What causes cardiac arrest

Definition and Mechanism

Cardiac arrest is a sudden, life-threatening loss of heart function where the heart either stops beating entirely (asystole) or beats ineffectively (pulseless rhythms). This differs from a heart attack, which involves blocked blood flow to heart tissue. During cardiac arrest, the brain and vital organs receive no oxygen-carrying blood, causing unconsciousness and potential death within minutes if untreated.

Common Causes

The most common cause of cardiac arrest is sudden coronary syndrome, typically a heart attack triggered by coronary artery blockage. Other significant causes include:

• Arrhythmias: Abnormal electrical rhythms including ventricular fibrillation, pulseless ventricular tachycardia, and asystole
• Respiratory failure: Severe breathing problems depriving the heart of oxygen
• Trauma: Severe injuries disrupting heart function or causing massive bleeding
• Electrolyte imbalances: Dangerously abnormal potassium, magnesium, or calcium levels
• Drug overdose: Toxic levels of medications or illicit substances

Cardiac Arrest Rhythms

The electrical rhythm during cardiac arrest significantly affects survival chances. Ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT) are "shockable" rhythms responding to defibrillation, with survival rates around 30-40% when treated immediately. Asystole and pulseless electrical activity (PEA) are "non-shockable" rhythms with poorer outcomes, typically 5-10% survival rates.

Risk Factors

Certain conditions increase cardiac arrest risk significantly. Previous myocardial infarction substantially elevates risk for sudden cardiac death. Other factors include left ventricular dysfunction, severe heart failure, uncontrolled diabetes, hypertension, smoking, and obesity. Age-related cardiac changes also increase vulnerability, particularly after age 50.

Time-Critical Treatment

Survival from cardiac arrest depends critically on rapid intervention. The "chain of survival" includes immediate recognition, early CPR, rapid defibrillation, and advanced life support. Each minute without treatment reduces survival probability by approximately 7-10%. Brain damage risk increases significantly after 4-6 minutes without circulation.

Post-Arrest Outcomes

Survivors of cardiac arrest face potential complications including hypoxic brain injury, anoxic encephalopathy, and reduced cognitive function. Therapeutic hypothermia and targeted temperature management during resuscitation have improved neurological outcomes in recent years.