Atrioventricular Nodal Reentrant Tachycardia

Abstract

A trioventricular nodal reentrant tachycardia (AVNRT) represents the most common regular supraventricular arrhythmia in humans. 1 The precise anatomic site and nature of the pathways involved have not yet been established, and several attempts to provide a reasonable hypothesis based on anatomic or anisotropic models have been made. 2 There has been considerable evidence that the right and left inferior extensions of the human atrioventricular (AV) node and the atrionodal inputs they facilitate may provide the anatomic substrate of the slow pathway, and a comprehensive model of the tachycardia circuit for all forms of AVNRT based on the concept of atrionodal inputs has been proposed. 2 Still, however, the circuit of AVNRT remains elusive. Recently, time-honored conventional schemes for the diagnosis and classification of the various forms of the arrhythmia have been refuted in part by evolving evidence. Recognition of the various types of AVNRT is important, however, to expedite diagnosis and allow implementation of appropriate ablation therapy without complications. We present an update on AVNRT with a particular emphasis on electrophysiological criteria used for the differential diagnosis of regular, supraventricular tachycardias. ECG PresentationTypically, AVNRT is a narrow-complex tachycardia, ie, QRS duration Ͻ120 ms, unless aberrant conduction, which is usually of the right bundle-branch type, or a previous conduction defect exists. Tachycardia-related ST depression and RR-interval variation may be seen. RR alternans in AVNRT has been attributed to the proposed model of a figure of 8 reentry with continuous crossing over of antegrade activation through an inferior input to the contralateral superior input via the node. 2 In the typical form of AVNRT (slow-fast), abnormal (retrograde) PЈ waves are constantly related to the QRS and in the majority of cases are indiscernible or very close to the QRS complex (RPЈ/RR Ͻ0.5). Thus, PЈ waves are either masked by the QRS complex or seen as a small terminal PЈ wave that is not present during sinus rhythm (Figure 1). In the atypical form of AVNRT (fast-slow), PЈ waves are clearly visible before the QRS, ie, RPЈ/PЈR Ͼ0.75 (Figure 2), denoting a "long RP tachycardia," and are negative in leads II, III, aVF, and V 6 but positive in V 1 . PЈ waves are shallow in the inferior leads in the rare form of anterior fast-slow AVNRT. 3 Although AV dissociation is usually not seen, it can occur because neither the atria or the ventricles are necessary for the reentry circuit. If the tachycardia is initiated by atrial ectopic beats, the initial (ectopic) PЈ wave usually differs from the subsequent (retrograde) PЈ waves (Figure 1).

Orthodromic atrioventricular reciprocating tachycardia conducted with intraventricular conduction disturbance mimicking ventricular tachycardia in an English Bulldog

“…2,15 Rarely atrioventricular dissociation can be observed in case of atrioventricular nodal reentrant tachycardia, because neither the atria nor the ventricles are necessary for the reentry circuit. 17 On the other hand, the recognition of P waves that occur in association to the wide QRS complexes can be indicative of SVT with ventricular pre-excitation, SVT with intraventricular conduction disturbance, and less frequently, in case of VT with 1:1 retrograde AV nodal conduction. 2 Moreover the presence of P 0 waves inscribed within the STeT segment with a short RP 0 interval and a RP 0 /P 0 R < 1 suggests the presence of an OAVRT.…”

“…However the identification of pre-excitation during a sinus rhythm strip might assist the differential diagnosis. 13,17 Precordial concordance occurs when all precordial leads show either negative or positive QRS complexes polarity, and if present, it strongly suggests the ventricular origin of the tachycardia. However a few exceptions exist, for example when the tachycardia uses a left posterior accessory pathway for the AV conduction.…”

Cryoablation of typical AVNRT: Younger age and administration of bonus ablation favor long-term success

“…Before performing the electrophysiological study (EPS), the clinical diagnosis of typical AVNRT was based on the (1) history of a regular narrow complex tachycardia documented by electrocardiogram (ECG), Holter monitoring, transient arrhythmia monitoring, or other cardiac rhythm strip; (2) absence of identifiable P waves or presence of small terminal retrograde P waves that are not present in sinus rhythm 9 ; and (3) exclusion of manifest accessory pathway and/or other atrial tachycardias. Patients who had previously undergone any ablation procedures (with either source of energy) and those with structural heart disease were excluded from the present study.…”

Regular Tachycardia With Abnormal QRS Axis

“…2 During tachycardia, negative P waves in the inferior leads ( Figure 2, interrupted arrows) are identified 120 ms from the beginning of the QRS complex, as is seen during either a slow-slow atypical atrioventricular nodal reentrant tachycardia or a posteroseptal bypass tract-mediated atrioventricular reentrant tachycardia. 3 In both arrhythmias, the ventricular activation precedes the atrial activation that is directed from inferior to superior (hence negative P waves in inferior leads). Electric alternans (beat-to-beat variation in QRS amplitude during tachycardia, beats 1-6) in the absence of pericardial effusion is usually a result of beat-to-beat changes in calcium fluxes into the ventricular myocardium and once again can be observed in both atrioventricular nodal reentrant tachycardia and atrioventricular reentrant tachycardia.…”