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
Premature Junctional Complex (PJC) 2

Typical appearance of PJCs:

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

Advanced Reading



LITFL Further Reading


Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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