Podcast 1018: Occult Ventricular Fibrillation on Echocardiography

Contributor: Aaron Lessen, MD

Educational Pearls:

• Big question in cardiac arrest: is the rhythm shockable?

  • Shockable: ventricular fibrillation (VF) and pulseless ventricular tachycardia

  • Non-shockable: asystole and pulseless electrical activity (PEA)

• Rhythm classification is typically based on ECG, but echocardiography can directly visualize myocardial fibrillation

  • Occult VF: a rhythm that appears non-shockable on ECG but demonstrates VF on echocardiography

• A 2025 multicenter prospective study looked at 811 patients with out-of-hospital cardiac arrest

  • 5.3% had occult VF detected by echocardiography

  • Of the patients with occult VF: 

    • 81.4% had PEA on ECG

    • 18.6% had asystole on ECG

  • Patients with occult VF were less likely to receive defibrillation because their ECG suggested a nonshockable rhythm

• Clinical takeaway: echocardiography during cardiac arrest may reveal a potentially shockable rhythm hiding behind an apparently nonshockable ECG

  • This identifies a subset of cardiac arrest patients who would otherwise be managed as PEA or asystole based on ECG

References

1. Gaspari R, Adhikari S, Gleeson T, Kapoor M, Lindsay R, Noble V, Nomura JT, Weekes A, Theodoro D. Occult Ventricular Fibrillation Visualized by Echocardiogram During Cardiac Arrest: A Retrospective Observational Study From the Real-Time Evaluation and Assessment for Sonography-Outcomes Network (REASON). J Am Coll Emerg Physicians Open. 2025 Jan 13;6(1):100028. doi: 10.1016/j.acepjo.2024.100028. PMID: 40012664; PMCID: PMC11853361.

Summarized by Meg Joyce, MS3 | Edited by Meg Joyce & Ahmed Abdel-Hafiz, NREMT-P

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