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AV nodal re-entrant tachycardia (AVNRT)

Etiology: 1) frequently occurs in the absence of structural heart disease 2) potentiating factors: a) physiologic or emotional stress b) increased levels of circulating catecholamines c) pain d) fever e) inflammation f) myocardial ischemia or infarction Epidemiology: - peak incidence in young women - most common form of paroxysmal supraventricular tachycardia (PSVT) 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) [3] Clinical manifestations: 1) palpitations 2) neck pounding 3) nervousness 4) light-headedness, fatigue 5) syncope or near-syncope 6) angina 7) dyspnea 8) abrupt onset 9) heart rate 150-250/min 10) episodes may be terminated by vagal maneuvers Special laboratory: electrocardiogram: 1) general a) narrow complex or wide complex secondary to pre-existing bundle branch block b) tachycardia @ 150-250/min 2) typical (slow-fast) AVNRT (95%) a) p-wave usually not apparent 1] generally within the QRS complex 2] atrial & ventricular depolarizations are nearly synchronous 3] retrograde p wave very close to QRS complex may appear as a very small pseudo R wave b) QRS complex usually normal c) initiated by premature atrial contraction (PAC) that conducts with a long PR interval typical of a slow conduction pathway d) short RP interval 3) atypical (fast-slow) AVNRT a) an inverted p-wave may be seen within the T-wave b) PR interval is normal or minimally prolonged c) initiated by a premature ventricular contraction (PVC) with a long RP interval Management: 1) acute therapy a) synchronized direct-current cardioversion for unstable AVNRT b) vagal maneuvers - carotid massage - Valsalva maneuver c) 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 d) edrophonium e) beta-blockers f) sedation 2) 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

General

narrow complex tachycardia cardiac conduction re-entry paroxysmal supraventricular tachycardia (PSVT)

References

  1. Manual of Medical Therapeutics, 28th ed, Ewald & McKenzie (eds), Little, Brown & Co, Boston, 1995, pg 142
  2. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 273-74
  3. Medical Knowledge Self Assessment Program (MKSAP) 11, 17, 18. American College of Physicians, Philadelphia 1998, 2015, 2018