Atrioventricular Nodal Reentrant Tachycardia

M.A.Sadr-Ameli MD

DPE-RHC

AVNRT

The most common form of paroxysmal supraventricular tachycardia in adults (60%)

More common in women ( 70% )Uncommon in childrenRate usually 130-250 bpm (110-or more than 250)

Atrioventricular nodal reentrant tachycardia ( AVNRT )

The concept of AVNRT as a mechanism of SVT was first purposed by Mines in 1913

Moe et al were the first to postulate that SVT could be due to longitudinal dissociation of the AVN ( two pathways)

These investigators postulated the presence of a dual AVN transmission system with a slowly conducting α- pathway with a short ERP and a fast conducting β- pathway with a long ERP

AVNRTElectrophysiological Mechanism

AVNRT results from reentry in the AV node as a result of the presence of functional longitudinal dissociation within the AV nodeSlow pathway (α pathway)

Slow conduction

Short refractory period

Fast Pathway (β pathway)Rapid conduction

Long refractory period

Longitudinal Dissociation Within AV Node

Slow Pathway

Fast Pathway

Atrium

His Bundle

AVNRT Mechanism

Limb A Limb B

Dual AV nodal Physiology

The hypothesis of functional longitudinal dissociation within AV node was based on

The presence of dual AV nodal physiology in 50-90% of documented AVNRT patients and only in 5-10% of normal people

Occasional dissociation of His bundle and ventricular activation from the tachycardia

An initial impression that atrium could be dissociated from the tachycardia

Atrial Participation

More recent studies suggest that fast and slow pathways represent conduction over

different atrionodal connectionsDifferent sites of atrial activation during retrograde

atrial activation over slow and fast pathwaysResetting of tachycardia by late atrial extrastimuli

delivered to posteroseptal right atrium or CSOSelective elimination of fast or slow pathways by

ablation in the atrium remote from compact AVN

Earliest Site of Retrograde Activation

AVNRT

At least four distinct forms of AVNRT can be identified

In a series of 499 patients:

1- slow / fast (common type) :76%

2- left variant slow / fast :1%

3- slow / slow :11%

4- fast / slow :12%

typical AVNRT: 85-90%, atypical AVNRT: 10-15%.

Fluoroscopic Correlates

Fluoroscopic Correlates

Koch’s Triangle

approach

approach

ECG MANIFESTATIONS OF DUAL AVN CONDUCTION*

Spontaneous abrupt prolongation of PR interval

SR with alternans of the PR interval Simultaneous conduction along Fast

and Slow pathway

*Charles Fisch, JACC 1997; 29

ADENOSINE can disclose dual AV nodal pathway during SR

ABOUT 30% OF PATIENTS HAS THIS MORPHOLOGY OF QRS

DURING TACHYCARDIA

R R

P P

RP < PR

typical AVNRT

Atypical AVNRT (Fast-Slow)

Tachycardia can cause SYNCOPE as a result of :

1- rapid ventricular rate

2- reduced CO

3- asystole when the tachycardia terminates as a result of tachycardia-induced depression of sinus node automaticity

AVNRT Mechanism

Possible Circuits for AVNRT

Electrophysiological Viewof Dual AV Nodal Physiology

Dual AV nodal physiology (AH Jump) is defined as atrial extrastimulus that causes an increase of at least 50 ms in A2H2 interval for a 10 ms decrease in the atrial coupling interval ( A1A2 )

Manifestations of dual AVN pathways

1- An increases of at least 50 ms in the AH interval with 10 ms decrease in coupling interval of the APD

2- Different PR interval or AH interval during sinus rhythm or at identical paced rate

3- A sudden jump in the AH interval during atrial pacing may be a manifestation of dual pathways

AH Jump

AH Jump

AH Jump

AH Jump

Normal AV NodalFunction Curve

Discontinuous AV NodalFunction Curve

Some patients with AVNRT may not have discontinuous refractory curves, and some people who do not have AVNRT can exhibit discontinuous refractory curves

Retrograde Jump

Retrograde Jump

Multiple slow pathways have been demonstrable in the AV nodal conduction curve in some patients with AVNRT

Multiple Jumps

Multiple Jumps

Multiple Jumps

Multiple Jumps

AV Nodal Echo Beat

AV Nodal Echo Beat

AV Nodal Echo Beat

Induction of AVNRT

The VA interval during tachycardia is usually less than 50 msec measured at the HBE , and less than 90 msec measured at HRA

Induction of AVNRT• Inducible by atrial extrastimuli or burst pacing

at Wenckebach point in virtually all cases

• Inducible by ventricular extrastimuli in 1/3

• Pharmacological provocation by atropine, isoproterenol or propranolol may be necessaryIf fast pathway conduction is suppressed (long AH at

all cycle lengths or VA block), isoproterenol infusion may be useful

If ERP of fast pathway is very short, increasing the degree of sedation or infusion of β blockers may be more helpful

Induction of AVNRT

Induction of AVNRT

Induction of AVNRT

Initiation of AVNRT by Spontaneous PAC

Initiation of AVNRT by Spontaneous PAC

AVNRT

AVNRT

Atypical AVNRT

AVNRT With LBBB Pattern

AVNRT With LBBB Pattern

AVNRT With RBBB Pattern

AVNRT With RBBB Pattern

AVNRT With 2:1 AV Block

AVNRT With 2:1 AV Block

AVNRT With 2:1 AV Block

PVC Superimposed on HisNo Advancement of A

PVC Superimposed on HisAdvancement of A in AVRT

Spontaneous TerminationAntegrade Block in Slow Pathway

Spontaneous Termination Retrograde Block in Fast Pathway

Spontaneous Termination AVNRT with 2:1 AV block

Termination With Atrial Extrastimulus

RA Burst ( Entrainment & Termination )

RV Burst ( Entrainment )

RV Burst ( Entrainment & Termination )

Amelioration of 2:1 AV Block by PVC

TREATMENT

The acute attackVagal maneuversAdenosine 6-12 mg iv rapidlyVerapamil 5-10 mg ivDiltiazem 0.25-0.35 mg/kg iv

Radiofrequency AblationIndications

Patients with frequent arrhythmic episodes despite administration of drugs with a high safety profile (β blockers, Ca blockers, Digoxin)

Poor tolerance of drugsPatients with pharmacologically controllable

PSVT who prefer to avoid drug side effectManagement of patients with single or

infrequent symptoms should be individualized

Radiofrequency AblationOther Indications

Empirical slow pathway ablation in patients with documented PSVT and dual AV nodal physiology, but without inducible AVNRT

Identification of inducible AVNRT during evaluation for ventricular tachycardia when the patient is a candidate for implantation of ICD

Radiofrequency Ablationin Children

RF ablation in the heart of young sheep is shown to result in serpiginous lesions that become larger as the heart grows

It appears prudent to avoid ablation when possible in young patients, especially if they are younger than 4 years of age

Radiofrequency AblationApproaches

• Fast pathway ablation, Anterior approach

• Slow pathway ablation, Posterior approach

Radiofrequency AblationSlow Pathway Approach

• Identification of target sitesElectrogram techniqueAnatomical techniqueIntegrated approach

• A prospective randomized trial comparing the two techniques found both to be equally efficacious

• It is safe to cross over from one technique to the other as long as AVNRT persists

p

Slow Pathway AblationElectrogram Approach

Fractionated atrial electrograms with AV ratios of 0.1 to 0.5

Discrete slow pathway potentials, disputed

Multicomponent atrial electrograms are sensitive but not specific marker for successful ablation

Successful Signals

Successful Signals

Successful Signals

Slow Pathway AblationAnatomic Approach

Slow Pathway Ablation

Slow pathway can be ablated along posteromedial TA close to CSO

Starting at the most posterior site (near CSO) and progressing to the more anterior locus (close to HB)

Slow Pathway AblationSuccessful Sites

Slow Pathway AblationSuccessful Site

Slow Pathway AblationSuccessful Site, RAO View

Slow Pathway AblationSuccessful Site, LAO View

Slow Pathway ApproachA Marker for Success

Accelerated junctional rhythm, a sensitive but not specific marker for successAn almost universal finding at effective target

sites (95%)Also at 65% of ineffective sites

A rapid junctional rhythm may be a harbinger of AV block

Accelerated Junctional Rhythm

Accelerated Junctional Rhythm

Accelerated Junctional Rhythm

Slow Pathway ApproachMonitoring During Ablation

Monitoring junctional ectopy for VA conduction and monitoring for prolongation of PR interval are important

Slowing of VA conduction during AJR may also be harbinger of AV block

AV block occurs almost exclusively after burns associated with VA block during junctional ectopy

Positive predictive value of VA block during AJR for occurrence of AV block is 20%

VA Block during RFA

Slow Pathway ApproachEnd Points

Successful ablation is achieved when the tachycardia is no longer inducible in the baseline state or during infusion of isoproterenol

Up to 40% will have residual slow pathway function as evidenced by either AH jumps or single AV nodal echo beats

Electrophysiological Changes Following Slow Pathway Ablation

Prolongation of Wenckebach cycle lengthProlongation of antegrade AV nodal refractory

periodNo change in AH intervalNo change in retrograde conduction propertiesEffective refractory period of fast pathway

shortens (electrotonic interaction)

AV Nodal Conduction Curve After Slow Pathway Ablation

Slow Pathway AblationRecurrence Rate

AVNRT recurs in 2-5% of patientsAbout 60% of recurrences are manifest within

3 monthsIn most studies, residual slow pathway

function does not predict recurrences as long as no more than single echo beat can be evoked during isoproterenol infusion

Radiofrequency AblationFast Pathway Approach

Ablation catheter positioned slightly posterior and superior to His recording catheter

AV electrogram ratio of 2:1 or less with small His is optimal

Look for PR prolongationVA block during junctional ectopy is expected

Fast Pathway Ablation Site

Electrophysiological Changes Following Fast Pathway Ablation

Prolongation of AH interval (average 50%)Elimination or significant attenuation of

retrograde fast pathway conductionElimination of dual AV nodal physiology (in 85-

100%) Insignificant changes in Wenckebach cycle

length and AV nodal refractory period

Fast versus Slow Pathway Ablation

Slow pathway approach is preferredSuccess rate higher, 99% vs. 85%Complete AV block lower, <1% vs. 10%

Fast pathway ablation may rarely be necessary whenSlow pathway ablation cannot be achievedWhen assessment of successful slow pathway ablation

is not possible because slow pathway conduction cannot be demonstrated reproducibly before ablation

Slow Pathway Ablation Quality of Life (QOL) and Cost

Marked improvement in quality of life*

The most cost-effective strategy in treatment of refractory cases**

Quickly pays for itself in as little as 2 years

*Bubien RS, et al. Circulation 94:1585-91, 1996.

** Kalbfleisch, et al. JACC 19:1583-87, 1992