Sudden collapse or loss of consciousness

  • No pulse or breathing

  • Chest pain or discomfort

  • Sudden shortness of breath

  • Rapid or irregular heartbeat

Immediate CPR and defibrillation within the first few minutes greatly improve survival rates.

Conclusion

Cardiac arrest is a medical emergency that can strike without warning. It results from a variety of causes — from electrical and structural heart problems to external factors like trauma or substance use.

Recognizing the underlying causes is vital for both prevention and timely treatment. Through lifestyle changes, risk factor management, and awareness, we can reduce the likelihood of this silent killer and improve survival outcomes.