AKA: Junctional Ectopics, Junctional Extrasystoles, Junctional Premature Beats, Junctional Premature Depolarisations
Definition of Premature Junctional Complex (PJC)
- 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 are much less common than PACs or PVCs.
- These arise from the region of the AV node, so the ventricles are usually activated normally.
- 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.
Typical appearance of PJCs:
- Premature QRS complexes without a preceding P wave.
- The QRS morphology is very similar to the sinus complexes.
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Hampton, JR. The ECG In Practice, 6e
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric, 6e
- Wagner, GS. Marriott’s Practical Electrocardiography 12e
- Chan, TC. ECG in Emergency Medicine and Acute Care
- Mattu, A. ECG’s for the Emergency Physician
LITFL Further Reading
- ECG BASICS — Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis –alphabetical diagnostic approach to the ECG
- ECG CLINICAL CASES — ECG’s placed in clinical context with a challenging Q&A approach
- 100 ECG Quiz — Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS — the best of the rest
- LITFL ECG IMAGE Database — Searchable database of LITFL ECG’s
- ECG and Cardiology Eponymous Syndromes — Cheats guide to eponymous emancipation
- ECG Exam Template — a framework for answering ECG exam questions.