Europace (2004) 6, 407e417
Typical atrial flutter ablation outcome:
correlation with isthmus anatomy using
intracardiac echo 3D reconstruction
Marco Scaglione), Domenico Caponi, Paolo Di Donna,
Riccardo Riccardi, Mario Bocchiardo, Giuseppe Azzaro,
Stefano Leuzzi, Fiorenzo Gaita
Electrophysiology Laboratory, Division of Cardiology, Civil Hospital, Via Botallo, 4, 14100 Asti, Italy
Submitted 4 December 2003, and accepted after revision 17 May 2004
KEYWORDS
atrial flutter;
radiofrequency
ablation;
intracardiac
echocardiography;
isthmus anatomy
Abstract Aims To verify if sites of conduction gaps on the isthmus correlate with
anatomical peculiarities using the intracardiac echo (ICE) and a new 3D device to reconstruct the isthmus in patients undergoing cavotricuspid isthmus ablation.
Methods and results Twenty patients underwent isthmus ablation using an 8 mm
tip ablation catheter. Two-dimensional and 3D ICE reconstruction of the isthmus
was made before, during and after ablation. At the end of the lesion line isthmus
block was validated by electrophysiological criteria. In case of its absence we closed
the remaining conduction gaps verifying the position of the sites with ICE. Fourteen
patients required a median of 8 RF pulses to obtain complete isthmus block (Group
A). In the remaining 6 patients isthmus block was obtained with a median of 25 RF
pulses due to conduction gaps ‘resistant’ to ablation (Group B). Conduction gap positions assessed by ICE were located in the central portion of the isthmus below the
coronary sinus os in 71% of cases in Group A and along a prominent Eustachian ridge
in Group B patients, respectively. 3D reconstruction showed a smooth isthmus in
Group A with a ‘peak and valleys’ isthmus in Group B. In these latter patients isthmus
block was obtained only after the complete ablation of the prominent Eustachian
ridge.
Conclusion The isthmus presents anatomical variants particularly due to Eustachian ridge peculiarities which may represent a site of conduction gaps ‘‘resistant’’
to ablation.
ª 2004 The European Society of Cardiology. Published by Elsevier Ltd. All rights
reserved.
) Corresponding author. Tel.:D39-0141-392240; fax: D39-0141-392220.
E-mail address: [email protected] (M. Scaglione).
1099-5129/$30 ª 2004 The European Society of Cardiology. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.eupc.2004.05.008
408
Introduction
Radiofrequency (RF) ablation of typical atrial flutter
(AFl) uses as target the inferior vena cava-tricuspid
annulus (IVC-TA) isthmus which represents the critical area of the reentry circuit [1e14].
The end point of the ablation procedure is the
production of an IVC-TA isthmus block [15e19].
The inability to produce such a block or the recurrence of AFl has been correlated with the presence
of conduction gaps along the RF lesion line [20].
A cooled tip catheter, producing deeper lesions,
has been used effectively [21,22] to overcome this
problem. These clinical results may imply that anatomical peculiarities exist between patients affecting the ablation outcome.
To our knowledge no data are available about
the correlation of anatomy and morphology of the
IVC-TA isthmus and AFl resistant to ablation.
The aim of this study was to perform a twodimensional and 3D intracardiac echo reconstruction of the IVC-TA isthmus in order to verify if the
isthmus anatomy correlated with the isthmus ablation outcome. In particular, we tried to locate the
sites of conduction gaps and to verify if sites of conduction gaps resistant to ablation correlated with
specific anatomical peculiarities.
Methods
Study population
This study included 20 patients, 14 males and 6
females (age 60G10 years) who had episodes of
typical counterclockwise AFl. Four patients had
cardiomyopathy (2 dilated cardiomyopathy, 1 ischaemic cardiomyopathy and 1 mitral regurgitation), 16 patients presented AFl not associated
with cardiac disease. All patients gave written informed consent.
Intracardiac echocardiography
At the beginning of the procedure we first performed intracardiac echocardiography (ICE) using
a 9-MHz ultrasound transducer mounted at the tip
of a 9F catheter (model 9900 Ultra ICE, Boston Scientific EP Technologies, Orchard Parkway, San Jose,
CA, USA). The catheter was positioned in the right
atrium through a long sheath with an angle of
120( at its distal portion (9F Soft Tip Sheath 60 cm
length, 120( III, Boston Scientific EP Technologies,
Orchard Parkway, San Jose, CA, USA) inserted via
the femoral venous approach. Two-dimensional
images were acquired with a Clear View Ultra
M. Scaglione et al.
System (Boston Scientific). The system provided
a maximal radial imaging depth up to 10 cm and
an optimum axial resolution of 0.2e0.3 mm. Images
were recorded on S-VHS videotapes for review. The
ICE catheter was positioned across the tricuspid (T)
valve and then withdrawn from the ventricular aspect of the T ring toward the IVC. The imaging plane
obtained with this scanning allowed visualization of
specific landmarks in the low right atrium such as
the T valve, the coronary sinus (CS) os, the fossa
ovalis and the Eustachian ridge.
The ICE was performed before, during and after
ablation analyzing the position of each RF ablation
site. During the mapping and ablation procedure
the distal ablation electrode was identified with
ICE by means of the characteristic and specific
fan-shaped acoustic shadow and its relative position
was established as previously described [23,24].
In addition to this manual scanning the ICE catheter was used in combination with a 3D ultrasound
system (TomTec, Munich).
The 3D ultrasound system consists of a device
that automatically pulls back the catheter stepwise
(0.5 mm for each step), gated by the ReR and respiration signal of the patient. Transthoracic electrodes are used to acquire the gating signals. In
each position of the transducer a clip of a full cardiac cycle is acquired. Postprocessing algorithms
transform the two-dimensional image slices into
a dynamic volumetric dataset representing the anatomical structures. The spatial resolution along
the catheter axis is determined by the size of the
individual steps which has been 0.5 mm. Image
transfer was performed via video channel (PAL)
which leads to a temporal resolution of the dynamic sequences of 25 frames/s.
The pullback length from the right ventricular
entry to the IVC was between 50 and 70 mm.
For later reviewing of the volumetric dataset the
3D ultrasound system allows retrieval of an infinite
number of cardiac cross-sections even imaging
planes that cannot be assessed originally by the
catheter. For the present study mostly oblique
planes were used to render 3D projections that
view the isthmus from a stand-point above the
IVC looking towards the T valve, with fossa ovalis,
CS and T valve itself as reference structures.
In order to verify the reproducibility of the 3D
reconstruction we performed each acquisition scan
twice for the first six patients.
Electrophysiological study
Antiarrhythmic drugs had been discontinued for at
least five half lives and no patient had received
Typical atrial flutter ablation
amiodarone in the preceding 6 months. The electrophysiological study was performed using a standard decapolar Halo catheter (Cordis-Webster Inc.,
Baldwin Park, CA, USA) positioned in the right
atrium. The Halo catheter was placed adjacent to
the tricuspid annulus with the distal bipole in the
low lateral right atrium and the proximal bipole
positioned on the interatrial septum above the
His bundle. An octapolar steerable catheter with
2 mm interelectrode distance (Cordis-Webster
Inc., Baldwin Park, CA, USA) was positioned in the
CS and was used to pace and to map the region of
the coronary sinus os and its proximal portion. Both
catheters were inserted via a femoral venous
approach. Bipolar digitized atrial electrograms up
to 28 simultaneous endocardial sites and 12 lead
surface ECG were simultaneously recorded (1 kHz
sampling frequency, 30e500 Hz band pass filters),
displayed on a multichannel recorder and stored
on magneto-optical disks (Cardiolab, Prucka GE
Marquette, Milwaukee, Wisconsin, USA).
In patients in AFl, endocavitary mapping was
performed before the ablation and concealed
entrainment was used to confirm that the IVC-TA
isthmus was part of the reentry circuit.
In patients in sinus rhythm (SR) we used the
pacing protocol to validate the isthmus conduction
at 600 and 400 ms cycle length as previously
described [15,17].
Ablation procedure
Radiofrequency ablation was performed with a generator EPT-1000 XP (EP Technologies, Mountain
View, CA, USA) that delivered continuous unmodulated current at 500 kHz in monopolar fashion and
had a maximum power output of 150 W.
RF lesions were performed using a 8 mm tip electrode catheter (Blazer XP large curve, EP Technologies, Mountain View, CA, USA) in a temperature
guided mode ( preset temperature of 60e70 (C).
The ablation catheter was introduced into the
right atrium by a right femoral venous approach.
Initial position of the ablation catheter within the
isthmus near the T annulus was such that a large
ventricular potential and a small atrial electrogram
were recorded (A/V ratio 0.1). The preset duration
of the pulse was 60 s.
The isthmus ablation was performed using the
point by point technique withdrawing the ablation
catheter, under fluoroscopic guidance, from the T
ring up to the junction between the right atrium
and the IVC in the posteroseptal area. The end
point of the procedure was the achievement of
409
a complete bidirectional block on the IVC-TA isthmus as previously described [15e19].
In patients in SR the ablation procedure was
performed during pacing from CS (output twice
threshold) at a drive cycle length of 600 ms. After
completion of the line or after the AFl interruption, we validated the presence or absence of
conduction block on the IVC-TA isthmus by pacing
from the low right atrium and the proximal CS. In
case of the absence of a complete bidirectional
block we mapped the lesion line looking for
conduction gaps defined as sites with single, fragmented or double but very close atrial electrograms between two sites with split electrograms
and a well defined isoelectric interval (Fig. 1).
The site of conduction gap defined by the above
mentioned electrophysiological criteria was correlated with the anatomical position by ICE because
it was possible to detect the tip of the ablation
catheter by means of the specific fan-shaped
acoustic shadow.
RF was delivered at each site of conduction gap
until a clear separation between the two atrial
components was obtained and consequently the
isthmus block was achieved.
Finally, AFl inducibility was tested using atrial
bursts up to 200 ms.
Results
At the time of the procedure 10 patients were in SR
and 10 patients presented typical AFl with mean
cycle length of 268.8G30.6 ms (range 240e320 ms).
Ablation results
The ablation procedure was performed successfully in all 20 patients. In the ten patients
presenting AFl at the time of the procedure, interruption of the arrhythmia during RF delivery
was obtained. The median number of RF pulses
was 10 (range 1e38). No immediate or late complications were seen.
After a retrospective analysis, it resulted that
14 patients required a median of 8 RF pulses to
obtain a complete isthmus block (Group A) while
in the remaining six patients a median of 25 RF
pulses was necessary to achieve the same ablation
endpoint (Group B). In the Group B patients,
sites of conduction gaps resistant to more than
2 RF pulses (delivered on the same site) were
present.
In Group A eight patients were in SR and six patients were in AFl at the time of the procedure.
Three patients of these 14 (two in SR and the other
410
M. Scaglione et al.
Figure 1 Top: Anatomical representation of the right atrium as shown in RAO view. IVC, inferior vena cava; FO, fossa
ovalis; CS, coronary sinus os; T, septal leaflet of the tricuspid valve. The black bar with white numbers represents
a schematic lesion line along the isthmus and numbers correlate with the mapping position. A, anterior portion of the
isthmus; C, central portion of the isthmus; I, inferior portion of the isthmus. Bottom: endocardial recordings during
mapping along the lesion line while pacing from proximal CS. CS, coronary sinus os; ABL, distal bipole of the ablation
catheter; I, V1, ECG surface leads; A, atrial electrogram. Panel 3 shows a fragmented atrial potential with separate
components but still very close to each other surrounded by sites with split atrial electrograms (A) and a well defined
isoelectric interval (recordings from panels 1, 2, 4). Panel 3 is a typical recording from a conduction gap site (black star).
in AFl) presented at the completion of the lesion
line (1, 5 and 7 RF pulses) complete block without
any residual conduction gaps. In the remaining 11
patients it was necessary to deliver more RF pulses
( from one to three) to close some conduction gaps,
after having completed the lesion line extending
from the TA to the edge of the IVC.
In Group B four patients were in SR and two patients were in AFl at the time of the procedure.
At the end of the completion of the lesion line
the isthmus conduction was still evident in all these
six patients because of the presence of a residual
single conduction gap. Closing these conduction
gaps to obtain complete isthmus block, required
Typical atrial flutter ablation
411
Table 1
Patient
No. of RF pulses
(line)
No. of conduction
gaps
No. of RF pulses
( gap)
No. of RF pulses
total
Gap site
CCI
C
E
E
E
E
E
E
Group A
1
2
3
4
5
6
7
8
9
10
11
12
13
14
9
8
7
8
5
7
6
9
9
6
1
6
7
6
2
1
0
2
0
2
1
1
1
1
0
1
1
1
3
1
1
1
2
12
9
7
10
5
10
8
11
10
7
1
7
8
8
Group B
15
16
17
18
19
20
7
8
10
10
9
11
1
1
1
1
1
1
10
16
28
8
16
16
17
24
38
18
25
27
2
3
2
2
1
1
ACC
CCI
C
C
I
C
C
C
C
Ablation data in the study population: No. of RF pulses (line), number of radiofrequency pulses to complete the initial line; No. of
conduction gaps, number of conduction gaps in the lesion line; No. of RF pulses ( gap), number of subsequent radiofrequency
applications to eliminate conduction gaps; No. of RF pulses (total), total numbers of radiofrequency pulses to obtain complete
isthmus block; Gap site, conduction gap site on the isthmus; A, anterior portion; C, central portion; I, inferior portion; E, prominent
Eustachian ridge.
a much higher number of additional RF deliveries
compared with the fewer number of RF pulses used
in the Group A patients (Table 1).
Conduction gap’s location assessed by ICE
Isthmus as viewed in the RAO projection was arbitrarily divided in an anterior (close to TA) central
and inferior (close to the IVC orifice) portion
(Fig. 1).
Group A: in 11 of the 14 patients a total of 14
gaps were found. Ten (71%) gaps were in the central portion of the isthmus, just in front of the CS
os, one (7%) was in an anterior portion close to
the TA and three (21%) were in an inferior portion
near the edge of the IVC orifice. No specific anatomical structures were identified as being correlated with these sites.
Group B: in the six patients with a total of six
gaps (one gap in each patient) all these gaps were
located at the same site: the border between the
central and inferior portion of the isthmus at the
level of a prominent Eustachian ridge.
This site correlated with an atrial electrogram
which was only slightly affected by initial RF
deliveries.
In these patients complete block was obtained
only after the complete abolition of electrical
conduction along this structure by means of RF
applications.
It was also possible to visualize the effects of RF
deliveries with two-dimensional ICE. One hundred
and ninety-two RF pulses were delivered in all 20
patients and in 107 (56%) after the RF delivery,
we were able to detect the appearance on the isthmus surface of a depression that in 46 of 107 (43%)
was surrounded by a more echogenic border probably expression of local oedema (Fig. 2).
Intracardiac echocardiography 3D
reconstruction
The intracardiac echo procedure and 3D reconstruction was feasible and reproducible.
By means of ICE reconstruction two different
types of isthmus anatomy were evident on a mere
morphological basis.
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M. Scaglione et al.
Figure 2 (A) Two-dimensional intracardiac echocardiographic (ICE) image of the anterior portion of the isthmus
(arrow) before the RF delivery in patient 2 (see Table 1). (B) Two-dimensional ICE image of the same anterior portion of
the isthmus shown in (A) after the RF delivery. The two-dimensional ICE plane makes a perpendicular cut of the anterior
portion of the isthmus, the interatrial septum and the lateral wall of the right atrium. In (B) it is possible to appreciate
that a portion of the isthmus has become more echogenic and thicker (arrow), which is most likely to be an expression
of local oedema due to RF delivery. FO, fossa ovalis; RA, right atrium.
No quantitative data (height and thickness)
were measured but the differentiation was made
only on the basis of the morphological aspects of
the isthmus.
(1) All Group A patients showed a smooth isthmus
with slight irregularities parallel to the TA,
probably due to the pectinate muscles coming
from the end of the crista terminalis in the low
lateral right atrium. In this type of isthmus the
Eustachian ridge was small and had a prevalent
vertical direction on the septum between the
IVC and CS os. This structure was not involved in
the IVC-TA isthmus (Fig. 3).
(2) All Group B patients presented a different
isthmus anatomy due to a prominent Eustachian ridge having a different course. The
Eustachian ridge looked like a membrane
outlining the anterior part of the IVC orifice
toward the T ring, coming from the low lateral
atrium and directed toward the CS os where it
became smoother. Therefore, in contrast to the
Figure 3 Two different projections of 3D reconstruction of the inferior vena cava-tricuspid isthmus ( patient 6 in Table
1). This picture shows an example of a smooth isthmus with slight irregularities. In this case the Eustachian ridge is
vertical, behind the coronary sinus os. ), coronary sinus os; IVC, inferior vena cava orifice; T, septal leaflet of the
tricuspid valve; E, Eustachian ridge.
Typical atrial flutter ablation
413
Figure 4 Left: Two examples of 3D reconstruction of the inferior vena cava-tricuspid (IVC-TA) isthmus (top patient 20,
bottom patient 15, Table 1). Right: anatomical specimens of isthmus (modified with permission from Waki et al. [25]).
This picture shows two examples of an isthmus with a prominent Eustachian ridge that looks like a membrane outlining
the anterior part of the IVC orifice directed towards the CS os. This kind of isthmus looks like a ‘peak and valleys’ shaped
structure. Note the amazing similarity to the anatomical specimens. ), coronary sinus os; IVC, inferior vena cava
orifice; T, septal leaflet of the tricuspid valve; E and arrows, Eustachian ridge; head arrows, tricuspid ring.
previous group the isthmus in these patients
was a ‘peak and valleys’ shaped structure
(Fig. 4). In all cases of ‘resistant’ AFl ablation
the site of conduction gap correlated with
a prominent Eustachian ridge crossing the
isthmus (Fig. 5).
In two patients of Group A, the above-mentioned
two-dimensional ICE visualization of the effects of
RF deliveries was documented for all the ablation
sites. In these patients the complete 3D reconstruction of the whole lesion line appeared as an
image of a rail along the isthmus (Fig. 6).
Follow up
After a mean follow-up of 13.1G2.01 months (range
9e17) no recurrence of typical AFl was noted.
Discussion
The present study has shown that the IVC-TA
isthmus is not uniform and different anatomical
variants can be demonstrated. These in vivo observations correlate well with what has been already
described in anatomical reports. Waki et al. [25]
examined 50 hearts obtained at autopsy demonstrating a non-uniform muscular trabecular
pattern in the lower part of the right atrium, the
zone known as the ‘flutter isthmus’. In particular
the non-uniformity was conspicuous in the area
immediately inferior to the coronary sinus os.
Two different anatomical patterns were evident,
one with a uniform trabecular pattern and the
other with a non-uniform trabecular pattern. Muscular defects between trabeculae were differently
distributed in the two groups. In both groups the
majority of the hearts presented the Eustachian
valve containing muscular extensions from the
terminal crest to the CS os.
Similar findings were also made in our study. In
fact, the 3D reconstruction allowed differentiation
of the isthmus zone into two types. One group (A)
presented a smooth isthmus while the second (B)
a ‘peak and valleys’ shaped structure. The major
anatomical difference between the two groups
was represented by a different extension and location of the Eustachian ridge. In Group A patients
the Eustachian ridge was small and had a prevalent
vertical direction on the septum between the IVC
and CS os. This structure was not involved in the
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M. Scaglione et al.
Figure 5 Top: Left and middle panels show two-dimensional intracardiac echocardiographic images of the isthmus
using a plane parallel to it. The left panel image shows the isthmus without catheters. Note that the Eustachian ridge
(E) originates in the low lateral right atrium (L) from the terminal portion of the crista terminalis. The middle panel
shows the ablation catheter (white arrow) positioned on the Eustachian ridge on the corresponding site of an
electrophysiologically determined conduction gap. Right panel shows a 3D reconstruction of the isthmus in the same
patient ( patient 20, Table 1). S, interatrial septum; E, Eustachian ridge; L, low lateral wall of the right atrium; white
arrow indicates the tip of the ablation catheter on the Eustachian ridge; ), coronary sinus os; T, septal leaflet of the
tricuspid valve; IVC, inferior vena cava; black star, site of conduction gap ‘resistant’ to ablation. Bottom: endocardial
traces during pacing from the coronary sinus os in (A) before and in (B) after RF delivery to a conduction gap site.
Endocardial recordings. H 1-2 up to H 19-20: Halo catheter positioned around the tricuspid valve with electrode 1-2 in
the low lateral right atrium; CS, coronary sinus os; ABL d, distal bipole of the ablation catheter; ABL p, proximal bipole
of the ablation catheter; II, V1, ECG surface leads; A, atrial electrogram; V, ventricular electrogram. (A) shows the
endocardial recordings from the conduction gap site shown on the above two-dimensional image. Note the presence of
a second small atrial component following a high amplitude signal on the distal ablation catheter recording associated
with a pattern compatible with an incomplete clockwise isthmus block on the Halo recordings before the RF delivery. In
(B), after the RF delivery, it is possible to appreciate the splitting of the atrial potential (double arrow) on the ablation
catheter recording correlating with the appearance of complete isthmus block pattern on the Halo recordings (arrow).
Black star with arrow matches the conduction gap electrogram to the anatomical site on the Eustachian ridge both on
the two-dimensional echo image (top, middle) and on the 3D reconstruction (top, right).
IVC-TA isthmus. In Group B patients the Eustachian
ridge looked like a membrane outlining the anterior
part of the IVC orifice toward the T ring, coming
from the low lateral atrium and directed toward
the CS os where it became smoother crossing the
isthmus. In addition to the in vivo morphological
reconstruction of the isthmus, the aim of the study
was also to correlate the anatomy with the ablation
outcome. It is well known that using a conventional
ablation catheter is not always possible to achieve
Typical atrial flutter ablation
Figure 6 3D reconstruction of the inferior vena cavatricuspid isthmus after successful ablation in patient 2
(see Table 1). In this patient the two-dimensional
intracardiac echocardiography was able to document
the effects of RF deliveries for all the ablation sites. As
shown in Fig. 2, 3D reconstruction of the whole lesion line
appears as an image of a rail crossing the isthmus from
the tricuspid ring up to the inferior vena cava orifice
(black and white arrows). CS, coronary sinus os; IVC,
inferior vena cava orifice; T, septal leaflet of the
tricuspid valve; V, right ventricle.
a complete bidirectional isthmus block [21]. The
exact reason for this resistance to conventional
RF ablation has not been clear. It has been speculated that it might be due to thicker than usual isthmus myocardium or to a particular topography of
the isthmus or even to the oedema associated with
RF lesions. In fact previous work has already shown
that the oedema can make it difficult to complete
the necrosis in deeper layers [26,27]. Also in our
study the oedema following RF deliveries was demonstrated in some cases using ICE (Fig. 2). In no
case was it associated with resistance to ablation.
Different authors reported that this resistance to
conventional RF ablation may be overcome by using
irrigated ablation catheters allowing production of
larger and deeper lesions [21,22,28e30].
From the results of our study it can be inferred
that, not unexpectedly, anatomical variants correlate with the ablation outcome. In a retrospective
analysis all the patients with an atrial flutter ‘resistant’ to ablation belonged to Group B. In these patients the Eustachian ridge was prominent and able
to conduct the electrical impulse and represented
the site of conduction gaps which were difficult
to ablate. Only the complete abolition of the Eustachian ridge conduction determined the occurrence
of complete bidirectional isthmus block. This
finding can be explained nicely by the anatomical
415
demonstration that the Eustachian ridge may contain, in the majority of cases, muscular fibres
[25]. The complex morphology and the extension
of the Eustachian ridge together with the fact that
muscular fibres are deep inside fibrous tissue may
explain the difficulty in obtaining a transmural
lesion and consequently complete block. Our
observations are similar to those described by Heidbüchel et al. [31] who used angiography to evaluate
the isthmus. In that study the presence of a Eustachian valve or concave isthmus was associated with
statistically more RF applications.
In such cases these anatomical findings support
the use of more powerful ablation catheters. However, the complex topography of this region implies very careful mapping in order to verify the
entire Eustachian ridge extension that has to be
ablated.
It should be also noted that conduction gaps
were present in the ‘non-resistant’ atrial flutter
as well. These gaps were eliminated by few RF deliveries and were located in the central portion of
the isthmus below the CS os in 71% of cases. However, in these cases the lack of specific ridges
makes it easier to achieve a transmural lesion with
few additional RF pulses resulting in complete
block.
In conclusion, what clearly emerges from our
study is that ICE is very useful in identifying endocardial details and anatomical structures not visible on fluoroscopy and confirming what has been
described by Morton et al. [32]. In that study ICE
was clearly able to characterize the complex anatomic structures of the cavo-tricuspid isthmus visualizing complex endocardial features such as
pouches, recesses and trabeculations. In addition
ICE permits demonstration of a direct correlation
of electrical behaviour with the underlying anatomy because the relative position and stability of
the ablation catheter can be well established with
ICE [5,10,14,23,24,26,27,32,33]. Therefore, in
our study we were able to correlate sites of resistant conduction gaps with peculiar anatomical
structures.
Up to now, due to the cost of the device, it may be
not reasonable to suggest routine use of ICE in the
ablation of the atrial flutter. However, in the very
few cases of resistant atrial flutter the use of ‘irrigated’ ablation electrodes in conjunction with ICE
may play a role in achieving a successful outcome.
Limitations
The small number of patients represents an important limitation of the study. Moreover, we have not
416
performed any measurements of length and depth
of the isthmus because the plane visualized by
ICE very often is an oblique line and consequently
the measurements do not correspond with anatomical perpendicular cross-sections.
Conclusions
The IVC-TA isthmus presents anatomical variants
preferentially due to Eustachian ridge peculiarities. During AFl ablation conduction gap sites
are located in the central/inferior zone of the
isthmus in most cases. In the event of conduction
gaps ‘resistant’ to ablation, a redundant Eustachian ridge represents the most likely site of conduction gap. ICE clearly unveiled this anatomical
peculiarity.
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