What are the key features and management strategies for Atrioventricular Nodal Reentrant Tachycardia (AVNRT)?

Key Features and Management of Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

Catheter ablation is the preferred treatment for symptomatic AVNRT patients due to its high success rate (>98%) and low complication risk, while minimally symptomatic patients can often be managed with observation alone or AV nodal blocking agents. 1, 2

Clinical Features of AVNRT

History and Presentation

• Most common form of paroxysmal supraventricular tachycardia (PSVT) 1, 3
• More prevalent in females 1
• Typical symptoms:
  • Palpitations (particularly neck pulsations/"frog sign")
  • Dizziness
  • Lightheadedness
  • Presyncope
  • Syncope (rare, as rates rarely exceed 180 bpm)
• Paroxysmal (sudden onset/offset) nature of attacks
• Heart rates typically between 140-250 bpm 1
• Not usually associated with structural heart disease

ECG Characteristics

• Narrow QRS complex (unless aberrant conduction)
• Two main types based on circuit direction:

  1. Typical AVNRT (slow-fast) (90% of cases) 1, 4:

     • P waves often hidden within QRS complex or appearing immediately after
     • Pseudo-r' wave in V1
     • Pseudo-S waves in inferior leads (II, III, aVF)
     • Short RP interval tachycardia

  2. Atypical AVNRT (fast-slow) (5-10% of cases) 1:

     • P wave precedes QRS complex
     • Negative P waves in leads III and aVF
     • Long RP interval tachycardia

Pathophysiology

• Dual AV nodal physiology with two functionally distinct pathways:
  • Fast pathway: Faster conduction but longer refractory period
  • Slow pathway: Slower conduction but shorter refractory period
• Reentrant circuit involves AV node and perinodal atrial tissue 1
• In typical AVNRT: Antegrade conduction via slow pathway, retrograde via fast pathway
• In atypical AVNRT: Antegrade conduction via fast pathway, retrograde via slow pathway

Management Approach

Acute Termination

1. First-line: Vagal maneuvers 1

   • Valsalva maneuver (bearing down against closed glottis for 10-30 seconds)
   • Carotid sinus massage (after confirming absence of carotid bruit)
   • Facial immersion in cold water

2. Pharmacologic options (if vagal maneuvers fail):

   • Adenosine: Drug of choice for acute termination 1, 3, 4
   • Calcium channel blockers: Verapamil or diltiazem
   • Beta-blockers

Long-term Management

1. Observation without therapy for minimally symptomatic patients 1

   • Nearly half of minimally symptomatic patients improve over time
   • Educate patients about vagal maneuvers and when to seek medical attention

2. Pharmacologic therapy for symptomatic patients who decline ablation:

   • First-line: AV nodal blocking agents

     • Beta-blockers
     • Non-dihydropyridine calcium channel blockers (verapamil, diltiazem)
     • Digoxin (less commonly used)

   • Second-line (for patients without structural heart disease):

     • Class Ic agents: Flecainide, propafenone 1, 5
     • Caution: Contraindicated in patients with structural heart disease or coronary artery disease

   • Third-line:

     • Sotalol or dofetilide (can be used in patients with structural heart disease) 1
     • Require inpatient monitoring due to risk of QT prolongation

3. Catheter ablation (definitive therapy) 1, 3, 6, 4, 2

   • Success rate >98% across all age groups
   • Low complication rate (<1% risk of AV block)
   • Preferred approach: Slow pathway modification
   • Increasingly considered first-line therapy for symptomatic patients
   • Equally effective and safe in elderly patients despite higher prevalence of structural heart disease 2

Special Considerations

AVNRT and Atrial Fibrillation

• AVNRT can trigger or coexist with atrial fibrillation in some patients 7
• More common in younger patients with AF
• Ablation of AVNRT alone may eliminate AF in selected patients 7

Pitfalls and Caveats

• Misdiagnosis: AVNRT can be mistaken for other SVTs (particularly AVRT)
• Avoid verapamil or diltiazem in patients with wide-complex tachycardia of uncertain origin (could be ventricular tachycardia) 1
• Class Ic antiarrhythmic drugs (flecainide, propafenone) are contraindicated in patients with structural heart disease due to proarrhythmic risk 1, 5
• "Pill-in-pocket" approach with flecainide requires careful patient selection and prior screening 1
• Elderly patients should not be denied catheter ablation based on age alone, as outcomes are excellent 2