AKA: Accelerated Ventricular Rhythm
- 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.
- Usually a well-tolerated, benign, self-limiting arrhythmia.
- Regular rhythm.
- Rate 50-110 bpm.
- Three or more ventricular complexes.
- QRS complexes >120ms.
- Fusion and capture beats.
Isorhythmic AV dissociation = AV dissociation with sinus and ventricular complexes occurring at similar rates; 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 from retrogradely conducted ventricular impulses (“interference-dissociation”), which leaves the AV node refractory to the anterograde sinus impulses.
Note the rate of AIVR distinguishes it from others rhythms of similar morphology.
There are multiple causes of AIVR including:
- Reperfusion phase of an acute myocardial infarction (= most common cause)
- Drug toxicity, especially digoxin, cocaine and volatile anaesthetics such as desflurane
- Electrolyte abnormalities
- Congenital heart disease
- 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 resolved 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 used to increase sinus rate and AV conduction.
Accelerated idioventricular rhythm:
- 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.
Accelerated Idioventricular Rhythm:
- 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.
Accelerated idioventricular rhythm:
- Broad complex at 90 bpm.
- No visible P waves.
This dysrhythmia occurred following reperfusion from an anterior STEMI.
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