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 children Rate 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

AVNRT Electrophysiological Mechanism AVNRT results from reentry in the AV node as a result of the presence of functional longitudinal dissociation within the AV node Slow 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 connections Different sites of atrial activation during retrograde atrial activation over slow and fast pathways Resetting of tachycardia by late atrial extrastimuli delivered to posteroseptal right atrium or CSO Selective 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

typical AVNRT RP < PR R R P P

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 View of 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 Nodal Function Curve

Discontinuous AV Nodal Function 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 necessary If 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 His No Advancement of A

PVC Superimposed on His Advancement of A in AVRT

Spontaneous Termination Antegrade 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 attack Vagal maneuvers Adenosine 6-12 mg iv rapidly Verapamil 5-10 mg iv Diltiazem 0.25-0.35 mg/kg iv

Radiofrequency Ablation Indications Patients with frequent arrhythmic episodes despite administration of drugs with a high safety profile (β blockers, Ca blockers, Digoxin) Poor tolerance of drugs Patients with pharmacologically controllable PSVT who prefer to avoid drug side effect Management of patients with single or infrequent symptoms should be individualized

Radiofrequency Ablation Other 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 Ablation in 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 Ablation Approaches Fast pathway ablation, Anterior approach Slow pathway ablation, Posterior approach

Radiofrequency Ablation Slow Pathway Approach Identification of target sites Electrogram technique Anatomical technique Integrated 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

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Slow Pathway Ablation Electrogram 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 Ablation Anatomic 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 Ablation Successful Sites

Slow Pathway Ablation Successful Site

Slow Pathway Ablation Successful Site, RAO View

Slow Pathway Ablation Successful Site, LAO View

Slow Pathway Approach A Marker for Success Accelerated junctional rhythm, a sensitive but not specific marker for success An 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 Approach Monitoring 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 Approach End 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 length Prolongation of antegrade AV nodal refractory period No change in AH interval No change in retrograde conduction properties Effective refractory period of fast pathway shortens (electrotonic interaction)

AV Nodal Conduction Curve After Slow Pathway Ablation

Slow Pathway Ablation Recurrence Rate AVNRT recurs in 2-5% of patients About 60% of recurrences are manifest within 3 months In 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 Ablation Fast 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 prolongation VA 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 conduction Elimination 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 preferred Success rate higher, 99% vs. 85% Complete AV block lower, <1% vs. 10% Fast pathway ablation may rarely be necessary when Slow pathway ablation cannot be achieved When 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