What is the definition of cardiac arrest?

Definition of Cardiac Arrest

Cardiac arrest is defined as the cessation of cardiac mechanical activity, confirmed by the absence of a detectable pulse, unresponsiveness, and apnea (or agonal respirations). 1

Key Components of the Definition

Cardiac arrest is characterized by three essential clinical findings:

1. Absence of detectable pulse - Complete cessation of effective cardiac mechanical activity
2. Unresponsiveness - Patient is unconscious and does not respond to stimuli
3. Respiratory abnormality - Either complete absence of breathing (apnea) or agonal gasping respirations

This clinical syndrome typically results in almost instantaneous loss of consciousness and collapse due to the sudden cessation of effective blood flow 1.

Associated Cardiac Rhythms

Cardiac arrest may be associated with any of four heart rhythms:

• Ventricular fibrillation (VF) - Rapid, grossly irregular electrical activity with marked variability in waveform, usually >300 bpm 1
• Pulseless ventricular tachycardia (pVT) - Organized ventricular rhythm without detectable pulse 1
• Asystole - Complete absence of electrical activity
• Pulseless electrical activity (PEA) - Previously termed electromechanical dissociation; presence of organized electrical activity without detectable mechanical cardiac function 1

Timing Considerations

While cardiac arrest itself is an immediate event, for classification purposes:

• In witnessed events, sudden cardiac death is defined as death within 1 hour of symptom onset
• In unwitnessed events, sudden cardiac death includes death in persons observed to be alive and well within 24 hours 1

Etiology

In adults, the most common cause of cardiac arrest is primary ischemic heart disease 1. However, cardiac arrest can result from various cardiac and non-cardiac causes:

• Cardiac causes: Myocardial infarction, cardiomyopathies, structural heart disease, primary arrhythmias
• Non-cardiac causes: Trauma, drowning, respiratory failure, asphyxia, electrocution, drug overdose, exsanguination 1

Practical Definition for Surveillance

For practical purposes in surveillance systems, cardiac arrest can be defined as an event in which a person:

1. Receives external defibrillation attempts (by lay responders or emergency personnel) OR
2. Receives chest compressions by organized EMS personnel, OR
3. Is found pulseless but does not receive defibrillation attempts or CPR from EMS personnel 1

Distinction from Related Terms

It's important to distinguish cardiac arrest from related terms:

• Sudden cardiac arrest (SCA): Focuses specifically on the malfunction or cessation of electrical and mechanical activity of the heart resulting in loss of consciousness and collapse 1
• Sudden cardiac death (SCD): The ultimate outcome of cardiac arrest when resuscitation efforts are unsuccessful or not attempted 1

Clinical Implications

Recognition of cardiac arrest requires immediate action following a specific algorithm:

1. Establish unresponsiveness
2. Check for absence of normal breathing
3. Check for absence of pulse (taking no more than 10 seconds)
4. Activate emergency response system
5. Begin high-quality CPR immediately 2

The prompt identification of cardiac arrest and initiation of resuscitation efforts are critical for survival, as the likelihood of successful resuscitation decreases rapidly with time 3.