Accelerated Idioventricular Rhythm (AIVR)
AIVR results when the rate of an ectopic ventricular pacemaker exceeds that of the sinus node. Often associated with increased vagal tone and decreased sympathetic tone.
- Proposed mechanism is enhanced automaticity of ventricular pacemaker, although triggered activity may play a role especially in ischaemia and digoxin toxicity.
- AIVR is classically seen in the reperfusion phase of an acute STEMI, e.g. post thrombolysis.
- Usually a well-tolerated, benign, self-limiting arrhythmia. Also known as Accelerated Ventricular Rhythm
- Regular rhythm.
- Rate 50-110 bpm.
- Three or more ventricular complexes.
- QRS complexes >120ms.
- Fusion and capture beats.
Isorhythmic AV dissociation
This refers to AV dissociation with sinus and ventricular complexes occurring at identical rates. This is in contrast to complete heart block, where the atrial rate is usually faster than the ventricular rate.
Isorhythmic AV dissociation is usually due to functional block at the AV node due to retrograde ventricular impulses. These ventricular impulses depolarise the AV node, leaving it refractory to incoming sinus impulses (= “interference-dissociation”).
Note the rate of AIVR distinguishes it from others rhythms of similar morphology.
- Rates < 50 bpm consistent with a Ventricular Escape Rhythm
- Rates > 110 bpm consistent with Ventricular Tachycardia
Causes of Accelerated Idioventricular Rhythm (AIVR)
There are multiple causes of AIVR including:
- Reperfusion phase of an acute myocardial infarction (= most common cause)
- Beta-sympathomimetics such as isoprenaline or adrenaline
- Drug toxicity, especially digoxin, cocaine and volatile anaesthetics such as desflurane
- Electrolyte abnormalities
- Cardiomyopathy, congenital heart disease, myocarditis
- Return of spontaneous circulation (ROSC) following cardiac arrest
- Athletic heart
- AIVR is a benign rhythm in most settings and does not usually require treatment.
- Usually self limiting and resolves when sinus rate exceeds that of the ventricular foci.
- Administration of anti-arrhythmics may cause precipitous haemodynamic deterioration and should be avoided.
- Treat the underlying cause: e.g. correct electrolytes, restore myocardial perfusion.
- Patients with low-cardiac-output states (e.g. severe biventricular failure) may benefit from restoration of AV synchrony to restore atrial kick – in this case atropine may be trialed in an attempt to increase sinus rate and AV conduction.
- Ventricular rhythm at 60 bpm.
- Multiple sinus capture beats.
Competing sinus and idioventricular pacemakers are present. There is underlying sinus arrhythmia, with sinus capture occurring when the sinus rate exceeds the idioventricular rate.
This patient was a healthy 36-year old marathon runner with presumably very high resting vagal tone causing sinus bradycardia and sinus arrhythmia.
Another ECG from the same patient showing:
- AIVR at 60 bpm.
- Isorhythmic AV dissociation with frequent sinus capture beats.
- A fusion beat.
- Ventricular rhythm at 75 bpm.
- AV dissociation — a dissociated P wave is seen in the rhythm strip, another in lead aVL. Elsewhere, dissociated P waves cause intermittent deformation of the QRS complexes.
- The taller left rabbit ear sign is present — there is a notched R wave in V1 with a taller initial R wave; this is highly specific for a ventricular origin of the QRS complexes.
- Broad complex at 90 bpm.
- No visible P waves.
This dysrhythmia occurred following reperfusion from an anterior STEMI.
- Dr Smith’s ECG Blog – AIVR cases
- Riera ARP, Barros RB, de Sousa FD, Baranchuk A. Accelerated Idioventricular Rhythm: History and Chronology of the Main Discoveries. Indian Pacing and Electrophysiology Journal;2010; 10(1):40-48 [PMC 2803604]
LITFL Further Reading
- ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis – ECG interpretation in clinical context
- ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
- 100 ECG Quiz – Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS – the best of the rest
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
- Wagner GS. Marriott’s Practical Electrocardiography 12e
- Chan TC. ECG in Emergency Medicine and Acute Care
- Rawshani A. Clinical ECG Interpretation
- Mattu A. ECG’s for the Emergency Physician
- Hampton JR. The ECG In Practice, 6e