Premature junctional complexes (PJC’s) are usually due to enhanced automaticity and commonly are associated with retrograde atrial conduction with retrograde P waves. If the AV junctional origin is the low atrium-proximal AV node, these retrograde P’s usually precede the QRS and can be considered the same as PAC’s, although often with a PR interval of less than 0.12 seconds. If the origin is the distal AV node-His bundle, the retrograde P’s may be hidden in the QRS or occur just after the QRS. In both cases, since atrial activation is retrograde, visible P’s will be negative in the inferior leads.
Premature junctional complexes are classified as supraventricular and usually have a narrow QRS similar to the sinus QRS. When arising from lower in the His bundle or when sufficiently premature, aberration can occur with a widened different morphology. Isolated PJC’s are typically benign and thus are similar to PAC’s. The following animation illustrates what we have just described.