Junctional Rhythm Characteristics and Causes

ECG Findings

The American College of Cardiology describes junctional rhythm on ECG as having a QRS rate faster than the resting P-wave or sinus rate, typically <100 beats/min with a narrow QRS complex, and may show AV dissociation or marked irregularity in the junctional rate 1, 2
The American Heart Association, as published in Circulation, notes that P waves may be absent, inverted, or dissociated from the QRS complexes in junctional rhythm 3, 4
The American College of Cardiology states that QRS morphology in junctional rhythm is characterized by narrow QRS complexes (<120 ms) unless conducted with aberrancy 1, 2
The heart rate in junctional escape rhythm typically ranges from 40-60 beats/min, but can be faster (up to <100 beats/min) according to the American College of Cardiology 1, 2
The rhythm regularity in junctional rhythm can be regular or irregular with marked variability in the junctional rate, as noted in Circulation 3, 4, 5

Retrograde P waves may appear as narrow negative deflections in inferior leads (II, III, aVF) in junctional rhythms, as described in Circulation 3, 5
P waves may be buried within the QRS complex, appear immediately before, or immediately after the QRS in junctional rhythms, according to Circulation 3, 4
AV dissociation, where the junctional pacemaker fires independently of atrial activity, can occur in junctional rhythms, as noted in Circulation 3, 5

Junctional rhythms can be distinguished from slow-fast AVNRT by variable conduction to the atria, marked irregularity in the junctional rate, and AV dissociation when present, as described in Circulation 3, 4, 5

In highly trained athletes, junctional escape rhythm is considered a normal variant related to increased vagal tone, with heart rates ≥30 beats/min considered normal in the absence of symptoms, according to the American College of Cardiology 1, 2
Athletic training can enhance parasympathetic tone, suppressing the sinus node and allowing junctional escape, as noted by the American College of Cardiology 1, 2

Beta-blockers can slow the sinus node sufficiently to allow junctional escape, as described in Circulation 7

The American College of Cardiology recommends considering the clinical context to determine the cause of junctional rhythm, which must be differentiated between junctional escape rhythm from sinus suppression and accelerated junctional rhythm from enhanced automaticity 1, 2
The American Heart Association, as published in Circulation, notes that junctional rhythms can be misdiagnosed as AVNRT, but can be distinguished by AV dissociation and/or marked irregularity 3, 5
The American College of Cardiology states that junctional escape rhythms are normal findings in highly trained athletes and should resolve with activity 1, 2