What is the difference between junctional (atrioventricular junctional) rhythm and nodal (atrioventricular nodal) rhythm on an electrocardiogram (ECG)?

Differentiating Junctional versus Nodal Rhythm on ECG

Junctional rhythm and nodal rhythm are the same entity, both originating from the AV node or His bundle, characterized by narrow QRS complexes and specific heart rate ranges depending on the subtype. 1, 2

Key Characteristics of Junctional/Nodal Rhythm

• Origin: Arises from the AV node or His bundle (also called the AV junction) 3, 2
• QRS Complex: Narrow (<120 ms) unless there's a pre-existing bundle branch block 1
• P Waves: May be absent, inverted (retrograde), or dissociated from QRS; when present, P waves may occur before, during, or after the QRS complex 1, 2
• Heart Rate Ranges:
  • Junctional escape rhythm: 40-60 bpm 1
  • Nonparoxysmal junctional tachycardia: 70-120 bpm 3, 2
  • Focal junctional tachycardia: 110-250 bpm 2

Types of Junctional/Nodal Rhythms

• Junctional Escape Rhythm:

  • Emerges when the sinus node fails to generate impulses or when there's AV block 2
  • Heart rate of 40-60 bpm 1
  • Serves as a "backup" pacemaker 2

• Nonparoxysmal Junctional Tachycardia:

  • Heart rate of 70-120 bpm 3
  • Shows typical "warm-up" and "cool-down" patterns 3
  • Cannot be terminated by pacing maneuvers 3
  • Often a marker for serious underlying conditions (digitalis toxicity, post-cardiac surgery, hypokalemia, myocardial ischemia) 3

• Focal Junctional Tachycardia:

  • Heart rate of 110-250 bpm 2
  • Often exercise or stress-related 3
  • Can lead to heart failure if untreated 3
  • Rare in adults 2

Clinical Significance

• Junctional rhythm may indicate underlying pathology such as 3, 2:

  • Digitalis toxicity
  • Myocardial ischemia/infarction
  • Electrolyte abnormalities (particularly hypokalemia)
  • Post-cardiac surgery
  • Chronic obstructive lung disease with hypoxia
  • Inflammatory myocarditis

• In some cases, junctional rhythm may be physiological when the AV junction's automaticity exceeds the sinus rate 3

Distinguishing from Other Arrhythmias

• Versus Idioventricular Rhythm:

  • Idioventricular rhythms have wide QRS complexes (>120ms) with left bundle branch block pattern 1
  • Idioventricular rhythms have slower rates (20-40 bpm for escape rhythm, 40-120 bpm for accelerated) 1

• Versus Atrial Tachycardia:

  • Atrial tachycardia shows P waves with morphology different from sinus rhythm 3
  • In atrial tachycardia, P waves drive the rhythm with normal conduction to ventricles 3

• Versus AVNRT/AVRT:

  • AVNRT/AVRT are reentrant tachycardias with specific P wave patterns 3
  • AVNRT typically shows pseudo S waves in inferior leads and pseudo R' in V1 3
  • AVRT shows P waves in early part of ST-T segment 3

Management Considerations

• Correct underlying abnormality (e.g., withhold digitalis if toxicity is suspected) 3, 2
• Beta blockers or calcium channel blockers for persistent symptomatic cases 3, 2
• Catheter ablation can be curative for focal junctional tachycardia but carries 5-10% risk of AV block 3, 2
• Atrial pacing when junctional rhythm results from sinus node dysfunction 3

Common Pitfalls

• Mistaking very slow AVNRT for junctional tachycardia - use pacing maneuvers to differentiate 4
• Failing to recognize junctional rhythm as a marker of serious underlying conditions 3, 2
• Not recognizing that junctional rhythm with VA block during slow pathway ablation in atypical AVNRT is common and indicates successful ablation 5
• Confusing physiological junctional rhythm (when AV junction automaticity exceeds sinus rate) with pathological causes 3