Cardiac Arrest

Cardiac arrest is the sudden cessation of effective cardiac mechanical activity, recognised clinically by unresponsiveness, absence of normal breathing, and no detectable pulse. Without immediate intervention it leads within minutes to loss of consciousness and, if uncorrected, to death; it is the central emergency that resuscitation is designed to reverse.

Definition

Cardiac arrest is the abrupt loss of effective cardiac function, confirmed by unresponsiveness, absent or abnormal (agonal) breathing, and no palpable central pulse, resulting in cessation of systemic circulation.

Scope

This topic defines cardiac arrest as a clinical entity, distinguishes its main rhythm presentations and the out-of-hospital and in-hospital settings in which it occurs, and outlines how it is recognised and categorised. It is a reference description of the condition and its evidence base, not a diagnostic protocol or treatment plan.

Key concepts

• Unresponsiveness and absent breathing
• Shockable rhythms (ventricular fibrillation, pulseless ventricular tachycardia)
• Non-shockable rhythms (asystole, pulseless electrical activity)
• Out-of-hospital versus in-hospital cardiac arrest
• Reversible causes
• Return of spontaneous circulation
• Sudden cardiac death

Mechanisms

Cardiac arrest occurs when the heart stops generating effective output, whether from a primarily electrical disturbance such as ventricular fibrillation, from pulseless electrical activity in which organised electrical activity fails to produce a pulse, or from asystole. The underlying triggers range from ischaemic heart disease and primary arrhythmia to hypoxia, hypovolaemia, metabolic derangements, tension pneumothorax, tamponade, toxins, and thrombosis — the reversible causes that resuscitation teams systematically consider. Once circulation stops, cerebral and myocardial perfusion ceases and irreversible injury accrues rapidly, which is why time to effective CPR and, for shockable rhythms, defibrillation are decisive.

Clinical relevance

Recognising cardiac arrest promptly is the trigger for the entire chain of survival, and how it is classified by rhythm and setting shapes the evidence used to study outcomes. This entry describes the condition for educational reference; it is not a diagnostic checklist and does not provide individualised treatment or dosing guidance.

Epidemiology

Cardiac arrest occurs both outside hospital, commonly in the community, and within hospitals, and is a leading contributor to mortality. Survival is strongly influenced by the initial rhythm, the setting, the speed of bystander response, and time to defibrillation, as summarised in international guideline syntheses.

History

Cardiac arrest became a treatable rather than uniformly fatal event with the mid-twentieth-century development of closed-chest compression, external defibrillation, and rescue ventilation, demonstrated in part by Kouwenhoven, Jude, and Knickerbocker in 1960. Subsequent registries and consensus guidelines refined how arrests are recognised, categorised by rhythm and setting, and reported, enabling systematic study of survival.

Key figures

• William Kouwenhoven
• Robert Merchant
• Ashish Panchal
• Jasmeet Soar

Seminal works

• kouwenhoven-1960
• merchant-2020
• panchal-2020

Frequently asked questions

How is cardiac arrest different from a heart attack?

A heart attack (myocardial infarction) is a circulation problem in which blood flow to part of the heart muscle is blocked; cardiac arrest is the sudden loss of all effective heart function. A heart attack can cause cardiac arrest, but they are not the same event.

What does it mean that a rhythm is shockable?

A shockable rhythm — ventricular fibrillation or pulseless ventricular tachycardia — is one that may be terminated by defibrillation, in contrast to asystole and pulseless electrical activity, which are not treated with shocks.