This document discusses how pacing can help during electrophysiology studies (EPS). It describes ventricular pacing and how it can show normal retrograde activation sequences or the presence of an accessory pathway. It also discusses ventricular refractory periods and how pacing can induce arrhythmias. The document then discusses assessing atrioventricular conduction, including basic conduction intervals and response to incremental atrial pacing. It notes the indications of infra-Hisian block and disease in the His-Purkinje system as potential reasons for permanent pacing in symptomatic patients.

1. Dr. Salah Atta, MDDr. Salah Atta, MD
Consultant Electrophysiolgist, SBCCConsultant Electrophysiolgist, SBCC
Professor of CardiologyProfessor of Cardiology,,
Assiut UniversityAssiut University..
Part3Part3,,

2. How can pacing help us
during EPS?!
Ventricular Pacing:Ventricular Pacing:
The RV is paced as before from the RVA andThe RV is paced as before from the RVA and
the RVOT if needed, and this can show:the RVOT if needed, and this can show:
-Normal sequence of retrograde activation-Normal sequence of retrograde activation
earliest at the His bundle electrogram,earliest at the His bundle electrogram,
otherwise accessory pathway exists e.g ifotherwise accessory pathway exists e.g if
earliest in the CS.earliest in the CS.
-VA block .-VA block .
-Ventricle becomes refractory to the pacing-Ventricle becomes refractory to the pacing
extra-stimulus (Ventricular refractory period).extra-stimulus (Ventricular refractory period).
-Arrhythmia induction.-Arrhythmia induction.

3. Normal sequence ofNormal sequence of
retrograderetrograde
activation earliest atactivation earliest at
the His bundlethe His bundle
electrogram,electrogram,
otherwise accessoryotherwise accessory
pathway exists e.g ifpathway exists e.g if
earliest in the CS.earliest in the CS.

4. Eccenteric Retrograde Conduction

6. • The presnce of VAThe presnce of VA
dissociation duringdissociation during
ventricular pacingventricular pacing
excludes theexcludes the
presence ofpresence of
accessoryaccessory
atrioventricularatrioventricular
pathway and provespathway and proves
successful ablation ifsuccessful ablation if
it was present beforeit was present before
the ablaation.the ablaation.

7. Ventricular Refractory PeriodVentricular Refractory Period
-Ventricle becomes-Ventricle becomes
refractory to therefractory to the
pacing extra-pacing extra-
stimulusstimulus
(Ventricular(Ventricular
refractory period).refractory period).

9. -Arrhythmia induction-Arrhythmia induction
bby pacing withy pacing with
extrastimulationextrastimulation
indicates a re-indicates a re-
entrant mechanismentrant mechanism
of the inducedof the induced
tachycardia.tachycardia.

11. Example of aggressive VT indction protocolExample of aggressive VT indction protocol::
Criteria for positive or negative EPS forCriteria for positive or negative EPS for
VT induction:VT induction:
• Positive: reproducible > 10 beats VT afterPositive: reproducible > 10 beats VT after
stimulation.stimulation.
• Negative: no VT induced during study.Negative: no VT induced during study.
• Borderline: short episodes VT (<10 beats)Borderline: short episodes VT (<10 beats)
induced.induced.

13. Complications of EP study
The complications associated with
diagnostic EP studies are low. Mortality
is extremely rare. Complications are
usually associated with catheterization
and catheter manipulation rather than
stimulation and the induction of
arrhythmias. The reported complications
include hemorrhage, venous
thromboembolism (<1%), phlebitis (<1%),
cardiac perforation and tamponade, and
refractory ventricular fibrillation.

14. Complications of EP study
Most reported deaths have resulted from
incessant ventricular fibrillation and have
occurred in patients with severe LV
dysfunction, active myocardial ischemia,
or hypertrophic obstructive cardio-
myopathy or because of the pro-
arrhythmic effect of drugs administered
during the evaluation.

15. Complications of EP study
Hemo-thorax and pneumothorax,
recognized complications, can occur
when the subclavian or internal jugular
venous approaches are used. Arterial
catheterization increases the associated
morbidity,including vascular complications,
stroke, systemic embolism, and protamine
reactions.

16. Sinoatrial Node Function TestsSinoatrial Node Function Tests
• Sinus Node Recovery Times:Sinus Node Recovery Times:
• The sinus node is the archetype of an automaticThe sinus node is the archetype of an automatic
focus. Automatic rhythms are characterized byfocus. Automatic rhythms are characterized by
spontaneous depolarization, by overdrivespontaneous depolarization, by overdrive
suppression, and by post-overdrive “warm-up” orsuppression, and by post-overdrive “warm-up” or
return to baseline cycle length (BCL).return to baseline cycle length (BCL).
• Pacing at rates in excess of the spontaneousPacing at rates in excess of the spontaneous
rate of an automatic focus results in temporaryrate of an automatic focus results in temporary
inhibition of spontaneous depolarization, withinhibition of spontaneous depolarization, with
gradual return to the original cycle length overgradual return to the original cycle length over
several beats following cessation of pacing.several beats following cessation of pacing.

17. Sinus node function testsSinus node function tests
Sinus node recovery timeSinus node recovery time ::
The HRA catheter is paced faster than theThe HRA catheter is paced faster than the
sinus rate by at least 30 ms for 30-60sinus rate by at least 30 ms for 30-60
seconds, then abruptly stopped. Sinus nodeseconds, then abruptly stopped. Sinus node
recovery time (SNRT) can be measured usingrecovery time (SNRT) can be measured using
this way of pacing.this way of pacing.
SNRT is the interval between the last pacedSNRT is the interval between the last paced
beat and the first returning sinus beat.beat and the first returning sinus beat.
Normal range < 1500ms.Normal range < 1500ms.
Corrected SNRT=SNRT-sinus cycle lengthCorrected SNRT=SNRT-sinus cycle length
which is normaly less than 525 ms.which is normaly less than 525 ms.

20. CSNRTCSNRT
• 1.1. CSNRT = SNRT-sinus cycle length.CSNRT = SNRT-sinus cycle length.
This is the most common correction.This is the most common correction.
Normal values have been reported fromNormal values have been reported from
350 to 550 milliseconds, with 500350 to 550 milliseconds, with 500
milliseconds being most commonly used.milliseconds being most commonly used.
• 2.2. CSNRT = X% of sinus cycle length.CSNRT = X% of sinus cycle length.
Normal values range up to 160%.Normal values range up to 160%.
• 3.3. CSNRT = 1.3 (mean sinus cycle lengthCSNRT = 1.3 (mean sinus cycle length
in milliseconds) + 101 milliseconds.in milliseconds) + 101 milliseconds.

21. Sinoatrial conductionSinoatrial conduction
timetime::
Two ways to calculate:Two ways to calculate:
• A single paced atrial stimulus is deliveredA single paced atrial stimulus is delivered
just before the next spontaneous sinus cycle,just before the next spontaneous sinus cycle,
thereby resetting the sinus node. SACT isthereby resetting the sinus node. SACT is
calculated from the interval between thecalculated from the interval between the
paced stimulus to the next sinus beat (returnpaced stimulus to the next sinus beat (return
interval) and equals half the differenceinterval) and equals half the difference
between the spontaneous cycle length andbetween the spontaneous cycle length and
the return cycle length. Normal range 50-125the return cycle length. Normal range 50-125
ms. Prolonged SACT indicates susceptibilityms. Prolonged SACT indicates susceptibility
to exit block.to exit block.
• CSNRT of a single beat, if divided by 2, yieldsCSNRT of a single beat, if divided by 2, yields
sino atrial conduction time (SACT).sino atrial conduction time (SACT).

23. • AV block is due to failure of conduction of
the atrial impulse to ventricle in the
absence of physiologic refractoriness. It is
generally due to interruption of the normal
conduction pathway or due to pathologic
refractoriness.
Atrioventricular ConductionAtrioventricular Conduction
assessmentassessment

26. Level of A-V block
• AV block can be proximal (above the His
bundle) indicating block in the AVN or it
can be intra-Hisian or it can be distal to
His bundle (infra-Hisian).
• The prognosis depends on the site of the
AV block.
• Block distal to His bundle implies poor
prognosis and thus indicates permanent
pacing.

27. • EPS can confirm the site of
spontaneous AV block or conduction
delay.
• EPS may identify indications for
permanent pacemaker implantation
in individuals with syncope of
unknown cause.
Atrioventricular Conduction
assessment

28. Atrioventricular Conduction
assessment
• Basic conduction intervals:
Prolongation of the H-V interval > 70 msec
is an indication of infra His disease and in
symptomatic patient this may indicate
permanent pacing in patients with 1st
degree HB or BBB while A-H prolongation
is not as significant.

30. Response to incremental atrial pacing
• As the atrial pacing rate increases, there is
normally a slight increase in the intra-atrial
conduction time, a progressive increase in
the AV node conduction time (the AH
interval), and little change in the HV
interval, with block usually at the AV node
level (supra His block with no His following
the A).

32. • AV nodal function is assessed by determining
the point at which 1:1 AV conduction ceases
and AV nodal Wenckebach begins.
• The normal response to incremental atrial
pacing at progressively faster rates is to
develop a longer AH interval and, ultimately,
block in the AV node.
• Most normal individuals develop
Wenckebach AV block at paced atrial cycle
lengths of 500 to 350 ms (heart rates of 120
to 170 beats/min).
Normal Response to atrial
pacing

34. • Wenckebach AV block occurs at longer cycle
lengths (slower pacing rates) in patients with
enhanced vagal tone or under drug effects and at
shorter cycle lengths (faster pacing rates) in patients
with enhanced sympathetic tone as during exercise.
• In contrast to the AH interval, the HV interval
remains relatively constant during incremental atrial
pacing, and block below His (infra-Hisian or intra-
Hisian block) is considered pathologic at pacing
cycle lengths greater than 400 ms (rates <150
beats/min).
Abnormal Response to atrial
pacing

35. Infra-His block

37. What is your diagnosis?

38. What is this?

39. • In symptomatic patients:
Long HV intervals (≥70 to 100 ms) and
block below the His bundle at atrial pacing
rates of less than 150 beats/min (≥ 400
ms) indicate disease in the His-Purkinje
system and are associated with a
relatively high incidence of subsequent
complete heart block.
Indication of Permanent Pacing

40. Till next time InshaALLAH
Thank you