Definition of Cardiac Arrest
Cardiac arrest is defined as the cessation of cardiac mechanical activity, as confirmed by the absence of signs of circulation. 1 This clinical syndrome involves the sudden loss of detectable pulse or the cessation of spontaneous breathing.
Clinical Definition and Characteristics
Cardiac arrest is characterized by:
- Absence of signs of circulation
- Unresponsiveness
- Absence of normal breathing or only gasping respirations
- No perceptible pulse
The International Liaison Committee on Resuscitation (ILCOR) has established this consensus definition to standardize reporting and research in resuscitation science. 1
Temporal Aspects
For witnessed events, cardiac arrest typically involves sudden (usually within 1 hour from onset of first symptoms until death) loss of detectable pulse. 1 For unwitnessed events, an alternative definition acknowledges that many cardiac arrests are not witnessed: sudden cardiac death includes death within 1 hour of the onset of symptoms for witnessed events or within 24 hours of being observed alive for unwitnessed events. 1
Distinguishing Cardiac Arrest from Sudden Cardiac Death
It's important to distinguish between these related but distinct terms:
Sudden cardiac arrest (SCA): The sudden cessation of cardiac activity such that the victim becomes unresponsive, with either persisting gasping respirations or absence of any respiratory movements, and no signs of circulation. 1 SCA refers to an event that can potentially be reversed through intervention.
Sudden cardiac death (SCD): Sudden and unexpected death occurring within an hour of the onset of symptoms, or occurring in patients found dead within 24 hours of being asymptomatic and presumably due to a cardiac arrhythmia or hemodynamic catastrophe. 1 SCD refers to the fatal outcome of SCA.
Etiology Classification
An arrest is presumed to be of cardiac etiology unless it is known or likely to have been caused by:
- Trauma
- Submersion
- Drug overdose
- Asphyxia
- Exsanguination
- Or any other non-cardiac cause as determined by rescuers 1
Practical Definition for Surveillance
For inclusion in surveillance systems, a pragmatic definition of out-of-hospital cardiac arrest would be an event in which a person is evaluated by organized Emergency Medical Services personnel and either:
- Receives external defibrillation attempts (by lay responders or emergency personnel) or receives chest compressions by organized EMS personnel, or
- Is pulseless but does not receive defibrillation attempts or CPR from EMS personnel 1
Rhythms in Cardiac Arrest
The initial cardiac rhythm in arrest may be:
- Ventricular fibrillation (VF)
- Pulseless ventricular tachycardia (pVT)
- Pulseless electrical activity (PEA)
- Asystole
In young people experiencing out-of-hospital cardiac arrest, asystole is more common than ventricular arrhythmias, though in primary cardiac arrests, the initial rhythm is often VF. 1
Clinical Importance
Understanding the definition of cardiac arrest is critical for:
- Accurate diagnosis and reporting
- Appropriate emergency response
- Research and quality improvement initiatives
- Development of prevention strategies
- Standardization of care protocols
The clear definition and recognition of cardiac arrest is the foundation for effective resuscitation efforts and improved survival outcomes.