1. Dr. Salah Atta, MDDr. Salah Atta, MD
Consultant Electrophysiolgist, SBCCConsultant Electrophysiolgist, SBCC
Professor of CardiologyProfessor of Cardiology,,
Assiut UniversityAssiut University..
Part2Part2,,

2. Sequence of Activation
• Determination of the sequence of antegrade and
retrograde activation during spontaneous
rhythms, atrial pacing, ventricular pacing, and
induced rhythms is essential in diagnosis of
normal vs abnormal rhythm and the type of
abnormal rhythm if present.

3. Sequence of Activation
• The atrial activation in sinus rhythm begins
in the high right atrium and spreads to the
low right atrium and His bundle, with left
atrial activation recorded from the
coronary sinus catheter occurring
signifcantly later.
• Ventricular activation normally earlier in His,
then RV then LV in CS from proximal to distal.

7. Retrograde conduction
When ventriculoatrial conduction is present
during ventricular pacing, the earliest retrograde
atrial activity is recorded in the His bundle
electrogram followed by the RA and coronary
sinus recordings.
Abnormal or eccentric sequences of retrograde
atrial activation occur in the presence of AV
accessory pathways. This is discussed in more
detail in subsequent sections dealing with
supraventricular tachycardia and catheter
ablation.

9. Normal sequence ofNormal sequence of
retrograde activationretrograde activation
earliest at the Hisearliest at the His
bundle electrogram-bundle electrogram-
(1st), otherwise(1st), otherwise
accessory pathwayaccessory pathway
exists e.g if earliest inexists e.g if earliest in
the CS (2nd,3rd).the CS (2nd,3rd).

10. Basic Intervals
• After the catheters are positioned,
basic conduction intervals are
measured, including the basic Sinus
Cycle Length (the A-to-A interval), P
wave duration, AH interval, and HV
interval. Measurements from the
surface ECG, including the PR interval,
QRS interval, and QT interval, are also
recorded.

11. • Can measure the intervals using the
system or the tracing using the ruler
and knowing the recording speed:
The duration in ms = distance in mm x
1000/speed in mm e.g if speed is 100
mm/sec, then 100 mm =1000 msec
and a distance of 20 mm=
20x1000/100=200 msec

12. Measurement of basic intervals:Measurement of basic intervals:
PA interval: 20-40ms,PA interval: 20-40ms, from the onset offrom the onset of
the earliest P wave on the surface ECG to thethe earliest P wave on the surface ECG to the
earliest rapid deflection of the atrialearliest rapid deflection of the atrial
electrogram from the His Catheter, measureselectrogram from the His Catheter, measures
atrial conduction.atrial conduction.
AH interval: 50-140ms,AH interval: 50-140ms, representsrepresents
conduction through the AV node to the Hisconduction through the AV node to the His
bundle, measured in the His Catheter,bundle, measured in the His Catheter,
How to
know ?!

13. • HV interval: 30-55 ms,HV interval: 30-55 ms, rpresentsrpresents
conduction from proximal His bundleconduction from proximal His bundle
to the ventricular myocardium.to the ventricular myocardium.
• Cycle Length:Cycle Length: (from peak to peak)(from peak to peak)
the R-R interval or the V-V intervalthe R-R interval or the V-V interval

14. A-H interval
• The AH interval represents conduction
time from the low right atrium at the
interatrial septum through the AV node to
the His bundle and approximates AV
nodal conduction time.
• The measurement is made from the
earliest reproducible rapid defection of the
atrial electrogram on the His bundle
recording to the onset of the His defection
on that electrogram. Normal values for
adults are reported to range from 50 to
140 ms.

15. A-H interval
• The AH interval is infuenced strongly by the
patient’ s autonomic tone and may vary by 50
ms during a study in a given patient.
• The AH interval normally increases in
response to increases in atrial pacing rates.
• It may also be altered by drugs that affect AV
conduction, and the measurement may be
infuenced artifcially by such factors as gain
setting and position of the atrial catheter.

17. The H-V interval
• The HV interval represents conduction time
from the proximal His bundle to the ventricular
myocardium. The measurement is made from
the earliest defection of the His spike on the His
bundle recording to the earliest onset of
ventricular activation recorded from any
intracardiac electrogram or surface ECG.
Normal values range from 30 to 55 ms. In
contrast to the AH interval, the HV interval
normally remains relatively constant and is not
signifcantly affected by variations in autonomic
tone or atrial pacing rates.

20. How to know ?!
During pacing:During pacing:
Pacing concept:Pacing concept: If an electronicIf an electronic
pacemaker or a stimulator applies smallpacemaker or a stimulator applies small
electrical pulses „Stimuli“ to the ventricularelectrical pulses „Stimuli“ to the ventricular
or atrial electrode tissue interface, theor atrial electrode tissue interface, the
electrical field radiates from the electrode,electrical field radiates from the electrode,
triggers rapid depolarization of few cellstriggers rapid depolarization of few cells
which spreads by cell-to-cell conductionwhich spreads by cell-to-cell conduction
throughout the entire muscle mass initiatingthroughout the entire muscle mass initiating
a cardiac impulse.a cardiac impulse.

21. Capture can be observed as aCapture can be observed as a
depolarization observeddepolarization observed
immediately after the stimulusimmediately after the stimulus
artifact.artifact.

22. Common terminology
used to describe the pacing stimuli and their subsequent
intracardiac electrograms:
• S1: drive train pacing stimulus usually delivered in
groups of 5–8 beats with a pause around 2 seconds
between successive trains.
• S2, S3, S4: respectively, a first, second, and third
extrastimulus
• S1–S2, S2–S3, S3–S4: coupling intervals respectively
between S1 and S2, S2 and S3, S3 and S4
• A1: atrial electrogram associated with S1 drive or
spontaneous atrial beat
• A2, A3: atrial electrogram associated with respectively
S2 and S3 or the first spontaneous atrial electrogram
respectively after A1 or A2

23. Follow terminology
• H1, H2, H3: His bundle electrogram
associated respectively with A1, A2, and
A3
• V1: ventricular electrogram associated
with S1 or spontaneous ventricular beat
• V2, V3: ventricular electrogram associated
with respectively S2 and S3 or the first
spontaneous ventricular electrogram
respectively after V1 and V2.

24. How to know ?!
Pacing methods:Pacing methods:
A pulse duration of 1 or 2 milliseconds at doubleA pulse duration of 1 or 2 milliseconds at double
the pacing threshold is most commonly used.the pacing threshold is most commonly used.
Both atrial and ventricularBoth atrial and ventricular
pacing can be done in any ofpacing can be done in any of
the following ways:the following ways:
Fixed rate pacingFixed rate pacing (at a fixed drive cycle).(at a fixed drive cycle).
Pacing with extrastimulationPacing with extrastimulation
Incremental pacingIncremental pacing: with progressive: with progressive
shortening of the pacing cycle length.shortening of the pacing cycle length.

25. Programmed Electrical Stimulation
The major purposes of programmed
electrical stimulation are to
• 1-characterize the electrophysiologic
properties of cardiac tissue (Refractory
periods)
• 2- to assess sequence of activation both
antegrade and retrograde
• 3- to induce and analyze the mechanism
of arrhythmias and to terminate
tachyarrhythmias.

26. Extrastimulus TechniquesExtrastimulus Techniques
• One or more extrastimuli (designated S2, S3,One or more extrastimuli (designated S2, S3,
SN) are introduced at specific coupling intervalsSN) are introduced at specific coupling intervals
based on previous drive S1s, or spontaneousbased on previous drive S1s, or spontaneous
beats. Thereafter the S1S2 interval is altered,beats. Thereafter the S1S2 interval is altered,
usually in- 10 to 20-millisecond steps, until anusually in- 10 to 20-millisecond steps, until an
end point, such as tissue refractoriness, orend point, such as tissue refractoriness, or
termination or induction of a tachycardia, istermination or induction of a tachycardia, is
reached.reached.
• When the physician is satisfied with the resultsWhen the physician is satisfied with the results
of S1S2 testing, a second extrastimulus (S3)of S1S2 testing, a second extrastimulus (S3)
may then be introduced, with the S2S3 intervalmay then be introduced, with the S2S3 interval
altered in a fashion similar to that used for S1S2.altered in a fashion similar to that used for S1S2.

28. Determination of Refractory
Periods
• The refractoriness of cardiac tissue is defned by
the response of the tissue to the introduction of
premature stimuli. For most routine EPS, the
ERP is defned as the longest coupling interval
between the basic drive and the premature
stimulus that fails to propagate through the
tissue. Normal values for AV nodal, atrial, and
ventricular refractory periods have been
established ). The ERP of cardiac tissue may be
affected by the current strength used, the pacing
rate, medications, and autonomic tone in the AV
node.

29. How to know ?!
Atrial pacing withAtrial pacing with
extrastimulation:extrastimulation:
Pacing with a train of 6-10 beatsPacing with a train of 6-10 beats
at a fixed cycle length followedat a fixed cycle length followed
by an extrastimulus at a shorterby an extrastimulus at a shorter
cycle length which is shortenedcycle length which is shortened
each time.each time.

30. Atrial extrastimulus testing
• Atrial extrastimulus testing can determine the
properties of the AV node (antegrade) and of the
atrium.
• By progressively shortening the S2
extrastimulus, the AV node RRP will be reached
first when A2H2 begins to be longer than A1H1
• As the S2 atrial extrastimulus cycle length
decreases, the conduction over the AV node
(represented by the A2H2 interval) progressively
increases, known as the decremental
conduction over the AV node

32. A-H Jump
• An increase in the A2H2 by 50 ms or more
is sometimes observed with a decrease of
the atrial S2 extrastimulus by 10 ms. This
A2H2 increase, also called a jump, is
evidence of dual AV node physiology.
Briefly, this means that antegrade
conduction over the AV node has shifted
from the usual fast pathway to a slow
pathway.

33. Dual AV nodal pathway if there is AH jump,
Arrhythmia induction

34. Refractory periods
• By further decreasing the S2 interval, the
ERP of the AV node will be achieved
when the atrium A2 is no longer followed
by the His H2 .
• Finally, the S2 spike will no longer capture
the atrium (atrial ERP, also called atrial
refractoriness).

37. Atrial pacing:Atrial pacing:
Incremental Atrial pacing:Incremental Atrial pacing:
Means continuos pacing the atrium withMeans continuos pacing the atrium with
progressive shortening of the pacing cycleprogressive shortening of the pacing cycle
length, shows:length, shows:
- the wenckebach point and excludes infra- the wenckebach point and excludes infra
His block,His block,
-may show pre-excitation, may induce the-may show pre-excitation, may induce the
tachycardia .tachycardia .
How to
know ?!

38. • Normal Antegrade decrementalNormal Antegrade decremental
conduction with gradual prolongationconduction with gradual prolongation
of the AH interval, till the wenckebachof the AH interval, till the wenckebach
point.point.

40. Atrioventricular Nodal Function
Curves
• AV nodal function curves can be constructed by
plotting of the coupling interval of the
premature stimulus (A1A2 interval) on the
horizontal axis versus the AH interval (AV nodal
conduction time) of the premature stimulus
(A2H2 interval) on the vertical axis. In individuals
without dual AV nodal pathways, a progressive
and gradual increase occurs in the AH interval
before the premature stimulus blocking in the
AV node, and the function curve is continuous .

41. A-H jump
• A sudden large increase (at least 50 ms) in the
AH interval (often referred to as a jump) in
response to a small decrement (10 ms) in the
coupling interval of the premature beat is
evidence of functional dual AV nodal pathways.
• This represents a shift from conduction over the
fast AV nodal pathway to conduction over the
slow AV nodal pathway (with a longer AH
interval), and the AV nodal function curve is
discontinuous.

43. Burst pacingBurst pacing
• Burst pacing for tachycardia induction:Burst pacing for tachycardia induction:
Stimuli are delivered at a constant fastStimuli are delivered at a constant fast
rate for a relatively short duration but atrate for a relatively short duration but at
successively faster rates with each burstsuccessively faster rates with each burst
until a predetermined maximum rate (oruntil a predetermined maximum rate (or
minimum interval) has been reached.minimum interval) has been reached.
• Bursts for termination of tachycardia: ThisBursts for termination of tachycardia: This
is similar to the technique used foris similar to the technique used for
induction. The initial pacing rate is fasterinduction. The initial pacing rate is faster
than that of the tachycardia.than that of the tachycardia.

44. RampsRamps
• Ramp pacing implies a smooth change inRamp pacing implies a smooth change in
the interval between successive stimuli.the interval between successive stimuli.
Ramps too can be incremental orRamps too can be incremental or
decremental as defined by either rate ordecremental as defined by either rate or
cycle length. Ramps have severalcycle length. Ramps have several
applications: for example as a test forapplications: for example as a test for
conduction, long ramps with small cycleconduction, long ramps with small cycle
length decrements between successivelength decrements between successive
stimuli provide results comparable tostimuli provide results comparable to
stepwise rate incremental pacing.stepwise rate incremental pacing.

45. Till next time InshaALLAH
Thank you