Accelerated idioventricular rhythm

ECG: The initial tracing shows sinus rhythm with right bundle branch block; slight slowing of the sinus rate and appearance of a ventricular-based rhythm (widened QRS) with left delay,  with atrioventricular dissociation (atrial sinus activity slower than the ventricular rhythm); ventricular rate of 80 bpm; 3 capture complexes (QRS complexes identical to the sinus complexes) following a P wave (atrioventricular conduction); diagnosis of accelerated idioventricular rhythm;

Comments: This young patient without known heart disease presented an accelerated idiopathic ventricular rhythm (AIVR). She received no treatment, the prognosis in this setting being excellent and the patient asymptomatic. AIVR corresponds to a spontaneous, ectopic ventricular activity, not very rapid (rate less than 120 bpm), most often monomorphic, originating from the bundle of His, the Purkinje network or the undifferentiated ventricular myocardium. The term slow ventricular tachycardia is inappropriate given that the rate is often less than 100 bpm, the limit defining a tachycardia. As in this patient, this type of arrhythmia occurs most often as a result of an increase in vagal tone and a decrease in sympathetic tone leading to a sinus slowing and facilitating the discharge of the ectopic focus. The underlying mechanism corresponds to a calcium-dependent automatism that affects phase 4 of the action potential. AIVR is frequently observed in the context of reperfusion following a coronary syndrome, has been described in certain overdoses of recreational (cocaine) or medicinal (digitalis) drugs, but can also occur, as in this example, in a young patient without heart disease. AIVR is generally a benign and clinically well-tolerated arrhythmia that does not require treatment. The prognosis in young patients without heart disease is excellent. It can, however, be associated with more severe ventricular arrhythmias requiring treatment.

The main electrocardiographic characteristics are therefore more or less the same as those of a “slow” ventricular tachycardia. We find:

• Ventricular rate by definition less than 120 bpm (beyond this level, the term ventricular tachycardia must be used); the rate is usually between 60 and 110 bpm; indeed, the ventricular hyperautomatism in relation to this ectopic focus induces a rhythm slightly greater than the sinus control;
• A broad QRS indicative of the ventricular origin;
• The tachycardia is usually monomorphic;
• The low rate of the “tachycardia” favors the occurrence of capture and fusion complexes;
• Atrial activity is most often dissociated but retrograde conduction is possible;
• The episode most often begins with a slight slowing of the sinus rate or a slight acceleration of the hyperautomatism;
• The episodes most often cease spontaneously with a gradual slowing of the rate of the ectopic focus;

Take-home message: AIVR corresponds to a rhythm of ventricular origin, with a broad QRS and a rate less than 120 bpm, frequently observed in the setting of reperfusion during an acute coronary syndrome.