ATRIOVENTRICULAR NODAL REENTRANT TACHYCARDIA - A REVIEW

BACKGROUND: Atrioventricular nodal reentrant tachycardia (AVNRT) is th e most common form of regular narrow complex tachycardia. It is due to dual atrioventricular nodal conduction over two pathways with differe nt electrophysiological properties. The first pathway ('fast' pathway) conducts faster but has longer refractory period than the second path way ('slow' pathway). OBJECTIVES: To review AVNRT. Clinically, AVNRT p atients usually have palpitations in their neck during attacks. On the surface electrocardiogram, the diagnosis is suggested by the absence of P waves during tachycardia or very discrete P waves immediately aft er the QRS or an rSr' pattern in lead VI. Electrophysiologically, it c an be reproducibly initiated or terminated by cardiac pacing. The reen trant circuit is limited to the atrioventricular node and a small amou nt of perinodal atrial tissue. Acute termination of tachycardia can be achieved by vagal manoeuvres or drugs. Adenosine compounds are excell ent drugs, as are calcium channel blockers, for acute termination of t he arrhythmia. If chronic therapy is indicated, digitaiis, calcium blo ckers and beta-blockers are effective and simple initial options. Cath eter ablation, especially using radiofrequency energy, antitachycardia pacing and surgery are therapeutic alternatives for the resistant pat ient. CONCLUSION: Because of its high success rate and low incidence o f complications, radiofrequency ablation is becoming the therapy of fi rst choice for the treatment of AVNRT.