Accelerated Idioventricular Rhythm (AIVR) – ECG

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Appcardio ECG Library · Rhythm Interpretation

ECG - Accelerated Idioventricular Rhythm (AIVR)

Recognize a ventricular rhythm that competes with the sinus pacemaker: identify its rate and wide-complex morphology, look for AV dissociation, capture and fusion beats, and interpret it in the clinical context—especially after myocardial reperfusion.

Wide-complex rhythmUsually self-limitingReperfusion-associated

1. Introduction

Accelerated idioventricular rhythm (AIVR) is a ventricular rhythm consisting of at least three consecutive ventricular beats, generated by an ectopic ventricular or His–Purkinje pacemaker whose rate is faster than the intrinsic ventricular escape rate and close to—or faster than—the prevailing sinus rate.

A commonly used rate range is approximately 50–110/120 beats/min. Published definitions differ at the upper and lower boundaries; therefore, rate alone does not establish the diagnosis. AIVR is usually regular, has a broad QRS morphology, and may show AV dissociation, sinus capture beats, or fusion beats.

Clinical context matters. AIVR is classically observed during the reperfusion phase of acute myocardial infarction, but it can also occur with increased vagal tone, reduced sympathetic drive, drug effects, electrolyte disturbance, cardiomyopathy, myocarditis, congenital heart disease, or after return of spontaneous circulation.

Most transient episodes are well tolerated and terminate spontaneously as sinus rate overtakes the ventricular focus. Recognition is important because AIVR may resemble ventricular tachycardia (VT), yet reflex treatment as VT with antiarrhythmic suppression may be unnecessary or harmful in a typical stable episode.

2. Electrophysiology and Pathophysiology

Competing pacemakers and enhanced automaticity

The leading proposed mechanism is enhanced automaticity in ventricular pacemaker tissue, often within the His–Purkinje system or ventricular myocardium. A faster phase-4 spontaneous depolarization allows the ectopic focus to discharge at an accelerated rate. When this rate approaches or exceeds sinus-node discharge, the ventricular rhythm intermittently or continuously captures ventricular activation.

Increased vagal tone and reduced sympathetic tone may slow sinus discharge and permit a latent ventricular pacemaker to become dominant. Ischemia and reperfusion can alter cellular electrophysiology and promote abnormal automaticity. Triggered activity has also been proposed in selected settings, including acute ischemia and digoxin toxicity; it should not be treated as the universal mechanism.

Why AV dissociation, capture and fusion occur

AV dissociation

Atria and ventricles are activated independently. P waves may march through the rhythm without a fixed relationship to QRS complexes.

Capture beat

A sinus impulse reaches the ventricles when they are excitable and produces a normally conducted, relatively narrow QRS amid the broad ventricular rhythm.

Fusion beat

A sinus impulse and ventricular ectopic impulse activate the ventricles simultaneously, producing a hybrid QRS morphology intermediate between conducted and ectopic beats.

Isorhythmic dissociation

Sinus and ventricular rates are similar. P waves may appear close to QRS complexes by chance, creating a false impression of a fixed atrioventricular relationship.

In isorhythmic AV dissociation, retrograde ventricular activation may render the AV node refractory to an incoming sinus impulse (“interference dissociation”). The apparent alignment of P waves and QRS complexes does not prove that the atria are driving the ventricles.

3. Characteristic ECG Features

Parameter	Typical AIVR finding	Interpretive point
Ventricular rate	Usually around 50–110/120 bpm	Ranges vary among references; there is overlap with slow VT.
Rhythm	Usually regular during the ventricular run	Onset and termination may be gradual; competing sinus activity can alter the sequence.
QRS	Broad, usually ≥120 ms, with ventricular morphology	Configuration depends on the site of origin; compare with baseline ECG if available.
P waves	May be absent, hidden, dissociated, or intermittently visible	Do not assume absence of visible P waves means atrial standstill.
AV relationship	AV dissociation is common; capture and fusion may occur	Capture/fusion strongly support ventricular origin in the right context.
ST–T	Secondary discordant ST–T changes may accompany a wide QRS	In acute coronary syndrome, assess ischemic changes independently and compare serial ECGs.

High-yield morphology clues

Capture beat: a narrow or baseline-like QRS interrupts the broad-complex rhythm.
Fusion beat: a hybrid QRS indicates simultaneous supraventricular and ventricular activation.
AV dissociation: P waves occur at their own rate and may deform QRS or T waves.
Taller-left-rabbit-ear sign: a notched R wave in V1 with the initial R-wave peak taller than the terminal peak is described in the supplied example as supporting ventricular origin. It is a supportive morphology clue, not a stand-alone diagnostic criterion for AIVR.

Original ECG tracing in lead V1 showing a taller initial R-wave peak than the terminal peak, the taller-left-rabbit-ear sign. — **Figure 1.** Taller-left-rabbit-ear morphology in V1, described in the source as supporting ventricular origin of the QRS complexes. Source: *Accelerated Idioventricular Rhythm (AIVR).pdf*, PDF page 5.

4. Systematic ECG Interpretation

Confirm a ventricular run. Identify at least three consecutive broad complexes with a consistent ventricular morphology.
Measure the ventricular rate. A rate around 50–110/120 bpm is compatible with AIVR, but do not classify by rate alone.
Inspect onset and termination. Gradual acceleration/deceleration and competition with sinus rhythm favor AIVR over re-entrant VT, which often starts and stops abruptly.
Search for atrial activity. Inspect long rhythm strips and multiple leads. Determine whether P waves march independently, conduct, or are hidden in QRS/T complexes.
Look for capture and fusion beats. A capture beat or fusion beat is a particularly useful clue to competing supraventricular and ventricular activation.
Compare with the clinical setting. Recent STEMI/PCI or thrombolysis, bradycardia/high vagal tone, medication exposure, and electrolyte abnormalities help establish plausibility.
Assess the patient—not just the tracing. Check blood pressure, perfusion, symptoms, heart failure, ischemia, and evidence of structural disease. Instability requires urgent evaluation regardless of the rhythm label.

5. Diagnostic Criteria and Limitations

AIVR is a pattern diagnosis based on the combination of ventricular activation, rate, and the relationship between competing pacemakers. There is no single rate cutoff that reliably separates every case of AIVR from slow VT.

Finding	Diagnostic weight	Practical limitation
≥3 consecutive ventricular complexes	Essential description of a ventricular run	Also occurs in VT; does not distinguish AIVR by itself.
Broad QRS (often ≥120 ms)	Supports ventricular activation	SVT with aberrancy and paced rhythms can also be broad.
Rate typically about 50–110/120 bpm	Supports accelerated idioventricular rhythm	Rate ranges overlap; references use different boundaries.
AV dissociation	Supports independent ventricular rhythm	Can occur in VT and complete AV block; assess atrial and ventricular rates.
Capture or fusion beats	Strong evidence of competing supraventricular and ventricular activation	May not be present in every recording.
Gradual onset/termination and clinical context	Supportive features	Not invariably documented on a short ECG strip.

Do not use a rigid rate rule. The supplied LITFL reference describes AIVR as typically 50–120 bpm, while other publications use ranges such as 50–110 bpm or define VT thresholds differently. The correct interpretation integrates morphology, AV relationship, onset/termination, prior ECGs, and clinical state.

6. ECG Examples from the Supplied PDF

The following figures are extracted directly from the supplied PDF. Waveforms have not been redrawn or annotated; the original image content and proportions are preserved.

Twelve-lead ECG showing a ventricular rhythm around 60 beats per minute with multiple sinus capture beats. — **Figure 2. Example 1a — AIVR at 60 bpm.** The source describes competing sinus and idioventricular pacemakers with multiple sinus capture beats; the clinical context is a healthy 36-year-old marathon runner with presumed high resting vagal tone. Source: *Accelerated Idioventricular Rhythm (AIVR).pdf*, PDF page 3.

Twelve-lead ECG from the same patient showing accelerated idioventricular rhythm and sinus capture beats. — **Figure 3. Example 1b — AIVR at 60 bpm.** Isorhythmic AV dissociation, frequent sinus capture beats, and a fusion beat are described. Source: *Accelerated Idioventricular Rhythm (AIVR).pdf*, PDF page 4.

Original rhythm strip labelled ventricular beats, capture beat, and fusion beat. — **Figure 4. Capture and fusion beats.** The original source labels ventricular complexes (V), a capture beat (C), and a fusion beat (F). Source: *Accelerated Idioventricular Rhythm (AIVR).pdf*, PDF page 4.

Twelve-lead ECG showing AIVR at approximately 75 beats per minute with AV dissociation. — **Figure 5. Example 2 — AIVR at 75 bpm.** The source describes AV dissociation, including dissociated P waves in the rhythm strip and aVL, with intermittent QRS deformation. It also describes a taller-left-rabbit-ear morphology in V1. Source: *Accelerated Idioventricular Rhythm (AIVR).pdf*, PDF page 5.

Rhythm strip with a dissociated P wave highlighted by a circle in the source image. — **Figure 6. Dissociated P wave.** The P wave is highlighted in the original source image. Source: *Accelerated Idioventricular Rhythm (AIVR).pdf*, PDF page 5.

Twelve-lead ECG showing a broad-complex rhythm at 90 beats per minute after reperfusion from anterior STEMI. — **Figure 7. Example 3 — AIVR at 90 bpm.** The source describes broad complexes at 90 bpm with no visible P waves, occurring after reperfusion from an anterior STEMI. Source: *Accelerated Idioventricular Rhythm (AIVR).pdf*, PDF page 6.

7. Differential Diagnosis

Differential	Potential similarity	Clues favoring the alternative
Slow ventricular tachycardia	Regular broad-complex rhythm; may have AV dissociation, capture, or fusion.	Rate may be faster, onset/termination often abrupt, and clinical context may suggest scar-related or ischemic re-entry. Rate overlap means morphology and context are essential.
Ventricular escape rhythm	Broad ventricular complexes and AV dissociation.	Usually slower (commonly below about 40–50 bpm) and emerges as a rescue rhythm after failure or suppression of higher pacemakers.
SVT with aberrancy	Regular wide-complex rhythm.	Often has a supraventricular activation sequence, with a consistent relationship between P waves and QRS; compare baseline bundle-branch morphology. A capture/fusion beat in a competing ventricular rhythm supports ventricular origin.
Junctional rhythm with aberrancy	May produce a regular rhythm with broad QRS if bundle-branch conduction is abnormal.	Junctional activation may show retrograde or absent P waves, but the QRS morphology and conduction pattern should be assessed against baseline ECG.
Complete AV block with ventricular escape	AV dissociation and broad escape complexes.	Atrial rate is generally faster than the ventricular escape rate; ventricular rate is usually slower than AIVR. Look for persistent independent P waves and the clinical context of conduction disease or infarction.

Safety principle: An undifferentiated wide-complex tachycardia in an unstable patient must be managed urgently according to resuscitation protocols. Do not delay treatment of instability while attempting to prove AIVR.

8. Clinical Significance and Red Flags

Typical transient AIVR

Often brief, self-limited, and hemodynamically tolerated.
Commonly occurs during the peri-infarct/reperfusion period and may be seen after PCI or thrombolysis.
Can occur in otherwise healthy individuals with marked vagal tone, including athletes.

When the rhythm deserves closer attention

Hypotension, syncope/presyncope, altered mental status, shock, ongoing ischemic chest pain, or acute pulmonary edema.
Persistent or recurrent high-burden AIVR, especially with reduced LVEF or symptoms.
Evidence of acute myocardial infarction, myocarditis, cardiomyopathy, digoxin toxicity, or significant electrolyte disturbance.
Very rapid broad-complex rhythm, polymorphic morphology, degeneration, or uncertainty about VT—reassess the diagnosis rather than assuming benign AIVR.

Red flag: Hemodynamic compromise is not “benign because it is AIVR.” Determine whether AV dyssynchrony, underlying ventricular dysfunction, ischemia, or another arrhythmia is responsible and escalate care accordingly.

AIVR occurring after reperfusion is associated with the reperfusion period, but its presence alone should not be used as proof of complete or durable coronary reperfusion. Continue standard assessment of symptoms, ST-segment evolution, hemodynamics, and coronary treatment success.

9. Clinical Evaluation and Management Principles

Initial assessment

Assess airway, breathing, circulation, mental status, blood pressure, perfusion, and symptoms.
Confirm the rhythm with a 12-lead ECG and continuous monitoring; compare prior ECGs and obtain a longer rhythm strip if needed.
In the appropriate setting, evaluate for acute coronary syndrome and reperfusion status. Check electrolytes and review medications/toxins, especially digoxin and sympathomimetic exposure.
Assess ventricular function and structural disease when clinically indicated, for example with echocardiography.

Management approach

Stable, transient AIVR

Usually observation and monitoring are sufficient. Treat the precipitating condition and correct reversible causes. Do not suppress an otherwise tolerated rhythm routinely.

Low-output state or instability

Urgently assess the cause of compromise and manage according to the clinical scenario and resuscitation protocols. Consider whether AV dyssynchrony is materially reducing cardiac output.

Routine antiarrhythmic therapy is generally not indicated for typical, transient AIVR; suppressing the ventricular focus may remove a useful escape mechanism or worsen hemodynamics. Address ischemia/reperfusion, electrolyte abnormalities, hypoxia, and causative drug toxicity. In selected patients with low cardiac output related to AV dyssynchrony, increasing sinus rate and restoring AV synchrony may be considered; atropine has been described as a trial in this setting. Persistent symptomatic or high-burden AIVR warrants specialist evaluation, including assessment for ventricular dysfunction and, in selected cases, electrophysiology consultation.

Do not confuse this conservative approach to stable AIVR with management of sustained VT, VF, or an unstable undifferentiated wide-complex rhythm.

10. Common Interpretation Pitfalls

Calling every broad-complex rhythm VT: examine rate, onset/termination, AV dissociation, capture/fusion, and clinical context.
Using rate as the only discriminator: AIVR and slow VT have overlapping rates.
Missing P waves: atrial activity can be buried in QRS or T waves; inspect multiple leads and longer strips.
Mistaking isorhythmic dissociation for sinus conduction: similar atrial and ventricular rates can create coincidental alignment.
Overcalling reperfusion success: AIVR is associated with reperfusion but is not a stand-alone confirmation of successful PCI or durable patency.
Treating the ECG rather than the patient: routine antiarrhythmic suppression is not appropriate for most stable transient episodes.
Ignoring the substrate: persistent AIVR, symptoms, ventricular dysfunction, or an underlying cardiomyopathy changes the clinical significance.

11. ECG Pearls

Think AIVR when a regular broad-complex ventricular rhythm runs near 50–110/120 bpm and competes with sinus rhythm.
At least three consecutive ventricular complexes define a run; the rate range is supportive, not definitive.
AV dissociation, capture beats, and fusion beats are key clues to ventricular origin.
Gradual onset and termination support an automatic rhythm rather than re-entrant VT.
Post-reperfusion AIVR is usually transient and does not routinely require antiarrhythmic treatment.
Always assess hemodynamic tolerance and the underlying cause before deciding that the rhythm is benign.

Quick ECG knowledge check

Which finding most strongly supports a ventricular rhythm competing with sinus activation?

Fixed 1:1 P-wave to QRS relationship with a narrow QRS A capture beat or fusion beat within a broad-complex run A ventricular rate above 150 bpm in every case

12. Quick Reference Summary

Feature	Take-home point
Definition	At least 3 consecutive ventricular beats from an accelerated ventricular pacemaker.
Rate	Usually approximately 50–110/120 bpm; thresholds vary and overlap with slow VT.
QRS	Broad ventricular morphology, often ≥120 ms.
Atrial activity	May show AV dissociation, capture beats, fusion beats, or hidden P waves.
Classic setting	Reperfusion phase of acute MI; also vagal predominance, drugs/toxins, electrolyte disturbance, or structural disease.
Usual course	Transient, self-limited, and well tolerated.
Management	Usually observe, monitor, and treat the underlying cause; avoid routine antiarrhythmic suppression.
Escalate when	Hemodynamic compromise, syncope, persistent/high-burden rhythm, reduced ventricular function, or diagnostic uncertainty with VT.

13. References

1. Burns E, Buttner R. Accelerated Idioventricular Rhythm (AIVR).Life in the Fast Lane (LITFL) ECG Library. 2020. Supplied source PDF; original online article: LITFL AIVR.

2. Pérez-Riera AR, Barros RB, de Sousa FD, Baranchuk A. Accelerated idioventricular rhythm: history and chronology of the main discoveries.Indian Pacing Electrophysiol J. 2010;10(1):40–48. PubMed.

3. Frampton J, Ortengren AR, Zeitler EP. Arrhythmias After Acute Myocardial Infarction.Yale J Biol Med. 2023;96(1):83–94. doi: 10.59249/LSWK8578.

4. Pérez-Riera AR, Barros RB, de Souza DHK, et al. Accelerated idioventricular rhythm in the adult: an update.J Hum Growth Dev. 2025;35(1). doi: 10.36311/jhgd.v35.17291.

5. Kalarus Z, et al. Cardiac arrhythmias in the emergency settings of acute coronary syndrome and revascularization: an EHRA consensus document.Europace. 2019;21(10):1603–1620. doi: 10.1093/europace/euz163.

6. Reddy V, et al. Idioventricular Rhythm.StatPearls [Internet]. NCBI Bookshelf. Updated review. NCBI Bookshelf.

Educational disclaimer: This content is intended for educational purposes and should not replace clinical judgment, professional medical assessment, local resuscitation protocols, or institutional guidelines. Management must be individualized to the patient's hemodynamic status and underlying condition.