Cavotricuspid isthmus angiography predicts atrial

Clinical research
European Heart Journal (2006) 27, 1833–1840
doi:10.1093/eurheartj/ehl121
Arrhythmia/electrophysiology
Cavotricuspid isthmus angiography predicts atrial
flutter ablation efficacy in 281 patients randomized
between 8 mm- and externally irrigated-tip catheter
´cile Romeyer-Bouchard1, Virginie Dauphinot2, Damien Lipp1,
Antoine Da Costa1*, Ce
1
´ro
ˆme The
´venin1, Jean-Claude Barthe
´le
´my2, and Karl Isaaz1
Loucif Abdellaoui , Marc Messier3, Je
1
Department of Cardiology, Faculty of Medicine J. Lisfranc, The Jean Monnet University, 42 055 Saint-Etienne, Cedex 2,
France; 2 Clinical Physiology and Exercise Laboratory, The Jean Monnet University, 42000 Saint-Etienne, France; and
3
The Bakken Research Center, 5 Endepolsdomein, 6229 GW Maastricht, The Netherlands
Received 3 March 2006; revised 27 May 2006; accepted 1 June 2006; online publish-ahead-of-print 28 June 2006
KEYWORDS
Aims Radiofrequency ablation (RFA) of cavotricuspid isthmus (CTI)-dependent atrial flutter can be
performed using various types of ablation catheters. Recent evaluations comparing externally cooledtip RFA (ecRFA) catheters and large-tip (8 mm) catheters found that ecRFA catheter may have a
higher efficacy for CTI ablation. The aim of this prospective study was to compare both catheters by
stratifying on CTI morphology in order to explain, in part, the discrepancies between previous randomized studies, and to validate predictive factors of difficult CTI ablation on clinical, echocardiographic,
and angiographic data.
Methods and results Over a period of 24 months, 281 patients were included and stratified on CTI morphology: ‘straight’, ‘concave’, and ‘pouch-like recess’. In straight CTI (n ¼ 150), the duration of application time with a median of 6 min [interquartile range (IQR) 4–9] vs. a median of 12 min (IQR 16–19;
P , 0.0001) and the duration of X-ray exposure with a median of 6 min (IQR 4.4–9.7) vs. a median of
10.4 min (IQR 7–17; P , 0.0001) were significantly lower with an 8 mm-tip when compared with
ecRFA catheter. In contrast, in concave CTI (n ¼ 95), a trend towards both shorter application time
with a median of 12.5 min (IQR 6–23) vs. a median of 19 min (IQR 7–28; P ¼ 0.08) and X-ray duration
exposure with a median of 10.4 min (IQR 6–20) vs. a median of 13 min (IQR 8–24; P ¼ 0.08) with an
ecRFA catheter when compared with 8 mm-tip catheter were evidenced. No significant difference
was shown between 8 mm-tip and ecRFA catheters in the pouch-like recess group (n ¼ 36). Predictive
factors of difficult ablation include right CTI length and morphology.
Conclusion This study demonstrates that the 8 mm-tip catheter is more effective for ablation in case of
a straight angiographic isthmus morphology and that the ecRFA catheter tends to be more effective in
case of concave angiographic isthmus morphology. Thus, angiographic isthmus evaluation may predict
both the effectiveness of an RF catheter, and the risk of an expensive crossover. These data may
explain, in part, the discrepancies of previous studies comparing both catheters.
Introduction
Radiofrequency catheter ablation (RFA) of the cavotricuspid
isthmus-dependent atrial flutter (CTI-AFL) is the optimal
treatment from the point of view of its high efficacy.1–4
Despite this high success rate, ablation of the CTI can be
extremely difficult.5–7 Multiple factors that affect the
lesion size8–16 include tissue contact,8,9 impedance,10 temperature at the tissue–electrode interface,10 blood flow at
the catheter–tissue interface,14 power and duration of
* Corresponding author. Tel: þ33 4 77 82 83 40; fax: þ33 4 77 82 84 51.
E-mail address: [email protected]
energy application,13 catheter orientation (perpendicular
or parallel),13,15 intracavitary blood flow,16 electrode–target
distance,16 electrode tip size, irrigation design, and more
recently CTI morphology.5–7 The 8 mm-tip and the externally
cooled-tip radiofrequency ablation (ecRFA) catheters are
most widely used to treat AFL.17–23 Unfortunately, studies
comparing cRFA and 8 mm-tip catheters showed questionable results because of small cohorts,19 irrigation design
that may influence the results,17,19 endpoint differences,22
and CTI anatomy.5–7 A recently published meta-analysis
demonstrating the equivalence between 8 mm-tip and
cRFA catheters disregarded the influence of ecRFA catheters.20 Open irrigated catheters seem to have greater
& The European Society of Cardiology 2006. All rights reserved. For Permissions, please e-mail: [email protected]
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Atrial flutter;
Catheter ablation;
Externally cooled-tip
catheter;
Large-tip catheter;
Angiography;
Structure;
Anatomy
1834
efficacy than solid large 8 mm electrode, in which they
dissociate the power produced from the local convective
effect, thus allowing the delivery of higher and more
stable power, causing larger and deeper lesions.15,24,25
In contrast, experimental studies with large electrodes
(8 mm-tip) showed an increase in both the cooling and the
electrode–tissue interface that induced larger and deeper
lesions, with this effect dependent on catheter orientation.21 Several studies have highlighted the influence of
anatomy on RFA parameters, yet, catheter assessments
have not stratified on tissue morphology.5–7 There was thus
a need for a prospective randomized comparison of the efficacy and safety of ecRFA and 8 mm-tip catheters with
randomized CTI anatomy to complement our study with
long CTIs.7
No large prospective study is available evaluating predictive factors of difficult CTI RFA. The aim of this prospective
study was two-fold: (1) to compare the efficacy of an
8 mm-tip and an ecRFA by considering CTI morphology and
(2) to evaluate predictive factors of difficult CTI AFL RFA.
Methods
Study population
The methodology of the right atrial angiography
Biplane angiography was performed after mapping, shortly before
RF energy delivery. An isthmogram was made by positioning a 5-F
pigtail catheter in the IVC.5–7 Contrast solution (50 cc) was injected
for 3–5 s (right anterior view at 258). The angiograms were digitally
acquired, allowing replay and storage. Measurements were calibrated by inter-electrode spaces projecting perpendicular to the
given cine-view. The length of the CTI was obtained at 258 in
the RAO projection between the IVC and the lower hinge point of
the tricuspid valve.5–7 CTI length measurements and morphology
analyses were made on the last atrial diastolic frame (confirmed
by tricuspid valve opening on the next frame). The perpendicular
distance between the line connecting the IVC (A) and the lower
hinge point of the tricuspid valve (B) with the deepest point of
the isthmus was measured.6 Patient groups were classified by CTI
length (short 32 mm or long .32 mm)5,6 and further sub-divided
in CTI morphology as straight, concave, or with a pouch-like
recess.6,7 The straight aspect was defined as a maximal distance
between A and B with an isthmus depth 2 mm (Figure 1). The
concave aspect was defined as a maximal distance between A and
B with an isthmus depth .2 mm with a concave CTI aspect
(Figure 2). When the isthmus could be divided into a recess
(inferoposterior to the CS ostium) and a flat vestibule (between
this recess and the tricuspid annulus), the CTI aspect was defined
as a pouch-like recess (Figure 3).5,6 An independent operator (BS)
performed all measurements and analyses.
Catheter ablation
Catheter randomization was performed on the entire population
after right atrium angiography. A radiofrequency current
(un-modulated, sine wave) was delivered in the unipolar mode
between the distal ablation catheter tip and a cutaneous patch
electrode placed over the left scapula. RF delivery was applied
point-by-point by the same operator (ADC) and was started at the
ventricular aspect of the tricuspid annulus when a stable electrogram with a small atrial and large ventricular amplitude was
observed. The central part of the isthmus was considered the
Electrophysiological study
Two catheters were introduced percutaneously through the right
femoral vein into the right atrium. A 6-F quadripolar catheter
with an inter-electrode distance of 5 mm (Bard Electrophysiology,
Tewksbury, MA, USA) was advanced to the His-bundle position;
then a dodecapolar catheter with a 5 mm bipolar separation
(Bard) was positioned in the coronary sinus (CS). The distal tip
was placed in the CS ostium with electrodes 1,2 (H1), 3,4 (H2),
5,6 (H3), and 7,8 (H4) close to the IVC and tricuspid isthmus,
while electrodes 9,10 (H5) and 11,12 (H6) recorded the low and
high right atrial activation, respectively. All measurements were
performed with the Cardiolab system (Prucka Engineering).
Figure 1 Short straight isthmus. Angiographic visualization of isthmus in
RAO during contrast injection. Isthmus width measured between IVC (A)
and lower hinge point of tricuspid valve (B). Figure shows an isthmus with
straight appearance (maximal distance between line A and B and the
isthmus is 2 mm) of average width 25.8 mm.
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All patients provided written informed consent. From November
2003 to October 2005, 332 consecutive patients with CTI AFL were
referred for RFA. AFL was diagnosed when: (1) the surface electrocardiogram (EKG) showed flutter waves that were predominantly
negative in leads II, III, aVF, and positive in lead V1 (counterclockwise AFL) or positive in leads II, III, aVF, and negative in lead V1
(clockwise AFL), with a regular atrial rate between 240 and
340 bpm; (2) the intracardiac EKG displayed the following activation
sequence for counterclockwise AFL: high right atrium, low right
atrium, a counterclockwise inferior vena cava (IVC)-tricuspid
isthmus activation sequence followed by left atrial activation established with a dodecapolar lead. The opposite activation sequence
applied to clockwise AFL.3 Isthmus involvement of the arrhythmic
circuit was demonstrated by entrainment manoeuvres (concealed
entrainment in the isthmus). Exclusion criteria were described
elsewhere.10
Catheter randomization between 8 mm-tip and ecRFA catheters
was performed, with stratification, in three isthmus anatomic
groups: ‘straight’, ‘concave’, and ‘pouch-like recess’.6,7 The prospective study was designed to demonstrate a 40% reduction in
fluoroscopy time exposition comparing externally irrigated and
8 mm-tip catheter ablation according to the anatomical status,
with 90% power. This required, for each anatomical category,
44 patients for each catheter ablation type, thus giving 88 patients
in each anatomical CTI. The size (means difference expected
7 min) and the standard deviation (10 min) of the fluoroscopy time
exposition, used for the sample calculation, were chosen using published data in similar studies.7,17,19
A. Da Costa et al.
AFL ablation catheters
Figure 2 Short concave isthmus aspect; illustrates a concave appearance
(maximal distance between line A and B and the isthmus is .2 mm) of
average width 26 mm and 4.2 mm depth.
1835
Echocardiographic measurements
Transthoracic Doppler Echocardiography (TTE) was performed
within 24 h after the electrophysiological procedure by an observer
(DL) blinded to the patients’ electrophysiological status. Ultrasound
studies were performed with a Vivid 7 imaging system using a
2.5-MHz transducer (second harmonic activation). M-mode and
bidimensional measurements were made according to the recommendations of the American Society of Echocardiography. The left
ventricular (LV) ejection fraction was calculated by the modified
Simpson rule.
Statistical analysis
Figure 3 Short pouch-like recess isthmus; shows a flat vestibular structure
against the tricuspid annulus and a pouch-like recess long near the IVC.
optimal site to ablate (inferior isthmus). This site of placement was
chosen to avoid the septal portion of the isthmus to preclude both
the AV block risk and very difficult ablation in a subset of patients
with pouches. RF delivery was applied until a bidirectional
isthmus block was obtained. Two types of catheters were used:
either an 8-F quadripolar bidirectional deflectable catheter with
an 8 mm-tip electrode (BLAZER II large curve XP 4500 TK2 Boston
EP-Technologies, San Jose, USA) used with a maximum power
output of 70 W and a maximum target temperature of 608 for 60 s
or an externally irrigated 5 mm-tip thermocouple catheter
(Cordis-Biosense-Webster Thermocool-F-curve, Diamond Bar, USA)
with a temperature-controlled RFA delivery with a maximum
power output of 50 W and temperature limit of 45–508C applied
for 60 s at each point. A saline solution (0.9%) was infused through
the irrigated catheter with a Gemini pump (battery powered to
Statistical analysis was performed using the software packages SPSS
12.OF (SPSS Inc., Chicago, IL, USA). Values were given as
mean + SD, if a normal distribution was validated. Otherwise
median and IQR were used. To take into account the randomization
and the stratification, the interaction between the two was
assessed, validating the stratification. If the distribution of the
values were skewed, the values were log-transformed before statistical analysis. We tested systematically normality distribution by
evaluating the heteroscedasticity of variance using the Levene
test. If normality was proven, the differences among groups were
analysed using MANOVA for effectiveness variables: the number of
applications, the X-ray exposure, and the procedure duration. A
two-sided probability value of P , 0.05 was defined as statistically
significant. Clinical, TTE, and right atrial angiographic variables
were tested to predict difficult ablation procedure pre-defined by
greater than 20 RFA unsuccessful applications (cumulated time of
1200 s). Predictive factors of difficult ablation procedure were
assessed by unpaired t-test.
Results
Study population
During 24-months, 332 consecutive patients were considered eligible, 51 patients had an exclusion criteria and
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avoid 50 Hz line noise) at a mean rate of 17 mL/min during RFA
delivery (20–40 mL/min). Between applications, a flow rate of
3 mL/min was used to maintain patency.17 When over 20 RFA
applications (cumulating 1200 s) were unsuccessful, the alternative
catheter was used.
The procedure endpoint was defined as a complete bidirectional
isthmus block as described elsewhere.1,2 Reversal of the right
atrial depolarization sequence was established by a complete cavotricuspid map using a multipolar mapping catheter straddling the
line of block,3 and by recording widely separated local double
potentials along the ablation line during atrial pacing.26 A differential pacing was performed to differentiate complete or incomplete
bidirectional isthmus block.27 When CTI block was not achieved
after the first ablation line, the conduction gaps were mapped
and ablated by searching for single or narrow-split potentials with
the ablation catheter moving along the original ablation line.
When signs of conduction block were observed during RF application
with proximal CS pacing, one extra RF application lasting 1 min was
performed at that site. Pacing was performed at a cycle length of
600 ms from the proximal CS and the low lateral right atrium.
The status of the bidirectional block was assessed continuously
over the 30 min period following bidirectional block occurrence.
On occasion, conduction resumed after ablation, which re-initiated
a complete RF ablation sequence until the bidirectional block
could be observed again, resetting the 30 min waiting period.
Cumulative time of RF delivery was recorded and fluoroscopy
time was calculated as total fluoroscopy time used for catheter
positioning and RF ablation, including the time to reach bidirectional block.
1836
A. Da Costa et al.
Table 1 Stratification of the randomization by CTI groups
8 mm-tip vs. ecRFA catheter
Straight CTI group
(n ¼ 150)
(n ¼ 78 vs. n ¼ 72)
Concave CTI group
(n ¼ 95)
(n ¼ 50 vs. n ¼ 45)
Pouch-like recess
CTI group (n ¼ 36)
(n ¼ 20 vs. n ¼ 16)
P-value
(8 mm vs. ecRFA
tip catheters)
Age (year + SD)
67 + 12 vs. 68 + 12
(P ¼ 0.8)
15/78 (19%) vs.
21/72(29%) (P ¼ 0.2)
59 + 10 vs. 56 + 13
(P ¼ 0.2)
32/78 (41%) vs. 33/72
(46%) (P ¼ 0.7)
37/78 (47%) vs. 36/72
(50%) (P ¼ 0.9)
4.4 + .7 vs. 4.4 + .6
(P ¼ 0.9)
25+6 vs. 26+6
(P ¼ 0.3)
10/77 (13%) vs. 11/68
(16%) (P ¼ 0.8)
31 + 11 vs. 30 + 10
P ¼ 0.6
33/78 (42%) vs. 32/72
(44%) (P ¼ 0.9)
68 + 10 vs. 69 + 10
(P ¼ 0.7)
15/50 (30%) vs. 10/45
(22%) (P ¼ 0.5)
59 + 12 vs. 56 + 11
(P ¼ 0.3)
26/50 (52%) vs. 17/45
(38%) (P ¼ 0.2)
25/50 (50%) vs. 20/45
(55%) (P ¼ 0.7)
4.4 + .6 vs. 4.6 + .7
(P ¼ 0.2)
31+7 vs. 30+7
(P ¼ 0.5)
11/48 (23%) vs. 9/41
(22%) (P ¼ 0.9)
36 + 12 vs. 36 + 11
P ¼ 0.8
22/50 (44%) vs. 12/45
(27%) (P ¼ 0.1)
68 + 10 vs. 63 + 14
(P ¼ 0.2)
5/20 (25%) vs. 1/16
(7%) (P ¼ 0.3)
62+8 vs. 58+8
(P ¼ 0.1)
11/20 (55%) vs. 7/16
(47%) (P ¼ 0.7)
10/20 (50%) vs. 11/16
(68%) (P ¼ 0.3)
4.7+1 vs. 4.7 + .7
(P ¼ 0.8)
30+5 vs. 30+4
(P ¼ 0.9)
6/20 (30%) vs. 3/15
(20%) (P ¼ 0.8)
32 + 11 vs. 30+9
P ¼ 0.6
11/20 (55%) vs. 2/16
(13%) (P ¼ 0.01)
0.4
Gender (% women)
LVEF
Pre-ablation history of Afib
Structural heart disease (%)
Left atrial size (mm)
CTI (mm)
Tricuspid regurgitation 3
Systolic pulmonary pressure
(mmHg)
Anti-arrhythmic drugs discharge
0.9
0.1
0.5
0.8
0.5
0.3
0.9
0.5
0.1
LVEF, left ventricular ejection fraction. 8 mm-tip vs. ecRFA: No difference were found for baseline characteristics between the randomized Irrigated-tip
and 8 mm-tip group LVEF.
AFL ablation results
Angiographic analyses
Anatomic morphology was assessed: 150 patients had a
straight CTI, 95 patients had a concave CTI with a mean
depth of 6.7 + 2.7 mm (from 2.6 to 11.7 mm), 36 patients
presented a pouch-like recess with a mean depth of
8.2 + 2.4 mm (from 2.1 to 12.4 mm) (Table 2).
X-ray exposure (P , 0.0001) were significantly lower with
an 8 mm-tip catheter when compared with an ecRFA catheter in straight CTI (n ¼ 150) (Figures 4 and 5). In contrast,
in concave CTI (n ¼ 95), a trend toward both shorter application time and X-ray exposure (P ¼ 0.08) with an ecRFA
catheter was evidenced (Figures 4 and 5). No significant
difference was shown between 8 mm-tip and ecRFA catheters in the pouch-like recess group (n ¼ 36). The number
of audible ‘pop’ did not differ between 8 mm and ecRFA
groups in both straight (n¼6 vs. n ¼ 7; P ¼ 0.7) and pouchlike recess CTI (n¼1 vs. n ¼ 2; P ¼ 0.2), but were significantly greater in concave CTI with an 8 mm group when
compared with the ecRFA catheter group (n¼9 vs. n ¼ 2,
P ¼ 0.03). Long isthmii (n ¼ 73) required similar RF application time (23 + 16 vs. 23 + 22) and X-ray exposure
(19 + 13 vs. 21 + 21) for the ecRFA (n ¼ 36) and 8 mm-tip
(n ¼ 37) catheters (Table 2).
Predictive factors of difficult CTI RFA
RF ablation results
Bidirectional block was obtained in 99% of cases with a mean
RF application time of 15 + 15 min and mean fluoroscopic
time of 14 + 13 min. There were two significant procedure-related complications: one false arterial femoral
aneurysm requiring surgical treatment and a stroke with
incomplete recovery in a 78-year-old woman because of an
AF episode 12 h after the RFA despite anticoagulation.
RF results with 8 mm-tip and ecRFA catheters
The Levene test was significant for straight (P ¼ 0.03) and
concave CTI (P ¼ 0.01) but not significant for pouch-like
recess group (P ¼ 0.3). When target tissue morphology was
considered, the total RF applications and the length of
Difficult ablation requiring .20 min of application appeared
in 66 patients (Tables 3 and 4). Predictive factors include
CTI length (32+7 vs. 27 + 6 mm; P , 0.0001), concavity
depth (7.4+3 vs. 6.4 + 2.5 mm; P ¼ 0.04), longitudinal
(5.7 + 0.8 vs. 5.3 + 0.7; P ¼ 0.003) and transversal
(4.5 + 0.8 vs. 4.1 + 0.7; P ¼ 0.005) RA dimensions, LVEF
(54.5 + 11 vs. 60 + 11; P ¼ 0.008), systolic arterial pulmonary pressure (37 + 11 vs. 32 + 11 mmHg; P ¼ 0.005),
isthmus morphology [‘straight’ (11%) vs. ‘concave’ (39%) or
‘pouch-like recess’ (33%); P , 0.0001], short (,32 mm) or
long CTI (32 mm) (17% vs. 42%; P , 0.0001) and evidence
of grade 3 or 4 tricuspid regurgitation (46 vs. 19%,
P ¼ 0.0002). In the subset with ecRFA catheter (n ¼ 33),
these difficult ablations showed a trend towards both
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281 gave their written consent. Patients’ characteristics are
summarized in Table 1. At the beginning of the procedure,
208 patients exhibited AFL, 60 sinus rhythm, and 13 atrial
fibrillation (AF). Patients showing sinus rhythm underwent
burst pacing in the CS or the low right lateral atrium
at cycle lengths as short as 180 ms to induce a flutter.
Sinus rhythm was restored by electric cardioversion
(internal or external) for patients in AFib (n ¼ 13) and the
decision to ablate these was based on a documented EKG
of typical AFL.
AFL ablation catheters
1837
Table 2 RFA results of the MANOVA comparing 8 mm-tip to ecRFA on CTI groups
Appl. duration time for validated RFA (min)
Straight CTI group
Concave CTI group
Pouch CTI group (n ¼ 36)
X-ray exposure (min)
Straight CTI group
Concave CTI group
Pouch CTI group (n ¼ 36)
Procedure duration (min)
Straight CTI group
Concave CTI group
Pouch CTI group (n ¼ 36)
8 mm-tip catheter group
Irrigated tip catheter group
X + SD (range)
Median (IQR)
X + SD (range)
Median (IQR)
P-value
8 + 8 (2–60)
24 + 22 (3–86)
15 + 18 (4–80)
6 (4–9)
19 (7–28)
9 (6–16)
14 + 10 (3–56)
16 + 13 (3–56)
22 + 19 (3–60)
12 (6–19)
12.5 (6–23)
18.5 (5–36)
,0.001
0.08
0.3
9+9 (1–51)
20 + 19 (2–85)
15 + 19 (3–75)
6 (4.4–9.7)
12.5 (8–24)
8.4 (6–12)
13 + 9 (2–47)
14 + 10 (2–40)
21 + 15 (4–51)
10.4 (7–17)
10.4 (6–20)
20 (6–31)
,0.001
0.08
0.2
61 + 16 (31–120)
83 + 33 (35–180)
72 + 30 (48–155)
55 (50–71)
75 (55–103)
62 (53–81)
71 + 21 (40–150)
74 + 23 (50–141)
86 + 35 (45–140)
70 (57–80)
70 (57–92)
71 (60–126)
,0.001
0.1
0.2
8 mm-tip vs. ecRFA. Values are presented as mean + SD (X + SD) and median (IQR). Significant difference (P-value 0.05) found between groups were
calculated on log-transformed values.
Figure 5 This box plot shows that a greater effect exists with the 8 mm-tip
catheter in straight CTI morphology when compared with the externally
cooled-tip catheter based on X-ray exposure. In contrast, there is a trend
towards a greater effect of the externally cooled-tip catheter in concave
CTI when compared with the 8 mm-tip catheter. Moreover, the cooling catheter seems to be less influenced by CTI anatomy.
shorter RF application time (33 + 11 vs. 40 + 21, P ¼ 0.1)
and shorter X-ray exposure (28 + 10 vs. 33 + 22, P ¼ 0.2)
when compared with the 8 mm-tip catheter group (n ¼ 33).
Role of 8 mm-tip catheter specificities in
various CTI anatomies
Discussion
Major findings
Our study demonstrates that the 8 mm-tip catheter is more
effective for ablation in case of a straight angiographic
isthmus morphology allowing to predict the effectiveness
of a catheter, which is cheaper and easier to use and may
prevent the risk of an expensive crossover to a second ablation catheter. In contrast, a trend towards a greater effectiveness was evidenced in concave CTI with an ecRFA
catheter (P ¼ 0.08). These results may explain the controversial data of previous comparative studies on the efficacy
of these two catheter types7,17–20,22,23 as CTI morphology
was not taken into account then. Thus, angiographic
isthmus evaluation may predict the effectiveness of an RF
catheter. However, difficult AFL ablation occurs in approximately one-fourth of the patients, which is related to
anatomic and haemodynamic factors.
Previous randomized studies comparing large (8 mm) and
cooled tip catheters in CTI AFL RFA have shown either equivalence or slightly superior results for ecRFA catheters.7,17–20,22,23 Some factors may explain these: sample
sizes too small to highlight differences, catheter specificities
that may have been different in various clinical situations,
different endpoint definitions,22 and the impact of CTI
anatomy.5–7 Multiple factors affecting the lesion size have
been identified in experimental studies.8–16,21,24,25,28–36
Considering all these factors, we assumed that RFA lesions
were expected to be deeper and larger with both cRFA and
8 mm-tip catheters, with variable results depending on CTI
anatomy. Experimental studies had shown that the 8 mm-tip
was the most effective and that even better results could
be obtained in specific clinical situations.8–11,21 Two mechanisms were described to account for deeper RF lesions produced by larger electrodes in experimental studies:8–11,21
.
an increase in convective cooling due to the larger surface
exposed to the blood flow,21 which maintains a lower
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Figure 4 This box plot shows that a greater effect exists with the 8 mm-tip
catheter in straight CTI morphology when compared with the externally
cooled-tip catheter based on duration application time. In contrast, there
is a trend towards a greater effect of the externally cooled-tip catheter in
concave CTI when compared with the 8 mm-tip catheter. Moreover, the
cooling catheter seems to be less influenced by CTI anatomy.
1838
A. Da Costa et al.
Table 3 Difficult ablation procedure
No. of appl. To interrupt AFL (min)
No. of appl. for validated RFA [.300 ] (min)
Number of conduction recurrence within 300
X-ray exposure (min)
Procedure duration (min)
Difficult procedure
(n ¼ 66) (24%)
Normal procedure
(n ¼ 215) (76%)
P-value
19 + 15
36.5 + 17
16/66 (24%)
30.3 + 17
103 + 27
4.8 + 4.4
8.3 + 5
31/215 (14%)
9+6
62 + 15
,0.001
,0.001
¼0.001
,0.001
,0.001
Difficult ablation procedure defined as .20 RFA unsuccessful applications cumulating .1200 s (P , 0.05).
Table 4 Significant predictive factors of difficult ablation procedure [defined by .20 RFA unsuccessful
applications (cumulating 1200 s)] [P , 0.05]
Difficult
procedure
(n ¼ 66)
.
66 + 10
14/66 (21%)
28/66 (42%)
35/66 (53%)
4.6 + 0.7
32 + 7
7.4 + 3
54 + 11
5.7 + 0.8
4.5 + 0.8
23/65 (35%)
37 + 11
17/150 (11.3%)
37/95 (39%)
12/36 (33.3%)
electrode–tissue interface temperature, thus allowing
greater power to be delivered resulting in higher tissue
current density and deeper direct resistive heating;21
an increase in electrode–tissue interface area.21
In both proposals the volume of resistive heating and
lesion depth is increased.21 These may be reduced owing
to the position of the catheter being perpendicular or parallel to the target tissue.12–16,21 The precise orientation of the
ablation catheter (relative to the tissue) determines the size
of the surface area in contact with the tissue and influences
the geometry and size of the RFA lesions created.15 In
straight CTI, creating a bidirectional block with an
8 mm-tip catheter, rapidly, can be related to the parallel
positioning of the large electrode tip lying on its side, thus
optimizing the electrode–tissue interface with a larger
volume of resistive heating, and with a convective cooling
effect improving the power delivered.12–14,16,21 Other
factors seem to contribute to a better result in this
subset, namely a constant high blood flow in the CTI
region across the ablation electrode and a continuous
sliding of the ablation electrode during RF application,
which allows for continuous linear lesion.12–14,21,35 In such
situations, the smaller electrode tip found on irrigated catheters may offset the potential advantages of irrigation.
P-value
66 + 11
54/215 (25%)
98/215 (46%)
104/215 (48%)
4.4 + 0.7
27 + 6
6.4 + 2.5
60 + 11
5.3 + 0.7
4.1 + 0.7
27/204 (13%)
32 + 11
0.3
0.7
0.8
0.6
0.2
,0.001
0.03
0.01
0.003
0.005
0.0001
0.005
133/150 (88.7%)
58/95 (61%)
24/36 (66.7%)
,0.0001
In contrast, the potential advantages of externally irrigated catheters had been demonstrated in cases of low
local convective cooling where power output is reduced. It
may be the case in concave CTIs.6,7 These advantages
include a higher electrode resolution improving mapping
accuracy and subsequently allowing gap detection particularly in difficult CTIs.36–38 This factor increases ablation
efficacy and decreases the number of RF applications in
concave CTIs. A shorter catheter tip increases catheter flexibility and mobility allowing access to difficult areas.15 All
these factors contribute to a more stable level of power
with the creation of larger lesions.15–17,19,20,24–29
When using cooled-tip electrodes, the duration of the
application is a major determinant of the size of the
lesion. This is important in difficult isthmii ablations, such
as concave CTIs, where the required duration of RFA application is recognized to be longer than in straight CTIs.6,7
As electrode cooling is provided by irrigation in ecRFA, the
voltage or power can be chosen and maintained independent of the local blood flow (‘extrinsic cooling’), leading
to a more consistent and predictable lesion size.15,27
In contrast, the power delivered and the lesion depth in
the temperature-control mode, without irrigation, varies
greatly with local blood flow.15,27 In low-flow areas, such
as inert concavities, the RFA delivery power is considerably
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Age year + SD
Gender (% female)
AFib history (%)
Structural heart disease
Left atrial size (mm)
CTI length (mm)
Concavity depth (mm)
LVEF (%)
Longitudinal right atrial dimension (mm)
Transversal right atrial dimension (mm)
Grade 3 or 4 tricuspid regurgitation
Systolic pulmonary pressure (mmHg)
Isthmus morphology
Straight
Concave
Pouch-like recess
Non-difficult
procedure
(n ¼ 215)
AFL ablation catheters
reduced, producing small non-transmural lesions.15,27 In
concave CTIs, the advantages of an 8 mm-tip catheter may
be lessened by a reduction in electrocardiographic resolution from the ablation electrode, whereas with a smaller
catheter tip, the identification of gaps is enhanced.17,34,36,37
Another factor is a greater variability in electrode–tissue
contact, depending on catheter tip orientation relative to
the endocardium, likely to cancel the potential benefit of
using a larger-tip catheter.15,28
In this complex isthmus architecture, the strictly parallel
orientation to the endocardial surface for efficient contact
pressure is almost impossible along the entire CTI and a
long application using a point-by-point technique in the
absence of optimal electrode–tissue contact may be
counterproductive.34
Predictive factors of difficult CTI ablation
Study limitations
The main limitation of this study might be due to the
absence of significant difference between both catheters
when the isthmus had pouch-like recess. In contrast, when
pouches occur, they are often found in the proximity to
the thebesian valve and in the septal portion of the
isthmus,5,6,31 while in our initial methodology, the site of
placement of the ablation line was the inferior isthmus
avoiding the septal zone. On another explanation, may be
because of the absence of study power achievement in the
subset of pouches with only 36 patients included, while 88
patients were expected. In addition, pouches form only a
third part of the isthmus, the other part constituted by
the vestibule is a straight area.5,6,31 Right atrial angiography
provides a guide to CTI anatomy, but no detailed information
on the thickness of the isthmus and the local vasculature.33,39
An RF application time at each point of maximal 60s is a
clear disadvantage for the cooled-tip catheter, as it lasts
much longer for the ecRFA catheter than for the 8 mm-tip
catheter to reach the maximal power output. In case of
straight CTI, the results for an ecRFA catheter might be
expected to be better with a continuous application and
the dragging method. This point should be taken into
account in further studies evaluating ecRFA catheters.
Furthermore, the different catheter designs between
cooled-tip and 8 mm-tip catheters (size of the deflectable
curve, rotation stability, and size of the distal non-steerable
catheter part) might influence the comparison results.
Perhaps, a better choice for evaluating both techniques
would have been a comparison of 8 mm-tip and ecRFA tip
catheters from the same company. The clinical implication
may be an angiographic isthmus evaluation that may
predict the effectiveness of an RF catheter, which is
cheaper and easier to use (8 mm-tip catheter in the case of
a straight CTI). However, this clinical implication is still hampered by the question, whether an individual angiographic
evaluation is really superior to an empirical use of ablation
catheters. A more relevant design would have been a catheter choice based on angiography in one set of patients
when compared with a ‘controlled set’ with no angiography.
Conclusions
This study demonstrates that the 8 mm-tip catheter is more
effective for ablation in case of a straight angiographic
isthmus morphology and that the ecRFA catheter tends to
be more effective in case of concave angiographic isthmus
morphology. Angiographic isthmus evaluation may predict
both the effectiveness of an RF catheter and the risk of an
expensive crossover. These data may explain, to a certain
extent, the discrepancies of previous studies comparing
both catheters.
Conflict of interest: none declared.
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