AV nodal re-entrant tachycardia (AVNRT)

Etiology

• frequently occurs in the absence of structural heart disease
• potentiating factors:
  • physiologic or emotional stress
  • increased levels of circulating catecholamines
  • pain
  • fever
  • inflammation
  • myocardial ischemia or infarction

Epidemiology

• peak incidence in young women, including pregnant women
• most common form of paroxysmal supraventricular tachycardia (PSVT)
  • two thirds of all supraventricular tachycardias

Pathology

• occurs when a circuit forms from 2 distinct electrical pathways that connect the right atrium with the distal part of the AV node
• an aberrant slow conduction pathway in conjunction with a premature atrial (typical AVNRT) or ventricular (atypical AVNRT) depolarization initiates the re-entry circuit giving rise to a narrow QRS complex tachycardia (in the absence of pre-existing bundle branch block)

Clinical manifestations

• palpitations
• neck pounding
• nervousness
• light-headedness, fatigue
• syncope or near-syncope
• angina
• dyspnea
• abrupt onset
• heart rate 150-250/min
• episodes may be terminated by vagal maneuvers

Diagnostic procedures

electrocardiogram:

• general
  • narrow complex or wide complex secondary to pre-existing bundle branch block
  • tachycardia @ 150-250/min (120-220/min)
• typical (slow-fast) AVNRT (95%)
  • p-wave usually not apparent
    • generally within the QRS complex
    • atrial & ventricular depolarizations are nearly synchronous
    • retrograde p wave very close to QRS complex may appear as a very small pseudo R wave
  • QRS complex usually normal
  • initiated by premature atrial contraction (PAC) that conducts with a long PR interval typical of a slow conduction pathway
  • short RP interval
• atypical (fast-slow) AVNRT
  • an inverted p-wave may be seen within the T-wave
  • PR interval is normal or minimally prolonged
  • initiated by a premature ventricular contraction (PVC) with a long RP interval

Differential diagnosis

• the absence of p waves rules out:
  • atrioventricular reciprocating tachycardia (AVRT)
    • an accessory pathway-mediated tachycardia
      • orthodromic AVRT has a narrow QRS complex with P waves
      • antidromic AVRT has a wider QRS complex with P waves
  • sinus tachycardia

Management

• acute therapy
  • synchronized direct-current cardioversion for unstable AVNRT
  • vagal maneuvers
    • carotid massage
    • Valsalva maneuver
  • AV nodal blocking agents (short-acting)
    • adenosine 6-12 mg IV
    • verapamil 5 mg IV every 5 min for a maximum of 3 doses
    • diltiazem 15-20 mg IV over 2 min for a maximum of 2 doses
  • edrophonium
  • beta-blockers
  • sedation
• chronic therapy for recurrent AVNRT
  • Ca+2-channel antagonists
  • beta-adrenergic receptor antagonists
  • digoxin
  • class IA, IC or III anti-arrhythmic agents
  • synchronized DC cardioversion (50 joules)
  • radio-frequency catheter ablation of accessory pathway

More general terms

• narrow complex tachycardia
• cardiac conduction re-entry
• paroxysmal supraventricular tachycardia (PSVT)
• atrioventricular reciprocating tachycardia (AVRT)