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 is reproducibly dependent on a critical AH interval :
• Classic for typical AVNRT
• Not always obvious with atypical AVNRT
• Maybe present in AT but not a prerequisite
• ORT often associated with AV delay but antegrade block in the AP is the key
5.
6. • Warm-up
• Characteristic but not exclusive of AT
• VA linking at induction
• Compare VA interval of the first tachycardia beat to the rest the of the SVT
• if reproducibly identical, AT is very unlikely
Initiation by AES or Atrial pacing
7. • HA interval : compare HA interval during SVT and HA interval
occurring after a VES
• HASVT < HAVES : AVNRT
• HASVT > HAVES : AVRT
Initiation by VES or Ventricular pacing
8.
9. Baseline Tachycardia Feature
• Atrial activation sequence
• Eccentric vs Concentric
• Is the earliest A near the AV ring ?
• PR/RP relationship
• AT : PR interval usually longer than during SR, the faster the AT, the longer the PR
interval
• Typical AVNRT : VA typically 40-75ms
• Atypical AVNRT : long RP tachycardia, but PR and AH interval often shorter than
during SR
• ORT : usually short RP but VA > 70ms
• VA block
11. Baseline Tachycardia Feature
• Oscillation in the TCL
• SVT CL variability of ≥ 15𝑚𝑠 occurs in around 70% of PSVT
• Changes in atrial CL precede the changes in ventricular CL : AT or Atypical AVNRT
• Changes in ventricular CL precede the changes in atrial CL : Typical AVNRT or ORT
13. • Variation P-QRS relationship (AH, HA, AH/HA ratio) especially in
the initiation or termination of tachycardia
• should not be missed diagnosed as AT
• often seen in atypical AVNRT
• may seen in typical AVNRT
• Spontaneous changes in PR(AH), RP(HA) intervals with fixed A-A
• favors AT
• exclude AVRT
Baseline Tachycardia Feature
Oscillation in TCL
15. Effects of BBB :
• BBB aberrancy during SVT is often suggestive of ORT
• BBB during SVT that does not prolong the VA (HA) interval excludes ORT using
ipsilateral AP, may still be AVNRT, AT or ORT using contralateral AP
• Prolongation of VA interval with BBB > 35ms indicates ORT with ipsilateral free wall
AP
• Prolongation of VA interval < 25ms suggests ORT utilizing a septal AP
Baseline Tachycardia Feature
16. Diagnostic Maneuvers during Tachycardia
• AES during tachycardia
• Resetting
• Termination
• Atrial pacing during tachycardia
• Entrainment
• Delta AH
• Acceleration
• Overdrive suppression
• Termination
• Differential site atrial pacing
• VA interval in return cycle following cessation of pacing
17. AES during SVT
Resetting
• AES can reset AT, AVNRT and ORT
• Resetting with manifest atrial fusion
• maybe seen in ORT and macroreentrant AT
• Not seen in AVNRT or focal AT
18. • Overdrive atrial pacing can entrain macroreentrant AT, AVNRT and ORT
• Automatic or triggered AT can not be entrained
• Entrainment with manifest fusion in ORT or macroreentrant AT (similar to AES
concept)
• VA linking : compare post pacing VA interval to SVT VA interval
Atrial pacing during SVT
Entrainment
19. • Return CL following the pacing train prolongs with increasing duration/ or rate
of pacing train, suggests automatic AT
• Warm up maybe seen in automatic AT after cessation of atrial pacing
Atrial pacing during SVT
Overdrive suppression
23. • VES during tachycardia
• Resetting (His refractory VES)
• Ventricular pacing during SVT
• Atrial activation
• Entrainment
• AV vs AAV response
• Termination
Diagnostic Maneuvers during Tachycardia
24. VES during SVT
His refractory
• VES delivered during SVT when the His potential is already manifest or within 35 to
55ms before the time of expected His potential
• Advancing the next A +/- termination of SVT
• confirms presence of retrogradely conducting AP
• excludes AVNRT but not AT with bystander AP
• Advancing the next A with activation sequence identical to SVT favors ORT over AT
with bystander
25.
26. VES during STV
His refractory
• Delay of the next A = ORT
• decremental conduction over AP
• an innocent bystander AP can not delay A during AT
• Termination of SVT without an A = ORT
• VA block in AP
• Note, even a well timed His refractory VES may not affect the atrial activation if the
stim is far from the site of AP
29. Ventricular Pacing during SVT
Atrial Activation Sequence
• 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
• AT
• Atrial activation during AT ≠ Retrograde atrial activation with V pacing
• Bystander AP with retrograde conduction
• resulting in retrograde atrial activation during V pacing ≠ SVT even if due to AVNRT
or ORT
33. • V-A-V = AVNRT or ORT
• Antegrade limb not refractory so able to conduct to V
• V-A-A-V = AT
• Antegrade limb(AVN) refractory since just used retrograde
• Pseudo V-A-V and pseudo V-A-A-V
Ventricular Pacing during SVT
V-A-V / V-A-A-V response
37. Diagnostic Maneuvers during NSR
after SVT termination
• Atrial Pacing at TCL
• Delta AH interval
• AV Block
• Ventricular pacing at TCL
• Delta HA interval
• VA Block
• Atrial activation sequence
• Difference RV pacing
• Parahisian pacing
38. Atrial Pacing at TCL
Delta AH interval
• AT/ORT
• AH during SVT comparable to during at A pacing at TCL due to similar activation
• AVNRT
• AH during SVT shorter than during A pacing at TCL due to different activation
• 𝝙 AH ( AH atrial pacing at TCL – AH svt)
• > 40msec suggests AVNRT
• < 20msec suggests AT or ORT
41. • AT/ORT
• Atrial pacing at the TCL should result in 1:1 AV conduction
• AVNRT
• Development of AV block/ Upper common pathway block
Atrial Pacing in SR at TCL
AV Block
42. • AVNRT
• HA activated in parallel during SVT and in series during V pacing
• HA during SVT shorter than during V pacing
• Δ HA = HA V pacing – HA svt > -10msec
• ORT
• HA activated in series during SVT and in parallel during V pacing
• HA during SVT is longer than during V pacing
• Δ HA more negative ( < -10msec)
Ventricular Pacing in SR at TCL
Δ HA interval
46. • VA block during ventricular pacing makers ORT with a fast retrograde AP
unlikely
• In the setting of VA block, it could be :
• AT
• AVNRT with lower common pathway block
• PJRT
Ventricular Pacing in SR at TCL
VA Block
47. • AVNRT
• Atrial activation sequence usually similar during AVNRT and ventricular pacing in
NSR
• ORT
• Retrograde VA conduction during pacing may procced over the AVN, the AP or both
• AT
• Atrial activation during AT ≄ retrograde atrial activation with V pacing
• Pitfall : AT originating close to AVJ
Ventricular Pacing in SR at TCL
Retrograde atrial activation sequence
48. • Compare VA interval and Atrial activation sequence with pacing from RV base vs RV apex
• (-) Retrogradely conducting septal AP
• Shorter VA interval when pacing from the apex
• Same atrial activation sequence
• (+) Retrogradely conducting septal AP
• Shorter VA interval when pacing from the base
• Atrial activation sequence can be the same or different depending on degree of contribution
AVN and AP
• Pitfall
• Doesn’t exclude free wall AP or slowly conducting AP
Maneuvers in NSR after SVT termination
Different RV Pacing
50. • Ventricle and HB capture
• relatively narrow QRS
• S-A interval = HA interval ( direct His capture)
• Only Ventricle capture
• wide QRS, LBBB
• S-A = SH + HA
Maneuvers in NSR after SVT termination
Parahisian Pacing
