This rhythm strip illustrates a junctional escape rhythm. The sinus rhythm has slowed or stopped, and the junctional tissue has taken over as the pacemaker of the heart. The "junction" is loosely defined as the area between the AV node and the Bundle of His. The intrinsic rate of the pacemaking tissue in this area is 40 - 60 beats per minute. This slow rate is usually overridden by the sinus node, and the junction is not allowed to express itself as a pacemaker. Should the sinus node fail or fall below the junctional rate, the junction "escapes" and takes control of the heart. The QRS complex in junctional rhythm will normally be narrow, because the impulse follows the bundle branches down through the ventricles in a normal fashion, resulting in quick and normal ventricular depolarization. If the QRS complex is wide in a junctional rhythm, there is another, separate cause, such as bundle branch block.
If the junctional impulse is able to penetrate the AV node and depolarlize the atria, the P wave will be deflected downward in Leads II, III, and aVF, as the impulse is travelling in a retrograde direction (backward). The P wave could end up slightly before the QRS, during the QRS, or after the QRS. In this strip, the P waves are seen after the QRS complexes.