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 are much less common than PACs or PVCs.
- These arise from the region of the AV node, so the ventricles are usually activated normally.
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.
Typical appearance of PJCs:
- Premature QRS complexes without a preceding P wave.
- The QRS morphology is very similar to the sinus complexes.
- Wiesbauer F, Kühn P. ECG Yellow Belt online course: Become an ECG expert. Medmastery
- Wiesbauer F, Kühn P. ECG Blue Belt online course: Learn to diagnose any rhythm problem. Medmastery
- Rawshani A. Clinical ECG Interpretation ECG Waves
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- Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
- Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
- Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
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- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography 1e, 2009
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
- Mattu A, Brady W. ECG’s for the Emergency Physician Part I 1e, 2003 and Part II
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- Smith SW. The ECG in Acute MI. 2002 [PDF]
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