Under normal circumstances, the tissue in the atrioventricular junction does not exhibit automaticity and is known as a latent pacemaker. It can become the dominant pacemaker in the following situations:
- When the sinus node's impulse rate slows down below the intrinsic rate of the latent pacemaker
- When conduction block prevents sinus impulses from reaching the latent pacemaker, leading to automatic depolarization and escape beats
Atrioventricular junctional escape beats are characterized by a normal QRS complex following a pause longer than the normal PP interval, with absent P waves or retrograde P waves appearing before or after the QRS complex. Additionally, sinus P waves not conducted to the ventricles may be observed.
Atrioventricular junctional rhythm is a rhythm formed by continuous AV junctional escape beats. ECG shows normally conducted QRS complexes at a rate of 40 - 60 beats per minute, with possible retrograde P waves or independent, slow atrial activity, leading to atrioventricular dissociation where the ventricular rate exceeds the atrial rate.
Figure 1 Atrioventricular junctional rhythm
The RR interval is 1.24 seconds, with a rate of 48 beats per minute; retrograde P wave appears after the QRS complex with an RP interval of 0.15 seconds.
The occurrence of AV junctional escape beats or rhythm is associated with increased vagal tone, significant sinus bradycardia, or atrioventricular block, serving as a physiological protective mechanism to prevent ventricular standstill. Generally, no treatment is required, but pacing therapy can be used if necessary.