Basics of Entrainment pacing and how to interpret entrainment pacing

1. 1
How to perform and interpret
entrainment pacing
Benjamin Jacob
CEPS (IBHRE)

2. 2
Early Experiences
• Waldo et al, observed that a critical rate of pacing
was required to terminate atrial flutter.
• At lower rates of pacing, continuation of the
arrhythmia occurred immediately after cessation of
pacing.
• Led to the recommendation of prophylactic
implantation of electrodes to terminate arrhythmias
by rapid pacing technique.
• Waldo AL, Plumb VJ, Arciniegas JG, et al. Transient entrainment and interruption of
the atrioventricular bypass type of paroxysmal atrial tachycardia. A model for
understanding and identifying re-entrant arrhythmias. Circulation 1983;67:73-83.
• Entrainment as an Electrophysiologic Phenomenon *. P Brugada & HJJ Wellens. JACC
Vol 3, No. 2, 1984

3. • Entrainment can occur during pacing at sites that are either within or outside
3
Definition
“.. an increase in the rate of the tachycardia to a faster pacing
rate, with resumption of the intrinsic rate of tachycardia upon
either abrupt cessation of pacing or slowing of the pacing rate
below the intrinsic rate of the tachycardia."
Waldo et al.
• The stimuli can enter the circuit and propagate in an antidromic and
orthodromic direction.
• Waldo AL, Plumb VJ, Arciniegas JG, et al. Transient entrainment and interruption of
the atrioventricular bypass type of paroxysmal atrial tachycardia. A model for
understanding and identifying re-entrant arrhythmias. Circulation 1983;67:73-83.
the circuit,
• Entrainment alone does not indicate that the location of the pacing site
relative to the circuit.
• Allows the study of site of origin, pathways and mechanisms of the
arrhythmia.#

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Prerequisites for Entrainment
• Gap of excitability is present during tachycardia in the
chamber being paced
– Time interval between the tail of refractoriness of the last
tachycardia impulse and the time of arrival of the next
tachy impulse during which stim could be delivered.
• The site of origin of tachycardia must not be protected by
entrance block.
• The paced impulses entering the site of origin must be
able to accelerate the tachycardia rate to the pacing rate.
• The paced impulses should not result in termination of
tachycardia.
• Brugada p & Wellens HJJ. Entrainment as an Electrophysiologic Phenomenon *.
JACC Vol 3, No. 2, 1984
• # - Wellens HJJ. Value and limitations of programmed electrical stimulation of the
heart in the study and treatment of tachycardias. Circulation 1978;57:845-53.

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Manifest Fusion Morphology
Pacing in Sinus
Pacing stimuli captures myocardium outside the reentrant circuit
resulting in different paced and Tachy complexes

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Concealed Entrainment Morphology
Entrainment from a Inner Loop site
1. Orthodromic Wavefront and Antidromic
Stimulated wave front collide upstream.
2. Orthodromic activation of the isthmus and
exit site produces identical paced and e.g.
VT morphology (concealed Fusion)
3. PPI = TCL

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What is Reset?
• The placement of a single
pacing impulse into a
tachycardia circuit that does
not terminate it, but effects
the tachycardia in some
fashion is called “resetting” or
“advancing” the tachycardia.
• This maneuver is dependent
on the impulse traveling in the
same direction as the
tachycardia wavefront
* - Clinical Arrhythmology and Electrophysiology: A Companion to
Braunwald's ... By Ziad Issa, et al.

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Types of Entrainment
• Entrainment with Fusion:
– QRS fusion is seen on the EKG
• Entrainment with Concealed Fusion:
– Paced QRS is identical to that of the tachycardia during
entrainment
• Concealed Entrainment:
– QRS is identical to the paced morphology in the absence of
tachycardia
1. Albert L. Waldo. Heart Rhythm (2004) 1, 94–106
2. Stevenson Et al. Entrainment Mapping. JACC 29 (6) May 1997: 1180-9
3. Stevenson Et al. Entrainment Techniques for Mapping Atrial and Ventricular
Tachycardias. JCE 6(3) March 1995; 201-216

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Criteria for Entrainment
1. Constant fusion during overdrive pacing except for the last
paced beat which is entrained but not fused
2. Progressive fusion during overdrive pacing.
3. Localized conduction block to a site for 1 paced beat
associated with interruption of the tachycardia, followed by
activation of that site by the next paced beat from a
different direction and with a shorter conduction time.
4. During pacing at 2 different rates during tachycardia, there is
change in conduction time and EGM morphology at the
electrode recording site (this is the equivalent of
demonstrating progressive fusion - the second criterion -
with intracardiac electrogram recordings).

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1st Criteria of Entrainment
1. Constant fusion during overdrive pacing except for the last
paced beat which is entrained but not fused
• When the reentrant circuit is very large, however,
fusion might be demonstrated by pacing from inside
the circuit.
• When both the paced and the tachycardia complexes
have a similar morphology, one is not able to
demonstrate progressive fusion between the paced
and tachycardia complexes.
• Absence of fusion during pacing does not mean that
entrainment is not occurring.
A
B
• Entrainment as an Electrophysiologic Phenomenon *. P Brugada
& HJJ Wellens. JACC Vol 3, No. 2, 1984
• * Images from Murgatryod et al.

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2nd Criteria of Entrainment
2. Progressive fusion during overdrive pacing.
1. Albert L. Waldo. Heart Rhythm (2004) 1, 94–106
2. Stevenson Et al. Entrainment Mapping. JACC 29 (6) May 1997: 1180-9
3. Stevenson Et al. Entrainment Techniques for Mapping Atrial and Ventricular
Tachycardias. JCE 6(3) March 1995; 201-216

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Criterion 2
Progressive fusion between paced and
tachycardia complexes at different rates of
pacing.
• At the slowest rate of pacing, the observed
complex is almost a pure tachycardia
complex.
• At the fastest rate of pacing, the complex is
almost a pure paced complex.
• At intermediate rates of pacing, different
degrees of fusion complexes occur.
A
B
Entrainment as an Electrophysiologic Phenomenon *. P Brugada & HJJ Wellens. JACC Vol 3, No. 2, 1984

13. 13
3rd Criteria of Entrainment
Localized conduction block to a site for 1 paced beat associated with
interruption of the tachycardia, followed by activation of that site by
the next paced beat from a different direction and with a shorter
conduction time.
E.G. : The tachycardia wave front travels in a clockwise direction
a) The paced beat is too premature to propagate, colliding with the
Head (X) and refractory tail (Y)
b) The next beat is a purely paced beat and the exit (R) is activated
from a different direction
c) If the central obstacle was a zone of functional block caused by the
tachycardia, the purely paced impulse may traverse this zone
activating (R) in a different direction altogether.
1. Albert L. Waldo. Heart Rhythm (2004) 1, 94–106
2. Stevenson Et al. Entrainment Mapping. JACC 29 (6) May 1997: 1180-9
3. Stevenson Et al. Entrainment Techniques for Mapping Atrial and Ventricular
Tachycardias. JCE 6(3) March 1995; 201-216
A
B
C

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4th Criteria of Entrainment
During pacing at 2 different rates during tachycardia, there is change in
conduction time to and EGM morphology at the electrode recording site (this
is the equivalent of demonstrating progressive fusion - the second criterion -
with intracardiac electrogram recordings).
1. Albert L. Waldo. Heart Rhythm (2004) 1, 94–106
2. Stevenson Et al. Entrainment Mapping. JACC 29 (6) May 1997: 1180-9
3. Stevenson Et al. Entrainment Techniques for Mapping Atrial and Ventricular
Tachycardias. JCE 6(3) March 1995; 201-216

15. 15
Determining Pacing Site
• How to Determine if the Pacing Site is Within the
Circuit
– Post Pacing Interval
– QRS Configuration during Entrainment
– S-QRS Interval During Entrainment with Concealed Fusion
1. Albert L. Waldo. Heart Rhythm (2004) 1, 94–106
2. Stevenson Et al. Entrainment Mapping. JACC 29 (6) May 1997: 1180-9
3. Stevenson Et al. Entrainment Techniques for Mapping Atrial and Ventricular
Tachycardias. JCE 6(3) March 1995; 201-216

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Post Pacing Interval
• Pace at rates slightly faster than the TCL and measure the
local activation time from the last paced beat to local EGM at
the pacing site.
• This interval is an indication of the proximity of the pacing site
to the reentry circuit and is the time from the stimulus to the
next nonstimulated delopalization
• A PPI for ischemic VT should be within 30ms, 20ms in atrial
flutter circuits.

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Post Pacing Interval
PPI :Post pacing interval
FCL: Flutter cycle length
With Concealed Fusion
15. Lesh et al. JCE Vol.7,No 4, April 1996

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Limitations of PPI
• Does not indicate whether the pacing site is in a narrow
isthmus in the circuit in comparison with a broad loop, in
which ablation may be difficult.
• If conduction slows in the reentry circuit during pacing (AAD,
Post ablation, Rapid pacing →20‐30 msec > TCL), the PPI will
falsely increase.

19. 19
SVT Diagnostic Algorithm
19
George D. Veenhuyzen et al. Single diagnostic pacing maneuver for
supraventricular tachycardia. Heart Rhythm 2008;5:1152–58

20. 20
QRS Configuration during Entrainment
• Pacing at sites remote from the circuit produces a QRS configuration
different from that of the tachycardia, (fusion of wavefronts propagating away from
the pacing site with those emerging from the tachycardia circuit).
• Pacing at a constant rate, produces a constant QRS fusion. (1st Criteria)
• When the pacing rate is increased there is progressive fusion and the QRS
configuration looks more like a purely paced beat. (2nd Criteria)
• Pacing at sites orthodromically proximal to the zone of slow conduction:
pacing entrains the tachycardia without changing the QRS configuration
and there is no QRS fusion. This is called entrainment with Concealed
Fusion.

21. 21
Entraining VT
a. Tachycardia cycle length is 470ms.
b. During overdrive pacing from the
RVA at 440ms, the tachycardia is
transiently accelerated to the pacing
rate, and the QRS morphology
represents a fusion between paced
and ventricular tachycardia beats.
c. When pacing stops, the ventricular
tachycardia resumes with an
entrained but not fused return beat.
d. The return cycle of this last beat
(510 ms) provides information
about the distance from the
stimulation site to the circuit.
Almendral et al.

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S-QRS Interval During Entrainment with
Concealed Fusion
• Useful to determine if the site you are located at is an adjacent bystander
• During entrainment with concealed fusion the interval from the stimulus
to the onset of the QRS indicates the conduction time from the pacing site
to the reentry circuit exit.
• When you are in the circuit, the S-QRS interval during entrainment with
concealed fusion approximates the electrogram to QRS interval during
tachycardia (+/- 20ms)
• When pacing at a bystander site the S-QRS interval does not approximate
the electrogram to the QRS interval.

23. 23
S-QRS Interval
Bystander sites can be identified, by measuring the interval between the diastolic
signal and the surface QRS (Electrogram-QRS) compared to the Stim-QRS. If the
pacing interval is longer, this suggests the mapping catheter is located in a
bystander region, taking longer to travel the extra distance out of this site. The
stim-QRS delay should be equal to the electrogram-QRS at sites within the isthmus
Vishal Luther, Michael Koa-Wing. Ventricular Tachycardia Ablation in the Post Infarct
Patient. http://bhrs.com/editorial-vt-ablation-in-the-post-infarct-patient

24. 24
S-QRS Interval
An illustration of a
typical conduction
channel, inner loop and
bystander, as well as all
the different
entrainment strategies
used to identify site
location within the
channel
Vishal Luther, Michael Koa-Wing. Ventricular Tachycardia Ablation in the Post Infarct
Patient. http://bhrs.com/editorial-vt-ablation-in-the-post-infarct-patient

25. 25
Types of Mapping Sites
• Remote Bystanders
• Adjacent Bystanders
• Outer Loop Sites
• Exit Site
• Central, Proximal, and Inner Loop Sites
1. Albert L. Waldo. Heart Rhythm (2004) 1, 94–106
2. Stevenson Et al. Entrainment Mapping. JACC 29 (6) May 1997: 1180-9
3. Stevenson Et al. Entrainment Techniques for Mapping Atrial and Ventricular
Tachycardias. JCE 6(3) March 1995; 201-216

26. 26
Remote Bystander
• Entrains with QRS fusion
• Post Pacing Interval
exceeds the Tachycardia
Cycle length
• RF ablation terminates
VT at 3%
Vishal Luther, Michael Koa-Wing. Ventricular Tachycardia Ablation in the Post Infarct
Patient. http://bhrs.com/editorial-vt-ablation-in-the-post-infarct-patient

27. 27
Adjacent Bystander
• Pacing entrains the
tachycardia with concealed
fusion.
• Post Pacing interval does not
approximate the tachycardia
cycle length
• S-QRS interval during
entrainment does not match
the electrogram QRS interval
during tachycardia
Vishal Luther, Michael Koa-Wing. Ventricular Tachycardia Ablation in the Post Infarct
Patient. http://bhrs.com/editorial-vt-ablation-in-the-post-infarct-patient

28. 28
Outer Loop Sites
• Post Pacing interval
matches the tachycardia
cycle length
• Pacing at these sites
produce QRS fusion
Vishal Luther, Michael Koa-Wing. Ventricular Tachycardia Ablation in the Post Infarct
Patient. http://bhrs.com/editorial-vt-ablation-in-the-post-infarct-patient

29. 29
Exit Site
• Pacing produces
entrainment with
concealed fusion
• Post Pacing interval
matches the tachycardia
cycle length
• S-QRS interval < 30% of the
tachycardia cycle length

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Central, Proximal, and Inner Loop Sites
• As the pacing site is moved further
from the exit to more proximal sites
the S-QRS interval increases.
• If the S-QRS interval is
– >31-50% of the tachycardia cycle length
they are designated as central sites
– 51-70% of the tachycardia cycle length
they are designated as proximal sites
– >70% of the tachycardia cycle length they
are designated as Inner Loop sites

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Entrainment Site Classification (VT)
Kristin E Ellison et al. Entrainment mapping and radiofrequency catheter ablation of
ventricular tachycardia in right ventricular dysplasia. J Am Coll Cardiol.
1998;32(3):724-728

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Success – Concealed / Fusion
Entrainment was performed at 64 of the 174 sites. Sites with concealed
entrainment had 53.5% of success of the 28 sites where this parameter was
obtained versus 5.5% of success of the 36 sites of entrainment with fusion
TAVORA, Maria Zildany P. et al. Characteristics and identification of
sites of chagasic ventricular tachycardia by endocardial mapping. Arq.
Bras. Cardiol. [online]. 1999, vol.72, n.4, pp. 463-474. ISSN 0066-782X.

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Examples

34. 34
Example 1
1. CS activation Pattern ?
2. Response to pacing
Michaud GF, et al. Differentiation of atypical atrioventricular node re-entrant
tachycardia from orthodromic reciprocating tachycardia using a septal accessory
pathway by the response to ventricular pacing. J Am Coll Cardiol 2001;38:1163
1. VAV
2. VAAV

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Entrainment of SVT (PPI)
1. CS activation Pattern ?
2. Response to pacing
Michaud GF, et al. Differentiation of atypical atrioventricular node re-entrant
tachycardia from orthodromic reciprocating tachycardia using a septal accessory
pathway by the response to ventricular pacing. J Am Coll Cardiol 2001;38:1163
1. VAV
2. VAAV
3. PPI ?

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SVT Diagnostic Algorithm
Heart Rhythm 2008;5:1152–58

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Beware
• Entrainment with concealed fusion can mimic failure
to capture
• Pacing isorhythmic to SVT can mimic constant fusion
• High output pacing at the RV base can capture the
His bundle
• Pseudo VAAV response with long RP tachys

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