ecgsweep

Asystole

critical
Lead II
25 mm/s10 mm/mV
HR—bpm
RR—
QT—

A flat line with no electrical activity: cardiac standstill, a non-shockable arrest rhythm with the poorest prognosis.

Updated

On the trace

Read the strip, then confirm it before you act.

Try each step, then check it.
  1. Look for any complex.
    Show There are none: no P waves, no QRS, no T waves. Only a flat line with a slow, slight drift.
  2. Rule out a false flat line.
    Show Check the patient, the leads and their connections, and turn up the gain. A disconnected lead looks exactly like this.
  3. Check a second lead.
    Show Fine VF can look flat in one lead; any fibrillatory activity in any lead makes it VF, which is shocked.
  4. Look for P waves.
    Show P waves with no QRS after them is ventricular standstill, sometimes called P-wave asystole: the atria still fire and the ventricles do not.

How to recognise it

FeatureValueNotes
QRSAbsentNo ventricular activity at all.
BaselineFlatSlight drift or artefact only; no organised waves.
P wavesUsually absentIf present without QRS, it is ventricular standstill.
PulseAbsentA flat line in a patient with a pulse is a lead or equipment problem.
ShockableNoDefibrillation does not treat it.

The strip

Thirty seconds of asystole in lead II, drawn by the simulator. Work through the steps above on it, then confirm it before acting.

Mechanism

No part of the heart is generating or conducting a ventricular impulse. It is where untreated VF ends, as the myocardium runs out of energy and the fibrillatory waves shrink to nothing, and it can also be the first rhythm found in profound bradycardia, hypoxia, massive haemorrhage or extreme vagal tone.

Go deeper

The Hs and Ts

Asystole is not shocked, so finding a reversible cause is the main hope of ROSC:

  • Hypoxia, hypovolaemia, hydrogen ion (acidosis), hypo- or hyperkalaemia, hypothermia.
  • Tension pneumothorax, tamponade, toxins, thrombosis (coronary or pulmonary).

Why atropine and pacing are not used

Atropine was removed from routine arrest algorithms because it did not improve outcomes, and pacing does not help true asystole, where there is no myocardial response to capture. Ventricular standstill with P waves is the exception in which pacing may work.

Prognosis

Out-of-hospital asystole has the lowest survival of any arrest rhythm: roughly 10% survive to admission and 0–2% to discharge.

Management

1

CPR now

Start high-quality CPR immediately and minimise interruptions. Check the rhythm every 2 minutes.

2

Adrenaline as soon as feasible

1 mg IV or IO as soon as access is obtained in a non-shockable rhythm, then every 3–5 minutes.

3

Do not shock

Defibrillation does not treat asystole and interrupts CPR. If the rhythm changes to VF, shock then.

4

Find a reversible cause

Work through the Hs and Ts while CPR continues. Without one, prolonged asystole is a point to consider stopping resuscitation.

Differential

Ventricular Fibrillation

Fine VF can look flat in a single lead. Confirm in a second lead and with the gain turned up; VF is shocked, asystole is not.

Idioventricular Rhythm

Occasional wide, slow complexes on an otherwise flat line are an agonal idioventricular rhythm, not asystole; check for a pulse.

References

  1. Asystole (Nursing) — StatPearls, 2024
  2. Guideline 11.5: Medications in Adult Cardiac Arrest — ANZCOR, 2025