Junctional Rhythms

Junctional Escape

A junctional escape rhythm occurs when there is either no supraventricular conduction through the AV node or the conduction through the AV node is slower (ie AV block) than the junctional conduction system (which actually arises from the AV node). Therefore, there is no association with P waves if they are present. The rate is 40-60bpm and the QRS is narrow (commonly 100-120ms). A junctional bradycardia occurs when the HR is <40bpm. The QRS width is still the same as above (differentiating it from a ventricular escape rhythm). These can be interspersed with normally conducted beats if a patient has sinus node dysfunction with intermittent sinus bradycardia.

An accelerated junctional rhythm occurs with a HR 60-100bpm. An accelerated junctional rhythm occurs when the junctional pacemaker sites outpace the sinus node; this can occur because of either sinus node disease or enhanced automaticity of the junctional pacemaker site. The most common cause of this is digoxin toxicity in a patient with atrial fibrillation/atrial flutter, though may also be caused by ischemia, post-cardiac surgery, congenital heart disease, or significant acute illness (ie severe sepsis or hyperkalemia). Retrograde P waves may be present just before the QRS complex, within it, or after it. Retrograde P waves before the QRS complex are too close to the QRS complex to conduct through to it (PR interval too short-<120ms). The only other times the PR interval is that short is when there is conduction through an accessory pathway (ie WPW) or with an ectopic atrial rhythm that originates very low in the atria. However, those patients with an accessory pathway will have a wide QRS complex. Those with an atrial ectopic rhythm should still have the same QRS morphology as the patient normally has (whereas a junctional rhythm should have a slightly altered QRS compared to the patient's baseline QRS).

Retrograde P waves are usually upright in aVR and V1 and inverted in the inferior leads (the opposite of normal/anterograde P waves). They occur as the junctional pacemaker site is very high in the AV node, causing the atria to actually be conducted before the ventricles. Junctional tachycardia is a junctional rhythm with a HR>100bpm.

Examples:

Further Reading:

https://litfl.com/junctional-escape-rhythm-ecg-library/

https://litfl.com/accelerated-junctional-rhythm-ajr/

http://hqmeded-ecg.blogspot.com/search/label/accelerated%20junctional%20rhythm

http://hqmeded-ecg.blogspot.com/search/label/junctional%20escape

http://hqmeded-ecg.blogspot.com/search/label/junctional%20tachycardia