Cardiac arrest is a sudden and often fatal medical emergency in which the heart abruptly stops pumping blood effectively, leading to the immediate cessation of circulation to the brain and other vital organs. Without rapid intervention, cardiac arrest results in loss of consciousness within seconds and death within minutes.

Cardiac arrest is distinct from a heart attack, although the two conditions are related. A heart attack involves blockage of blood flow to heart muscle, while cardiac arrest involves failure of the heart’s electrical system, causing the heart to stop beating effectively.

The condition is a major cause of mortality worldwide and requires immediate emergency treatment, including cardiopulmonary resuscitation (CPR) and defibrillation.

Physiological Mechanism 🧬

The heart normally beats through coordinated electrical signals that originate in specialized cardiac tissue.

The electrical impulse typically begins in the Sinoatrial node, located in the right atrium. This natural pacemaker generates rhythmic impulses that propagate through the heart’s conduction system.

The sequence involves:

electrical impulse from the sinoatrial node
transmission through the atria
delay at the Atrioventricular node
conduction through the Bundle of His and Purkinje fibers
coordinated contraction of the ventricles

During cardiac arrest, this electrical coordination fails, preventing the heart from pumping blood.

Types of Cardiac Arrest Rhythms ⚡

Cardiac arrest usually results from life-threatening cardiac arrhythmias, abnormal heart rhythms that disrupt circulation.

Ventricular Fibrillation

Ventricular fibrillation is the most common cause of sudden cardiac arrest.

In this condition:

electrical activity becomes chaotic
the ventricles quiver instead of contracting
blood circulation stops

This rhythm requires defibrillation, an electric shock that resets the heart’s rhythm.

Ventricular Tachycardia

Ventricular tachycardia involves an extremely rapid heartbeat originating in the ventricles.

If sustained, it may progress to ventricular fibrillation.

Asystole

Asystole is often called “flatline.”

In this state:

there is no measurable electrical activity
the heart does not contract

Asystole has a very poor survival rate.

Pulseless Electrical Activity

Pulseless electrical activity occurs when electrical signals are present but the heart fails to produce an effective contraction.

Causes ⚠️

Cardiac arrest can result from many underlying medical conditions.

Cardiovascular Causes

The most common causes involve heart disease, including:

Coronary artery disease
Myocardial infarction (heart attack)
cardiomyopathy
congenital heart defects

Damage to heart muscle can destabilize the heart’s electrical system.

Non-Cardiac Causes

Other causes include:

severe trauma
respiratory failure
drug overdose
electrolyte imbalances
severe blood loss

These conditions can disrupt the heart’s electrical and metabolic stability.

Symptoms and Warning Signs 🚨

Cardiac arrest typically occurs suddenly and without warning, but some individuals experience preceding symptoms.

Possible warning signs include:

chest discomfort
shortness of breath
dizziness
palpitations

When cardiac arrest occurs, the person rapidly develops:

collapse
loss of consciousness
absence of breathing or abnormal gasping
absence of pulse

Emergency Treatment 🚑

Immediate treatment is essential to restore circulation.

Cardiopulmonary Resuscitation (CPR)

Cardiopulmonary resuscitation involves manual chest compressions that artificially circulate blood.

CPR:

maintains blood flow to the brain
buys time until defibrillation or advanced care is available

Defibrillation

Defibrillator devices deliver a controlled electric shock to the heart.

This shock can terminate dangerous arrhythmias such as ventricular fibrillation and allow normal rhythm to resume.

Automated external defibrillators (AEDs) are widely deployed in public spaces.

Advanced Medical Care

Hospital treatment may include:

airway management
intravenous medications
cardiac catheterization
targeted temperature management to protect the brain

Survival and Prognosis 📊

Survival depends strongly on speed of treatment.

Key factors include:

immediate recognition
rapid CPR
early defibrillation
advanced medical care

Without treatment, brain injury begins within about 4–6 minutes due to lack of oxygen.

Survival rates improve dramatically when bystanders initiate CPR before emergency responders arrive.

Prevention 🧠

Preventive measures focus on reducing cardiovascular risk factors.

Strategies include:

controlling high blood pressure
treating coronary artery disease
avoiding smoking
maintaining healthy weight
managing diabetes

High-risk patients may receive implantable cardioverter-defibrillators (ICDs), devices that automatically detect and correct dangerous heart rhythms.

Public Health Importance 🌍

Cardiac arrest is a leading cause of death worldwide. In the United States alone, hundreds of thousands of cases occur annually outside hospitals.

Efforts to improve survival emphasize:

public CPR training
widespread availability of AEDs
rapid emergency response systems

These measures collectively form the “chain of survival,” a concept used in emergency medicine to maximize survival outcomes.