A junctional rhythm occurs when the electrical activation of the heart originates near or within the AV node instead of from the SA node. Since the normal ventricular conduction system (His-Purkinje) is used, the QRS complex is frequently narrow. A junctional rhythm is normally slow (< 60 beats per minute) and when faster is referred to as an accelerated junctional rhythm.
Since the electrical activation originates at or near the AV node, the P wave frequently is not seen. It can be buried within the QRS complex, slightly before the QRS complex or slightly after the QRS complex. The morphology of the P wave will not be similar to the sinus P wave (which is normally upright in lead II and biphasic in lead V1). Frequently, the P wave is inverted in lead II if it can be seen at all. A pacemaker may be needed to relieve symptoms when no reversible cause is found such as AV blocking medications or electrolyte disturbances.
The below strip shows a junctional rhythm with retrograde P waves seen just before the QRS complex. The second rhythm strip shows retrograde P waves just after the QRS complex.