Idioventricular Rhythm
Idioventricular rhythm is a slow, wide complex rhythm originating from a ventricular escape pacemaker, typically at 20–40 bpm.
Also known as: IVR, Ventricular Escape Rhythm
ECG Characteristics
| Heart Rate | 20–40 bpm (escape); 40–100 bpm (accelerated idioventricular rhythm, AIVR) |
| Rhythm | Regular |
| P Wave | May show AV dissociation or retrograde P waves |
| PR Interval | Not applicable |
| QRS Duration | > 0.12 seconds (wide, bizarre morphology) |
Mechanism
When both the SA node and AV junction fail as pacemakers, ventricular myocytes with intrinsic automaticity (Purkinje fibers) generate escape impulses at their inherent rate of 20–40 bpm. AIVR represents enhanced ventricular automaticity at a faster rate.
Key Features on ECG
- Wide QRS (> 0.12s) at 20–40 bpm
- Regular rhythm
- AV dissociation may be present
- Morphology depends on ventricular origin
- AIVR: same morphology at 40–100 bpm, often follows reperfusion
Causes
- Third-degree AV block (escape rhythm)
- Sick sinus syndrome with junctional failure
- AIVR: myocardial reperfusion (post-thrombolysis or PCI)
- Digitalis toxicity
- Myocardial ischemia
Clinical Significance
Ventricular escape rhythm is a life-sustaining mechanism and must never be suppressed. AIVR (accelerated, 40–100 bpm) is typically benign, self-limiting, and considered a sign of successful reperfusion in the setting of MI treatment. It rarely requires intervention.
Frequently Asked Questions
What is accelerated idioventricular rhythm?
AIVR is a ventricular rhythm at 40–100 bpm — faster than a typical escape rhythm but not fast enough to be ventricular tachycardia. It is most commonly seen as a 'reperfusion arrhythmia' following successful restoration of coronary blood flow and is considered a positive sign. It is usually hemodynamically well-tolerated and self-terminating.
Why should you never suppress a ventricular escape rhythm?
A ventricular escape rhythm is the heart's last-resort pacemaker. If all faster pacemakers (SA node, AV junction) have failed, the ventricular escape rhythm is the only thing maintaining cardiac output. Suppressing it with antiarrhythmics or other drugs would result in asystole and death. Instead, the underlying cause of pacemaker failure should be addressed.
How do you distinguish AIVR from slow VT?
The distinction is primarily rate-based: AIVR is defined as 40–100 bpm while VT is ≥ 100 bpm. AIVR is typically hemodynamically stable, self-limiting, and associated with reperfusion. VT is often associated with hemodynamic compromise and may require treatment. The morphology may be similar, but the clinical context and rate differentiate them.
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