Junctional Rhythm
Junctional rhythm originates from the AV junction when the SA node fails to pace or its impulses are blocked, producing a narrow complex escape rhythm.
Also known as: AV Junctional Rhythm, Nodal Rhythm
ECG Characteristics
| Heart Rate | 40–60 bpm (junctional escape); 60–100 bpm (accelerated junctional); > 100 bpm (junctional tachycardia) |
| Rhythm | Regular |
| P Wave | Absent, retrograde (inverted in II, III, aVF), or hidden within QRS — P waves may appear before, during, or after the QRS |
| PR Interval | Short (< 0.12s) if retrograde P wave precedes QRS |
| QRS Duration | < 0.12 seconds (narrow, since it uses the His-Purkinje system) |
Mechanism
The AV junction takes over as the dominant pacemaker, either as an escape mechanism when SA node function fails or as an accelerated automatic rhythm. The impulse conducts both anterograde (to ventricles) and retrograde (to atria) from the AV junction.
Key Features on ECG
- Regular, narrow complex rhythm at 40–60 bpm
- Absent P waves, or retrograde P waves (inverted in inferior leads)
- P waves may appear before, during, or after the QRS
- Narrow QRS (conduction proceeds normally through His-Purkinje system)
Causes
- Sick sinus syndrome (SA node failure)
- Digitalis toxicity (accelerated junctional rhythm)
- Post-cardiac surgery
- Inferior MI (AV nodal ischemia)
- Increased vagal tone
- Beta-blocker or calcium channel blocker excess
Clinical Significance
Junctional escape rhythm is a protective mechanism when the SA node fails — suppressing it would be dangerous. Accelerated junctional rhythm (60–100 bpm) is often associated with digitalis toxicity or post-operative state. Junctional tachycardia (> 100 bpm) may indicate serious underlying pathology.
Frequently Asked Questions
Why do P waves appear inverted in junctional rhythm?
In junctional rhythm, atrial depolarization occurs in a retrograde direction — from the AV junction upward toward the atria, which is the opposite of normal SA node activation. This produces P waves that are inverted (negative) in the inferior leads (II, III, aVF) and upright in aVR.
What determines whether P waves are before, during, or after the QRS?
The relative speed of retrograde atrial conduction versus anterograde ventricular conduction determines P wave position. If retrograde conduction is faster, P waves appear before the QRS. If both are equal, the P wave is hidden within the QRS. If atrial activation is slower, the P wave follows the QRS.
Should you treat junctional escape rhythm?
Never suppress a junctional escape rhythm — it is a safety mechanism preventing asystole when the SA node fails. Treatment should address the underlying cause of SA node failure. If the junctional rate is too slow and causing symptoms, atropine or temporary pacing may be needed until the underlying issue is resolved.
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