Premature Junctional Complex (PJC)

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

Definition

  • A premature beat arising from an ectopic focus within the AV junction.

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) preceded by an abnormal P wave with a PR interval of < 120 ms (these “retrograde” P wave 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.

Retrograde P wave

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

Further Reading

Author Credits

References

  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.
  • Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice (6th edition), Saunders 2008.
  • Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.
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