AVNRT

INTRODUCTION

most common of the PSVTs, accounting for nearly two-thirds of cases.

synonyms AV junctional reentrant tachycardia.Reciprocal or reciprocating AV nodal reentrant

tachycardia.Junctional reciprocating tachycardia.

no apparent precipitating cause . However, in some patients, nicotine, alcohol,

stimulants, exercise, or surges in vagal tone can initiate episodes.

Familial AVNRT has been reported

SYMPTOMS

• Palpitations • Dizziness• Dyspnea • Chest pain • Fatigue • Syncope • polyuria

Pathophysiology

AVNRT

• Presence of a narrow complex tachycardia with regular R-R intervals and no visible p waves.

• P waves are retrograde and are inverted in leads II,III,AVF.

• P waves are buried in the QRS complexes –simultaneous activation of atria and ventricles – most common presentation of AVNRT –66%.

• If not synchronous –pseudo s wave in inferior leads ,pseudo r’ wave in lead V1---30% cases .

• P wave may be farther away from QRS complex distorting the ST segment ---AVNRT ,mostly AVRT.

Atrioventricular node reentrant tachycardia (the Jaeggi algorithm),

• pseudo S/R waves,• the RP interval, • the lack of significant ST depression in

multiple leads a correct diagnosis of typical AVNRT can be

made by ECG analysis 76% of the time

ST segment depression

• represent either repolarization changes or a retrograde atrial activation

• more commonly seen in those with an AV reentrant tachycardia associated with an accessory pathway

• aVL notch: any positive deflection at the end of the QRS during tachycardia and its absence during sinus rhythm.

relevant ECG parameters.

• ST-segment elevation in aVR lead.– According to the definition, the percentage

of patients with aVR ST-segment elevation was significantly greater in AVRT than in AVNRT

• Although AV dissociation is usually not seen, it can occur because neither the atria or the

ventricles are necessary for the reentry circuit

Clinical course more likely to begin in young adults.

EP characteristics of the AV node can evolve over time

The refractory periods of both the fast and slow pathways increased.

The incidence of retrograde conduction through the AV node decreased.

The cycle length of induced AVNRT increased

ELECTROPHYSIOLOGIC FEATURES

Dual AV nodal physiology may be distinct anatomic structures, or may

be functionally separate fast or beta pathway : conducts rapidly and

has a relatively long refractory period. slow or alpha pathway : conducts relatively

slowly and has a shorter refractory period.

Dual atrioventricular nodal conduction

• Denes et al. in 1973,• Antegrade dual pathways are demonstrable

in 75% of patients. • Conversely, antegrade dual pathways can be demonstrated without tachycardia

• optical mapping studies: multiple nondiscrete atrial inputs to transitional zone surrounding the AV node that is asymmetric- allowing an excitable gap

• Unidirectional block occurring in the transitional zone can transform the nondiscrete pathways model into a classic dual pathways physiology for AVNRT

Schematic representation of koch's triangle and environment

• Schematic representation of Koch's triangle which is bounded by the tricuspid ring and the tendon of Todoro. The tendon of Todoro and the tricuspid ring are in close proximity forming the apex of the triangle near the His bundle at the membranous septum. Koch's triangle can be divided into thirds: the anterior contains the compact AV node; the posterior contains the coronary sinus; and the middle or mid-septal third is between the anterior and posterior portions. The anterior third is associated with fast pathways, and the middle and posterior thirds with slow pathways.

Electrophysiologic study in a dual AV nodal pathways

• The tracing shows three surface ECG leads (I, II, V1) and intracardiac recordings from the high right atrium (HRA), bundle of His (HIS), right ventricular apex (RVA), and coronary sinus (CS). During atrial pacing (S1) at a cycle length of 600 ms (100 beats per minute); the AH interval is 120 ms. An atrial premature beat (S2) is added at a coupling cyle of 420 ms; this results in a prolongation of the PR interval and increase in the AH interval to 184 ms.

AVNRT Slow/Slow• Characteristics• Dual AV Nodal Physiology and jump with initiation• Retrograde VA > 60 ms• AH > HA• Earliest Atrial Activation in posterior septal region• Diferentiation of AVNRT Slow/Slow from AVRT with AVRT using a Concealed

Bypass Tract• P wave morphology

– Negative in the Inferior Leads in both

• Delta RP (V1-II) > 25 ms• Delta RP (V1-III) > 23 ms• Delta RP (V1 - aVF) > 30ms

posterior or type B AVNRT - 2% of patients with slowfast AVNRT; VA times are prolonged, but the AH/HA ratio remains >1.

Thus, it appears posterior slow-fast AVNRT may actually represent the slow-slow form

MANAGEMENT

In patients with documented SVT (which is morphologically consistent with AVNRT) but in whom only dual AV-nodal physiology (but not tachycardia) is demonstrated during electrophysiological study.

Slow-pathway ablation may be considered at the discretion of the physician when sustained (more than 30 seconds) AVNRT is induced incidentally during an ablation procedure directed at a different clinical tachycardia

Posterior approach• Koch's triangle can be divided into

thirds: the anterior contains the compact AV node; the posterior contains the coronary sinus; and the middle or mid-septal third is between the anterior and posterior portions. The anterior third is associated with fast pathways, and the middle and posterior thirds with slow pathways. The anterior and posterior approaches to ablate the fast and slow pathways, respectively, are indicated by the position of the catheters (shown in green).

• furthest from the His bundle - the lowest risk of AV block.

• preserves fast pathway function- normal PR interval after the ablation.

• Reliable anatomic and electrophysiologic landmarks facilitate selection of a safe and effective ablation site.

• A good ablation site records a small fractionated or multicomponent atrial potential, generally less than 10 percent of the ventricular electrogram amplitude

• occurrence of transient junctional rhythm - efficacy .

Identification of site for ablation of AV nodal reentrant tachycardia

• Application of radiofrequency (RF) energy to the tip of the HBE catheter (HBE1-2) promptly causes an accelerated junctional rhythm (*), further evidence of a good ablation site. Note that during the accelerated junctional rhythm, there is rapid 1:1 retrograde conduction to the atria (A), evidence that the fast AV nodal pathway is intact. Following this energy application, there was no evidence of slow pathway conduction and no inducible AVNRT.

• If the slow pathway is damaged but not completely abolished, it may be possible to induce single atrial echoes even though the sustained arrhythmia has been eliminated

Anterior approach

In rare patients, AVNRT may occur in patients who, during normal sinus rhythm, have a markedly prolonged PR interval and absent antegrade fast pathway conduction.

who have previously had unsuccessful slow pathway ablation

Anatomic variants

• exceptionally large coronary sinus ostium distorts the usual fluoroscopic anatomy

• horizontal orientation

either with multiple fluoroscopic views or electroanatomic mapping,

Atypical forms of AVNRT

• earliest retrograde atrial activation in fast-slow - posteroseptal right atrium outside the coronary sinus ostium.

• slow-slow form of AVNRT - within the proximal coronary sinus, particularly the superior portion

complications

Atrioventricular block posterior displacement of the fast pathway superior displacement of the slow pathway

(and coronary sinus) or inadvertent anterior displacement of the

catheter during RF application

Risk factors for AV block Age fast junctional tachycardia (cycle length <350

ms) during the ablation Baseline PR prolongation relatively long refractory period in the fast

pathway

• Palpitations - 20 to 30 percent ; generally transient - due to premature atrial or ventricular contractions.

• inappropriate sinus tachycardia : disruption of the parasympathetic and/or sympathetic inputs into the sinus and AV nodes .

• RADIOFREQUENCY ABLATION VERSUS CRYOABLATION

• (CYRANO) study, 509 patients were randomized late recurrence of AVNRT was significantly more frequent in the cryoablation group (9.4 versus 4.4 percent)