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
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