2. Atrioventricular Nodal Reentrant Tachycardia
M.A.Sadr-Ameli MD
DPE-RHC

3. AVNRT
The most common form of paroxysmal supraventricular tachycardia in adults (60%)
More common in women ( 70% )
Uncommon in children
Rate usually bpm (110-or more than 250)

4. 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

5. 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

6. Longitudinal Dissociation Within AV Node
Slow Pathway
Fast Pathway
Atrium
His Bundle

7. AVNRT Mechanism
Limb A
Limb B

8. 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

9. 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

10. Earliest Site of Retrograde Activation

11. 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%.

12. Fluoroscopic Correlates

13. Fluoroscopic Correlates

14. Koch’s Triangle

16. approach
approach

18. 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

22. ADENOSINE can disclose dual AV nodal pathway during SR

23. ABOUT 30% OF PATIENTS HAS THIS MORPHOLOGY OF QRS DURING TACHYCARDIA

26. typical AVNRT
RP < PR R R P P

27. Atypical AVNRT (Fast-Slow)

28. 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

29. AVNRT Mechanism

32. Possible Circuits for AVNRT

33. 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 )

34. 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

35. AH Jump

36. AH Jump

40. AH Jump

41. AH Jump

42. Normal AV Nodal Function Curve

43. Discontinuous AV Nodal Function Curve

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

46. Retrograde Jump

47. Retrograde Jump

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

49. Multiple Jumps

50. Multiple Jumps

52. Multiple Jumps

53. Multiple Jumps

54. AV Nodal Echo Beat

55. AV Nodal Echo Beat

56. AV Nodal Echo Beat

58. Induction of AVNRT

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

61. 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

62. Induction of AVNRT

63. Induction of AVNRT

64. Induction of AVNRT

65. Initiation of AVNRT by Spontaneous PAC

66. Initiation of AVNRT by Spontaneous PAC

67. AVNRT

68. AVNRT

69. Atypical AVNRT

70. AVNRT With LBBB Pattern

71. AVNRT With LBBB Pattern

72. AVNRT With RBBB Pattern

73. AVNRT With RBBB Pattern

74. AVNRT With 2:1 AV Block

75. AVNRT With 2:1 AV Block

76. AVNRT With 2:1 AV Block

77. PVC Superimposed on His No Advancement of A

78. PVC Superimposed on His Advancement of A in AVRT

80. Spontaneous Termination Antegrade Block in Slow Pathway

81. Spontaneous Termination Retrograde Block in Fast Pathway

82. Spontaneous Termination AVNRT with 2:1 AV block

83. Termination With Atrial Extrastimulus

84. RA Burst ( Entrainment & Termination )

85. RV Burst ( Entrainment )

86. RV Burst ( Entrainment & Termination )

87. Amelioration of 2:1 AV Block by PVC

89. TREATMENT The acute attack Vagal maneuvers
Adenosine 6-12 mg iv rapidly
Verapamil 5-10 mg iv
Diltiazem mg/kg iv

90. 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

91. 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

92. 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

93. Radiofrequency Ablation Approaches
Fast pathway ablation, Anterior approach
Slow pathway ablation, Posterior approach

94. 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

95. p

96. 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

97. Successful Signals

98. Successful Signals

99. Successful Signals

100. Slow Pathway Ablation Anatomic Approach

101. 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)

102. Slow Pathway Ablation Successful Sites

103. Slow Pathway Ablation Successful Site

104. Slow Pathway Ablation Successful Site, RAO View

105. Slow Pathway Ablation Successful Site, LAO View

106. 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

107. Accelerated Junctional Rhythm

109. Accelerated Junctional Rhythm

110. Accelerated Junctional Rhythm

111. 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%

112. VA Block during RFA

113. 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

114. 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)

115. AV Nodal Conduction Curve After Slow Pathway Ablation

116. 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

117. 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

118. Fast Pathway Ablation Site

119. 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 %)
Insignificant changes in Wenckebach cycle length and AV nodal refractory period

120. 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

121. 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: , 1996.
** Kalbfleisch, et al. JACC 19: , 1992