Cardiac Arrest

Cardiac arrest occurs when the heart’s electrical system malfunctions, causing it to stop beating effectively. The most common cause is an abnormal heart rhythm (arrhythmia) known as ventricular fibrillation (VF).

Ventricular Fibrillation (VF) – The Leading Cause of Cardiac Arrest

VF is a life-threatening arrhythmia where the ventricles quiver chaotically instead of contracting properly, leading to a sudden loss of cardiac output. Without immediate defibrillation, VF rapidly leads to cardiac arrest and death.

Common Causes of VF

1. Coronary Artery Disease (CAD) and Heart Attack (Myocardial Infarction)

• Most common cause of VF (responsible for up to 80% of cases).
• Blocked coronary arteries reduce oxygen supply to the heart, leading to electrical instability and VF.
• Scar tissue from previous heart attacks can also trigger VF.

2. Cardiomyopathy (Heart Muscle Disease)

• Dilated Cardiomyopathy (DCM): The heart becomes enlarged and weakened, disrupting electrical conduction.
• Hypertrophic Cardiomyopathy (HCM): Thickened heart walls can cause arrhythmias and sudden cardiac arrest.
• Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): A genetic condition where heart muscle is replaced with fatty and fibrous tissue, increasing VF risk.

3. Electrical Abnormalities and Genetic Arrhythmia Syndromes

• Long QT Syndrome (LQTS): Affects repolarization, increasing the risk of sudden VF.
• Brugada Syndrome: Affects sodium channels, predisposing individuals to VF.
• Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT): Triggered by exercise or emotional stress, leading to VF.

4. Electrolyte Imbalances

• Low potassium (hypokalemia) or high potassium (hyperkalemia) can disrupt the heart’s electrical function.
• Low calcium (hypocalcemia) or magnesium (hypomagnesemia) can contribute to VF, particularly in critically ill patients.

5. Drug-Induced VF and Toxicity

• Cocaine, amphetamines, and certain antiarrhythmic drugs can provoke VF.
• Opioid overdose and sedative toxicity can depress heart function and increase VF risk.

6. Structural Heart Disease and Congenital Abnormalities

• Congenital heart defects can lead to arrhythmias that trigger VF.
• Wolff-Parkinson-White Syndrome (WPW) can cause rapid electrical conduction, leading to VF in some cases.

7. External Triggers and Trauma

• Commotio Cordis: A blunt force to the chest (e.g., in sports) at a critical moment in the cardiac cycle can cause VF.
• Electrocution: Can directly disrupt the heart’s electrical system, leading to VF.

8. Pulmonary Embolism (PE) and Hypoxia

• Large pulmonary embolism can block circulation to the lungs and heart, triggering VF.
• Severe hypoxia (from drowning, suffocation, or respiratory failure) can lead to ventricular arrhythmias and cardiac arrest.

In Advanced Life Support (ALS), reversible causes of cardiac arrest are categorized into 4 Hs and 4 Ts. Identifying and treating these improves survival outcomes.

The 4 H’s

1. Hypoxia – Oxygen deprivation leading to cardiac arrest.
2. Hypovolemia – Severe blood/fluid loss causing circulatory failure.
3. Hypo-/Hyperkalemia and Electrolyte Imbalances – Can lead to fatal arrhythmias.
4. Hypothermia – Severe cold exposure affecting heart function.

The 4 T’s

1. Tension Pneumothorax – A collapsed lung impairing circulation.
2. Tamponade (Cardiac Tamponade) – Fluid buildup in the pericardium, restricting the heart.
3. Toxins (Drug Overdose, Poisoning) – Opioids, stimulants, and other drugs can trigger cardiac arrest.
4. Thrombosis (Pulmonary or Coronary) – Blood clots leading to heart attack or PE.

• Sudden loss of consciousness (unresponsiveness)
• No detectable pulse or breathing
• Sudden collapse
• Gasping or abnormal breathing (agonal breathing)

Immediate emergency action is required. If you witness a cardiac arrest, call 999 and begin CPR immediately.

1. Cardiopulmonary Resuscitation (CPR)

• Keeps oxygenated blood flowing to vital organs.
• Bystander CPR can more than double survival rates.

2. Defibrillation

• Automated External Defibrillators (AEDs) deliver an electric shock to restore rhythm.
• Early defibrillation (within 3-5 minutes) significantly increases survival rates.

3. Post-Resuscitation Care

• Advanced Cardiac Life Support (ACLS) in hospitals focuses on stabilizing the patient.
• Targeted temperature management may be used to prevent brain injury.

4. Implantable Devices for High-Risk Patients

• Implantable Cardioverter Defibrillator (ICD): Detects and shocks the heart if VF occurs.
• Pacemaker: Used for patients with slow heart rhythms (bradycardia).

Cardiac Arrest vs. Heart Attack – What’s the Difference?

A cardiac arrest heart attack is caused by an electrical malfunction which is caused by a blockage in blood flow to the heart.

The heart stops beating suddenly as the heart muscle is damaged but continues beating.

Immediate CPR and defibrillation is required and urgent medical attention is needed but not always CPR.

This can occur as a result of a heart attack and increases the risk of sudden cardiac arrest

Key Facts

• More than 30,000 out-of-hospital cardiac arrests occur annually in the UK.
• Less than 10% of people survive an out-of-hospital cardiac arrest.
• Effective CPR and early defibrillation can double the chances of survival.