4.4 PEA, Asystole, and Reversible Causes

4.4 PEA, Asystole, and Reversible Causes

Pulseless electrical activity (PEA) and asystole are the nonshockable arrest rhythms. There is no shock to give, so the algorithm rests on three pillars: high-quality CPR, early epinephrine, and an aggressive search for reversible causes. Outcomes in these rhythms are worse than in VF/pVT precisely because survival usually depends on finding and reversing an underlying problem rather than delivering a single decisive shock.

The nonshockable pathway

1. Confirm the rhythm. PEA is any organized electrical activity without a pulse; asystole is a true flat line — confirm by checking lead connections and monitor gain, and look in more than one lead before calling it.
2. Give epinephrine 1 mg IV/IO as soon as possible, then repeat every 3-5 minutes. Early epinephrine in nonshockable arrest is associated with better return of spontaneous circulation.
3. Continue CPR in 2-minute cycles, swapping compressors to prevent fatigue and keeping interruptions minimal.
4. Work the H's and T's continuously, directing treatment at the most likely cause based on the SAMPLE history and bedside findings.
5. Rhythm check every 2 minutes. If the rhythm becomes shockable, move to the VF/pVT pathway; if it organizes with a pulse, begin post-arrest care.

Unlike VF/pVT, epinephrine is given immediately rather than waiting for a second shock, because there is no shock step ahead of it.

The H's and T's — full list

These are the reversible causes the AHA teaches for every pulseless arrest, especially PEA and asystole.

A practical mental tool: hyperkalemia (dialysis), hypoxia (airway), and hypovolemia (bleeding) are among the most common and most treatable, so they deserve early attention.

How this is tested and common traps

PEA/asystole questions reward two behaviors: never shocking and acting on the most likely reversible cause. Stems load the history with a clue — a dialysis patient (hyperkalemia), a trauma patient (hypovolemia or tension pneumothorax), an overdose (toxins), or a long-bone fracture cast in a hypotensive patient (PE). The right answer usually pairs continued CPR/epinephrine with the targeted treatment for that cause.

Common traps:

• Shocking PEA because the organized complexes look like a perfusing rhythm.
• Calling asystole without confirming leads/gain — a disconnected lead mimics a flat line.
• Reciting the H's and T's but not treating the obvious one (e.g., not giving calcium/insulin to a dialysis patient with peaked T-wave history).
• Defibrillating asystole "just in case" — this is never indicated and interrupts CPR.
• Delaying epinephrine in nonshockable arrest; here it should be given as soon as possible.

The takeaway: in nonshockable arrest, the defibrillator stays idle, the compressions stay excellent, epinephrine starts early, and the team treats the cause it can actually fix.

Narrow-complex vs wide-complex PEA

A useful clinical refinement is to read the QRS width of a PEA rhythm as a clue to its cause, which narrows the H's and T's search:

• Narrow-complex PEA (QRS < 0.12 s) more often reflects a mechanical/obstructive problem — hypovolemia, cardiac tamponade, tension pneumothorax, or pulmonary embolism. These respond to fluids, decompression, drainage, or thrombolysis.
• Wide-complex PEA (QRS ≥ 0.12 s) more often reflects a metabolic or toxic problem — severe hyperkalemia, sodium-channel-blocker toxicity (e.g., tricyclics), or profound acidosis. These respond to calcium, sodium bicarbonate, and cause-specific antidotes.

This is not a rigid rule, but it helps a team prioritize which H or T to chase first while CPR and epinephrine continue.

Termination of resuscitation

Nonshockable rhythms also raise the question of when to stop. There is no single rule, but the AHA describes factors that support termination after a reasonable resuscitation effort: an unwitnessed arrest, no bystander CPR, no ROSC before transport, no shock delivered, and — in an intubated patient receiving high-quality CPR — a persistently low ETCO2 (under 10 mmHg after about 20 minutes). None of these alone is decisive; they are weighed together with the clinical context, the suspected cause, and whether any reversible H or T remains untreated.

, hypothermia, where 'no one is dead until warm and dead', or a treatable toxin) argues for prolonged effort.

Common confirmation discipline

Before calling asystole, run the quick checklist: leads connected, gain/amplitude turned up, monitor on the correct lead, and the rhythm confirmed in two leads. A loose lead or low gain can make fine VF or even an organized rhythm look flat — and that mistake changes the entire treatment branch.