This document outlines techniques for differentiating supraventricular tachycardias (SVTs). It discusses features of SVT induction and baseline tachycardia characteristics, as well as diagnostic maneuvers that can be performed during tachycardia and after termination in sinus rhythm. These include the effects of atrial and ventricular extrastimulation or pacing on SVT cycle length, VA intervals, and atrial activation sequences to help identify the mechanism as atrial tachycardia, atrioventricular nodal reentrant tachycardia, or orthodromic reentrant tachycardia using an accessory atrioventricular connection. The document provides detailed descriptions and examples of applying these diagnostic tests.

1. Hany S. Abed
B . P h a r m a c y , M B B S , P h D , I B H R E C e r t i f i e d E P a n d C a r d i a c D e v i c e s S p e c i a l i s t
C l i n i c a l C a r d i a c E l e c t r o p h y s i o l o g y F e l l o w L o y o l a U n i v e r s i t y M e d i c a l C e n t e r
Techniques for Differentiating
Supraventricular Tachycardias
Concepts and Cases
April 25th 2014

2. Outline
 Induction of tachycardia
 Baseline tachycardia features
 Diagnostic maneuvers during tachycardia
 Diagnostic maneuvers in sinus rhythm after
tachycardia termination

3. Induction of Tachycardia
 Initiation by AES or atrial pacing
 Requirement of AV conduction delay
 Warm-up
 VA interval
 Initiation by VES or ventricular pacing
 HA interval

4. Initiation by AES or Atrial Pacing:
Requirement of AV Conduction Delay
 SVT initiation that is reproducibly dependent on a
critical AH interval:
 Classic for typical AVNRT
 Not always obvious with atypical AVNRT
 May be present in AT but not a prerequisite
 ORT often associated with AV delay but anterograde block in
the AAVC is key

5. Initiation by AES or Atrial Pacing:
Requirement of AV Conduction Delay

6. Initiation by AES or Atrial Pacing
 Warm-up
 Characteristic but not exclusive of automatic AT
 VA linking at induction
 Compare VA interval of first tachycardia beat to the rest of SVT
 If reproducibly identical, AT is very unlikely

7. Initiation by VES or Ventricular Pacing
 His Bundle-Atrial interval
 Compare HA interval during during SVT with the HA interval
occurring after a VES that results in an H-H interval similar to
H-H during SVT
 AVNRT
 HASVT < HAVES
 AVRT
 HASVT > HAVES

8. Baseline Tachycardia Features
 Atrial activation sequence
 Eccentric vs. Concentric
 Is earliest “A” near AV rings?

9. Baseline Tachycardia Features:
PR/RP relationship
 AT
 PR interval usually longer than during SR
 The faster the AT, the longer the PR interval
 PR interval can be >, < or = to RP
 Watch out for PR=RR resulting in P falling within QRS
(AVNRT)
 Typical AVNRT: VA typically -40 to 75 msec
 Atypical AVNRT: long RP tach
 PR and AH intervals often shorter than during SR
 ORT: usually short RP but VA > 70 msec

10. Baseline Tachycardia Features:
AV block

11. Baseline Tachycardia Features:
AV block
 Where is the block?

12. Baseline Tachycardia Features:
AV block

13. Baseline Tachycardia Features:
Oscillation in the TCL
 SVT CL variability of ≥15 msec occurs in 73% of
PSVT
 Equally prevalent in AT, ORT, AVNRT
 Changes in atrial CL precede and predict changes in
ventricular CL
 AT or atypical AVNRT
 Changes in ventricular CL precede and predict
changes in atrial CL
 Typical AVNRT or ORT

14. Baseline Tachycardia Features:
Oscillation in the TCL

15. Baseline Tachycardia Features:
Oscillation in the TCL

16. Baseline Tachycardia Features:
Oscillation in the TCL and P-QRS
 Variations in P-QRS relationship (AH, HA, AH/HA
ratio) especially at initiation or termination of SVT
 Should not be misdiagnosed as AT
 Often seen in atypical AVNRT
 May be seen in typical AVNRT
 Spontaneous changes in PR (AH) or RP (HA)
intervals with fixed A-A favor AT and exclude AVRT

17. Baseline Tachycardia Features:
Oscillation in the TCL and P-QRS

18. Baseline Tachycardia Features:
Effects of Bundle Branch Block
 LBBB aberrancy during SVT is suggestive of ORT
 BBB during SVT that does not prolong the VA (HA)
interval excludes ORT using ipsilateral AAVC
 May still be AVNRT, AT or ORT using contralateral
AAVC
 Prolongation of VA interval with BBB > 35 msec
indicates ORT with ipsilateral free wall AAVC
 Prolongation of VA interval < 25 msec suggests ORT
utilizing a septal AAVC

19. Baseline Tachycardia Features:
Effects of Bundle Branch Block

20. Outline
 Induction of tachycardia
 Baseline tachycardia features
 Diagnostic maneuvers during tachycardia
 Diagnostic maneuvers in sinus rhythm after
tachycardia termination

21. Diagnostic Maneuvers During Tachycardia
 AES during tachycardia
 Resetting
 Termination
 Atrial pacing during tachycardia
 Entrainment
 Δ AH
 Acceleration
 Overdrive suppression
 Termination
 Differential site atrial pacing
 VA interval in return cycle following cessation of pacing

22. Atrial Extrastimulation During SVT:
Resetting
 AES can reset AT, AVNRT and ORT
 Resetting with manifest atrial fusion
 May be seen in ORT and macroreentrant AT
 Not seen in AVNRT or focal AT

23. Atrial Pacing During SVT:
Entrainment
 Overdrive atrial pacing can entrain macroreentrant
AT, AVNRT and ORT
 Automatic or triggered AT cannot be entrained
 Entrainment with manifest fusion in ORT or
macroreentrant AT (similar to AES concept)
 VA linking
 Compare postpacing VA interval to SVT VA interval

24. Atrial Pacing During SVT:
Entrainment

25. Atrial Pacing During SVT:
Overdrive Suppression
 Return CL following the pacing train prolongs with
increasing duration and/or rate of pacing train
 Suggests automatic AT
 Entrained reentrant circuits have constant return
cycles regardless of the length of pacing drive
 Warm up may be seen in automatic AT after
cessation of atrial pacing

26. Atrial Pacing During SVT:
Differential-Site Atrial Pacing

27. Atrial Pacing During SVT:
Differential-Site Atrial Pacing
Δ VA < 14 msec = ORT/AVNRT

28. Atrial Pacing During SVT:
Differential-Site Atrial Pacing
Δ VA > 14 msec = AT

29. Atrial Pacing During SVT:
Differential-Site Atrial Pacing

30. Diagnostic Maneuvers During Tachycardia
 VES during tachycardia
 Resetting (His refractory VES, Preexcitation index)
 Termination
 Ventricular pacing during SVT
 Atrial activation sequence
 Entrainment
 AV vs AAV response
 Termination

31. VES During SVT:
His Refractory VES
 VES delivered during SVT when the His potential is
already manifest or within 35 to 55 msec before the
time of the expected His potential
 Advancing the next A +/- termination of SVT
 Confirms presence of retrogradely conducting AAVC
 Excludes AVNRT but not AT with bystander AAVC
 Advancing the next A with activation sequence
identical to SVT favors ORT over AT with bystander

32. VES During SVT:
His Refractory VES

33. VES During SVT:
His Refractory VES
 Delay of the next A = ORT
 Decremental conduction over AAVC
 An innocent bystander AAVC cannot delay A during AT
 Termination of SVT without an A = ORT
 VA block in the AAVC
 Note, even a well timed His refractory VES may not
affect the next atrial activation if the stim is far from
the site of the AAVC

34. VES During SVT:
His Refractory VES

35. VES During SVT:
His Refractory VES

36. VES During SVT:
Preexcitation Index
 Preexcitation index: VES usually reset ORT
 Distance between stim and ventricular insertion of AAVC
 VES coupling interval (Preexcitation index)
 PI > 75 msec suggests left free wall AAVC
 PI < 45 msec suggests septal AAVC
 The inability of single or double VESs to reset SVT
despite advancement of all ventricular EGMs
(including local V in EGM with earliest A) by > 30
msec excludes ORT

37. VES During SVT:
Preexcitation Index

38. VES During SVT:
Preexcitation Index

39.  AVNRT or ORT
 Ventricular pacing during AVNRT and ORT reaches the atrium
over the tachycardia retrograde limb
 Atrial activation sequence during SVT = Retrograde atrial
activation with V pacing during SVT
 AT
 Atrial activation during AT ≠ retrograde atrial activation with
V pacing
 Pitfall: AT originating close to AVJ
 Beware bystander AAVC with retrograde conduction
resulting in retrograde atrial activation during
V pacing ≠ SVT even if due to AVNRT or ORT
Ventricular Pacing During SVT:
Atrial Activation Sequence

40. Ventricular Pacing During SVT:
Entrainment
 PPI – TCL and SA – VA
 Original paper evaluated 30 patients with atypical
AVNRT and 44 patients with ORT using a septal
AAVC
 Same criteria apply to typical AVNRT
 For borderline values pace RV base instead of apex
 PPI-TCL will be exaggerated in AVNRT (farther from circuit)
 No significant change in ORT (still in the circuit for septal
AAVCs)

41. PPI - TCL and SA - VA
AVNRT
PPI - TCL = 150 msec SA – VA = 120 msec
*S-A measured from last pacing stimulus to HRA

42. PPI - TCL and SA - VA
ORT
PPI - TCL= 80 msec SA – VA = 40 msec
*S-A measured from last pacing stimulus to HRA

43. PPI - TCL and SA - VA

44. Corrected PPI - TCL

45. Traditional vs. Corrected PPI - TCL

46. Manifest Ventricular Fusion During
Entrainment

47. Analysis of Transition Zone During
Entrainment
 Not dependent on tachycardia continuation after
RVP
 His bundle recording is unnecessary
 AVNRT was identified with PPV and NPV of 100%
using criteria of > 1 QRS of fixed morphology to
accelerate TCL to PCL
 A cut-off of ≤ 1 QRS of fixed morphology resulting in
acceleration of TCL to PCL had a PPV and NPV of
100% for identifying ORT

48. “Transition Zone”
concepts:
• AVRT circuit is large
• AVNRT circuit is small
• It is easier to get into the AVRT
circuit when pacing from the
RV apex
• You will fuse and manifest into
the QRS quickly as you entrain
the atrium in AVRT
• You will require more
progressive fusion of the QRS
(less quickly) as you entrain the
atrium in AVNRT
• Advantage is it is independent
of SVT termination after VOP
• Need to look at all 12 ECG
leads

49. Fixed
morphology
RVP beats
required to
accelerate
TCL to PCL
Analysis of Transition Zone During
Entrainment

50. Ventricular Pacing During SVT:
A-V vs. A-A-V Response
 A-V = AVNRT or ORT
 Antegrade limb not refractory so able to conduct to V
 A-A-V = AT
 Antegrade limb (AVN) refractory since just used retrograde
 Must confirm entrrainment before applying
 Pseudo A-V and Pseudo A-A-V

51. A-V Response

52. A-A-V Response

53. Pseudo A-V Response

54. Pseudo A-V Response

55. Pseudo A-A-V Response

56. AAV or AV Response?

57. Diagnostic Maneuvers in NSR After SVT
Termination
 Atrial pacing at TCL
 ΔAH interval
 AV block
 Ventricular pacing at TCL
 ΔHA interval
 VA block
 Atrial activation sequence
 Differential RV pacing
 Parahisian pacing

58. Atrial Pacing at TCL: ΔAH Interval
 AT/ORT
 AH during SVT comparable to during A pacing at TCL due to
similar activation
 AVNRT
 AH during SVT shorter than during A pacing at TCL due to
different activation (parallel vs. series)
 Δ AH (AHatrial pacing at TCL - AHSVT)
 > 40 msec suggests AVNRT
 < 20 msec suggests AT or ORT

59. Atrial Pacing in Sinus Rhythm at TCL:
ΔAH interval

60. Atrial Pacing in Sinus Rhythm at TCL:
ΔAH interval

61. Atrial Pacing in Sinus Rhythm at TCL:
ΔAH interval

62. Atrial Pacing in Sinus Rhythm at TCL:
AV block
 AT/ORT
 Atrial pacing at the TCL should result in 1:1 AV conduction
 Should test shortly after SVT termination to maintain similar
autonomic tone
 The development of AV block with atrial pacing at
TCL is consistent with AVNRT
 Upper common pathway block

63.  AVNRT
 HA activated in parallel during SVT and in series during
ventricular pacing
 HA during SVT shorter than during ventricular pacing at TCL
 ORT
 HA activated in series during SVT and in parallel during
ventricular pacing
 HA during SVT is longer than during ventricular pacing at TCL
 Δ HA (HAV pacing at TCL – HASVT) more negative (<)
than -10 msec = ORT
 Δ HA > -10 msec = AVNRT
Ventricular Pacing in Sinus Rhythm at TCL:
ΔHA interval

64. Ventricular Pacing in Sinus Rhythm at TCL:
ΔHA interval

65. Ventricular Pacing in Sinus Rhythm at TCL:
ΔHA interval

66. Ventricular Pacing in Sinus Rhythm at TCL:
ΔHA interval

67. Ventricular Pacing in Sinus Rhythm at TCL:
ΔHA interval
Greg Michaud et al

68. Ventricular Pacing in Sinus Rhythm at TCL:
VA Block
 VA block during ventricular pacing makes ORT with
a fast retrograde AAVC unlikely
 More likely in setting of VA block
 AT
 AVNRT with lower common pathway block
 PJRT

69. Ventricular Pacing in Sinus Rhythm at TCL:
Retrograde Atrial Activation Sequence
 AVNRT
 Atrial activation sequence usually similar during AVNRT and
ventricular pacing in NSR
 ORT
 Retrograde VA conduction during ventricular pacing may proceed
over the AVN, the AAVC, or both
 Atrial activation sequence may be similar or different during
ORT and ventricular pacing in NSR
 AT
 Atrial activation during AT ≠ retrograde atrial activation with
V pacing
 Pitfall: AT originating close to AVJ

70. Maneuvers in NSR After SVT Termination:
Differential RV Pacing
 Compare VA interval and atrial activation sequence
with pacing from RV base vs. RV apex
 (-) Retrogradely conducting septal AAVC
 Shorter VA interval when pacing from the apex
 Same atrial activation sequence
 (+) Retrogradely conducting septal AAVC
 Shorter VA interval when pacing from base
 Atrial activation sequence can be same or different depending
on degree of contribution of AVN and AAVC
 Pitfalls
 Doesn’t exclude free wall AAVC or slowly conducting AAVC

71. Maneuvers in NSR After SVT Termination:
Differential RV Pacing

72. Maneuvers in NSR After SVT Termination:
Differential RV Pacing
2

73. Maneuvers in NSR After SVT Termination:
Parahisian Pacing
 Ventricle and HB capture
 Relatively narrow QRS
 S-A interval = HA interval (direct His capture)
 Only ventricular capture
 Wide QRS, LBBB
 S-A = S-H interval + HA interval

74. Maneuvers in NSR After SVT Termination:
Parahisian Pacing

75. Maneuvers in NSR After SVT Termination:
Parahisian Pacing

76. Maneuvers in NSR After SVT Termination:
Parahisian Pacing

77. Case 1: Which arrhythmia mechanism can be excluded?

78. Case 2: What arrhythmia mechanism can be confirmed?

79. Cases 1 and 2: Coumel and Reverse Coumel
BCT LBBB and NCT, VA association, eccentric CS activation, no change in CL or VA time with
change from LBBB to NCT

80. Case 3: What is the diagnosis and why?

81. Case 3: Tachycardia termination
• NCT with A>V. Short VA time
• Cannot be AVRT
• AT or AVNRT (“atypical”)
• His refractory PVC terminates the
tachycardia without affecting the
atrium
• Can only be AVNRT with block below
the final common pathway

82. Case 4: Describe the following?

83. Case 5: Describe the following?

84. Case 4 and 5: Para-His bundle pacing?
• No pathway: High output captures His and
myocardium via HPS
• No pathway: Low output captures septum
myocardium, travels to distal HPS to invade
retrograde
• Pathway present:
High output captures
His and pathway
(short-cut to atrium)
• Pathway present:
Low output captures
pathway and septum
myocardium (short-
cut to atrium)

85. Case 4 and 5: Para-His bundle pacing elaborated

86. Case 6: Which tachycardia mechanism is ruled out?

87. Case 6: Tachycardia termination
Eccentric activation of the coronary sinus catheter suggests left lateral AP
However AVNRT utilising a leftward nodal extension cannot be excluded
• PVC terminated the
tachycardia without an early
(“pulling in”) atrial
electrogram
• Indicates the SVT is AVN
dependent – thus ruling out
FAT
• Note subtle delay in atrial
electrogram – suggests
decremental retrograde
conduction

88. Case 6: PVC during SVT

89. Case 7: Which tachycardia mechanism does the following
maneuver “rule-in”?

90. Case 7: Which tachycardia mechanism does the following
maneuver “rule-in”?
• Note the PAC is delivered away from the septum. Being able to perturb the circuit far away
from the septum suggests a wide excitable gap.
• Compare that to AVNRT or Nodoventricular/Nodofascicular accessory pathway, which
have a narrow excitable gap
• If AVNRT with bystander accessory pathway: A His refractory PAC will advance next V,
BUT not “pull-in” the subsequent A.
• This is an antidromic AVRT using an AV
accessory pathway
• Delivering a PAC during His bundle
refractoriness advances the ventricle
• QRS morphology remains identical

91. Case 8: What is the most likely tachycardia mechanism?

92. Case 8: What is the most likely tachycardia mechanism?
• Pacing during sinus rhythm from
the His bundle region does not
conduct in the retrograde direction
to the atrium.
• This makes AVRT very unlikely,
AVNRT unlikely. AT is most likely

93. The End
Hany S. Abed
B . P h a r m a c y , M B B S , P h D , I B H R E C e r t i f i e d E P a n d C a r d i a c D e v i c e s S p e c i a l i s t
C l i n i c a l C a r d i a c E l e c t r o p h y s i o l o g y F e l l o w
L o y o l a U n i v e r s i t y M e d i c a l C e n t e r
A p r i l 2 0 1 4