Which clinical finding best distinguishes asystole from pulseless electrical activity (PEA) during cardiopulmonary resuscitation?

Explanation

## Distinguishing Asystole from PEA ### Electrocardiographic Findings **Key Point:** The cardinal discriminator between asystole and PEA is the presence or absence of organized electrical activity on the monitor. | Feature | Asystole | PEA | |---------|----------|-----| | **ECG appearance** | Flat line (no electrical activity) | Organized complexes (QRS, P waves, or both) | | **Mechanical activity** | None | None (dissociation between electrical and mechanical) | | **Pulse** | Absent | Absent | | **Prognosis** | Extremely poor | Poor but slightly better than asystole | ### Clinical Significance **High-Yield:** PEA is a state of **electrical-mechanical dissociation**—the heart generates organized electrical signals but produces no mechanical output (no pulse, no perfusion). Asystole shows a completely flat ECG with no electrical activity whatsoever. **Clinical Pearl:** The presence of organized electrical activity in PEA should prompt the rescuer to search for reversible causes (hypovolemia, hypoxia, hypothermia, tension pneumothorax, tamponade, thromboembolism, toxins, or trauma)—the "H's and T's" mnemonic. In asystole, the prognosis is uniformly grim unless a reversible cause (e.g., severe hypothermia, drug overdose) is identified. **Mnemonic:** **ACLS Rhythms** — Shockable (VF, pulseless VT) vs. Non-shockable (Asystole, PEA). Asystole = "straight line," PEA = "organized but no pulse." ### Why This Matters in CPR Both require continuous high-quality CPR and epinephrine, but the **monitor pattern** is the only reliable way to distinguish them in real time. Clinical findings like pupil size and cyanosis are non-specific and appear in both conditions. [cite:AHA ACLS Guidelines 2020]