What is accelerated idioventricular rhythm (AIVR) on an electrocardiogram?

Accelerated Idioventricular Rhythm on ECG

Accelerated idioventricular rhythm (AIVR) is a ventricular rhythm with 3 or more consecutive wide QRS complexes at a rate of 40-120 beats per minute (typically <200 bpm in infants), occurring at approximately the same rate as the patient's sinus rhythm with characteristic alternation between the two rhythms. 1, 2

ECG Characteristics

AIVR displays the following diagnostic features on electrocardiogram:

• Wide QRS complexes (≥0.09 seconds in infants, >0.12 seconds in adults) that differ morphologically from the patient's normal sinus QRS 1
• Ventricular rate between 40-120 bpm (or <200 bpm in neonates), which is faster than the normal ventricular escape rate of 30-40 bpm but slower than ventricular tachycardia 1, 2
• Gradual onset and termination, often with fusion beats at the beginning and end of the rhythm 2, 3
• Long coupling interval at onset, distinguishing it from ventricular tachycardia 2
• Rate approximation with sinus rhythm, with the rhythms tending to alternate as the ventricular rate and sinus rate compete 1, 4
• Possible AV dissociation, retrograde P waves, or no visible P waves during the arrhythmia 1

Clinical Context and Significance

AIVR is most commonly observed in acute myocardial infarction, particularly after successful reperfusion therapy following thrombolysis or primary PCI. 1, 2, 5 The European Society of Cardiology notes that AIVR is more closely related to the extent of infarction than to reperfusion itself 1.

In structurally normal hearts, AIVR is fundamentally benign. The European Society of Cardiology explicitly states that AIVR in otherwise healthy individuals "is a benign arrhythmia and, similar to PVCs in infants, generally disappears without treatment" 6. This rhythm can occur in adults or children without structural heart disease 2, 7, 4.

Key Distinguishing Features from Ventricular Tachycardia

AIVR differs critically from ventricular tachycardia in several ways:

• Slower rate: AIVR is also known as "slow VT" with rates generally <200 bpm in infants 1 and 40-120 bpm in adults 2
• Gradual onset/termination rather than abrupt start/stop 2
• Long coupling interval at onset 2
• Benign prognosis without association with malignant ventricular arrhythmias 2
• Hemodynamically well-tolerated in most cases 2

Common Pitfall to Avoid

Do not misdiagnose AIVR as ventricular tachycardia requiring immediate cardioversion or aggressive antiarrhythmic therapy. Given its morphologic similarities to life-threatening forms of VT, AIVR can be misdiagnosed in emergency settings, leading to unnecessary interventions 7. The gradual onset, slower rate, and hemodynamic stability distinguish AIVR from true VT requiring urgent treatment 2, 7.

When Workup Is Indicated

Despite its generally benign nature, a workup similar to ventricular tachycardia is indicated when AIVR is identified. 1 This includes:

• Careful QT interval measurement during periods of sinus rhythm 1
• 24-hour Holter monitoring to quantify arrhythmia burden 1, 6
• Echocardiography to determine ventricular function and exclude structural abnormalities 1, 6
• Cardiac MRI if any suspicion of subtle structural abnormalities, particularly right ventricular involvement 6

Very frequent ventricular ectopy (>10,000-20,000 beats per day) can cause reversible left ventricular dysfunction termed "PVC-induced cardiomyopathy," even with benign rhythms like AIVR. 1, 6 Do not dismiss symptoms without quantifying arrhythmia burden, as even "benign" rhythms can cause cardiomyopathy if the burden exceeds 10-20% of total beats 6.