What is junctional arrhythmia?

Junctional Arrhythmia

Junctional arrhythmia is an abnormal heart rhythm originating from the atrioventricular (AV) node or His bundle region, characterized by narrow QRS complexes and often presenting with atrioventricular dissociation. 1

Types and Definitions

Junctional arrhythmias can be classified into two main categories:

1. Focal Junctional Tachycardia (FJT):

   • Also known as automatic or paroxysmal junctional tachycardia
   • Heart rates typically between 110-250 bpm
   • Characterized by narrow QRS complexes or typical bundle branch block patterns
   • Often presents with AV dissociation, though transient retrograde conduction may occur
   • Mechanism thought to be abnormal automaticity or triggered activity 1

2. Nonparoxysmal Junctional Tachycardia:

   • Benign arrhythmia with heart rates of 70-120 bpm
   • Shows characteristic "warm-up" and "cool-down" patterns
   • Cannot be terminated by pacing maneuvers
   • Often a marker for underlying conditions such as digitalis toxicity, post-cardiac surgery, hypokalemia, or myocardial ischemia 1

Diagnostic Features

The key ECG characteristics of junctional arrhythmias include:

• Origin from the AV node or His bundle
• Narrow QRS complexes (unless aberrant conduction is present)
• Heart rates varying from 70-250 bpm depending on the type
• AV dissociation often present
• Each ventricular depolarization preceded by a His bundle deflection during electrophysiological study
• Sometimes presents with erratic rhythm that may mimic atrial fibrillation
• Isolated concealed junctional extrasystoles may cause episodic AV block 1

Clinical Significance

Focal junctional tachycardia is uncommon in adults and rare in the pediatric population. The clinical importance varies by type:

• Focal (Paroxysmal) Junctional Tachycardia:

  • Usually presents in young adulthood
  • Often exercise or stress-related
  • Can occur in structurally normal hearts or with congenital abnormalities
  • Patients are frequently symptomatic
  • If untreated, may lead to heart failure, especially if incessant 1

• Nonparoxysmal Junctional Tachycardia:

  • Important as a marker for underlying conditions
  • Associated with digitalis toxicity, post-cardiac surgery, electrolyte abnormalities, myocardial ischemia, COPD with hypoxia, or inflammatory myocarditis 1

Management Approaches

Treatment depends on the type of junctional arrhythmia:

1. For Nonparoxysmal Junctional Tachycardia:

   • Primary focus is treating the underlying condition
   • Withhold digitalis if toxicity is suspected
   • Beta-blockers or calcium channel blockers may be used for persistent cases 1

2. For Focal Junctional Tachycardia:

   • Pharmacological therapy:
     • Beta-blockers show some effectiveness
     • IV flecainide can slow or terminate the tachycardia
     • Long-term oral therapy has variable success
   • Catheter ablation:
     • Considered when drug therapy is ineffective
     • Can be curative by targeting foci adjacent to the AV node
     • Carries 5-10% risk of AV block
     • Has shown good success rates (10/11 patients with acute tachycardia elimination in one series) 1

Important Considerations and Pitfalls

• Diagnostic challenges: Junctional rhythm may be mistaken for other arrhythmias, particularly when irregular
• Risk assessment: Nonparoxysmal junctional tachycardia requires investigation for underlying causes
• Treatment risks: Catheter ablation carries risk of AV block due to proximity to the conduction system
• Monitoring: Patients with focal junctional tachycardia may develop heart failure if tachycardia is incessant and untreated 1

Junctional arrhythmias, while relatively uncommon, require careful evaluation to determine their mechanism, clinical significance, and appropriate management strategy to prevent potential complications like heart failure or conduction disturbances.