Accelerated Idioventricular Rhythm (AIVR)

Accelerated Idioventricular Rhythm (AIVR) Overview

AIVR, also known as Accelerated Ventricular Rhythm, 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.

ECG Features of AIVR
  • Regular rhythm
  • Rate 50-110 bpm
  • Three or more ventricular complexes
  • QRS complexes > 120ms
  • Fusion and capture beats

Pathophysiology
  • 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.

Ventricular Rate

Note the rate of AIVR distinguishes it from others rhythms of similar morphology.


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

Management
  • 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

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”).


ECG Examples
Example 1a
Accelerated Idioventricular Rhythm (AIVR) ECG 1
  • 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.


Example 1b
Accelerated Idioventricular Rhythm (AIVR) ECG 2

Another ECG from the same patient showing:

  • AIVR at 60 bpm
  • Isorhythmic AV dissociation with frequent sinus capture beats
  • A fusion beat

Fusion-capture-AIVR
AIVR showing ventricular complexes (V), capture beat (C), fusion beat (F)

Example 2
Accelerated Idioventricular Rhythm (AIVR) ECG 3
  • 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
AIVR-dissociated-P-wave
AIVR showing dissociated P waves (circled)

left-rabbit-ear-AIVR
Taller left rabbit ear = ventricular origin of QRS complexes

Example 3
Accelerated Idioventricular Rhythm (AIVR) ECG 5
  • Broad complex at 90 bpm
  • No visible P waves

This dysrhythmia occurred following reperfusion from an anterior STEMI.



References

Advanced Reading

Online

Textbooks


LITFL Further Reading

ECG LIBRARY 700

ECG LIBRARY

Electrocardiogram

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

One comment

  1. Hi guys
    Recently came across this to add to your list of causes for AIVR
    Freire, G., Dubrow, I. Accelerated Idioventricular Rhythm in Newborns: A Worrisome But Benign Entity with or without Congenital Heart Disease. Pediatr Cardiol 29, 457–462 (2008). https://doi.org/10.1007/s00246-007-9024-z

    Cheers
    J

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