From Beth Israel Deaconess Medical Center, Harvard Medical School,
Boston, Mass (L.M.E., T.W.S.) and the University of Virginia School of
Medicine, Charlottesville (M.A.M., D.E.H.).
Correspondence to Laurence M. Epstein, MD, Division of Cardiology, Beth Israel Deaconess Medical Center, East Campus, 330 Brookline Ave, Boston, MA 02215. E-mail lepstein{at}bidmc.harvard.edu
Methods and Results—The creation of 3 linear atrial lesions was
attempted in each of 10 dogs, half guided by fluoroscopy alone and half
by ICE. Coil-tissue contact was prospectively graded. After ablation,
animals were euthanized, and the location and continuity of lesions
were evaluated. ICE guidance led to a higher percentage of successful
applications (P=0.02) and mean achieved temperature
(P=0.004). The contact scores of excellent, fair, and
poor correlated well with successful energy delivery, mean temperature,
and efficiency of heating (P<0.0001). In 25% of the
blinded energy deliveries, the location, as determined by the ablation
operator, differed from that of ICE. Pathological evaluation revealed
improved lesion formation in the ICE-guided compared with the
ICE-blinded group. Lesions were found outside the target areas in the
ICE-blinded but not the ICE-guided group.
Conclusions—Compared with fluoroscopy, ICE guidance improved
targeting, energy delivery, and lesion formation in this canine model.
This study suggests that ICE guidance improves lesion formation and
prevents energy delivery to potentially dangerous sites.
Linear lesions were created with a multielement ablation catheter (MECA
ablation system, EP Technologies, Inc). These steerable 7F catheters
contain 2 to 6 flexible 12.5-mm stainless steel coil electrodes with 2
thermocouples embedded in each coil. The coils can be activated
simultaneously, but for this study, each was
activated individually. After positioning, radiofrequency
energy was delivered via a radiofrequency generator capable of
delivering up to 150 W (XP-1000, EP Technologies, Inc). The generator
was set to deliver energy for up to 60 seconds and achieve a
temperature of 70°C. The power drawn was regulated by feedback from
the 2 thermocouples mounted on opposite sides of each ablation coil.
Temperature, impedance, and power were monitored for each energy
delivery. To avoid charring, especially at the electrode edges, energy
delivery was conservatively set to automatically terminate if the
current required to achieve the preset temperature exceeded 0.9 A.
Intracardiac ultrasound imaging was performed with a 9F/9-MHz catheter
(Boston Scientific). These catheters have a tip-mounted mechanical
ultrasound transducer connected to a motor unit by a flexible
driveshaft. Images were viewed in real time on a Sonos ultrasound
imaging console (Hewlett Packard) and recorded on videotape for
later review. Via the 10F sheath in the left femoral vein, the ICE
catheter was positioned in the right atrium. Before each energy
delivery, the ICE catheter was manipulated to obtain the optimal view
of the desired coil electrode. The catheter was withdrawn and/or
advanced to ensure that the entire length of the coil was
visualized.
In each dog, formation of 3 linear lesions was attempted as seen in
Figure 1
The multicoil ablation catheter was positioned across the desired
region with an attempt to have as many coils in contact with the
endocardium as possible. Linear lesions were created by applying energy
to the ablation coils sequentially. In some regions, the linear lesion
could not be completed with a single catheter placement. In these
cases, the catheter was repositioned, under either fluoroscopic or ICE
guidance, to extend lesion formation from the location of the previous
energy applications. There was no preset number of energy applications
per lesion set. Attempts were continued until the ablation operator
thought the lesion was completed. Blinded and guided experiments were
alternated to avoid any effect of a learning curve on the outcome of
the study.
Before each radiofrequency energy delivery, the ICE operator scored the
quality of coil-tissue contact as poor, fair, or excellent as defined
below. In the ICE-blinded procedures, the ablation operator and the ICE
operator independently recorded the expected location of the energy
application on the basis of the fluoroscopic and ICE images,
respectively.
For each radiofrequency delivery, mean achieved temperature, efficiency
of heating (temperature/power), and occurrence of automatic termination
of energy delivery due to excessive current draw were monitored. These
variables were compiled for all procedures and compared with the
ICE assessment of quality of coil-tissue contact.
After completion of the procedure, the animals were euthanized, and the
hearts were excised for dissection and examination of the ablation
lesions formed. The right atrium was opened, and the endocardial
lesions were identified. The atrium was stained with nitro blue
tetrazolium (0.5 mg/mL, 0.2 mol/L Sorensen's buffer) to better
identify nonviable myocardium. Lesions were bisected
longitudinally to assess the depth of lesion formation and to
determine whether they were transmural. Each linear lesion was assessed
for continuity, completion, and location. The percent completion of
each linear lesion, as defined below, was compared for ICE-blinded and
ICE-guided ablations.
Definitions
Coil-tissue contact was defined as follows: poor, <50% of the
ablation coil in contact with the endocardium throughout the entire
cardiac cycle; fair, between 50% and 90% of coil electrode in contact
with the endocardium throughout the cardiac cycle; and excellent,
>90% of the coil in contact with the myocardium
throughout the cardiac cycle.
For each linear lesion, the percent completion was defined as follows:
100%, transmural lesion completely traverses the desired area;
Statistical Analysis
ICE guidance resulted in a higher rate of successful energy application
compared with fluoroscopic guidance alone. Overall, 61% (102/167) of
ICE-guided attempts were successful, whereas only 48% (78/161) of the
ICE-blinded attempts were successful (P=0.02). The mean
temperature achieved in ICE-guided ablation attempts (60.3±9.8°C)
was also significantly higher than that achieved without ICE guidance
(56.8±11.1°C) (P=0.004). Although the difference in
efficiency of heating did not reach significance, there was a trend
toward a higher value in ICE-guided procedures (1.8±0.9°C/W versus
1.6±1.0°C/W).
On the basis of ICE imaging, a coil-tissue contact score was assigned
prospectively for all 328 energy deliveries. The contact score proved
to be an excellent predictor of successful energy application (Table 1
There were 118 attempts for which contact was deemed excellent. These
accounted for a higher percentage of applications in the ICE-guided
(58%, 69/167) than in the ICE-blinded (42%, 49/161) procedures. There
were 166 attempts for which the contact was scored fair. Again, these
accounted for a higher percentage of applications in the ICE-guided
(59%, 98/167) than in the ICE-blinded (41%, 68/161) procedures.There
were 44 attempts when coil-tissue contact was scored poor. All of these
applications were in ICE-blinded procedures (27%, 44/161), because no
energy deliveries were attempted in the ICE-guided group if contact was
deemed poor.
Pathological evaluation revealed that ICE guidance improved the
continuity, completion, and placement of the linear right atrial
lesions. Three linear lesions (anterior, transcaval, and flutter) were
attempted in each animal for a total of 30 lesions (15 in each group).
Figure 3
Compared with fluoroscopic guidance alone, ICE guidance improved
positioning of the ablation coils. In 25% (40/161) of energy
applications in the ICE-blinded group, the location of the ablation
coil, according to the ablation operator, differed significantly from
ICE assessment. The mean percentage of such applications for each
animal was 24±15%, with a range of 12% to 50%. The most common
misplacements of the ablation coil were as follows: across the
tricuspid valve into the right ventricle (14), in the IVC or SVC
instead of the right atrium (10), in the right atrial appendage (9),
and on the crista terminalis (5). One ablation attempt, seen to be high
on the crista terminalis by ICE, resulted in sinus arrest. In Figure 2B
ICE evaluation of coil-tissue contact was an excellent predictor of
successful energy delivery and directly correlated with achieved
temperature and efficiency of heating. The assessment of contact as
poor, fair, and excellent used in the present trial was modified
from that used by Kalman et al.17 In a canine
model, they evaluated the correlation between ICE assessment of
electrode-tissue contact, efficiency of heating, and lesion formation.
Although their ablation electrode was smaller (4 mm) and the ICE
catheter different (10F/10 MHz), their findings were similar to ours.
There was a significant correlation between ICE evaluation of tissue
contact, parameters of tissue heating, and lesion size.
They also speculated that ICE could be used prospectively to improve
the percentage of good contact applications during ablation procedures.
This proved to be true in our study. In the ICE-blinded group, ablation
attempts were made with poor contact 25% of the time and with
excellent contact <33% of the time. The higher percentage of
successful energy applications in the ICE-guided group was due to
improved tissue contact made possible by directly visualizing the
coil/tissue interface.
Although there was a higher percentage of successful energy
applications overall, slightly more than 33% of applications were
still unsuccessful in the ICE-guided group. These were almost all
confined to the applications in which contact was deemed fair. Many of
these applications might have been successful if not for the
conservative energy delivery system used, which limited the current
draw to 0.9 A. Suboptimal contact can sometimes be overcome with higher
energy output. The radiofrequency energy generator used in this study
was capable of an output of up to 150 W. However, it has been shown
that high-energy delivery with a high current can result in charring,
especially at the edge of electrodes, due to a high current
density.18 We thought it better to terminate
energy delivery than to risk charring. Therefore, with the ablation
system used, excellent contact along the entire length of the coil must
be sought and can only be assessed with ICE.
Incomplete linear lesions not only may lead to procedure failure but
also may be proarrhythmic.19 ICE guidance clearly
improved the ability to create continuous lesions in this animal model.
With the ablation system used, half of the linear lesions were <50%
complete and only 1 was >90% complete in the ICE-blinded group. This
was most likely a result of a combination of inadequate lesion
formation and poor localization of target sites. This was most apparent
in the isthmus region. Although the coils in these catheters were
flexible, it was difficult to gain contact along the complex
architecture of the IVC–tricuspid valve
isthmus.20 21 22 ICE imaging allowed excellent
contact and lesion formation in all animals in the flutter region as
opposed to the inability to create lesions in this region with
fluoroscopy alone.
One of the most striking findings in this study was how often the
assessment of location by the ablation operator differed from that of
the ICE operator. In the ICE-blinded group, 25% of all energy
applications and 50% of the applications in 1 animal were to
unintended sites. Although not all of the applications resulted in
lesion formation, lesions were found outside of target areas in all
animals of this group. These are not only inefficient but possibly
dangerous. The safety of creating multiple lesions throughout the
atrium is unknown. Lesions outside intended areas can only add to the
potential deleterious effects, unnecessarily increasing the mass of
atrial tissue ablated or unintentionally damaging important structures.
For example, in this study, 1 energy application unintentionally placed
high on the crista terminalis resulted in sinus arrest, and others
created lesions in the right ventricle.
Other Studies
Limitations
Although some reports suggest that atrial fibrillation can be prevented
with ablation in the right atrium alone, it appears that most patients
will require lesions in the left atrium.9 25 26
Current ICE technology offers only limited views of the left atrium
from the right atrium. Advances in ICE technology will be
required to guide left atrial ablation attempts in the future.
Conclusions
Received February 5, 1998;
revision received May 13, 1998;
accepted May 27, 1998.
© 1998 American Heart Association, Inc.
Basic Science Reports
Comparative Study of Fluoroscopy and Intracardiac Echocardiographic Guidance for the Creation of Linear Atrial Lesions
Abstract
Top
Abstract
Introduction
Methods
Results
Discussion
References
Background—Recently, attempts
have been made to cure atrial fibrillation by creating multiple linear
atrial lesions with radiofrequency energy. Intracardiac
echocardiography (ICE) offers imaging of
endocardial anatomy and the ablation electrode–tissue
interface not available with standard fluoroscopy. This study sought to
prospectively compare fluoroscopic with ICE guidance for the creation
of linear atrial lesions in a canine model.
Key Words: echocardiography • catheter ablation • atrial fibrillation
Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
Atrial fibrillation is the most prevalent cardiac
arrhythmia, and current therapy for the most part remains
unsatisfactory.1 The low efficacy and potential
proarrhythmia of drugs has led to a search for
nonpharmacological approaches. The surgical "maze" procedure
developed by Cox and coworkers is an attempt to prevent the multiple
reentrant wavelets thought to be required to sustain atrial
fibrillation.2 3 4 5 Despite encouraging short-term
results, this procedure carries the mortality, morbidity, and expense
of open-heart surgery, and long-term effects are unknown. The early
success of the surgical procedure has prompted investigation into the
possibility of a percutaneous maze procedure that uses
radiofrequency energy to create linear atrial lesions. Preliminary data
suggest the feasibility of this approach with a variety of techniques
used to create these lesions.6 7 8 9 These
approaches include dragging standard ablation catheters while
delivering energy and the development of specialized multielectrode
catheters.10 11 12 13 For the most part, these
procedures are anatomically guided, with the goal of creating lesions
resulting in conduction block across predetermined regions. Positioning
of catheters during these procedures has been guided solely by
fluoroscopy. Fluoroscopic imaging of intracardiac structures is, at
best, limited. In addition, it does not provide information regarding
electrode-tissue contact, the major determinant of lesion formation.
Therefore, misplaced and/or ineffective lesion formation may be
expected with fluoroscopic guidance alone. Intracardiac
echocardiography (ICE) is a new technology that
allows high-resolution imaging of intracardiac structures and the
electrode-tissue interface. ICE imaging has proved useful in guiding
other procedures that require precise anatomic guidance, such as
ablation of typical atrial flutter,14 sinus node
modification,15 and transseptal
catheterization.16 In addition,
previous animal work has shown ICE to be capable of evaluating the
electrode/tissue interface and improving radiofrequency energy
delivery.17 In this study, we sought to compare
intracardiac echocardiography with fluoroscopic
guidance for the creation of linear right atrial lesions in an animal
model.
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
The study was approved by the Animal Research Committees of the
Beth Israel Deaconess Medical Center and the University of Virginia
School of Medicine. Ablation procedures were performed on 10 adult
mongrel dogs. The dogs were premedicated with ketamine and
morphine and intubated. Anesthesia was maintained with 1%
halothane, and animals were continuously ventilated. The level of
anesthesia and surface ECG were monitored throughout the
procedure. Via cutdowns, an 8F vascular sheath was placed in the right
femoral vein and a 10F long vascular sheath was placed in the left
femoral vein for the introduction of the ablation and ICE
catheters, respectively. 
: (1) intercaval: lateral right
atrium (RA) from the superior vena cava (SVC)-RA junction to the
inferior vena cava (IVC)-RA junction; (2) anterior: from
the SVC-RA junction to the tricuspid valve annulus; and (3) isthmus:
across the isthmus from the IVC to the tricuspid valve annulus. ICE
imaging was performed in all procedures. In 5 dogs, the ablation
operator was blinded to the ICE images, and ablation locations and
catheter stability were determined with fluoroscopic guidance alone.
The C-arm fluoroscopic unit used allowed imaging in multiple
projections. In these experiments, care was taken to keep the
ablation operator blinded to the ICE images. The monitor of the ICE
console was positioned so that it could be seen only by the ICE
operator. In the other 5 dogs, the ablation operator used the ICE
images (in addition to fluoroscopy) to guide placement of the ablation
coils and optimize coil-tissue contact. In this group, energy was not
delivered if the coil/tissue contact was thought to be poor on the
basis of the ICE image. In addition, ICE was used to optimize
completion of each linear lesion by ensuring that a successful energy
delivery was made along the entire endocardial length of the desired
target region.
View larger version (208K):
[in a new window]
Figure 1. Schematic of 3 right atrial linear lesions: 1,
intercaval lesion: from superior vena cava (SVC) to
inferior vena cava (IVC); 2, anterior lesion: from SVC to
TA (tricuspid annulus); and 3, isthmus lesion: from IVC to TA.
CS indicates coronary sinus; FO, fossa ovalis.
A radiofrequency energy application was considered successful if
energy was delivered for the full 60 seconds and a tissue temperature
of 
60°C was attained. 90%,
transmural lesion almost complete, with single gap accounting for
10% of the total lesion; 75%, transmural lesion with 1 gap
accounting for 10% to 25% of total lesion; and <50%, transmural
lesion formation over <50% of desired area.
Values are represented as mean±SD. Variables
were compared by ANOVA and 
2 analysis
as indicated. Differences were considered significant if the
P value was <0.05.
Results
Top
Abstract
Introduction
Methods
Results
Discussion
References
Right atrial endocardial anatomy was well visualized in
all animals, and the ablation coils were easily identified. With ICE
imaging, coil-tissue contact was easily evaluated for each of the 328
attempted energy applications. Of the total energy deliveries, 161 were
in the 5 dogs in which the ablation operator was blinded to the ICE
images, and 167 were in 5 dogs in which lesions were attempted with ICE
guidance in addition to fluoroscopy (P=NS). ). None of the ablation
attempts with poor contact were successful, 43% of fair contact
attempts were successful, and 92% of the attempts with excellent
contact were successful (P<0.0001). In addition, the mean
temperature achieved and efficiency of heating were well correlated
with the ICE assessment of contact score. As can be seen in Table 2, the excellent predictive
value of ICE imaging was universal among the 3 lesion sets. An example
of ICE images representing excellent and poor contact
during attempts to create the isthmus lesion can be seen in Figure 2.
View this table:
[in a new window]
Table 1. Correlation Between Coil-Tissue Contact Score and
Parameters of Radiofrequency Energy Delivery
View this table:
[in a new window]
Table 2. Correlation Between Coil-Tissue Contact Score and
Parameters of Radiofrequency Energy Delivery for Each Linear Atrial
Lesion
View larger version (147K):
[in a new window]
Figure 2. ICE images demonstrating (A) excellent and (B)
poor coil-tissue contact during attempted creation of isthmus lesion.
A, Distal ablation coil can be seen in excellent contact with
endocardium of low right atrium (RA), adjacent to tricuspid
annulus (TV). B, Distal ablation coil can clearly be seen across
tricuspid valve in right ventricle (RV). On the basis of fluoroscopy,
ablation operator thought this coil to be on atrial side of tricuspid
annulus. Therefore, this represents not only poor coil-tissue
contact but also potentially dangerous misplacement of ablation coil.
ICE indicates ICE catheter. shows the percent completion of
the lesions produced in the ICE-blinded and ICE-guided procedures. All
of the ICE-guided linear lesions had >75% completion, and 8 of 15
lesions (53%) were 90% complete. This differed significantly from
the ICE-blinded group, in which only 1 lesion was 90% complete (7%)
and 7 of 15 (47%) were <50% complete (P0.002). The most
striking difference between the ICE-guided and ICE-blinded lesions were
in the flutter isthmus (from the IVC to the tricuspid annulus). In the
ICE-guided procedures, 5 of 5 of the lesions were 100% complete,
whereas 0 of 5 of the flutter lesions without ICE guidance were
complete with this ablation system.
View larger version (19K):
[in a new window]
Figure 3. Graphic representation of percent
completion of linear lesions for ICE-guided and ICE-blinded groups. See
text for definitions of percent completion. 
, an ablation coil can be seen crossing the tricuspid valve into the
right ventricle during an attempt to create an isthmus lesion. On the
basis of fluoroscopy, the distal ablation coil was thought to be on the
right atrial side of the annulus by the ablation operator. These
differences were also seen at pathological evaluation. In none of the
animals that underwent ICE-guided procedures were individual ablative
lesions found outside of targeted areas. In contrast, ablation lesions
were found outside of targeted areas in all animals in which
fluoroscopy alone was used for guidance. These included lesions within
the right ventricle in 2 animals and on the crista terminalis in 2
animals.
Discussion
Top
Abstract
Introduction
Methods
Results
Discussion
References
The present study prospectively compared intracardiac
echocardiographic with fluoroscopic guidance for the
creation of linear atrial lesions. In this animal model, ICE was
clearly superior to fluoroscopy in assessing coil-tissue contact
and anatomic location.
Other studies have demonstrated the utility of ICE imaging as an
adjunct to fluoroscopy for guiding radiofrequency catheter ablation
procedures in animals and humans. Chu et al14
used ICE to help guide the ablation of a variety of arrhythmic
substrates in the right atrium: anatomic structures such as the crista
terminalis, tricuspid annulus, coronary sinus ostium,
eustachian ridge, fossa ovalis, and remnants of prior surgical
procedures. Successful ablations of atrial flutter, atrial
tachycardia, sinus node reentry, AV nodal reentrant
tachycardia, and sinus node reentry were assisted by ICE
guidance. Assessment of electrode-tissue contact was possible for only
60% of energy applications in this study. This was most likely due to
the limited maneuverability of the "over-the-wire" ICE catheter
used. In a study of sinus node ablation or modification for the
treatment of inappropriate sinus tachycardia, Lee et
al23 found ICE imaging very useful in identifying
the superior aspects of the crista terminalis at the superior vena
cava–right atrial junction. In 1 patient, ICE imaging identified
unsuspected significant narrowing of the SVC due to multiple ablation
attempts, preventing further damage. Olgin et
al24 recently used ICE to create linear lesions
in the right atrium in an animal model. With a
10F/10-MHz ICE catheter and a 4-coil ablation catheter, linear lesions
were created in the right atrium of pigs. Before radiofrequency energy
application, ICE imaging of the coil/tissue interface was used to
optimize contact and direct anatomic placement. After tissue contact
was optimized, all energy applications were successful, and lesions
were found to be within 0.3 mm of target sites. The coils in this
trial were significantly smaller (5 mm) than those used in the
present study (12.5 mm), and there was no limitation on
current. This most likely resulted in the higher success rate of energy
applications. These trials demonstrate the utility of ICE guidance for
a variety of catheter ablation procedures. To the best of our
knowledge, however, the present trial is the only study to
prospectively compare ICE with fluoroscopic guidance for the creation
of linear atrial lesions.
The goal of this trial was to evaluate the use of ICE guidance to
create linear atrial lesions. Although the ultimate goal of any such
ablation procedure is to prevent atrial fibrillation, this was not
evaluated in this trial. Animals were not in atrial fibrillation.
Therefore, no conclusions concerning the utility of ICE for curing
atrial fibrillation can be drawn from the present study. However,
if percutaneously created linear atrial lesions can
prevent atrial fibrillation, then any modality that can improve lesion
creation should improve the success and safety of the procedure. In
addition, patients with atrial fibrillation may have much larger atria
than the normal dog. The ICE catheter used in this study offered
excellent resolution with a field of view of up to 10 cm, which
should be more than adequate to visualize even the largest atria.
Because of these limitations, the findings in this study cannot be
directly translated to human atrial fibrillation therapy, and further
study is warranted.
Intracardiac echocardiography was superior to
fluoroscopy for the guidance of linear lesion creation in the right
atrium in this canine model. Compared with fluoroscopy, ICE guidance
improved targeting, energy delivery, and lesion formation. This study
suggests that ICE guidance may be an important component of clinical
procedures designed to cure atrial fibrillation by improving lesion
formation and preventing energy delivery to potentially dangerous
sites.
References
Top
Abstract
Introduction
Methods
Results
Discussion
References
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