Junctional rhythm recognition on ECG for new nurses and students
What comes to mind when you hear the term “junctional?” Where is the AV junction located? How does this affect the ECG?
If the sinus pacemaker fails, the next in line should take over as the new pacemaker of the heart. After the sinus and atrial mechanisms, the AV junction is the next downstream to pick up responsibilities of pacing the heart.
The AV bundle (bundle of His) permits electrical conduction across the insulation between the atria and ventricles. This communication is regulated by the AV node. The pacemaker cells surrounding the AV junction can initiate regular impulses but at a slightly lower natural rate than their sinus and atrial superiors.
The heart is built this way so that when the pacemaker cells with the fastest intrinsic rate are in action, those below with slower intrinsic rates are suppressed and function primarily to pass along the impulse from above.
When the impulse starts at the AV junction, the upper atria may depolarize in retrograde, meaning in reverse from the natural depolarization pathway. This makes sense since the AV junction is downstream and must feed the impulse back upstream to the upper chambers, traveling away from the positive electrode (utilizing Lead II in this example). The impulse is also conducted normally, down to the ventricles. Therefore, we expect to see a narrow QRS with junctional rhythms.
P waves associated with junctional rhythms have three potential appearances: inverted before the QRS, buried within the QRS, or inverted after the QRS. The appearance will depend on how high or low the impulse is located along the conduction pathway (below).
The sinus node typically outpaces other inferior pacemaker sites within the heart. Junctional origin rates are inherently slower, and ventricular origin rates are even slower than junctional. To properly identify junctional rhythms, we need to have a firm grasp on identifying both P waves as well as heart rates. Use the overview heart rate graphic below together with what we now know regarding P waves in junction rhythms to aid in recognition.
Hope this helps!
-Tyler
*All of the above from a very basic rhythms perspective. Exceptions do exist in the real world.
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Antzelevitch, C., & Burashnikov, A. (2011). Overview of Basic Mechanisms of Cardiac Arrhythmia. Cardiac electrophysiology clinics, 3(1), 23–45. doi: 10.1016/j.ccep.2010.10.012
Zheng, T. (2021). Electrocardiography and cardiac rhythm. In E. M. Perpetua & P. A. Keegan (Eds.), Cardiac nursing: The red reference book for cardiac nurses (pp. 289-359). Wolters Kluwer.
Katz, A. M. (2011). Arrhythmias. In F. DeStefano (Ed.), Physiology of the heart. (pp. 432-487). Lippincott, Williams, & Wilkins.
