Premature Junctional Complex (PJC)

Premature Junctional Complex (PJC)

A premature beat arising from an ectopic focus within the Atrioventricular (AV) junction.

AKA: Junctional Ectopics, Junctional Extrasystoles, Junctional Premature Beats, Junctional Premature Depolarisations

Origin of Ectopic Beats

• Groups of pacemaker cells throughout the conducting system are capable of spontaneous depolarisation.
• The rate of depolarisation decreases from top to bottom: fastest at the sinoatrial node; slowest within the ventricles.
• Ectopic impulses from subsidiary pacemakers are normally suppressed by more rapid impulses from above.
• However, if an ectopic focus depolarises early enough — before the arrival of the next sinus impulse — it may “capture” the ventricles, producing a premature contraction.
• Premature contractions (“ectopics”) are classified by their origin — atrial (PACs), junctional (PJCs) or ventricular (PVCs).

Junctional Ectopics

• Junctional ectopics are much less common than PACs or PVCs.
• These arise from the region of the AV node, so the ventricles are usually activated normally.

Electrocardiographic Features

PJCs have the following features:

• Narrow QRS complex, either (1) without a preceding P wave or (2) with a retrograde P wave which may appear before, during, or after the QRS complex. If before, there is a short PR interval of < 120 ms and the  “retrograde” P waves are usually inverted in leads II, III and aVF.
• Occurs sooner than would be expected for the next sinus impulse.
• Followed by a compensatory pause.
• PJCs that arrive early in the cycle may be conducted aberrantly, most commonly with a RBBB morphology.

ECG Example

Typical appearance of PJCs:

• Premature QRS complexes without a preceding P wave.
• The QRS morphology is very similar to the sinus complexes.

Related Topics

• Premature atrial complex (PAC)
• Premature ventricular complex (PVC)

Advanced Reading

Online

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
• Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
• Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.

Textbooks

• Zimmerman FH. ECG Core Curriculum. 2023
• Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Hampton J, Adlam D. The ECG Made Practical 7e, 2019
• Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest