Electrophysiologic studies use pacing techniques like programmed electrical stimulation (PES) to evaluate cardiac properties. PES involves pacing the heart with drive trains and extrastimuli to measure refractory periods, conduction dynamics, and induce arrhythmias. Pacing can be unipolar or bipolar, and incremental, decremental, or with extrastimuli. Refractory periods like the effective refractory period and relative refractory period are measured using premature extrastimuli during pacing. These techniques provide important information about normal cardiac function and arrhythmia mechanisms.

1. Electrophysiologic Study
Pacing Methods & EP Testing
1

2. Pacing Methods: Programmed Electrical
Stimulation (PES)
 PES is a pacing technique using an intermittent or
continuous introduction of an electrical current to
the intracardiac surface through an electrode
catheter.
 Cells near the electrodes depolarize and begin a
wave of depolarization that propagates throughout
the heart.
 This facilitates the evaluation of cardiac refractory
periods, conduction dynamics, automaticity and
arrhythmic mechanisms.
2

3. Unipolar versus Bipolar Pacing Thresholds
Pacing Threshold Strength-Interval curve
Unipolar Cathodal
_
Unipolar Anodal
+
Bipolar
3 +
_

4. Programmed Electrical Stimulation
 PES consists of three types of pacing:
– Incremental (burst)
– Decremental (ramp)
– Extrastimulus
 PES is used to measure and evaluate ….
– Refractory periods
– Conduction properties
– Pattern of myocardial activation
– Tachycardia Characteristics
 Initiation
 Termination
 Differentiation
4

5. Definitions and Types of PES
 Pacing Drive Train – a series of 6-10 fixed
paced stimuli at a constant rate that are
separated by a pause. Referred to as “S1s”
(stimulus cycle length #1) .
Sensed S1 S1 S1 S1 S1 S1 S1 S1S2 S3 S4
DRIVETRAIN
5

6. Definitions and Types of PES
 Incremental Pacing - is pacing the heart at a fixed
rate. The rate is increased (pacing interval
decreased) with each set of beats.
S1-S1 = 400 S1-S1 = 390 S1-S1 = 380 S1-S1 = 370
6

7. Definitions and Types of PES
 Decremental Pacing – pacing at a progressively
increasing heart rate by decreasing the amount of
time between each paced beat. Used primarily to
induce or terminate tachycardias. It is also called
“ramp” pacing.
Click to start
Sns Sns Sns Sns S 1 S 1 S 1 S 1 S 1 Sns Sns Sns
7 TACHY.SENSE RAMP

8. Definitions and Types of PES
 Exrastimulus Pacing
Sensed S1 S1 S1 S1 S1 S1 S1 S1S2
For the standard EP study
to test the refractory
periods, one extrastimulus Single extras
(S2) will be used. If a
second extrastimulus is
DRIVETRAIN
used, it is usually for
arrhythmia induction and is Sensed S1 S1 S1 S1 S1 S1 S1 S1S2 S 3
called “S3”. Up to 3 (S4)
extrastimuli (S2, S3, S4)
can be given in a standard Double extras
EPS. Any more than 3
extrastimuli would induce a
DRIVETRAIN
non-clinical arrhythmia.
That is, it could induce an Sensed S1 S1 S1 S1 S1 S1 S1 S1S2 S3 S4
arrhythmia in a normal
subject.
Triple extras
DRIVETRAIN
8

9. Common Extrastimulus Induction Protocol
Type of Basic Single extrastimuli Double extrastimuli (ms) Triple extrastimuli (ms)
arrhythmia cycle (ms)
length
(ms)
S1-S1 S1-S1 S1-S2 S1-S1 S1-S2 S2-S3 S1-S1 S1-S2 S2-S3 S3-S4
Atrial 600, 400 600, 400 600- 200 or 600, 400 600-200 or 600-200 or 600, 400 600-200 or 600-200 or 600-200 or
ERP in ERP in ERP in ERP in ERP in ERP in
10ms 10ms 10ms 10ms 10ms 10ms
decrements decrements decrements decrements decrements decrements
Ventricular 600, 400 600, 400 ERP + 60- 600, 400 ERP + 60- ERP + 60- 600, 400 ERP + 60- ERP + 60- ERP + 60-
200 or ERP 200 or ERP 200 or ERP 200 or ERP 200 or ERP 200 or ERP
in 10ms in 10ms in 10ms in 10ms in 10ms
in 10ms decrements decrements decrements decrements decrements
decrements
For triple extrastimuli (S4), the S1-S2 and S2-S3 may be reduced with either the S1-S2 being long and the S2-S3 being short or vice versa. They can also be
decreased simultaneously. Some arrhythmias are often easily induced by a short (S1-S2) - long (S2-S3) configuration.
9

10. Pacing Protocols in EPS
 Typical Pacing Protocols
– Right Atrial Straight (Incremental) Pacing
– Decremental Atrial Pacing
– Programmed Atrial Stimuli with Atrial
Extrastimuli
– Right Ventricular Straight (Incremental)
Pacing
– Decremental Ventricular Pacing
– Programmed Ventricular Pacing with Single,
Double and Triple Extrastimuli
10

11. Refractory Periods
General Overview
11

12. Absolute and Relative Refractory Periods
Absolute (Effective) refractory period - no matter how strong
the stimulus is, the cell can not depolarize.
Relative refractory period - if the stimulus is strong enough
(PAC, PVC or high pacing output) the cell may depolarize
12

13. Absolute and Relative Refractory Periods
The ventricular relative refractory period (RRP) falls around the
middle of the “T wave”, and this is called the vulnerable period.
The same occurs for the atrium. If a stimulus or PVC in the
ventricle or PAC in the atrium falls in this period, it may induce
either atrial fibrillation (if in the atrial RRP), or ventricular
tachycardia or ventricular fibrillation (if in the ventricular RRP).
13

14. Refractory Periods
Premature impulses are used to measure refractory periods of cardiac tissue. They are the:
• Effective refractory period (ERP) – Phase 2 - longest coupling interval that a
premature impulse fails to propagate through cardiac tissue = absolute refractory
period
• Cardiac cells cannot be depolarized during the ERP
• Coupling interval – time between the last paced impulse and premature impulse.
• Relative refractory period (RRP) – time from the end of the ERP to the beginning of
Phase 4 (Phases 3 & 4) – longest coupling interval that a premature impulse results in
slow conduction. Time when cells can be depolarized again with a strong enough
stimulus.
• If a cardiac cell is stimulated during the RRP, the resulting action potential has a
slower Phase 0 slope and the impulse propagates at a slower conduction velocity.
• Functional refractory period (FRP) – shortest time between 2 successive
conducted impulses (time when cells can be depolarized again - usually used
14 describe AV node function). The shortest output of any given input.
to

15. AV Nodal Conduction Curves
15

16. AV Node Conduction (Refractory) Curves
 There are 2 main plots used to show the
conduction properties obtained during
programmed stimulation:
– A1-A2 versus H1-H2 and V1-V2.
 This gives an assessment of the FRP of the AV
conduction system.
– A1-A2 versus A2-H2 and H2-V2 .
 Allows to actually determine conduction times through
the AV conduction system.
rd
16 Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3
Edition), Lippincott, Williams and Wilkins, 2002, pp.47.

17. AV Node Conduction (Refractory) Curves
A1-A2 versus H1-H2 and V1-V2
The doctor will pace to determine the conduction properties of the AVN. The
conduction curve will look as below.
V1-V2
H1-H2
(msec) 700
A
600
C
Line of Identity
500
FRP
400
B
300 400 500 600 700
A1-A2
ERP (msec)
17

18. Responses to Atrial Extrastimuli
 There are 3 main patterns of the response to atrial
stimuli:
– Type I – Most common and involves the impulse
propagation meeting a progressively greater delay in the
AV node without any change in the infranodal (His-
Purkinje) conduction. Thus, the AH interval prolongs, but
the HV interval does not. Block will occur in the AV node
or the atrium.
– Type II – Delay is initially noted in the AV node, but at
shorter coupling intervals (S1-S2), delay is noted in the
His-Purkinje system. However, block still usually occurs in
the AV node first, but may occur in the atrium or
occasionally in the His-Purkinje system.
– Type III – Least common and initially conduction slows in
the AV node, but at a critical S1-S2, a sudden and marked
prolongation occurs in the HV interval (His-Purkinje
system). Block first occurs in the His-Purkinje system.
rd
18 Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3
Edition), Lippincott, Williams and Wilkins, 2002, pp.46-47.

19. AV Node Conduction (Refractory) Curves
A1-A2 versus A2-H2 and H2-V2 – Type I Response
The doctor will pace to determine the conduction properties of the AVN. The
conduction curve will look as below.
400
A2-H2
H2-V2
300
(msec) 700
200
100
200 300 400 500 600
ERP A1-A2
19 (msec)

20. AV Node Conduction (Refractory) Curves
A1-A2 versus A2-H2 and H2-V2 – Type II Response
The doctor will pace to determine the conduction properties of the AVN. The
conduction curve will look as below.
400
A2-H2
H2-V2
300 (msec) 700
200
100
200 300 400 500 600
ERP A1-A2
20 (msec)

21. AV Node Conduction (Refractory) Curves
A1-A2 versus A2-H2 and H2-V2 – Type III Response
The doctor will pace to determine the conduction properties of the AVN. The
conduction curve will look as below.
400
A2-H2
H2-V2
300 (msec) 700
200
100
200 300 400 500 600
ERP A1-A2
21 (msec)

22. Types of Conduction Properties
 Decremental Conduction
– Normal nodal tissue exhibits decremental conduction.
– A propagated impulse at a progressively decreasing
interval causes a progressive increase in the impulse
conduction delay.
(i.e. The increasing prematurity of the impulse = Slower
impulse conduction)
Non-Decremental Conduction
– Atrial and ventricular myocardium and most accessory
pathways (Kent) exhibit non-decremental conduction.
– There is no delay in the propagation of an impulse
through the tissue despite an increasing prematurity of an
impulse.
22 (i.e All or none conduction)

23. Conduction Properties – AV Decremental Conduction
With the AV decremental properties, as the pacing rate is increased,
eventually the rate of conduction will progressively slow, as seen by
progressively longer and longer AH intervals as the S1-S2 or S1-S1 pacing
interval is increased. This prolongation indicates the pacing has entered the
relative refractory period.
S1-S2
AH interval prolongs
23

24. AV Node Conduction Curve – AV Wenckebach
During incremental pacing Wenckebach occurs due to progressively
entering the relative refractory period (RRP) until a beat drops. The ERP
also prolongs as each stimulus enters deeper into the RRP.
Phase
0
Dropped beat
No “H” and “V”
S1
24 S1 S1 S1 S1

25. AV Node Conduction Curve – AV Wenckebach
AV Wenckebach is associated with:
 Group beating
 Progressively prolonging AH intervals
Prolonging AH
Grouped beats Dropped beats
intervals
25

26. AV Node Conduction Curve – AV Wenckebach
AH Intervals
Dropped beat
With Wenckebach there are grouped beats with gradual prolongation of the AH interval
until conduction to the ventricle eventually drops. Therefore only an occasional “A”
wave will not conduct to produce a “V” (see the dropped “V” above). This occurs as
pacing is hitting far into the relative refractory period.
26

27. Drugs Used in EP Studies
27

28. Autonomic Nervous System
 Increases in sympathetic tone increases
conduction velocity and decreases refractory
periods.
 Increases in parasympathetic tone decreases
conduction velocity and increases refractory
periods.
28

29. Determining Refractory
Periods in an EPS
29

30. Relative Refractory Period
The relative refractory period (RRP) is the period of
time when only a stimulus greater than normal
results in an action potential. The RRP is the
longest S1-S2 coupling interval (premature impulse)
that causes prolonged conduction of the S2 relative
to the basic cycle length (S1-S1). The start of the
RRP is just after the end of the full recovery period
where the conduction of the S2 and S1 is the same
(i.e. the RRP will have slower conduction for S2
than for S1).
30

31. Relative Refractory Period
V1 V2
S1-S2 = 320ms
A1-A2 = 320ms
S1 H1 S2 H2
A1 A2 A A2-H2 = 50ms
S1-A1 = 5ms
S2-A2 = 5ms
V1 V2
S1-S2 = 310ms
H2 A1-A2 = 310ms
S1 H1 S2
A1 A2 A A2-H2 = 50ms
S1-A1 = 5ms
S2-A2 = 5ms
V1 V2
S1-S2 = 300ms
H2
A1-A2 = 310ms
S1 H1 S2
A1 A2 A A2-H2 = 80ms
S1-A1 = 5ms
S2-A2 = 10ms
31

32. Refractory Periods: RRP
Physiology of the Heart, Katz, Ch.14; p. 248.
RRP
Relative, (phase 3,4) (RRP).
• Time when cells can be depolarized again with a strong enough
stimulus. The longest premature coupling interval at which delay
in conduction (prolongation of conduction) occurs.
32

33. Relative Refractory Periods
If a stimulus falls in the relative refractory period, and if it is strong
enough the cell will depolarize. However, depolarization (slope of
phase 0) will become slower and slower the closer you approach the
ERP. For the AV node this is expressed as a progressively
lengthening AH interval as you pace closer and closer to the ERP.
33

34. Determination of the Relative
Refractory Period
34

35. Relative Refractory Period: Antegrade
Antegrade Relative Refractory Periods:
Atrial RRP or ARRP:
• The longest S1 - S2 interval at which the S2-A2 interval
exceeds the S1-A1. This is called latency. (-ms)
Atrioventricular Nodal RRP or AVNRRP:
• The longest A1 - A2 at which the A2-H2 interval exceeds the
A1-H1. (-ms)
His Purkinje System RRP or HPRRP:
• The longest H1 - H2 at which the H2-V2 interval exceeds the
H1-V1 or results in an aberrant QRS complex. (-ms)
rd
35 Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3
Edition), Lippincott, Williams and Wilkins, 2002, pp.39.

36. Atrial Relative Refractory Period
S1-S2 = 310ms
V1 V2 A1-A2 = 310ms
A2-H2 = 50ms
S1-A1 = 5ms
S1 H1 S2 H2
A1 A2 A S2-A2 = 5ms
H2-V2 = 30ms
V1 V2 S1-S2 = 290ms
A1-A2 = 300ms
AVNRRP A2-H2 = 80ms
ARRP
S1 S2 H2 S1-A1 = 5ms
H1
A1 A2 A S2-A2 = 10ms
H2-V2 = 30ms
V2
V1 S1-S2 = 270ms
HPRRP
A1-A2 = 285ms
H2 A2-H2 = 110ms
S1 H1 S2 A S1-A1 = 5ms
A1 A2
S2-A2 = 15ms
H2-V2 = 40ms
36

37. Latency (ARRP)
Latency is defined as the time difference (delay)
between the initiation of a stimulus and the observed
response to that stimulus. As an extra stimulus is
introduced with shorter coupling intervals, the ability
of the targeted tissue to accept and conduct this
impulse becomes more compromised. Increasing the
rate of pacing results in less time for recovery of tissue
(shortening of the action potential). This is especially
true of AV nodal cells.
37

38. Latency con’t.
S1-A1 S1-A1 S2-A2
HIS 3-4
38

39. Relative Refractory Period: Retrograde
 Retrograde Relative Refractory Periods:
Ventriculoatrial RRP or VARRP:
• The longest S1 - S2 interval at which the S2-A2 interval
exceeds the S1-A1. (-ms)
Ventricular RRP or VRRP:
• The longest S1 - S2 interval at which the S2-V2 interval
exceeds the S1-V1. This is called latency. (-ms)
Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition),
39 Lippincott, Williams and Wilkins, 2002, pp.39.

40. Ventriculoatrial Relative Refractory Period
V1 V2 S1-S2 = 290ms
V1-V2 = 300ms
H1-A1 = 60ms
H2 H2-A2 = 60ms
S1 H1 S2
A1 A2 S2-V2 = 10ms
S1-A1 = 180ms
S2-A2 = 140ms
V1 V2
VRRP S1-S2 = 270ms
V1-V2 = 285ms
H2 H1-A1 = 60ms
S1 H1 S2 VARRP
A1 A2 H2-A2 = 90ms
S2-V2 = 15ms
S1-A1 = 180ms
S2-A2 = 140ms
V1 V2
H2 S1-S2 = 250ms
S1 H1 S2 V1-V2 = 280ms
A1 A2
H1-A1 = 60ms
H2-A2 = 140ms
S2-V2 = 30ms
40

41. Determination of the
Functional Refractory Period
41

42. Functional Refractory Period (FRP)
 The minimum interval between two consecutively
conducted impulses through the cardiac tissue.
 The FRP of the AV node can vary, but it tends to
decrease with decreasing cycle lengths.
 For atrial and ventricular tissue it tells you how fast
that tissue can conduct on a beat to beat basis.
42

43. Functional Refractory Period
FRP
S1 S2
43

44. Functional Refractory Period: Antegrade
Antegrade Functional Refractory Periods:
Atrial FRP or AFRP
The shortest A1 - A2 in response to any S1- S2.
Atrioventricular Nodal FRP or AVNFRP
The shortest H1- H2 in response to any A1-A2 (320-
680ms).
Atrioventricular Conduction System FRP or AVFRP
The shortest V1 - V2 in response to any S1- S2.
Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition),
44 Lippincott, Williams and Wilkins, 2002, pp.39.

45. Atrioventricular Functional Conduction System Refractory Period
S1-S2 = 220ms
S1-A1 = 5ms
S2-A2 = 25ms
A1-A2 = 240ms
A1-H1 = 50ms
S1 H1 S2 H2
A2-H2 = 60ms
A1 A2 A H1-H2 = 250ms
H1-V1 = 25ms
H2-V2 = 30 ms
V1-V1 = 255ms
V1 V2 S1-S2 = 200ms
S1-A1 = 5ms
AVNFRP S2-A2 = 25ms
A1-A2 = 225ms
A1-H1 = 50ms
S1 H1 S2 H2
A2-H2 = 60ms
A1 A2 A H1-H2 = 240ms
H1-V1 = 25ms
H2-V2 = 35 ms
V1-V1 = 255ms
V1 AFRP V2 S1-S2 = 180ms
AVFRP S1-A1 =5ms
S2-A2 = 35ms
A1-A2 = 230ms
S1 H1 S2 H2 A1-H1 = 50ms
A1 A2 A A2-H2 = 100ms
H1-H2 = 260ms
H1-V1 = 30ms
H2-V2 = 40 ms
V1-V1 = 265ms
45

46. Functional Refractory Period: Retrograde
Retrograde Functional Refractory Periods:
Retrograde Atrioventricular Nodal FRP or AVNFRP
The shortest A1- A2 in response to any S1-S2.
Ventriculoatrial Conduction System FRP or VAFRP
The shortest A1- A2 in response to any H1-H2.
Ventricular FRP or VFRP
The shortest V1-V2 in response to any S1-S2 or
shortest V1-V2 as measured on the surface leads.
Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition),
46 Lippincott, Williams and Wilkins, 2002, pp.39.

47. Retrograde AV Nodal Functional Refractory Period
V1 V2
S1-S2 = 300ms
A1-A2 = 440ms
H1-A1 = 60ms
S1 H2 H2-A2 = 200ms
H1 S2
A1 A2 S2-H2 = 120ms
S2-A2 = 240ms
A1-A2 = 440ms
V1 V2
A1-A2 = 435ms S1-S2 = 290ms
H1-A1 = 60ms
H2 H2-A2 = 205ms
S1 H1 S2 Retrograde
A1 A2 S2-H2 = 120ms
AVNFRP S2-A2 = 245ms
A1-A2 = 435ms
V1 V2
A1-A2 = 445ms S1-S2 = 280ms
H1-A1 = 60ms
H2-A2 = 220ms
S1 H1 S2 H2
A1 A2 S2-H2 = 120ms
S2-A2 = 260ms
A1-A2 = 440ms
Retrograde Atrioventricular Nodal FRP or AVNFRP
47 The shortest A1- A2 in response to any S1-S2

48. Ventricular Functional Refractory Period
V1 V2
S1-S2 = 300ms
V1-V2 = 355ms S1-V1 = 5ms
S1 S2 H2 S2-V2 = 60ms
H1
A1 A2 V1-V2 = 355ms
V1 V2
S1-S2 = 290ms
V1-V2 = 350ms
S1-V1 = 5ms
S2-V2 = 65ms
S1 H1 S2 H2
A1 A2 VFRP V1-V2 = 350ms
V1 V2
V1-V2 = 360ms S1-S2 = 280ms
S1-V1 = 5ms
S1 H1 S2 H2 S2-V2 = 75ms
A1 A2 V1-V2 = 360ms
Ventricular FRP or VFRP
The shortest V1-V2 in response to any S1-S2 or shortest V1-V2 as
48
measured on the surface leads.

49. Determination of the Effective
Refractory Period
49

50. Effective Refractory Period
Effective or absolute, (phase
2) (ERP) is the longest
amount of time when cells
cannot be depolarized
again. The longest input that
fails to conduct.
 Atria 200-270 msecs
 Ventricles 200-270 msecs
 AV node 280-450 msecs
Ch 22 intracardiac Eectrophysiology. John
Dimarco
S1 S2
50 Physiology of the Heart, Katz, Ch.14; p. 248

51. Effective Refractory Period Measurement
The ERP is measured using extrastimulus pacing with an
early beat inserted following 8-10 beats at a fixed rate
(pacing train). The pacing train allows the refractoriness to
stabilize. This stabilization usually occurs after 3-4 beats.
Also the current strength of the stimulus will influence the
ERP. The greater the current strength, the shorter the ERP
(in msec). The ERP will continue to shorten as the current
increases, but eventually becomes fixed at further increases.
Increasing the current strength to 10 mA usually results in
shortening the ERP by 30 msec.
51 •(Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition), Lippincott,
Williams and Wilkins, 2002, pp.39-40.)

52. ERP: Effect of Current Strength
Atrial and ventricular ERPs decrease with the increased current
strength of the impulse. Normal ERP measurements are taken at twice
the diastolic threshold, but if the current strength is increased up to
10mA, the ERP will shorten on average by 30msec. The important thing
is to be consistent with the method you use.
10
8
Current (mA)
6
4
2
0
180 200 220 240
VERP (msec)
52
Josephson, M. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition), Lippincott, Williams and Wilkins, 2002, pp. 39-40.

53. Affect of Pacing on the ERP
 ERP of atrial and ventricular tissue shortens
with pacing, allowing introduction of
premature beats.
 ERP of AV node lengthens with pacing, and
results in blocking of conduction to the
ventricles.
53

54. ERP Response to Different Cycle Lengths
The ERPs of ventricular tissue and the His-Purkinje system differ in their response to different drive
cycle lengths and extrastimuli (abrupt cycle length changes). Ventricular refractoriness demonstrates
the cumulative effect of the preceding cycle lengths (several beats of a drive cycle), whereas the His-
Purkinje system is effected greatly by the immediately preceding cycle length. Thus a change from a
long to short cycle length will shorten both the His-Purkinje and ventricular ERPs, but a short to long
cycle length will drastically prolong the His-Purkinje ERP, but will have only a slight effect if at all on
the ventricular ERP. This is even more exaggerated if only a single extrastimulus is used. Below shows
the effect on the His-Purkinje system.
His-Purkinje System
A. Constant CL
600 600 600 600 Cycle length (CL)
Action Potential Duration
350 350 350 350 350 (APD)
250 250 250 250 Diastolic Interval
B. Long to short
800 800 600
450 450 450 300
350 350 150
400 400 400 600 Effect on His-
C. Short to Long
Purkinje System,
but not on the
250 250 250 250 400 VERP
150 150 150 350
54
Josephson, M. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition), Lippincott, Williams and Wilkins, 2002, pp. 40-44.

55. ERP Response to Multiple Stimuli
The determinate factor of the ventricular ERP appears to be the diastolic interval. The
ventricular refractory period (VERP) following one extrastimulus is shorter than that
following two. In A, S2 hits making the diastolic interval only 40ms. Because it is short,
it makes the resultant VERP shorter at 180ms. In B, the same thing occurs after S2,
but when S3 is placed at the same cycle length as S1-S2 (260ms), because the
VERP was only 180ms, the diastolic interval becomes 80ms. Since that is longer than
the previous 40ms one, now the VERP is longer at 195ms. If this were the His-
Purkinge system, the ERP both after the S2 and S3 would have been much more
prolonged.
40ms
Diastolic Interval: 180ms 180ms
VERP: 220ms 220ms 220ms 180ms
Coupling Interval: 400ms 400ms 260ms
A
S1 S1 S1 S2
40ms 80ms
Diastolic Interval: 180ms 180ms
VERP: 220ms 220ms 220ms 180ms 195ms
Coupling Interval: 400ms 400ms 260ms 260ms
B
S1 S1 S1 S2 S3
Josephson, M. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition), Lippincott, Williams and Wilkins, 2002, pp.44.
55

56. Effective Refractory Periods: Antegrade
Antegrade Effective Refractory Periods:
Atrial ERP or AERP:
The longest S1 - S2 that fails to capture the atrium (150-
360ms)
Atrioventricular Nodal ERP or AVNERP:
The longest A1 - A2 measured from the His Bundle
electrogram that fails to conduct to the His (230-430ms)
Atrioventricular conduction system (AVCS) ERP or AVERP:
The longest S1 - S2 that fails to result in a ventricle
depolarization
Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition),
56 Lippincott, Williams and Wilkins, 2002, pp.39.

57. Atrial and AV Node Effective Refractory Periods
V1 V2
S1-S2 = 290ms
A1-A2 = 300ms
S1 H1 S2 H2
A1 A2 A2 A2-H2 = 60ms
S2-A2 = 10ms
V1 V
S1-S2 = 270ms
AVNERP A1-A2 = 285ms
S1 H1 S2 No H2 H A2-H2 = 90ms
A1 A2 A S2-A2 = 15ms
V1 V
S1-S2 = 250ms
A1-A2 = 280ms
No A2
AERP H
A2-H2 = NA
S1 H1 S2
A1 A S2-A2 = NA
Atrial ERP or AERP: The longest S1 - S2 that fails to capture the atrium (150-
360ms)
Atrioventricular Nodal ERP or AVNERP: The longest A1 - A2 measured from the
57 His Bundle electrogram that fails to conduct to the His (230-430ms)

58. AV Conduction system Effective Refractory Period
V1 V2
S1-S2 = 310ms
A1-A2 = 315ms
S1 H1 S2 H2 A2-H2 = 50ms
A1 A2 A2 S2-A2 = 5ms
V1 V
Recovery of S1-S2 = 270ms
AVERP sinus beat A1-A2 = 100ms
S1 H2 No V H A2-H2 = NA
H1 S2
A1 A2 A S2-A2 = 15ms
V1 V
AVERP Recovery of S1-S2 = 270ms
sinus beat A1-A2 = 285ms
S1 No H2 H A2-H2 = NA
H1 S2
A1 A2 A S2-A2 = 15ms
Atrioventricular conduction system (AVCS) ERP or AVERP: The longest S1 -
58 S2 that fails to result in a ventricle depolarization

59. Effective Refractory Periods: Retrograde
Retrograde Effective Refractory Periods:
Retrograde His Purkinje System ERP or Retrograde HPERP:
The longest S1 - S2 or V1-V2 in which S2 or V2 block below the
bundle of His. Can only measure if H2 is recorded before the retrograde
block.
Retrograde AV Node ERP or Retrograde AVNERP:
The longest S1 - H2 or H1-H2 that H2 fails to conduct to the atrium
Ventriculoatrial Conduction System (VACS) ERP or VAERP:
The longest S1 - S2 that fails to conduct to the atrium
Ventricular ERP or VERP:
The longest S1 - S2 that fails to capture the ventricle (170-290ms)
Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition),
59 Lippincott, Williams and Wilkins, 2002, pp.39.

60. Retrograde AV Node Effective Refractory Period
V1 V2
S1-S2 = 290ms
V1-V2 = 300ms
S1 H2 H2-A2 = 60ms
H1 S2
A1 A2 H1-H2 = 295ms
S1-H2 = 340ms
V1 V2 S1-S2 = 270ms
V1-V2 = 285ms
H2-A2 = 90ms
S1 H1 S2 H2
A2
H1-H2 = 280ms
A1
S1-H2 = 335ms
V1 V2 S1-S2 = 250ms
Retrograde AVNERP V1-V2 = 280ms
H2-A2 = NA
S1 H1 S2 H2 H1-H2 = 265ms
A1 No A2 S1-H2 = 330ms
Retrograde AV Node ERP or Retrograde AVNERP: The longest S1 - H2 or H1-
60 H2 that H2 fails to conduct to the atrium

61. VA Conduction System (VACS) ERP: Block in the AV Node an His-
Purkinje System
V1 V2
S1-S2 = 290ms
V1-V2 = 300ms
S1 H1 S2 H2 H2-A2 = 60ms
A1 A2 S2-V2 = 10ms
V1 V2
S1-S2 = 250ms
VAERP V1-V2 = 280ms
S1 H1 S2 H2
A1 No A2 H2-A2 = NA
S2-V2 = 30ms
S1-S2 = 250ms
V1 V2 V1-V2 = 280ms
VAERP S1-V1 = 5ms
S2-V2 = 20ms
S1 H1 S2 No H2 S1-H1 = 40ms
A1 No A2 S2-H2 = NA
Ventriculoatrial Conduction System (VACS) ERP or VAERP: The longest S1 - S2 that fails
to conduct to the atrium
61
Ventricular ERP or VERP: The longest S1 - S2 that fails to capture the ventricle (170-290ms)

62. Ventricular Effective Refractory Period
V1 V2
S1-S2 = 270ms
V1-V2 = 285ms
S1 H1 S2 H2 H2-A2 = 90ms
A1 A2
S2-V2 = 15ms
V1 V2
S1-S2 = 250ms
V1-V2 = 280ms
S1 H1 S2 H2 No A2 H2-A2 = NA
A1 S2-V2 = 30ms
V1 V
S1-S2 = 230ms
VERP V1-V2 = NA
H H2-A2 = NA
S1 H1 S2 No V2
A1 A S2-V2 = NA
Ventricular ERP or VERP: The longest S1 - S2 that fails to capture the ventricle
62 (170-290ms)

63. Performing a Basic EP Study
Programmed Electrical Stimulation
Baseline EGM Recordings
Refractory Periods
Sinus Node Recovery Time (SNRT)
Sinoatrial Conduction Time (SACT)
Basic EP Tasks
63

64. What is an EP Study?
 Electrical stress test
 An invasive study to assess the
heart’s electrical conduction system
 Patient under conscious sedation
 Often classified outpatient
 Done in EP lab, part of cardiac cath labs
64

65. Why Conduct an EP Study?
 To evaluate conduction system function
 To confirm supraventricular tachycardia
 To evaluate ventricular tachyarrhythmias
 To classify the extent of bradycardia
 To test efficacy of antiarrhythmic drugs
 To test efficacy of implanted devices
65

66. EP study Indications
ACC/AHA
Guidelines
66

67. Which Type of EP Study?
Clinical Presentation Recommended Study
 Documented SVT or  Comprehensive EPS
atrial flutter with ablation
 Suspected SVT  Comprehensive EPS
 Syncope  Tilt, Baseline EPS, or
loop recorder
 Nonsustained VT  Baseline EPS
 Suspected brady  Baseline EPS only if VT
suspected
67

68. EP Study Outcomes
EP Study
Pharmacologic Device
Device Surgical
Catheter No
Therapy Implant Ablation Therapy
Therapy Therapy Therapy
68

69. Basic Steps in an EP Study
 Equipment in room and functional
 Patient info in recording system
 Check plan with physician
 Gather sheaths, catheters, connectors
 Patient in room and prepped
 Prep sterile table, open products
 Sedate patient
 Catheters placed with acceptable thresholds
 Baseline intervals and stimulation protocols
 Ablate, wait, re-test
 Pull and hold
69

70. TESTING
USED
IN EPS
70

71. Electrophysiology Study
 Measurement of baseline conduction intervals
 Atrial Pacing
- Assessment of SA nodal automaticity and
conductivity
- Assessment of AV nodal conductivity and
refractoriness
- Assessment His-Purkinjie system conductivity and
refractoriness
- Assessment of atrial refractoriness
71

72. Electrophysiology Study con t
 Ventricular pacing
– Access retrograde conduction
– Access ventricular refractoriness
 Arrhythmia Induction
– Atrial extrastimulus testing
– Atrial burst pacing
– Ventricular extrastimulus testing
– Ventricular burst pacing
72

73. Catheters used in a Conduction
System Study
 Quadripolar for HRA Evaluate sinus node function
Evaluate antegrade AV node
 Quadripolar for HBE conduction
 Quadripolar for RVA Evaluate retrograde AV node
conduction
73

74. Catheters used in a EP Study
Catheters used in standard EP studies:
Quadripolar in the HRA (usually fixed curve)
Quadri, hexa, octa, or decapolar at the HBE
(fixed curve or steerable)
Quadripolar in the RVA (usually fixed curve)
Hex, octa, or decapolar in the CS (fixed curve
or steerable)
74

75. Catheters used in SVT and VT Studies
Catheters used in SVT studies:
 Quadripolar in the HRA (usually fixed curve)
 Quadri, hexa, octa, or decapolar at the HBE (fixed curve or
steerable)
 Quadripolar in the RVA (usually fixed curve)
 Hex, octa, or decapolar in the CS (fixed curve or steerable)
 Steerable large tip (4mm) mapping catheter
Catheters used in VT studies:
 Quadripolar in the HRA (sometimes omitted)
 Quadripolar (most common) at the HBE (fixed or steerable)
 Quadripolar in the RVA (steerable is common so that it can
be moved to the RVOT)
 Steerable large tip (4mm) mapping catheter
75

76. Standard Conduction System Study
 Evaluate sinus node function
 Sinus node recovery time (SNRT)
 Sino-atrial conduction time (SACT)
 Evaluate antegrade AV node conduction
 AV Decremental Properties
 AVNERP
 AERP
 AV Wenckebach cycle length (Incremental pacing only)
 Evaluate retrograde AV node conduction (S1S2
and Incremental pacing)
 VAERP
 VERP
 VA Wenckebach cycle length (Incremental pacing only)
76

77. Standard EP Study Protocol
Atrial Pacing
Pacing spike
A wave
Atrial pacing is performed with the HRA catheter to determine
the following:
– AV decremental properties
– AVNERP
– AV Wenckebach cycle length
77
– AERP

78. Standard Conduction System Study -
Antegrade Stimulation
 For SA node evaluation two tests are performed
– SNRT
– SACT
 If just one of these tests are performed, the evaluation of the
SA node may not be accurate, therefore it is recommended to
perform both
 Since the autonomic nervous system can highly influence
these tests, it is recommended to perform a pharmacological
blockade to observe the true state of the SA node
– Atropine to eliminate the parasympathetic influence
– Propranolol to eliminate the sympathetic influence
 Depending on the results of these tests, a pacemaker may be
implanted, so a correct evaluation should be made
78

79. Standard Conduction System Study – Sinus Node
Recovery Time (SNRT)
 Sinus node recovery time (SNRT) – time it takes for the SA node to recover from overdrive
suppression of normal automaticity.
 Test: To suppress SA nodal automaticity, overdrive pacing impulses are delivered via
the HRA at a rate faster than the intrinsic sinus rate at a constant rate for at least 30
seconds; then abruptly stopped and the SNRT measured. The SNRT is the longest
pause between the last paced beat and the first intrinsic beat after overdrive pacing
ends. SNRT measurements are typically taken at 800, 700, 600, 500, 450, 400, 350
and possibly 300 ms intervals. The longest interval observed during recovery is the
SNRT. An SNRT longer than 1,500 ms is considered abnormal.
 Since the first cycles after the sinus node recovery are usually slightly longer than the
BCL, either a corrected sinus node recovery time (CSNRT) or an SNRT:BCL ratio is
used as below:
 CSNRT = SNRT – BCL A CSNRT longer than 525 ms is considered abnormal.
 SNRT / BCL x 100%. A ratio greater than 160% is considered abnormal.
79

80. Standard Conduction System Study – Sinus Node
Recovery Time (SNRT)
Sinus node recovery times (SNRT's)
A A A1 A1 A1 A2 A3
HRA
SCL
S1 S1 SNRT
SNRT=A1A2 (NORMAL < 1500 MSEC)
80 CSNRT=A1A2-SCL (NORMAL < 525 MSEC)

81. Standard Conduction System Study – Sinoatrial
Conduction Time (SACT)
SA Node (with pacemaker cells)
Transitional
cells
Last pacing Conduction from the
impulse atrium into the SA
node
Conduction from the SA
node to the atrium
 Sinoatrial conduction time (SACT) – time it takes for a sinus impulse to conduct
through perinodal (surrounding) atrial tissue
 When SA node disease (sick sinus syndrome) occurs, it is due to poor conduction
in the transitional cells and not failure of the pacemaker cells firing
 A prolonged SACT suggests sinus exit block.
81

82. Standard Conduction System Study – Sinoatrial
Conduction Time (SACT)
SA Node (PAcells) Transitional
cells
Conduction from the Conduction from the SA node to
atrium into the SA node the atrium
A A
First sinus A wave
Last pacing spike
Return cycle
A SCL A
Pace from the HRA catheter at a rate slightly above the sinus rate for 30 - 60
seconds and then stop abruptly and measure from the last pacing spike to the
82 first sinus A wave

83. Standard Conduction System Study – Sinoatrial
Conduction Time (SACT)
SA Node (PAcells) Transitional
cells
A A
Return cycle
A SCL A
SACT = the return cycle (last S1 to the first sinus A wave) minus the SCL and then
divided by 2 (i.e. A + A)
*SCL = A-A interval measured on the HRA catheter in sinus rhythm
83 A = SACT (normal 50-125ms)

84. Standard Conduction System Study – Antegrade
Extrastimulus Pacing
 After completing the SA node evaluation, the
doctor will use both extrastimulus pacing and
incremental pacing
 Both antegrade (atrial pacing) and
retrograde (ventricular pacing) studies will be
performed.
84

85. Standard EP Study Protocol
Antegrade Study
 Antegrade study
– Extrastimulus pacing: The HRA catheter is used to deliver single
extrastimulation (S2) following an 8-10 beat pacing train (S1) during
sinus rhythm to assess the AV node and atrial conduction properties.
This is often performed at 2 different cycle lengths (Ex. 600 and 500
ms) and up to 300bpm (200ms) or the AERP to assess the following:
 AV Activation
 AV Decremental Conduction
 AVNERP
 AERP
– Incremental pacing: The HRA catheter is used to deliver
incremental pacing with progressive increases in the rate by
decreasing the pacing cycle length (S1-S1) by 10-20ms decrements to
assess the following:
 AV Activation
 AV Decremental Conduction
 AV Wenckebach cycle length
 AVNERP
85
 AERP

86. Standard EP Study Protocol
AV Decremental Conduction
With the AV decremental property, as the pacing rate is increased, eventually the rate
of conduction will progressively slow, as seen by progressively longer and longer AH
intervals as the S1-S2 or S1-S1 pacing interval is increased. This prolongation
indicates the pacing has entered the releative refractory period.
S1-S2
AH interval prolongs
86

87. Standard EP Study Protocol
AV Wenckebach
AH Intervals
Dropped beat
With Wenckebach there are grouped beats with gradual prolongation of the AH interval
until conduction to the ventricle eventually drops. Therefore only an occasional “A”
wave will not conduct to produce a “V” (see the dropped “V” above). This occurs as
pacing is hitting far into the relative refractory period.
87

88. Standard EP Study Protocol
AVNERP
Pacing spike
A
V No His or “V”
The ERP of the AV node is reached when conduction from the atrium
to the ventricle is blocked due to reaching the refractory period of the
AV nodal tissue. This would be evidenced by an “A” wave after the
pacing spike not followed by a His potential or a “V” wave. AVNERP =
280 - 450 msecs
88

89. Standard EP Study Protocol
AVNERP
To identify the ERP of the AV Node a series of programmed stimulation trains are conducted to
find the longest A1-A2 interval that fails to conduct to the His. Identifying the ERP of other
cardiac tissues is done in the same fashion:
 Atrial ERP (AERP): The longest S1 - S2 that fails to capture the atrium
 Ventricular ERP (VERP): The longest S1 - S2 that fails to capture the ventricle.
ERP of the AV Node
This is the longest A1-A2 that fails to conduct
89 This A1-A2 is longer but it DOES conduct
145

90. Standard EP Study Protocol
AERP
No local atrial
Pacing “spike” electrogram AERP
90 AERP = 200 - 270 msecs

91. Standard EP Study Protocol
AVNERP and AERP
AVNERP
AERP
91

92. Standard EP Study Protocol
Effective Refractory Periods
ERPs of the various cardiac tissue
 Atria 200-270 msecs
 Ventricles 200-270 msecs
 AV node 280-450 msecs
Ch 22 intracardiac Eectrophysiology. John Dimarco
92

93. Standard EP Study Protocol
AH Jump
AH = 80msec
AH = 90msec
AH = 180msec
This sequence is showing evidence of what?
93

94. Standard Conduction System Study
Retrograde Study
 Retrograde study
– Extrastimulus pacing: The RVA catheter is used to deliver single
extrastimulation (S2) following an 8-10 beat pacing train (S1) during sinus
rhythm to assess the VA and ventricular conduction properties. This is often
performed at 2 different cycle lengths (Ex. 600 and 500 ms) and up to 250bpm
(240msec) or the VERP to assess the following:
 VA Activation
 VA Decremental Conduction
 VAERP
 VERP
– Incremental pacing: The HRA catheter is used to deliver incremental pacing
with progressive increases in the rate by decreasing the pacing cycle length
(S1-S1) by 10-20ms decrements to assess the following:
 VA Activation
 VA Decremental Conduction
 VA Wenckebach cycle length
 VAERP
 VERP
94

95. Standard EP Study Protocol
Retrograde Conduction Study
– Right Ventricular Straight Pacing
 performed to
 Check and set pacing thresholds
 Check to see if the AV Node works backwards (retrograde conduction)
 Check to see if there is an accessory pathway with retrograde
conduction (if no conduction can go retrograde up the normal
conduction system, yet you see retrograde conduction, then it means
there is an accessory pathway)
 Do “rescue” pacing
 Terminate or induce tachycardias
95

96. Standard EP Study Protocol
Retrograde Conduction Study – Ventricular Pacing
V A
VA
In this example pacing is being performed from the right
ventricular apex (RVA). Therefore you will first have a “V”
wave. Conduction will then conduct up the conduction system
resulting in a His potential and then an “A” wave. This is
called retrograde conduction. However, although it is a
normal phenomenon, not everyone has retrograde
96
conduction.

97. Standard EP Study Protocol
Retrograde Conduction Study – VA Block
V A V A V A V V A V
No “A” wave
Note that on the 4th and 6th beats no “A” wave follows the
“V” wave. This is called VA block.
97

98. Standard EP Study Protocol
Retrograde Conduction Study – VA Decremental Conduction
V HA V H A
Just as when you pace faster and faster from the atrium, when you pace at faster and
faster rates in the ventricle, you will have decremental conduction. That is, as you
pace faster and faster, the VA or HA interval will progressively prolong the faster you
go. This is because as you begin to enter the relative refractory period (RRP) of the
AV node, conduction begins to slow. The further into the RRP you pace, the slower
the conduction. In the example above, you can see that the VA and HA (not easily
seen) widened with the shorter (faster) pacing interval.
98

99. Standard EP Study Protocol
Retrograde Conduction Study – VERP
The ventricular ERP
(VERP) is reached when
you pace at a rate faster VERP
than the absolute
refractory period of the
ventricular tissue. This
would be evidenced by
a pacing spike not No local ventricular
electrogram
followed by a “V” wave.
Consequently there
would be no His
potential or “A” wave. Pacing “spike”
99 VERP = 200 - 270 msecs

100. Arrhythmia Induction
100

101. Standard EP Study Protocol Cont. –
Arrhythmia Induction - SVT
1. 1 or 2 extrastimuli (S2 and S3) during SR from the RV apex
2. 1 or 2 extrastimuli (S2 and S3) during ventricular pacing (S1) at
100, 120 and 150 bpm (600, 500 and 400msec) from the apex
3. Incremental pacing from RV apex up to 250bpm (240msec) in
10-20msec decrements
4. 1 or 2 extrastimuli (S2 and S3) during SR from the HRA
5. 1 or 2 extrastimuli (S2 and S3) during atrial pacing (S1) at 100,
120, and 140 bpm (600,500,400msec) from the HRA
6. Incremental pacing from the HRA up to Wenckebach or 300
bpm (200msec), or until an arrhythmia is initiated in 10-20msec
decrements
7. Repeat steps 4-6 from the CS or left atrium
8. If not inducible with above give an isoproterenol infusion at a
rate of 1 to 6 µg/min to increase patients’ heart rate to at least
20% above the resting sinus rate or shorten the sinus CL to
450 msec and repeat steps 1-7
101

102. Standard EP Study Protocol
Arrhythmia Induction - VT
Atrial Protocol
1.1 extrastimuli (S2) during SR from the HRA
2.1 extrastimuli (S2) during atrial pacing at 100, 120 and 150 bpm (600, 500
and 400msec) from the HRA
3.Incremental pacing from the HRA up to the Wenckebach point, or 300
bpm (200msec), or initiation of SVT in 10-20msec decrements
Ventricular Protocol
1.1 - 2 extrastimuli (S2 and S3) during SR from the RV apex
2.1 - 2 extrastimuli during ventricular pacing at 100, 120 and 150 bpm (600,
500 and 400msec) from the RV apex
3.Incremental pacing from RVA up to 250bpm (240msec) in 10-20msec
decrements
4.3 extrastimuli (S2, S3 and S4) during SR from the RV apex
5.3 extrastimuli (S2, S3 and S4) during ventricular pacing at 100, 120 and
150 bpm (600, 500 and 400msec) from the RV apex
6.Repeat steps 1-5 from the right ventricular outflow tract
7.If not inducible with above give an isoproterenol infusion starting at a rate
102
of 2.5µg/min to increase patients’ heart rate to at least 20% above the
resting rate and repeat steps 1-6

103. Standard EP Study Protocol Cont. –
Arrhythmia Induction
In an EP study various types of pacing are used to induce the arrhythmias so that it
can be evaluated for its type and origin. In the example above a single (S2)
extrastimulus is used to induce the arrhythmia.
103

104. Standard EP Study Protocol Cont. –
Basic EP Tasks - Summary
EP Protocol:
• Measure baseline conduction intervals (BCL, IACT, AH, HV, QRS and
QT) in sinus rhythm
• Ventricular extrastimulus testing (VAERP, VERP, and retrograde
conduction)
• Incremental ventricular pacing (VA conduction, VAERP, VERP, VA
Wenckebach, FRP) - Pace at a rate slightly faster than the BCL and
increase until VA block. Pacing is typically no faster than 240 ms.
• PES in the ventricle (arrhythmia induction) - Drive train (S1) of 600,
500 and then 400 ms with extrastimuli until the VERP.
• Ventricular burst pacing (fixed, incremental or decremental – arrhythmia
induction).
• Atrial extrastimulus testing to measure the AV nodal and atrial
refractory periods.
• Incremental atrial pacing to assess AV and atrial conduction
(AVNERP, AV Wenckebach, AERP)- Pace at a rate slightly faster than
the BCL and decrease until AV block, but not faster than 200 ms.
• PES in the atrium (arrhythmia induction) - Drive train (S1) of 600, 500
and 400 ms with extrastimuli.
• Atrial burst pacing (fixed, incremental or decremental-arrhythmia
104 induction).

105. Induction of Reentrant Arrhythmias
105

106. Reentry Requirements
 Reentry circuits consist of a fast
pathway and slow pathway and
reentry requires an area of “slow” This is a longer path to this point...
conduction with a short refractory
period
– this could be caused by:
 The AV Node;
 An area of disease;
 Or, simply a physically longer path
(like this example).
 The fast pathway has fast
conduction, but a long refractory
period
– This can be the:
 Fast pathway of the AV node
 Accessory Pathway
 Atrial tissue
 Or a shorter path (as in the example)
 Note how the wavefront cancels out
in the longer path (slow pathway) …than this one
106

107. Requirements for Reentry
“Sinus” “Reentry”
http://rezidentiat.3x.ro/eng/tulbritmeng.htm
 Two limbs joined at their ends The other conducts faster but has
 One conducts more slowly but a longer refractory period
107
has a shorter refractory period Unidirectional block in one limb

108. Reentry Requirements
 Reentry requires
an area of
unidirectional
block-
– this also can come
from the AV Node
or disease, as well
as normal
variations in
refractoriness in
the presence of an
abnormal structure
(bypass tract).
108

109. Reentry Requirements
 Reentry
requires a
complete circuit
that has both an
area of “slow”
conduction and
Unidirectional
block in it.
109

110. Terminating a Reentrant Circuit
 Pacing
 Pharmacological (Ex. Adenosine)
 Ablation…
– Eliminates the complete circuit.
110

111. Reentrant Circuits and Pacing Maneuvers –
Resetting and Advancing the Tachycardia
“Resetting” or “Advancing” a tachycardia:
If you can pace faster than the tachycardia and speed the tachycardia up to
the pacing rate with one or more beats (entrainment) thus resetting or
advancing the tachycardia, then the mechanism is reentry.
111

112. Reentrant Circuits and Pacing Maneuvers –
Resetting and Advancing the Tachycardia
112

113. Reentrant Circuits and Pacing Maneuvers –
Entrainment
 Entrainment:
– The placement of several pacing impulses
into a tachycardia circuit that does not
terminate it.
 The intent of entrainment is to determine
if the pacing site is in the tachycardia
circuit…
 If the pacing site is in the circuit, it might
be an effective ablation site
113

114. Reentrant Circuits and Pacing Maneuvers –
Entrainment
 Entrainment is continuous pacing during a tachycardia
that accelerates the activation to the pacing cycle
length and does not terminate the arrhythmia.
 The ability to entrain a tachycardia supports reentry as
the tachycardia mechanism.
 Entrainment pacing can occur outside of or within the
actual tachycardia circuit.
 If it occurs outside the circuit, the ECG will be a
combination of the tachycardia morphology and what
the morphology would look like when pacing in normal
sinus rhythm (fusion).
 If entrainment occurs within the circuit, the ECG
morphology remains constant (concealed entrainment).
114

115. Reentrant Circuits and Pacing Maneuvers –
Entrainment – Pacing with Fusion
This is a demonstration of pacing with fusion.
115

116. Reentrant Circuits and Pacing Maneuvers –
Entrainment – Pacing with Concealed Entrainment
This is a demonstration of pacing with concealed
entrainment.
116

117. Reentrant Circuits and Pacing Maneuvers –
Entrainment – Post Pacing Interval
 This is known as the Return Cycle Length, or the Post Pacing Interval (PPI) and it
is the time it takes for the tachycardia to resume after pacing is stopped.
 If the pacing occurred outside of the tachycardia circuit, the time it takes for the
tachycardia to resume will be longer than if it were inside the circuit.
= pacing site The reentry circuit = Tachycardia cycle length (TCL)
PLUS
Time from pacing site to the circuit
PLUS
Time from circuit to the pacing site
=Return Cycle Length
117 Return cycle length= (Time from pacing site)x2 +TCL

118. Reentrant Circuits and Pacing Maneuvers –
Entrainment – Post Pacing Interval
 If the pacing occurred inside of the tachycardia circuit, the time it
takes for the tachycardia to resume will be the tachycardia cycle
length only, since there is no distance outside of the circuit to add
time. A PPI < 30 msec is considered in the tachycardia circuit.
Return cycle length= (Time from pacing site)x2 +TCL
The reentry circuit = Tachycardia cycle length (TCL)
PLUS
Time from pacing site to the circuit (in this case it’s 0)
PLUS
Time from circuit to the pacing site (also 0)
=Return Cycle Length
118

119. Reentrant Circuits and Pacing Maneuvers –
Concealed Entrainment – Post Pacing Interval = TCL
PPI :Post pacing interval FCL: Flutter cycle length
15. Lesh et al. JCE Vol.7,No 4, April 1996
119