What is junctional rhythm?

Junctional Rhythm Definition

Junctional rhythm is an arrhythmia originating from the AV node or His bundle, characterized by heart rates of 70-120 bpm (nonparoxysmal form) or 110-250 bpm (focal junctional tachycardia), with narrow QRS complexes and often AV dissociation. 1

Types of Junctional Rhythm

• Focal Junctional Tachycardia: Characterized by heart rates of 110-250 bpm, narrow QRS complexes (or typical bundle branch block pattern), and often atrioventricular dissociation 1
• Nonparoxysmal Junctional Tachycardia: A benign arrhythmia with heart rates of 70-120 bpm, showing typical "warm-up" and "cool-down" patterns that cannot be terminated by pacing maneuvers 1

Diagnostic Features

ECG Characteristics

• Origin from the AV node or His bundle 1
• Narrow QRS complex or typical bundle branch block pattern 1
• Heart rates of 70-120 bpm (nonparoxysmal) or 110-250 bpm (focal) 1
• Atrioventricular dissociation is often present, though one-to-one retrograde conduction may be transiently observed 1
• During electrophysiological study, each ventricular depolarization is preceded by a His bundle deflection 1

Distinguishing Features

• Isorhythmic AV dissociation is a characteristic finding 1
• May occasionally present with an erratic rhythm that can be mistaken for atrial fibrillation 1
• Isolated, concealed junctional extrasystoles may produce episodic AV block by rendering the AV node intermittently refractory 1

Mechanisms

• The precise electrophysiological mechanism is thought to be either abnormal automaticity or triggered activity 1
• This is supported by the response to beta-adrenergic stimulation and calcium-channel blockade 1
• Recent research suggests that junctional rhythm may have different characteristics depending on the type of AVNRT being treated 2, 3

Clinical Significance

Focal Junctional Tachycardia

• Very uncommon arrhythmia, rare in pediatric population and even less common in adults 1
• Usually presents in young adulthood 1
• Often exercise or stress related 1
• May occur in patients with structurally normal hearts or congenital abnormalities 1
• Patients are often quite symptomatic and may develop heart failure if untreated, particularly with incessant tachycardia 1

Nonparoxysmal Junctional Tachycardia

• May be a marker for serious underlying conditions such as:
  • Digitalis toxicity 1
  • Post-cardiac surgery complications 1
  • Hypokalemia 1
  • Myocardial ischemia 1
  • Chronic obstructive lung disease with hypoxia 1
  • Inflammatory myocarditis 1

Clinical Management

Focal Junctional Tachycardia

• Beta blockers are reasonable for both acute treatment and ongoing management 1
• Intravenous diltiazem, procainamide, or verapamil are reasonable for acute treatment 1
• Catheter ablation can be curative but carries a 5-10% risk of AV block 1

Nonparoxysmal Junctional Tachycardia

• The mainstay of management is to correct the underlying abnormality 1
• Withholding digitalis when junctional tachycardia is the only manifestation of toxicity is usually adequate 1
• Persisting junctional tachycardia may be suppressed by beta blockers or calcium-channel blockers 1

Important Considerations

• Junctional rhythm during slow pathway ablation for AVNRT is often considered a marker of successful ablation 4
• Recent research indicates that junctional rhythm characteristics may differ based on the type of AVNRT being treated 2, 3
• A critical reassessment of junctional tachycardia suggests that some cases may actually represent infra-atrial narrow QRS re-entrant tachycardia, which has implications for ablation approaches 5