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
- ECG BASICS – Waves, Intervals, Segments and Clinical Interpretation
- ECG CLINICAL CASES – Your favourite ECG’s placed in clinical context with a challenging Q&A approach
- ECG and Cardiology Eponymous Syndromes – Cheats guide to eponymous emancipation
- ECG Reference Sites on the WEB – the best of the rest
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.
About Edward Burns
