What does cardiac arrest mean, and is it defined by a specific cardiac rhythm?

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Last updated: October 18, 2026 • View editorial policy

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What Cardiac Arrest Means

Cardiac arrest is defined as the cessation of cardiac mechanical activity with absence of circulation—it is NOT a specific rhythm but rather a clinical state characterized by the absence of a pulse, regardless of the underlying electrical activity. 1

The Clinical Definition

Cardiac arrest occurs when organized cardiac contractility ceases and circulation stops. The critical diagnostic feature is pulselessness—not the presence of any particular rhythm on a monitor 2. According to the 2020 AHA guidelines, cardiac arrest is identified clinically when a person is:

  • Not breathing or only gasping, AND
  • No pulse is definitely felt within 10 seconds 3

The Four Arrest Rhythms

While cardiac arrest itself is not a specific rhythm, it manifests through four distinct electrical patterns that can be documented during the arrest 3:

Shockable Rhythms (Better Prognosis)

  • Ventricular Fibrillation (VF) - 17% of in-hospital arrests
  • Pulseless Ventricular Tachycardia (pVT) - 7% of in-hospital arrests
  • Combined survival to discharge: 37% for both rhythms 4

Non-Shockable Rhythms (Worse Prognosis)

  • Pulseless Electrical Activity (PEA) - 37% of in-hospital arrests
    • Organized electrical activity on monitor but no mechanical contraction/pulse
    • Survival to discharge: 12% 4
  • Asystole - 39% of in-hospital arrests
    • Flatline; no electrical activity
    • Survival to discharge: 11% 4

Key Clinical Distinctions

The rhythm determines treatment approach but not the diagnosis. The 2020 AHA Adult Cardiac Arrest Algorithm branches based on whether the rhythm is shockable (VF/pVT requiring immediate defibrillation) or non-shockable (PEA/asystole requiring CPR and identification of reversible causes) 3.

Common Pitfall to Avoid

Do not wait to check a rhythm before starting CPR. If someone is unresponsive, not breathing normally, and pulseless, begin CPR immediately and check the rhythm only when a defibrillator/monitor arrives 3. The absence of a pulse defines cardiac arrest clinically—the rhythm check comes second to guide specific interventions.

Important Prognostic Note

Survival is substantially more likely with shockable rhythms (VF/pVT) compared to non-shockable rhythms (adjusted OR 1.68), emphasizing why early defibrillation is critical 4. However, approximately 26% of patients with initial PEA or asystole will develop subsequent VF/pVT during resuscitation, though these patients have worse outcomes than those with initial shockable rhythms 4.

References

1
Research

Cardiac arrest and disorders of consciousness.

Handbook of clinical neurology, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.