What is the treatment and etiology of Atrioventricular Nodal Reentrant Tachycardia (AVNRT)?

Treatment and Etiology of Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

Catheter ablation of the slow pathway is the definitive treatment of choice for patients with symptomatic AVNRT, offering a permanent cure with high success rates and minimal risk of complications. 1

Etiology of AVNRT

AVNRT is the most common form of supraventricular tachycardia (SVT), accounting for the majority of regular narrow complex tachycardias. The underlying mechanism involves:

• The anatomic substrate of AVNRT is dual AV nodal physiology, which consists of two distinct pathways within the AV node region 1
• The first pathway (fast pathway) conducts more rapidly but has a longer refractory period than the second pathway (slow pathway) 2
• During typical AVNRT (seen in ~90% of cases), the slow pathway conducts in the anterograde direction while the fast pathway conducts in the retrograde direction, creating a reentrant circuit 3
• In atypical AVNRT (less common), the circuit direction is reversed with anterograde conduction over the fast pathway and retrograde conduction over the slow pathway 3

Clinical Presentation

AVNRT typically presents with:

• Sudden onset of palpitations, often described as "pounding in the neck" 1
• Possible shortness of breath, dizziness, and neck pulsations 1
• Syncope is rare 1
• Heart rates typically between 180-200 bpm (range 110-250 bpm) 1
• May occur spontaneously or be provoked by exertion, caffeine, tea, or alcohol 1

Acute Treatment Algorithm

1. Hemodynamically Stable Patients:

First-line:

• Vagal maneuvers (Class I recommendation) 1
  • Valsalva maneuver: patient bears down against closed glottis for 10-30 seconds (30-40 mmHg pressure) 1
  • Carotid sinus massage: after confirming absence of carotid bruit, apply steady pressure over carotid sinus for 5-10 seconds 1
  • Cold stimulus: applying ice-cold wet towel to face 1

Second-line:

• Adenosine IV (Class I recommendation) 1
  • Terminates AVNRT in approximately 95% of patients 1
  • Caution: can cause transient side effects including flushing, chest discomfort, and dyspnea 4
  • Contraindicated in patients with severe asthma or COPD 4

Third-line:

• IV calcium channel blockers (diltiazem or verapamil) or beta blockers (Class IIa recommendation) 1
  • Particularly effective for converting AVNRT to sinus rhythm 1
  • Caution with verapamil: avoid in patients with heart failure, hypotension, or pre-excited AF 5
  • Diltiazem may be more effective than beta blockers for terminating SVT 1

Fourth-line:

• Oral beta blockers, diltiazem, or verapamil (Class IIb recommendation) 1
• IV amiodarone may be considered when other therapies are ineffective or contraindicated (Class IIb) 1

2. Hemodynamically Unstable Patients:

• Immediate synchronized cardioversion (Class I recommendation) 1
  • Also indicated in stable patients when pharmacological therapy fails or is contraindicated 1

Long-term Management Options

First-line (definitive treatment):

• Catheter ablation of the slow pathway (Class I recommendation) 1
  • High success rate (>95%) with low risk of complications 3, 6
  • Considered curative therapy and increasingly becoming first-line treatment 2, 3
  • Targets the slow pathway using radiofrequency energy 6

Alternative pharmacological options (if ablation not preferred):

• Oral verapamil or diltiazem (Class I recommendation) 1
• Oral beta blockers (Class I recommendation) 1
• Flecainide or propafenone for patients without structural heart disease (Class IIa recommendation) 1
• Sotalol or dofetilide may be reasonable in some cases (Class IIb) 1
• Oral digoxin or amiodarone may be considered in patients who cannot undergo other treatments (Class IIb) 1

Important Considerations and Pitfalls

• Diagnostic pitfall: Ensure the rhythm is truly AVNRT before treatment, as verapamil or diltiazem can be dangerous in VT or pre-excited AF 1, 5
• Treatment pitfall: Avoid calcium channel blockers in patients with heart failure or hypotension 1, 5
• Medication caution: Beta blockers should be avoided in patients with severe conduction abnormalities or sinus node dysfunction 1
• Follow-up consideration: Clinical follow-up without pharmacological therapy may be reasonable for minimally symptomatic patients 1
• Ablation advantage: While medications can control symptoms, only catheter ablation offers a permanent cure with high success rates 3, 6

By following this treatment algorithm, most patients with AVNRT can achieve excellent symptom control or complete cure with minimal risk of complications.