Download Maintaining Contact for Effective Mapping and Ablation

Editorial
Maintaining Contact for Effective Mapping and Ablation
Suraj Kapa, MD; Samuel J. Asirvatham, MD
F
Downloaded from http://circep.ahajournals.org/ by guest on May 12, 2017
contact at the site where it is delivered is critical to ensuring
that the result seen at the end of the procedure will persist
over follow-up.
The importance of attaining and maintaining contact during
ablation is not limited to ensuring effective ablation but also
to avoid complications. Oftentimes, arrhythmias may occur
close to other critical structures (eg, the His-bundle, coronary arteries, or the phrenic nerve). When the targeted substrate occurs close to such structures, ensuring that catheter
contact is stable is important to avoid collateral injury. One
way of attaining stable contact is with the use of cryoablation.
However, ablation with cryo-energy does not have the same
long-term success rates as radiofrequency.5–7 If there was a
way to maintain not just effective but also stable contact with
the underlying myocardium during radiofrequency ablation,
this would carry the benefit of minimizing complication risk
attributable to inadvertent delivery of energy to close-by structures. This may be achieved either by limiting motion of the
catheter or by limiting when energy is delivered.
or radiofrequency ablation to be effective, we need to
reliably identify the arrhythmogenic substrate and then
deliver sufficient energy to that substrate to create local injury.
For effective energy delivery, (a) sufficient power must be
applied over an adequate time, and (b) tissue contact must be
maintained. The recent development of catheters with the ability to sense tissue contact has begun to fulfil the enormous
potential to improve ablation by partly solving the problem of
gauging adequate contact when delivering energy. However,
there is still the need for stable contact with the underlying
substrate to limit collateral energy and optimize target lesion
formation. Indeed, for adequate mapping of the underlying
myocardial substrate, contact is just as essential. In this issue
of Circulation Arrhythmia & Electrophysiology, Chik et al
offer an innovative way of achieving this—by gating energy
delivery to the sensed electrogram.1
Article see p 920
Importance of Contact
How Do We Know When We Are in Contact?
To achieve effective ablation, contact is critical. Lack of contact during radiofrequency ablation can result in heating of tissue, which may result in termination of arrhythmia but without
permanent destruction of the arrhythmogenic substrate.2,3 In
turn, even after careful mapping, if there is insufficient contact
with the underlying tissue and the operator does not recognize
the lack of contact, inappropriate assumptions may be made
regarding the potential for successful ablation or the accuracy
of the mapping performed.
In addition, operators should recognize the concept that
every lesion counts. If, after extensive careful mapping of an
arrhythmia, repeated ablation lesions are attempted but there
is inconsistent contact, repetitive injury to local tissue may
result in edema that may make permanent destruction of the
substrate during the index procedure difficult if not impossible.3,4 Thus, so-called reconnections may not be because
of regrowth of tissue, but rather ineffective lesion formation
during the first procedure. As a result, ensuring that each and
every ablation lesion is effective with appropriate, stable
Although the importance of catheter contact during ablation is
well recognized, achieving and ensuring contact can be much
more difficult. Standard components of ablation procedures
in the majority of laboratories are fluoroscopy and a system
to record electrograms. Properties of the local electrogram (a
sharp, near-field electrogram as opposed to a wide, far-field
electrogram) may help suggest contact. Similarly, the ability
to pace local tissue may be helpful in assessing contact. However, both attributes assume that the local tissue is normal.
In the setting of abnormal myocardium, one may be unable
to capture the local tissue even with maximal pacing output,
and electrograms may also be abnormal. Fluoroscopy similarly can be useful to assess contact by observing the motion
of the catheter relative to the heart. However, the application
of excess catheter pressure against the heart may increase the
risk of perforation and is difficult to assess with fluoroscopy.
In addition, fluoroscopy offers limited spatial resolution and
would not allow the operator to evaluate lateral sliding against
the underlying myocardium.8 Thus, although fluoroscopy, the
sensed electrogram, and pacing threshold may suggest contact, they are not perfect indicators.
Another method of assessing catheter contact is by using
intracardiac echocardiography (ICE).9 However, visualization
of the catheter tip may be difficult in certain areas (eg, along
the ventricular septum), and keeping the tip in view throughout the cardiac cycle can be difficult because of motion in and
out of view of the 2-dimensional field. Thus, although it may
be possible to assess myocardial contact and lesion formation, lateral motion of the catheter tip against the underlying
tissue may not be apparent. Newer ICE systems may improve
catheter tip visualization (eg, 3-dimensional ICE and systems
The opinions expressed in this editorial are not necessarily those of the
editors or of the American Heart Association
From the Department of Medicine, Division of Cardiology (S.K.,
S.J.A.), and Division of Pediatric Cardiology (S.J.A.), Mayo Clinic
College of Medicine, Rochester, MN.
Correspondence to Samuel J. Asirvatham, MD, Division of
Cardiovascular Diseases and Department of Pediatrics and Adolescent
Medicine, Mayo Clinic, Rochester, MN 200 First St SW, Rochester, MN
55905. E-mail [email protected]
(Circ Arrhythm Electrophysiol. 2014;7:781-784.)
© 2014 American Heart Association, Inc.
Circ Arrhythm Electrophysiol is available at
http://circep.ahajournals.org
DOI: 10.1161/CIRCEP.114.002204
781
782 Circ Arrhythm Electrophysiol October 2014
that integrate the ICE image with the electroanatomic map),
but still assume that the tip can be consistently seen and thus
limit the operator’s ability to account for minor degrees of
translational motion across the tissue that can either raise the
risk of collateral injury or reduce the likelihood of effective
lesion formation.
Methods of Optimizing Catheter Contact
and Minimizing Catheter Motion
Downloaded from http://circep.ahajournals.org/ by guest on May 12, 2017
Several methods to both optimize catheter contact and minimize catheter motion have been developed over the past
decade. In atrial fibrillation ablation, integration of preacquired tomographic reconstructions of the heart with the
electroanatomic map allows for checking the accuracy of
the electroanatomic map created during the procedure. In
turn, system-specific indicators of catheter proximity to the
volume-rendered map surface may be used as a surrogate for
catheter contact.10 The limitations of this approach include
the fact that although the quality of the map may be checked
against the preacquired tomographic image, it is still difficult
to account for endocardial surface variation (eg, ridges) that
may make the operator think they are not in contact when they,
in fact, are. Furthermore, given that the map renders the volume between acquired points, the map is only as good as the
contact achieved with the mapping catheter and the number of
points obtained. Thus, reliance on the electroanatomic mapping system’s assessment of catheter contact based on proximity to the rendered surface has several limitations.10
Randomized studies on the use of steerable introducer
sheaths and high-frequency ventilation have been shown in
randomized studies to improve the outcome of atrial fibrillation ablation, likely by improving catheter stability and
contact.11,12 Achieving effective lesion size depends on both
sufficient contact force and the duration of time over which
energy is applied. In atrial fibrillation, the use of steerable
introducer sheaths has been shown to improve outcomes,
likely because of improved contact. By using a more rigid
system, the effects of cardiac and respiratory excursion on
catheter motion is likely to be minimized using these sheaths.
In addition to the use of steerable introducer sheaths, the
use of high-frequency jet ventilation has similarly been shown
to improve outcomes in atrial ablation by better controlling/
minimizing the degree of respiratory excursion.12,13 Thus,
catheter stability may be optimized by removing the effects
of uncontrolled respirations. The limitations of this approach,
however, are that the benefit is likely limited to atrial ablation
and requires the use of general anesthesia.
The use of alternative energy sources is yet another way
to improve both catheter stability and contact. In the case of
cryoablation, once a sufficient temperature has been reached,
the catheter will be effectively stuck to the underlying myocardium until the rewarming phase.14 Thus, there will be limited
catheter motion and optimal stability. Although these features
of cryoablation may be useful in areas of the heart where the
targeted substrate is close to critical structures (eg, the His
bundle) and where small degrees of translational motion of an
unstuck catheter tip during energy application would increase
the risk of complications, the risk of arrhythmia recurrence
tends to be greater with cryo- than radiofrequency ablation.5–7
Thus, in areas where there is no concern about collateral damage, the use of cryoablation would likely not be preferred.
Newer techniques for ensuring catheter contact include the
use of force sensing catheters. These catheters measure realtime contact force against tissue. Integration of a force sensor
at the distal tip of the ablation catheter allows for measurement of the degree of force being applied during both mapping and energy delivery. Use of this technology has been
suggested to both improve assessment of contact and decrease
the risk of complications by offering the operator feedback
about both when too little or too much force is being applied
against the underlying myocardium.15–17 However, there are
2 important limitations to force-sensing catheters. First, the
measurement of contact force assumes proper calibration of
the catheter once placed inside the heart. If the tip of the catheter is in contact with tissue when being calibrated, this may
result in inaccurate measurement of contact force. In addition,
a stable contact force does not necessarily imply a stable ablation catheter tip. Lateral sliding of the catheter may still occur,
despite a seemingly stable contact force, which may in turn
limit effective energy delivery and lesion formation.
Electrogram-Gated Ablation
All prior innovations in catheter contact and catheter stability
have relied on either limiting the degree of catheter motion
(eg, by use of cryoablation or steerable introducer sheaths),
respiratory motion (eg, by use of high-frequency jet ventilation), or using specialized catheters that can measure the force
applied at the tip of the catheter. However, it has been previously demonstrated that seemingly stable catheter positions
may still be prone to lateral sliding throughout the cardiac
cycle.1,8 The combination of all the aforementioned innovations along with the use of ICE may help identify and limit the
degree of sliding. However, when this is not possible because
of excess cardiac or respiratory motion, energy should ideally be delivered only when in contact with the spot desired
and not to adjacent tissue. This avoids creating lesions with
unpredictable dimensions due in part to the lower efficiency of
heating described by Kalman et al in earlier studies.8
Chik et al provide a novel method for achieving the targeted
delivery of radiofrequency energy—an electrogram-gated,
duty cycle–pulsed power ablation technique.1 Rather than
using continuous energy delivery (where surrounding tissue
would be similarly heated as the catheter slides), energy is
delivered based on the local electrogram. Using a thermochromic phantom model, they demonstrated the significant negative effects of lateral sliding motion of the ablation catheter
on lesion geometry (in particular, decreased lesion depth and
increased lesion length) as well as evidence that using an electrogram-gated approach allows for the creation of consistently
deeper lesions more quickly and with less collateral damage to
surrounding tissue irrespective of the amount of sliding. This
last point is critical because during ablation, it is impossible
to predict the amount of sliding of the catheter tip. By gating
to the local electrogram, such that energy is only delivered
during a specific point in the electrogram, it may be possible
to avoid inappropriate energy delivery to surrounding tissue
while the catheter is in motion. The critical assumption Chik
et al1 make, however, is that movement of the catheter away
Kapa and Asirvatham Motion Effects on Cardiac Ablation 783
Downloaded from http://circep.ahajournals.org/ by guest on May 12, 2017
from the target point primarily occurs during cardiac systole,
but that the tip will come back to the same spot over fixed
points in the cardiac cycle defined by the local electrogram.
Thus, energy delivery to tissue may be gated to end at the
onset of the local electrogram, with sliding assumed to occur
over the latter portion of the cardiac cycle (when, in turn,
energy delivery may be ceased).
Several limitations need to be recognized before applying
the findings of Chik et al1 to existing ablation technology.
First, the sliding motion imposed on the catheter was fixed in a
2-dimensional plane and thus may not account for the variable
and unpredictable degree of 3-dimensional motion of the catheter, which is also not just affected by the cardiac cycle but by
respiratory excursion. In addition, local electrograms can occur
at various timings relative to one another, especially when the
ablation catheter is along a line of block where double potentials may exist. The effects of sliding over an area where the
electrograms may be widely separated because of a line of
electric block needs to be considered, especially because the
timing of the electrogram may not necessarily reflect a specific
point in the cardiac cycle when significant electric delay exists.
This issue with the electrogram becomes more complex
when one considers patients with abnormal substrate, where
long fractionated potentials and late potentials may affect gating. Another limitation is that during ablation of microreentrant or macro-reentrant arrhythmias, electrograms at critical
ablation sites may involve the entire cardiac cycle and thus
negate the possibility of gating. Finally, electrograms will often
change during ablation (eg, delay or loss of late potentials/fractionation or widening of the local electrogram). The effects of
a locally changing electrogram over the course of ablation on
electrogram-gated ablation will need to be studied as well. A
further problem that arises during ablation is significant electric noise and at times saturation of the signals associated with
the retrieved electrogram. Indeed, any tool that can allow us
to truly know that the loss of an electrogram is due to ablation
rather than loss of contact will be important for recognizing
when we have completed ablation at a given site.
Thoughtful Application of New
Tools to Old Principles
Chik et al1 provide a novel approach for solving a known problem with modern ablation—sliding of the catheter over the
myocardium even when contact has already been ensured. The
problem with sliding, as clearly described in their study, is the
negative effect on lesion geometry, which limits the possibility
of creating effective, deep/transmural lesions at targeted sites.
Electrogram gating over the cardiac cycle holds the potential
to limit the timing of energy delivery to when it is needed (ie,
when the catheter is in contact with the local target) as opposed
to the remainder of the cardiac cycle when the catheter may be
sliding against the underlying myocardium. However, as with
adoption of any new technology, the potential limitations and
the need to rethink how one practices needs to be considered.
For example, it remains to be seen whether an electrogramgated ablation approach may be used for all arrhythmias or
would assume the need for relatively normal electric substrate
(because of the potential effect of fractionated, late, or double
potentials on electrogram sensing). Furthermore, before recent
innovations to improve catheter contact, ablation techniques by
some providers may have traditionally involved using higher
energy ablation, longer duration of energy delivery, or both.
With techniques to achieve better contact, it is possible that
ablation practices adopted before the existence of such innovations may have the undesirable effect of increasing complication risk (eg, steam pops or cardiac perforation). Thus, as with
implementation of any new technology, other practice considerations may be needed that may not be readily obvious at the
time of initial in vitro studies.
Conclusions
Contact is critical for sensing and energy delivery for ablation. The present suggestion of being able to create safer and
more effective lesions by gating energy delivery to the sensed
electrogram holds promise and may well solve most of the
problem of catheter stability. Rather than requiring the catheter to be consistently stable, electrogram gating accepts catheters sliding and intermittent dislocation. The electrogram as
the basis for energy delivery is limited when the underlying
substrate is itself abnormal and possibly dynamic and by electric noise during energy delivery.
Disclosures
S.J. Asirvatham receives no significant honoraria and is a consultant with Abiomed, Atricure, Biosense Webster, Biotronik, Boston
Scientific, Medtronic, Spectranetics, St. Jude, Sanofi-Aventis,
Wolters Kluwer, Elsevier.
References
1. Chik WWB, Barry MA, Pouliopoulos J, Byth K, Midekin C, Bhaskaran
A, Sivagangabalan G, Thomas SP, Ross DL, McEwan A, Kovoor P,
Thiagalingam A. Electrogram-gated radiofrequency ablations with duty
cycle power delivery negate effects of ablation catheter motion. Circ
Arrhythm Electrophysiol. 2014;7:920–928.
2. Wittkampf FH, Nakagawa H. RF catheter ablation: lessons on lesions.
Pacing Clin Electrophysiol. 2006;29:1285–1297.
3. Haines DE. Determinants of lesion size during radiofrequency catheter ablation: the role of electrode-tissue contact pressure and duration of energy
delivery. J Cardiovasc Electrophysiol. 1991;2:509–515.
4. Arujuna A, Karim R, Caulfield D, Knowles B, Rhode K, Schaeffter T,
Kato B, Rinaldi CA, Cooklin M, Razavi R, O’Neill MD, Gill J. Acute
pulmonary vein isolation is achieved by a combination of reversible and
irreversible atrial injury after catheter ablation: evidence from magnetic
resonance imaging. Circ Arrhythm Electrophysiol. 2012;5:691–700.
5. Rodriguez-Entem FJ, Expósito V, Gonzalez-Enriquez S, Olalla-Antolin
JJ. Cryoablation versus radiofrequency ablation for the treatment of atrioventricular nodal reentrant tachycardia: results of a prospective randomized study. J Interv Card Electrophysiol. 2013;36:41–45; discussion 45.
6. Buddhe S, Singh H, Du W, Karpawich PP. Radiofrequency and cryoablation therapies for supraventricular arrhythmias in the young: five-year
review of efficacies. Pacing Clin Electrophysiol. 2012;35:711–717.
7. Thornton AS, Janse P, Alings M, Scholten MF, Mekel JM, Miltenburg M,
Jessurun E, Jordaens L. Acute success and short-term follow-up of catheter ablation of isthmus-dependent atrial flutter; a comparison of 8 mm tip
radiofrequency and cryothermy catheters. J Interv Card Electrophysiol.
2008;21:241–248.
8. Kalman JM, Fitzpatrick AP, Olgin JE, Chin MC, Lee RJ, Scheinman MM,
Lesh MD. Biophysical characteristics of radiofrequency lesion formation
in vivo: dynamics of catheter tip-tissue contact evaluated by intracardiac
echocardiography. Am Heart J. 1997;133:8–18.
9. Ren JF, Schwartzman D, Callans DJ, Brode SE, Gottlieb CD, Marchlinski
FE. Intracardiac echocardiography (9 MHz) in humans: methods, imaging
views and clinical utility. Ultrasound Med Biol. 1999;25:1077–1086.
10. Okumura Y, Watanabe I, Kofune M, Nagashima K, Sonoda K, Mano H,
Ohkubo K, Nakai T, Sasaki N, Kogawa R, Maruyama A, Hirayama A.
Effect of catheter tip-tissue surface contact on three-dimensional left atrial
784 Circ Arrhythm Electrophysiol October 2014
and pulmonary vein geometries: potential anatomic distortion of 3D ultrasound, fast anatomical mapping, and merged 3D CT-derived images. J
Cardiovasc Electrophysiol. 2013;24:259–266.
11. Piorkowski C, Eitel C, Rolf S, Bode K, Sommer P, Gaspar T, Kircher
S, Wetzel U, Parwani AS, Boldt LH, Mende M, Bollmann A, Husser D,
Dagres N, Esato M, Arya A, Haverkamp W, Hindricks G. Steerable versus
nonsteerable sheath technology in atrial fibrillation ablation: a prospective, randomized study. Circ Arrhythm Electrophysiol. 2011;4:157–165.
12. Hutchinson MD, Garcia FC, Mandel JE, Elkassabany N, Zado ES, Riley MP,
Cooper JM, Bala R, Frankel DS, Lin D, Supple GE, Dixit S, Gerstenfeld EP,
Callans DJ, Marchlinski FE. Efforts to enhance catheter stability improve
atrial fibrillation ablation outcome. Heart Rhythm. 2013;10:347–353.
13. Goode JS Jr, Taylor RL, Buffington CW, Klain MM, Schwartzman D.
High-frequency jet ventilation: utility in posterior left atrial catheter ablation. Heart Rhythm. 2006;3:13–19.
14. Gaita F, Montefusco A, Riccardi R, Giustetto C, Grossi S, Caruzzo E,
Bianchi F, Vivalda L, Gabbarini F, Calabro R. Cryoenergy catheter ablation: a new technique for treatment of permanent junctional reciprocating
tachycardia in children. J Cardiovasc Electrophysiol. 2004;15:263–268.
15. Sasaki N, Okumura Y, Watanabe I, Sonoda K, Kogawa R, Takahashi K,
Iso K, Nakahara S, Maruyama A, Takemura S, Hirayama A. Relations
between contact force, bipolar voltage amplitude, and mapping point distance from the left atrial surfaces of 3D ultrasound- and merged 3D CTderived images: implication for atrial fibrillation mapping and ablation.
Heart Rhythm. 2014 [Epub ahead of print]
16. Natale A, Reddy VY, Monir G, Wilber DJ, Lindsay BD, McElderry HT,
Kantipudi C, Mansour MC, Melby DP, Packer DL, Nakagawa H, Zhang
B, Stagg RB, Boo LM, Marchlinski FE. Paroxysmal AF catheter ablation
with a contact force sensing catheter: results of the prospective, multicenter SMART-AF trial. J Am Coll Cardiol. 2014;64:647–656.
17.Di Biase L, Paoletti Perini A, Mohanty P, Goldenberg AS, Grifoni G,
Santangeli P, Santoro F, Sanchez JE, Horton R, Joseph Gallinghouse G, Conti
S, Mohanty S, Bailey S, Trivedi C, Garg A, Grogan AP, Wallace DT, Padeletti
L, Reddy V, Jais P, Haïssaguerre M, Natale A. Visual, tactile, and contact
force feedback: which one is more important for catheter ablation? Results
from an in vitro experimental study. Heart Rhythm. 2014;11:506–513.
Key Words: Editorial ◼ ablation ◼ contact force ◼ arrhythmia
Downloaded from http://circep.ahajournals.org/ by guest on May 12, 2017
Maintaining Contact for Effective Mapping and Ablation
Suraj Kapa and Samuel J. Asirvatham
Downloaded from http://circep.ahajournals.org/ by guest on May 12, 2017
Circ Arrhythm Electrophysiol. 2014;7:781-784
doi: 10.1161/CIRCEP.114.002204
Circulation: Arrhythmia and Electrophysiology is published by the American Heart Association, 7272 Greenville
Avenue, Dallas, TX 75231
Copyright © 2014 American Heart Association, Inc. All rights reserved.
Print ISSN: 1941-3149. Online ISSN: 1941-3084
The online version of this article, along with updated information and services, is located on the
World Wide Web at:
http://circep.ahajournals.org/content/7/5/781
Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published
in Circulation: Arrhythmia and Electrophysiology can be obtained via RightsLink, a service of the Copyright
Clearance Center, not the Editorial Office. Once the online version of the published article for which
permission is being requested is located, click Request Permissions in the middle column of the Web page
under Services. Further information about this process is available in the Permissions and Rights Question and
Answer document.
Reprints: Information about reprints can be found online at:
http://www.lww.com/reprints
Subscriptions: Information about subscribing to Circulation: Arrhythmia and Electrophysiology is online at:
http://circep.ahajournals.org//subscriptions/