Junctional Ectopic Tachycardia in an 18-Year-Old Female
Aetiology
In an 18-year-old presenting with junctional ectopic tachycardia, the most likely mechanism is enhanced abnormal automaticity from an ectopic focus in the AV junction, though this arrhythmia is uncommon in adults and requires careful evaluation for underlying causes. 1
Primary Mechanism
- Enhanced automaticity from an ectopic focus in the AV junction (including the His bundle) is the fundamental mechanism 1
- JET is characterized by heart rates of 120-220 bpm with narrow QRS complexes and often demonstrates AV dissociation 1, 2
Key Underlying Causes to Evaluate
Metabolic and toxic causes:
- Digoxin toxicity is a major cause of nonparoxysmal junctional tachycardia (though less likely in this age group) 1, 2
- Electrolyte abnormalities, particularly hypokalemia 2
Cardiac causes:
- Myocardial ischemia or infarction (uncommon but must be excluded in symptomatic patients) 1, 2
- Inflammatory myocarditis affecting the conduction system 2
- Post-cardiac surgery (most common in pediatric congenital heart disease repairs, but relevant if surgical history exists) 3, 4
Other causes:
Important Clinical Context
- JET is very uncommon in adults and far more typical in infants post-cardiac surgery 1, 3
- In adults, the related rhythm "nonparoxysmal junctional tachycardia" (70-130 bpm) is more common than true paroxysmal JET 1
- The arrhythmia may be exercise or stress-related and can lead to heart failure if untreated 2
Management
For acute symptomatic junctional tachycardia in this patient, intravenous beta blockers are the reasonable first-line therapy, with ongoing management using oral beta blockers or calcium channel blockers. 1
Acute Treatment
First-line therapy:
- Intravenous beta blockers are reasonable for acute treatment (Class IIa recommendation) 1
Alternative acute therapies:
- Intravenous diltiazem, procainamide, or verapamil are reasonable alternatives (Class IIa recommendation) 1
Address Underlying Causes First
Critical initial steps:
- Withhold digoxin if toxicity is suspected 2
- Correct electrolyte abnormalities, particularly hypokalemia 2
- Treat myocardial ischemia if present 2
- Evaluate for inflammatory myocarditis or other structural heart disease 2
Ongoing Management
Preferred long-term therapy:
- Oral beta blockers are reasonable for ongoing management (Class IIa recommendation) 1, 2
- Oral diltiazem or verapamil are reasonable alternatives (Class IIa recommendation) 1
Second-line options (if no structural heart disease):
- Flecainide or propafenone may be reasonable in patients without structural heart disease or ischemic heart disease (Class IIb recommendation) 1, 2
- Note: Drug therapy for focal JET is only variably successful 2
Catheter Ablation
When to consider ablation:
- Catheter ablation may be reasonable when medical therapy is not effective or contraindicated (Class IIb recommendation) 1
- Ablation can be curative but carries a 5-10% risk of AV block requiring permanent pacemaker 2, 6
- In adults, ablation is associated with high recurrence rates (53%) often requiring multiple procedures 6
- Mapping typically shows earliest activation postero-superior to the AV node in 73% of cases 6
Important Caveats
Diagnostic pitfalls:
- JET may be misdiagnosed as atrial fibrillation or multifocal atrial tachycardia if irregular 1
- AV dissociation, when present, excludes AVRT and makes AVNRT highly unlikely 1
- Recording atrial electrograms can be especially useful for diagnosis 2
Prognosis considerations:
- In adults, JET typically has a relatively benign course, unlike in infants where it can cause heart failure 2
- Medical treatment is often difficult, making identification and correction of underlying causes paramount 3
- Amiodarone has been shown to be safe and effective in some series, particularly in postoperative settings 7
Clinical monitoring: