Idioventricular Rhythm
Idioventricular Rhythm
The ventricle's last-resort escape pacemaker at 20–40 bpm, firing when both the SA node and AV junction have failed. It is a protective mechanism: never suppress it.
On the trace
Read the strip in this order.
- Count the rate.
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20–40 bpm, here 35: slow enough that the patient is unlikely to be well. - Look at the complexes.
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Wide (over 120 ms) and identical: the ventricle is pacing itself, cell to cell. - Look for P waves.
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None here, as in sinus arrest. In complete heart block the P waves are there but march at their own rate, unrelated to the QRS. Either way, the ventricle is running alone. - Check the rhythm.
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Regular. One stable escape focus.
How to recognise it
| Feature | Value | Notes |
|---|---|---|
| Rate | 20–40 bpm | The ventricle's own escape rate. |
| Rhythm | Regular | One stable focus. |
| QRS width | > 120 ms | Often over 160 ms when the focus is in ventricular muscle rather than Purkinje fibres. |
| P waves | Absent or dissociated | Absent in sinus arrest; present but unrelated in complete heart block. |
| Haemodynamics | Usually compromised | Hypotension, pallor and confusion are common. |
The strip
Mechanism
Every level of the conduction system can pace the heart, and each is kept quiet by the faster one above it: the sinus node at 60–100 bpm, the AV junction at 40–60, the ventricles at 20–40. Idioventricular rhythm appears when the two above have both failed, or when complete block cuts the ventricles off from them. It is the last backstop before asystole, which is why it must never be suppressed.
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Where it appears
- Complete heart block: the commonest cause. A wide escape suggests the block is below the His bundle, the more serious site and more likely to need permanent pacing. A narrow junctional escape suggests a block higher up.
- Sinus arrest and sick sinus syndrome: long pauses ending in wide escape beats when no junctional escape takes over.
- After cardiac arrest: often one of the first organised rhythms after ROSC, accelerating through AIVR to sinus as the conduction system recovers.
Why not suppress it
Antiarrhythmics such as lidocaine and amiodarone suppress automaticity. When the escape focus is the only pacemaker left, suppressing it produces asystole. Atropine acts on the sinus node and AV node, so it rarely helps an escape rhythm arising below them.
Clinical impact
Management
Do not suppress it
No antiarrhythmics and no cardioversion: the escape focus may be the only reason the heart is beating. Atropine can be tried under the bradycardia algorithm, but it rarely works on a ventricular escape and must not delay pacing.
Pace: transcutaneous now, transvenous next
Apply pads and pace at 60–70 bpm, raising the current until capture is confirmed. An adrenaline or isoprenaline infusion can bridge while pacing is arranged.
Treat the cause
Complete heart block needs urgent transvenous pacing and cardiology review. Consider digoxin, beta-blocker or calcium-channel blocker toxicity, and check potassium, magnesium and thyroid function. After cardiac arrest the rhythm often recovers on its own; support the circulation meanwhile.
Permanent pacing for irreversible causes
Symptomatic complete heart block and irreversible sinus and junctional failure are indications for a permanent pacemaker.
Differential
The same wide complex at 50–110 bpm, and a different situation: usually benign, often a sign of reperfusion, and not paced.
Complete heart block usually has a ventricular escape underneath it. P waves marching independently of the wide QRS make it heart block with an idioventricular escape; both need pacing.
A narrow escape at 40–60 bpm: the junction is still working. A wide escape at 20–40 means it has failed too.
References
- 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy — European Heart Journal, 2021
- 2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death — European Heart Journal, 2022