Cardiac arrest

Cardiac arrest, sometimes called sudden cardiac arrest (SCA), happens when the heart abruptly stops beating or beats in a way that cannot generate a pulse. Without effective pumping, blood cannot circulate properly, reducing flow to the brain and other organs. If the brain lacks oxygen, a person may lose consciousness, and brain cells begin to die within minutes. Potential outcomes include coma or a persistent vegetative state. The condition is typically recognized by the absence of a central pulse and abnormal or absent breathing.

The collapse in circulation often stems from arrhythmias, or irregular heart rhythms. Ventricular fibrillation and ventricular tachycardia are the most commonly recorded types, though because many cardiac arrests occur outside a hospital or without heart monitoring, the exact mechanism in each case is often unclear. Structural heart disease, particularly coronary artery disease, is a frequent underlying condition. Major risk factors include age and cardiovascular disease, along with heart failure, inherited arrhythmias, major blood loss, lack of oxygen, electrolyte disturbances like very low potassium, electrical injury, and intense physical exercise.

Diagnosis is made when no pulse can be found in an unresponsive person. Treatment aims to quickly restore spontaneous circulation through interventions such as CPR, defibrillation, or cardiac pacing. Two CPR protocols exist: basic life support (BLS) and advanced cardiac life support (ACLS). If circulation returns, the event is called sudden cardiac arrest; if the person does not survive, it is termed sudden cardiac death. For those whose pulses are re-established, care may focus on preventing brain injury and preserving neurological function. This can involve airway management and mechanical ventilation, maintaining blood pressure and organ perfusion with fluids and vasopressors, correcting electrolyte imbalances, EKG monitoring, managing reversible causes, and temperature management. Targeted temperature management may improve outcomes. In post-resuscitation care, an implantable cardiac defibrillator might be considered to reduce the chance of recurrence.

According to the 2015 American Heart Association Guidelines, about 535,000 cardiac arrests occur annually in the United States, or roughly 13 per 10,000 people. Of these, 326,000 (61%) happen outside a hospital, and 209,000 (39%) occur inside one. Cardiac arrest becomes more common with age and affects males more often than females. In the U.S., black people are twice as likely to die from cardiac arrest as white people, while Asian and Hispanic people are affected less frequently than white people.

**Signs and symptoms** About half of people experience no warning symptoms before cardiac arrest. When symptoms do occur, they are usually nonspecific, such as new or worsening chest pain, fatigue, blackouts, dizziness, shortness of breath, weakness, or vomiting. If a layperson suspects cardiac arrest due to unconsciousness, abnormal breathing, or no pulse, they should assume the victim is in cardiac arrest, call emergency services (like 911, 999, or 112), and start CPR.

**Risk factors** Major risk factors include age and underlying cardiovascular disease. A prior episode of cardiac arrest raises the likelihood of future episodes. A 2021 meta-analysis found that 15% of out-of-hospital cardiac arrest survivors experienced a second event, most often within the first year, and 35% of those had a third episode. Other significant risk factors include cigarette smoking, high blood pressure, high cholesterol, history of arrhythmia, lack of physical exercise, obesity, diabetes, family history, cardiomyopathy, alcohol use, and possibly caffeine intake. Current smokers with coronary artery disease have a two- to threefold increased risk of sudden death between ages 30 and 59, while former smokers' risk is closer to that of never-smokers. Statistical analysis shows that about 50% of all cardiac arrests occur in the 10% of the population deemed at greatest risk, due to the combined effect of multiple risk factors, where cumulative harm exceeds the sum of each risk individually.

**Causes and mechanisms** Underlying causes can be cardiac or non-cardiac, and the most common ones vary by age. Cardiac causes include coronary artery disease, non-atherosclerotic coronary artery abnormalities, structural heart damage, and inherited arrhythmias. Non-cardiac causes include respiratory arrest, diabetes, medications, and trauma. The most common mechanism is an arrhythmia. Without organized electrical activity, the ventricles contract inconsistently, preventing the heart from generating enough cardiac output to pump blood forward.