Diagnostic Considerations
Accelerated idioventricular rhythm (AIVR) is diagnosed based on its characteristic electrocardiography findings. Its main differential diagnosis includes slow ventricular tachycardia, complete heart block, junctional rhythm with aberrancy, supraventricular tachycardia with aberrancy, and slow antidromic atrioventricular reentry tachycardia.
AIVR is a wide QRS ventricular rhythm with rate of 40-120 bpm, often with variability during the episode. However AIVR should not be diagnosed solely by its ventricular rate because of the rate overlap between AIVR and some slow ventricular tachycardia. See the image below.
Accelerated Idioventricular Rhythm. AIVR and sinus rhythm: AIVR starts and terminates gradually, competing with sinus rhythm. A possible ventricular fusion beat (arrow) and isoarrhythmic AV dissociation (arrowheads: sinus P waves) are present. During AIVR, ectopic ventricular rate is just faster than sinus rate. AIVR has a wide QRS morphology different from the QRS morphology in sinus rhythm.
The following characteristics are important for establishing the diagnosis of AIVR:
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AIVR starts gradually as a long-coupled, premature, ventricular beat when the rate of firing in ectopic ventricular focus (with enhanced automaticity) surpasses that of sinus rate. At the onset of AIVR, the rates of AIVR and sinus rhythm are often similar; therefore, it is not uncommon to see ventricular fusion beats at its onset due to partial ventricular capture from both rhythms.
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During AIVR, the rate of AIVR is usually slightly faster than or similar to sinus rate, often resulting in nearly isorhythmic AV dissociation (a misnomer, but reflecting that the ventricular rate is similar to or just faster than atrial rate). Due to isorhythmic AV dissociation, ventricular fusion and sinus ventricular capture may be present. Sometimes 1:1 retrograde atrial capture may occur, especially during long AIVR episodes.
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AIVR often terminates gradually when sinus rate just surpasses that of AIVR due to either sinus rate acceleration or AIVR rate deceleration, sometimes resulting in ventricular fusion beats.
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AIVR can occur in atrial fibrillation (see image below) and other rhythms when the rate of firing in ectopic ventricular focus surpasses that of the underlying dominant ventricular rate.
Accelerated Idioventricular Rhythm. AIVR in atrial fibrillation: AIVR starts and terminates gradually, competing with the ventricular capture beats (arrow) from atrial fibrillation. Ventricular fusion beat (arrowhead) is present. AIVR has a wide QRS morphology different from the QRS morphology of ventricular capture beats.
The characteristic gradual onset and termination of AIVR are helpful in differentiating it from slow ventricular tachycardia, which is associated with sudden onset and termination.
The AV dissociation during AIVR is isorhythmic AV dissociation with ventricular rate similar to or faster than atrial rate. In contrast, in complete heart block, the AV dissociation is not isorhythmic with atrial rate much faster than ventricular rate.
Accelerated Idioventricular Rhythm. Complete heart block with escaped junctional rhythm: The AV dissociation in complete heart block is not isoarrhythmic AV dissociation, because the atrial rate is much faster than the escaped junctional ventricular rate.
Unlike junctional/accelerated junctional rhythm, AIVR has a wide QRS morphology that is different from the narrow QRS morphology in sinus rhythm without aberrancy and the wide QRS morphology with typical bundle branch block patterns.
The ventricular rate that is faster than the atrial rate during AIVR differentiates it from most supraventricular tachycardia with aberrant conduction or antidromic atrioventricular reentry tachycardia.
Other considerations
Misdiagnosis of AIVR as slow ventricular tachycardia or complete heart block may lead to inappropriate therapies with potential complications. Ventricular tachycardia can also be slowed by antiarrhythmic medications. This is often true in patients on chronic amiodarone therapy. A diagnostic hint for this is a morphology similar to one seen at a faster rate at an earlier time.
Occasionally, AIVR may be the patient's only rhythm. In this situation, treating the patients with lidocaine or other antiarrhythmic drugs may lead to cardiac asystole.
Differential Diagnoses
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Accelerated Idioventricular Rhythm. AIVR and sinus rhythm: AIVR starts and terminates gradually, competing with sinus rhythm. A possible ventricular fusion beat (arrow) and isoarrhythmic AV dissociation (arrowheads: sinus P waves) are present. During AIVR, ectopic ventricular rate is just faster than sinus rate. AIVR has a wide QRS morphology different from the QRS morphology in sinus rhythm.
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Accelerated Idioventricular Rhythm. AIVR in atrial fibrillation: AIVR starts and terminates gradually, competing with the ventricular capture beats (arrow) from atrial fibrillation. Ventricular fusion beat (arrowhead) is present. AIVR has a wide QRS morphology different from the QRS morphology of ventricular capture beats.
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Accelerated Idioventricular Rhythm. Complete heart block with escaped junctional rhythm: The AV dissociation in complete heart block is not isoarrhythmic AV dissociation, because the atrial rate is much faster than the escaped junctional ventricular rate.
