EP Flashcards
Characteristics of Typical AVNRT
Dual nodal physiology
Down the slow, up the fast = short VA
Doesn’t involve A & V = tachy can end on A or V
VA time of typical AVNRT
<50ms
BBB and typical AVNRT
No change in VA time as A & V and bundle branches are not involved in tachy
Tachycardias involving the ventricle and AVN
AVRT
PJRT
Tachycardias not involving ventricles and AVN
AVNRT
AT
Intraatrial re-entry tachy
SA nodal re-entry
AF/AFlutter
BBB and AVRT
In AVRT or macro re-entrant, BBB on same side as AP will increase tachy cycle length
LBBB with left sided pathway - tachy now has to travel to RBB then myocardium before back up AP causing longer VA time.
Parahissian pacing
high outputs = narrow QRS as capturing AVN, HIS and local RV
low outputs = broad QRS as capturing only RV
Only excludes right sides postreoseptal APs
Parahissian pacing response
VA time increased = no evidence of septal accessory pathway
- with loss of HIS capture suggests VA time is dependent on HIS-bundle
VA time unchanged = evidence of accessory pathway
-
When can atrial capture during Vp be suspected?
When VA time is <60ms
Repetitive V
Ventricular response during curve with similar morphology and axis to paced beat
RVOT paced morphology
LBBB
Positive in inferior leads
avL negative
LVOT paced morphology
LBBB
Negative in inferior leads
avL positive
Response to entrainment
VAAV
AT
both antegrade and retrograde conduction occurs via AVN so last entrained atrial beat hits a refractory AVN
Response to entrainment
VAV (VAHisV)
AVRT or AVNRT
entrainment of atrium due to retrograde conduction over the ascending limb of AVNRT (regardless of type of AVNRT) or up the AP i.e. ORT then antegrade down the AVN
What does it mean if tachy terminates during entrainment?
- Termination of tachy without affecting the atrium excludes AT i.e. end with a V
- Tachy ends with A – likely AVRNT or AVRT
HIS sync VPBs :
No change in AA timing means?
exclusion of right sided AP
if AA changed, the only way for it to reach atrium that quickly would be because of an AP that conducts retrogradely
HIS sync VPBs :
Atrial advancement with resetting means?
AP that contributes to SVT mechanism is present i.e. ORT
next A is advanced, which subsequently advances next HIS and V
HIS sync VPBs:
Atrial advancement without resetting means?
AVNRT with bystander AP
no reset means next A is advanced but doesn’t advance next HIS and V
HIS sync VPBs :
Atrial advancement with different atrial activation sequence means?
bystander AP
e.g. from concentric to eccentric or 9-10 first to 5-6 first
HIS sync VPBs :
Atrial post excitation means?
ORT or decremental AP
delay of next A after HIS sync VPB
HIS sync VPBs :
Termination of SVT
ORT
What is the problem when a wobble is present?
Treating during SVT tachy with wobble (variations in cycle length more than 30ms) is un-useful.
What is the importance of post pacing interval (PPI)?
Used to differentiate between atypical AVNRT and AVRT that uses a septal AP.
What is para-HISian pacing?
Testing used to exclude presence of right sided septal AP
Purpose of an EP study
a) Antegrade and retrograde conduction properties of AVN/AP/ANVRT
b) If present, is AP/AVNRT safe?
c) Allows for SVT?
In Concentric atrial activation, where is A seen first on the CS channel?
channel 9-10
In eccentric atrial activation, where is A seen first on the CS channel?
Can be anywhere on CS channel depending on diagnosis and localisation
What does it mean if the on the MAP channels signals on channel 3-4 are seen to be ahead of signals on channel 1-2?
The ablation catheter tip (channel 1-2) has gone past the hot spot
What is the advantage of using adenosine/verapamil?
VA and AV block which allows for hyperpolarisation of AP if still present before or after ablation
Define Eccentric activation
atrial activation other than by AV node during V pacing
or early activation of ventricle during A pacing
Define concentric activation
normal AVN activation of atria
*earliest atrial activation on HIS catheter first
Define Wenckbach CL
The point at which the AP or AVN becomes refractory during incremental pacing
Purpose of IVP
Discover what retrograde routes connecting ventricles to atria are available for impulse conduction
No VA conduction suggests lack of VA connection via AVN or AP and AT is more likely
Define AV nodal echo beat
One beat of non-sustained tachycardia caused by anterograde conduction via the slow pathway. and subsequent retrograde activation via the fast pathway
Conventional ablation therapy for AVNRT is what?
slow pathway modification
*aim to disrupt tachycardia substrate by ablating slow pathway and changing conduction properties
What can indicate the operator is on the wrong site for ablation during AVNRT cases?
HIS signal on ablation catheter (Map)
Why is Ablation of AVNRT is performed during Sinus rhythm?
Sinus Rhythm
*to increase stability of catheter and monitor AV association
How many seconds of ablation for AVNRT should elicit Junctional Rhythm?
15s
*Accelerated junctional rhythm >120bpm could suggest ablation of fast pathway or AVN which increases risk of CHB
What targets for ablation can be seen on the Map catheter to indicate good contact with the slow pathway?
Large V signal
Small A signal
No HIS signal
Identify the primary endpoints for AVNRT ablation
complete elimination or modification of slow pathway assessed by:
- Presence of slow Junctional rhythm during ablation
- Non inducibility of AVNRT
Differential diagnosis for a wide complex tachycardia with RBBB and long RP in tachycardia
- atypical (fast-slow) AV nodal reentrant tachycardia
- orthodromic reciprocating tachycardia
- atrial tachycardia with an underlying bundle branch block
Identifying AP location:
Late Transition in chest leads
Late (V3 and onwards) = lateral
Identifying AP location:
Inferior leads (aVR, II,III)
All neg = posterior
All Pos = Anterior
Mismatch = midline
Identifying AP location:
V1/V6
LBBB = right sided (Bigger S wave in V1)
RBBB = left sided (Bigger R wave in V1)
Antidromic AVRT has a long or short RP?
Long
Contraindications of adenosine
second and third degree AV block
allergy
care with asthma and COPD
Why should adenosine not be administered for suspected VT?
Andenosine in VT can accelerate the frequency and aggravate the arrhythma.
If suspected SVT and adenosine is administered and the response is no effect or tachy acceleration then likely VT
End point criteria for AVNRT slow pathway ablation
No jump
No echo
Slow pathway block
When to tell operator to stop during AVNRT ablation
Getting close to AVN
Too many ablation points with no true junctional response
How do you reveal a pathway?
- Adenosine - disable the AVN
- Ap fast enough to cause decrement in the AVN to allow AP to beat it and conduct first
- pace closer to the pathway
How do you pace close to an AP without moving a catheter or using a RA catheter?
Pace from different poles on the CS.
9-10 to pace the right side of the atrium (RA)
5-6/7-8 for septal
1-2 to pace left side of atrium (LA)
PPI for right sided pathways short or long?
Short usually 30-40ms because the tachy is within the RV circuit
What is atrial fusion?
when the atria is activated partly by a sinus impulse and partly by a retrograde impulse from the AVN or ventricle
What do changes to atrial activation during SVT or Vp suggest?
Multiple bypass tracts
Where is the usually the earliest site of atrial activation during AVRT tachy?
Adjacent to the mitral or tricuspid annulus and atrial activation is identical to during Vp.
What would retrograde atrial activation (I.e. during Vp) for an A tach look like?
Normal midline pattern across the AVN and not near the annuli which differs from eccentric (antegrade) during AT. *could be similar if AT is located in the same region as a septal pathway)
Note: remember eccentric atrial activation during AVRT/AVNRT tachy would be identical to retrograde atrial activation.
Eccentric atrial activation during Vp and tachy is more likely to be diagnostic of what?
AP
Eccentric atrial activation during tachy rules out AT because AT has normal nodal midline retrograde activation.
VA dissociation during tachy rules out what?
AVRT
What does it mean to bracket the earliest site with a deca nav catheter?
To demonstrate later activation on either side of the earliest site.
If not reachable via the CS, left sided mapping should be performed
Why is it important to map along the tricuspid annulus for a right sided pathway?
SA node activation combined with pathway activation might give high low appearance on map causing incorrect diagnosis of sinus node re-entrant tachy or intra atrial reentrant tachy
Septal bypass tracts, anterior or posterior, demonstrate what?
A normal retrograde atrial activation sequence
Differentiate between AVN and AP via fixed or decremental properties.
Why is VA time in AVRT longer than in typical AVNRT?
SVT using AP goes to ventricle first before returning to atrium
- but in atypical AVNRT, long RP means VA times could be similar to AVRT
Localising accessory pathways:
Early transition in chest leads
Early (by V2/V3) = septal
