4.2 Shockable vs Nonshockable Rhythms
Key Takeaways
- VF and pulseless VT are shockable cardiac arrest rhythms.
- PEA and asystole are nonshockable cardiac arrest rhythms.
- Pulse status matters; organized electrical activity without a pulse is PEA.
- A rhythm check should be short, organized, and immediately followed by the next action.
4.2 Shockable vs Nonshockable Rhythms
Cardiac arrest algorithms split first by rhythm class. Correctly identifying shockable versus nonshockable rhythms prevents two dangerous errors: shocking PEA/asystole and delaying defibrillation for VF/pVT.
Current official baseline
The adult advanced life support guidance covers cardiac arrest rhythms, defibrillation, airway decisions, drugs, peri-arrest tachycardia and bradycardia, and termination decisions. Use the official AHA 2025 Adult Advanced Life Support Guidelines page when your course materials or training-center instructions differ from third-party summaries: AHA 2025 Adult Advanced Life Support Guidelines.
What you need to know
| Decision point | What to do |
|---|---|
| Shockable | VF and pulseless VT require CPR plus rapid defibrillation. Early shock is a survival-critical intervention. |
| Nonshockable | PEA and asystole require CPR, epinephrine, and aggressive search for reversible causes. They are not treated with defibrillation. |
| Pulse check | If the monitor shows organized complexes, confirm whether there is a pulse. No pulse plus organized rhythm equals PEA. |
| Pause control | Prepare the team before a rhythm check so the pause is brief and the next task is ready. |
How this shows up on BLS/ACLS questions
BLS and ACLS items usually test priority. Read the patient state first: age, pulse status, breathing status, rhythm, stability, and number of rescuers. Then choose the action that protects perfusion, oxygenation, defibrillation timing, or the correct algorithm branch. If an answer sounds advanced but delays CPR, shock delivery, ventilation, or an urgent stability intervention, it is usually a distractor.
Scenario anchor
A patient has organized narrow complexes on the monitor but no carotid pulse. The rhythm is not stable SVT; it is PEA, so CPR resumes and epinephrine/reversible causes become priorities.
Common traps
- Shocking asystole.
- Calling pulseless VT stable because the monitor has a regular rhythm.
- Taking a long rhythm strip interpretation break during CPR.
Study action
Write this section as a one-line rule in your own words, then test it with mixed questions from the BLS/ACLS practice bank. Do not review only the matching topic. Mix it with nearby branches so you can tell when the rule applies and when it does not. For example, compare respiratory arrest with a pulse against pulseless arrest, or compare unstable tachycardia against VF/pVT arrest. The exam rewards that discrimination more than memorizing isolated facts.
Pulseless Electrical Activity (PEA) is defined as:
A patient in cardiac arrest has PEA. Bedside ultrasound reveals cardiac tamponade. What is the definitive treatment?