How to perform and interpret entrainment pacing Basics

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How to perform and interpret entrainment pacing

Benjamin JacobCEPS (IBHRE)

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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.

• Entrainment as an Electrophysiologic Phenomenon *. P Brugada & HJJ Wellens. JACC Vol 3, No. 2, 1984

• 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.

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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.

• 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 stimuli can enter the circuit and propagate in an antidromic and orthodromic direction.

• Entrainment can occur during pacing at sites that are either within or outside 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 stimuli captures myocardium outside the reentrant circuit resulting in different paced and Tachy complexes

Pacing in Sinus

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Concealed Entrainment Morphology

Entrainment from a Inner Loop site1. 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, 94–1062. Stevenson Et al. Entrainment Mapping. JACC 29 (6) May 1997: 1180-93. Stevenson Et al. Entrainment Techniques for Mapping Atrial and Ventricular

Tachycardias. JCE 6(3) March 1995; 201-216

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Criteria for Entrainment1. Constant fusion during overdrive pacing except for the last

paced beat which is entrained but not fused2. 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 Entrainment1. 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 Entrainment2. Progressive fusion during overdrive pacing.



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Criterion 2

• 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.

Progressive fusion between paced and tachycardia complexes at different rates of pacing.

A

B

Entrainment as an Electrophysiologic Phenomenon *. P Brugada & HJJ Wellens. JACC Vol 3, No. 2, 1984

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3rd Criteria of EntrainmentLocalized 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.

A

B

C

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4th Criteria of EntrainmentDuring 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).



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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



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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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PPI :Post pacing interval FCL: Flutter cycle length

15. Lesh et al. JCE Vol.7,No 4, April 1996

Post Pacing IntervalWith Concealed Fusion

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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.

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SVT Diagnostic Algorithm

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

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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.

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Entraining VT

Almendral et al.

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.

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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.

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S-QRS IntervalBystander 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

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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


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Types of Mapping Sites• Remote Bystanders• Adjacent Bystanders• Outer Loop Sites• Exit Site• Central, Proximal, and Inner Loop Sites



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Remote Bystander

• Entrains with QRS fusion

• Post Pacing Interval exceeds the Tachycardia Cycle length

• RF ablation terminates VT at 3%


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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


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Outer Loop Sites

• Post Pacing interval matches the tachycardia cycle length

• Pacing at these sites produce QRS fusion


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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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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

Entrainment Site Classification (VT)

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Success – Concealed / FusionEntrainment 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

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Example 1

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. CS activation Pattern ?2. Response to pacing

1. VAV2. VAAV

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Entrainment of SVT (PPI)

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. CS activation Pattern ?2. Response to pacing

1. VAV2. 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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How to perform and interpret entrainment pacing Basics