CLINICAL RESEARCH
Europace (2015) 17, 1526–1532
doi:10.1093/europace/euu410
Ablation for atrial fibrillation
In vivo contact force measurements and
correlation with left atrial anatomy during
catheter ablation of atrial fibrillation
Fabienne Schluermann 1, Tobias Krauss 2, Juergen Biermann 1, Maximilian Hartmann 1,
Luca Trolese 1, Gregor Pache 2, Christoph Bode 1, and Stefan Asbach1*
1
Cardiology and Angiology I, Heart Center, Freiburg University, Freiburg, Germany; and 2Department of Radiology, University Hospital, Freiburg, Germany
Received 6 October 2014; accepted after revision 24 December 2014; online publish-ahead-of-print 5 March 2015
Aims
Lesion formation during catheter ablation crucially depends on catheter-tissue contact. We sought to evaluate the impact
of anatomical characteristics of the left atrium (LA) and the pulmonary veins (PVs) on contact force (CF) measurements.
.....................................................................................................................................................................................
Methods and
An anatomical map of the LA was obtained in 25 patients prior to catheter ablation of atrial fibrillation. Contact force
results
(operator blinded) and local bipolar electrogram amplitudes (EGM) were measured in eight pre-defined segments
around the PVs. After unblinding, points with low CF (≤5 g) were corrected to CF .5 g, and the distance between
points was measured. In a pre-procedural computed tomography of the heart, LA volume as well as sizes and circumferences of the PV ostia were measured and correlated to CF measurements. Four hundred and twenty-six points in eight
pre-defined LA locations were assessed. Low CF (,5 g) was found in 25.0% (43.5%) of points superior, 33.3% (66.7%)
anterior, 32.1% (44.4%) inferior, and 15.5% (15.9%) posterior to the right (left) PVs. The mean distance after correction
was 5.8 + 3.4 mm. Local bipolar electrogram amplitudes between low- and high-CF points did not differ (1.21 + 1.54 vs.
1.13 + 1.3 mV, P ¼ ns). The mean CF at the left PVs was significantly lower than at the right PVs (7.91 + 3.74 vs.
13.95 + 6.34 g, P , 0.001), with the lowest CF anterior to the left PVs (5.2 + 3.6 g). Contact force measurements did
not correlate to LA volume, size, and circumference of the PVs.
.....................................................................................................................................................................................
Conclusion
Contact force during LA mapping significantly differs according to the location within the LA. These differences are
independent of LA volume and anatomy of the PV ostia.
----------------------------------------------------------------------------------------------------------------------------------------------------------Keywords
Atrial fibrillation † Contact force † Left atrial volume † Area of pulmonary veins † Circumference of pulmonary veins
Introduction
Electrical isolation of the pulmonary veins (PVI) is an accepted treatment option for patients with symptomatic atrial fibrillation (AF).1
A standard approach is to create point-by-point lesions around the
pulmonary veins (PVs), usually guided by an electroanatomical
mapping system. Studies have shown a high rate of conduction recurrence,2 which also is a major determinant of clinical arrhythmia recurrence. Optimal lesion formation therefore is a major goal during
ablation, and this crucially depends on adequate catheter-tissue
contact. While this usually is estimated by tactile feedback, interpretation of local electrograms, and impedance drop during ablation, new
technologies allow for direct measurement of amount, and direction
of contact force (CF) applied with the catheter. In experimental
studies, it has been shown that CF correlates with lesion size and
depth, and that excessive CF predisposes to thrombus formation
and cardiac perforation.3,4 Clinical trials demonstrated the safety
and beneficial effects regarding procedural parameters.5 – 7 It has
been shown that reconnection of the PVs occurs at sites with poor
CF,8 – 11 and consistent with this, evidence for a correlation of CF
and arrhythmia recurrence is emerging.12 – 15 Beyond CF, anatomical
conditions have also been related to outcomes in AF ablation.
A major predictor has been shown to be the left atrial (LA)
volume, with increasing volumes the chances of sustained rhythm
control are decreasing.16,17 Data on the role of pulmonary vein
anatomy and its impact on AF recurrence after ablation are
* Corresponding author. Cardiology and Angiology I, Heart Center, Freiburg University, Hugstetter Str. 55, 79106 Freiburg, Germany. Tel: +49 761 270 34010; fax: +49 761 270 33882.
E-mail address: [email protected]
Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2015. For permissions please email: [email protected].
1527
In vivo contact force measurements and correlation with left atrial anatomy
What’s new?
† Despite detailed mapping of the left atrium, low local contact
force (CF) is a frequent finding during left atrial (LA) mapping,
and CF cannot be estimated by local electrogram amplitude.
† Low CFs cluster in the anterior region of the left pulmonary
veins.
† The distribution of low CFs is independent of LA volume.
† The distribution of low CFs is independent of pulmonary vein
anatomy.
conflicting.17 – 19 It may be argued that larger LA volumes provide a
substrate for AF beyond PV triggers, thus resulting in higher recurrence rates, however, larger LA volumes also could impose a
greater challenge for the operator to achieve adequate cathetertissue contact and create optimal lesions.
We, therefore, conducted the present study to evaluate the relationship of CF and anatomical LA and PV characteristics.
Methods
Twenty-five consecutive patients referred for ablation of paroxysmal
(n ¼ 16) or persistent (n ¼ 9) AF (15 male, 63.3 + 15.5 years) were
included at a single centre from April to December 2012.
Ablation procedure
After written informed consent was obtained, the ablation procedure was performed under analgosedation and spontaneous breathing in the catheter laboratory. Guiding by intracardiac ultrasound
(AcuNavTM , Siemens) was used in all procedures as previously described.20 A decapolar electrophysiology catheter was placed into
the coronary sinus allowing pacing manoeuvres to verify PV isolation
at the end of the procedure. Double transseptal access was obtained
to deploy the circular, decapolar mapping catheter (LassoNavw,
Biosense Webster, Inc.) and the CF measuring ablation catheter
(Thermocoolw SmarttouchTM , bidirectional navigation catheter,
D/F curve, Biosense Webster, Inc.). A steerable transseptal sheath
(AgilisTM , St Jude Medical) was used for the CF catheter in all cases.
Saline-irrigation rate during LA mapping was 2 mL/min.
Using the CARTOw3-System (Biosense Webster, Inc.), a fast
anatomical map (FAM) of the LA was performed using the LassoTM
Navw catheter at highest possible resolution. The AccuResp
Module was used to reduce the effect of respiration on FAM acquisition. Thereafter, the CF measuring catheter was positioned in
the eight pre-defined areas around both PVs in order to delineate
the planned ablation circle. These points were taken with the
operator blinded to CF measurements. Orientation was supported
by tactile feedback, the pre-acquired FAM, and local bipolar
signal amplitude. Signal amplitude was recorded for each acquired
point. After unblinding, points with CF ≤5 g were re-assessed
and points in vicinity as close as possible with CF .5 g were taken.
Distances between points were measured with the CARTOintegrated software algorithm. During subsequent PV isolation,
the operator remained unblinded for CF measurements. A single
LSPV
LAA
LIPV
Figure 1 Example of a FAM with points taken blinded to CF measurements (white) and after correction (grey), with an example of
distance measurement between points. LSPV, left superior pulmonary vein; LIPV, left inferior pulmonary vein; LAA, left atrial appendage.
operator performed all procedures. Figure 1 shows an example
of a FAM with points, uncorrected and corrected, and the distance
measurement.
Computed tomography data acquisition
and post-processing
All examinations were performed using a 320-detector-row CT
(MDCT) scanner (Aquillion One; Toshiba, Otawara, Japan). For
contrast-enhanced data acquisition, 80– 90 mL of iodinated contrast
agent (Imeron 350, Bracco Imaging Konstanz, Germany) was injected
(flow rate 4 mL/s. followed by 50 mL chaser bolus of saline solution).
Patients were scanned in a supine position during breath hold, with
the scan extending from the carina to the diaphragm. The scan was
started with a delay of 6 s after automatic detection of contrast in
the LA with a threshold of +180 Hounsfield Units. The centre of
the data acquisition window was set at 40% of the R–R interval.
Volume data were reconstructed into axial images with a slice thickness of 1.0 mm and a medium smooth-tissue convolution kernel.
Three-dimensional assessment of LA
anatomy
Multiplanar reconstructions of the MDCT dataset were used to
calculate the LA volume and to assess ostial dimensions using dedicated software (Aquarius 3D Workstation, TeraRecon, San Mateo,
CA, USA). LA volumetry was performed by tracing around the
margins of LA from the level of the mitral annulus to the roof.
The LA appendage was excluded.
Multiplanar reformations were manually oriented to display the
orthogonal view of the cross-section of each PV ostium. Ostial diameter and cross-sectional area of each PV were calculated automatically. Figure 2A and B show examples of CT measurements of areas
and circumferences of PV ostia, and a LA volume, respectively.
Statistical analysis
Continuous variables are reported as mean + standard deviation, discrete variable as counts (percentages). The x2 and Fisher’s exact tests
1528
F. Schluermann et al.
A
B
Figure 2 (A) An example of left atrial volumetry, (B) an example of a measurement of a pulmonary vein ostium.
1529
In vivo contact force measurements and correlation with left atrial anatomy
50
40
CF (g)
were used to test for differences in discrete variables. Means of
intra-individual CF measurements were calculated overall and for
each of the eight pre-defined regions within the LA. These values
were averaged over all patients. Two-tailed analysis of variance was
used to test for overall differences in means, and Student’s paired
t-test was used to test for differences in pairwise comparisons. For correlation, Pearson’s correlation coefficient r was calculated. All tests
were two-sided with a significance level a ¼ 5%. Analyses were per&
formed using GraphPad Prism, version 5.0c, GraphPad Software, Inc.
30
20
10
Results
n
Figure 3 Local distribution of CF within the left atrium in different locations around the right (RPV) and left (LPV) pulmonary veins.
Anterior
Analysis of CF
We analysed CF and local bipolar signal amplitude of 426 points.
The overall mean CF was 11.0 + 3.7 g. CF ≤5 g was measured in
152 (35.7%), 6– 10 g in 111 (26.1%) and .10 g in 163 (38.3%)
points. Significant differences were found with respect to the LA location. The mean CF at the left PVs was lower than at the right PVs
(7.9 + 3.7 vs. 14.0 + 6.3 g, P ¼ 0.0003). Lowest CF was found anterior to the left PVs, at the ridge between the left PVs and the atrial appendage (5.2 + 3.6 g). Contact force here was lower than superior
(7.5 + 5.7 g, P ¼ 0.09), posterior (11.3 + 6.4 g, P ¼ 0.0001), and inferior (7.6 + 6.1 g, P ¼ 0.09) to the left PVs. Highest CF was found
posterior to the right PVs (15.7 + 8.9 g). Please refer to Figure 3
for distribution of CF according to the LA region.
Consistent with the distribution of CF within the LA, points with
very low (,5 g) CF also clustered around the anterior parts of
the left and right PVs, with significant differences in the distribution
(P , 0.0001). Figure 4 shows the distribution of very low CF.
Signal amplitude of the local bipolar electrogram (EGM) did
not differ between points with low vs. high CF (1.21 + 1.54 vs.
1.13 + 1.3 mV, P ¼ ns). No correlation between EGM and CF was
found (r 2 ¼ 0.002, P ¼ 0.391).
Distance measurements
The overall mean distance of corrected points to their counterpart
with low CF (≤5 g) was 5.8 + 3.4 mm. While no regional differences
of the distances could be noted, we found a significant correlation of
low CF and distance after correction, i.e. points with lower CF also
needed a larger distance to correct these points to achieve better
contact (r ¼ 20.30, P , 0.001, Figure 5).
R
ea
M
The procedure was performed in all 25 patients (63.3 + 15.5 years)
without complications. The echocardiographically determined LA
diameter was 43.7 + 8.2 mm, left ventricular ejection fraction was
52.0 + 7.1%. Ejection fraction did not differ between patients with paroxysmal and persistent AF (52.2 + 7.7 vs. 51.7 + 6.1%, P ¼ 0.9),
whereas the LA diameter was larger in patients with persistent AF
(49.2 + 8.7 vs. 40.6 + 6.2 mm, P ¼ 0.008). The total procedure time
(including ablation) was 3.1 + 0.6 h, fluoroscopy time 12.3 + 4.8 min.
ov
er
PV all
p
R ost
PV
R ant
PV
s
R up
PV
m
e a in
n f
R
LP PV
V
po
LP st
V
LP ant
V
su
LP p
M Vi
ea nf
n
LP
V
0
Clinical characteristics
0g
1g
2g
3g
4g
5g
Posterior
Anterior
LSPV
RSPV
LIPV
RIPV
L
A
A
Figure 4 Distribution of points acquired with low CF (,5 g)
around the pulmonary veins. LAA, left atrial appendage; LSPV, left
superior pulmonary vein; LIPV, left inferior pulmonary vein; RSPV,
right superior pulmonary vein; RIPV, right inferior pulmonary vein.
the PV ostia. The ostial area of the right superior PV (2.9 +
0.9 cm2) was significantly larger than the ostial areas of the left superior PV (2.1 + 0.7 cm2) and the left inferior PV (2.2 + 0.9 cm2)
(P , 0.05). In four patients with a left common PV (LCPV), the
areas and circumferences were measured at the level of separation
of the veins. Patients with an LCPV did not differ according to LA
volume (123.2 + 36.9 vs. 124.5 + 32.5 cm3, P ¼ 0.9) and area or
circumference of the PVs.
Analysis of computed tomography scans
The mean LA volume was 124.3 + 32.4 cm3. A good correlation
was found with LA diameter as determined by echocardiography
(r ¼ 0.69, P ¼ 0.0001). Please refer to Table 1 for dimensions of
Correlation of CF and LA anatomy
The mean CF was not different in patients with smaller (,124 cm3)
LA volumes (10.8 + 3.3 g) vs. larger (.124 cm3) LA volumes
1530
F. Schluermann et al.
(11.1 + 4.2 g, P ¼ 0.83). Correlation was found neither for CF and
LA volume nor for CF and size or circumference of the right of left
PV ostia (Figures 6 and 7A and B).
Patients with an LCPV were neither different with respect to mean
CF (12.7 + 1.0 vs. 10.7 + 3.9 g, P ¼ 0.33) nor were regional differences in CF noted (P ¼ ns).
Discussion
The main findings of the presented study are (i) CF is heterogeneously distributed around the PVs, with lowest values found anterior to
the left PVs at the ridge to the LA appendage. (ii) Areas with very
low CF have a similar distribution pattern and here, (iii) CF and distances to adjacent points with CF .5 g inversely correlate.
(iv) Despite an elaborate anatomical reconstruction of the LA, still
a significant number of points exhibit low CF. (v) LA volume and
PV anatomy do not influence CF.
After the introduction of the catheter technology that allows
online measurement of CF, a number of studies have revealed
that CF is a major determinant of lesion formation.3,4 It has also
become quantifiable what has been clinically suspected; CF
sensing technology reduces ablation and procedure times,6,13 and
adequate catheter-tissue contact is harder to achieve at specific
anatomical locations, especially at the ridge between the left PVs
and the LA appendage.8 – 10,12 The results of the presented study
in this regard confirm this observation, even in a setting with
much effort for a precise anatomical map, including the FAM
with highest resolution, thorough interpretation of local signal
amplitude, intracardiac ultrasound, and the use of a steerable
sheath. Without CF, a large number of points were taken with inadequate low CF (36% ,5 g) and would presumably not have produced transmural lesions. This further emphasizes the additional
benefit of CF measurements during mapping and ablation. Data
from the EFFICAS I trial suggest that a much higher CF (20 g)
should be targeted to achieve a transmural lesion.9 Even if the distance measurements are afflicted with some inaccuracy (such as
that the measured distance not necessarily represents the shortest
possible distance to the LA surface), still the unexpected long
average distance of .5 mm and the correlation of distance with
CF clearly support the notion that no effective lesion can be
achieved in such a position.
While a relationship of CF and lesion formation is firmly established, CF is not the only predictor of AF recurrence. Hof et al.
have shown that for each 10 mL increase in LA volume, the risk
of AF recurrence after catheter ablation increases by 14%, and
Abecasis et al. 16,17 found that patients with an LA volume of
.145 mL have higher recurrence rates after catheter ablation.
Both studies, similar to our study, used LA volumes derived from
CT scans. Similar results could be obtained when LA volume is
assessed by echocardiography or electroanatomical mapping,21,22
and volumetry has been shown to have more predictive value
than LA diameter derived from echocardiography.23 However, these studies did not provide CF values from the ablation
procedures. Therefore, it still remained unclear whether the reported relation of AF recurrence and LA dimensions is due to a difference in the substrate that underlies AF, or due to technical
challenges imposed on the operator when ablating in a larger LA.
25
200
LA volume (mm3)
LA diameter (mm)
Distance (mm)
20
15
10
LA diameter
LA volume
150
100
50
5
0
0
0
0
2
4
6
5
10
15
20
25
CF (g)
CF (g)
Figure 5 Linear regression of CF and distance to adjacent points
after correction to adequate catheter contact.
Figure 6 No correlation was found between LA diameter
(as measured by echocardiography) or volume (as measured by
CT) and CF.
Table 1 Anatomical characteristics of the LA and PVs
RSPV
RIPV
LSPV
LIPV
P-value
...............................................................................................................................................................................
2
Area (cm )
Circumference (mm)
2.9 + 0.9
2.5 + 0.9
2.1 + 0.7
2.2 + 0.9
0.0087
62.4 + 9.0
57.5 + 11.5
55.0 + 7.7
55.2 + 10.6
0.0299
1531
In vivo contact force measurements and correlation with left atrial anatomy
Limitations
The overall number of studied patients is limited. Procedures were
performed by a single operator in order to reduce inter-operator
variations in CF, which have previously been demonstrated.5 This
limits generalization of our observations to a broader operator population. All procedures were performed during spontaneous breathing
without a systematic assessment of the effect of respiration. As it has
been shown that the mode of ventilation influences CF,24 timing
within the breathing cycle during spontaneous breathing also may
have affected CF measurements.
LPV area (cm2) LPV circumference (cm)
A
80
70
60
50
40
6
3
Conclusion
0
0
10
20
Mean CF LPVs (g)
30
RPV area (cm2) RPV circumference (cm)
B
Contact force during LA mapping significantly differs according to
the location within the LA. The lower the CF, the larger is the distance to the adjacent point with adequate CF. Local differences within
the LA are independent of LA volume and anatomy of the PV ostia.
80
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70
60
50
40
6
3
0
0
10
20
Mean CF RPVs (g)
30
Figure 7 (A and B) No correlation was found for mean CF around
the left (LPV, A) and right (RPV, B) pulmonary veins and area or circumference of the pulmonary veins.
The results of our study are in favour of the former assumption,
since CF was equally distributed without relationship to LA
volume, area or circumference of the PVs. With this observation,
it seems plausible to accept that CF is linked more to anatomical
features within the LA (e.g. low CF at the ridge anterior to the
left PVs), and possibly the angle of the transseptal access site to
the specific mapping/ablation site, more than to the overall volume
of the LA.
It has recently been shown that the presence of an LCPV is
a predictor for freedom of AF after AF ablation.19 The authors
speculated that the presence of an LCPV facilitates greater CF
especially in the anterior parts, and that the LCPV may more frequently harbour triggers that initiate AF. While the authors recognized the limitation in their study that they could not provide CF
data, we did not find differences in CF in patients with LCPV
when compared with those that had two discrete left PVs. This
would favour the latter speculation, that an LCPV more often harbours triggers for AF, though we are unaware of further supportive
evidence.
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EP CASE EXPRESS
doi:10.1093/europace/euv199
Online publish-ahead-of-print 2 September 2015
.............................................................................................................................................................................
Clipping to sinus rhythm: cardioversion of atrial fibrillation
by a thoracoscopic left atrial appendage occlusion
Vedran Velagić*, Gian-Battista Chierchia, and Mark La Meir
Centre for Cardiovascular Diseases, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, 101 Laarbeeklaan, 1090 Brussels, Belgium
* Corresponding author. Tel: +385 91 7929284; fax: +322 477 6851, E-mail address: [email protected]
A 52-year-old male patient underwent a hybrid
procedure for the treatment of a long-standing
persistent atrial fibrillation (second ablation).
A thoracoscopic video-assisted approach was
used for the epicardial, radiofrequent pulmonary
vein isolation, and the ‘box lesion’ set creation. Epicardial electrograms at the different sites in the left
atrium were recorded, before and after the completion of ablation. The cycle length of the left
atrium appendage activation decreased after the
ablation, and electrograms became fractionated
(Figure A). Afterwards, the epicardial appendage
clipping was performed during which patient converted to sinus rhythm. There was no more electrical activity in the appendage, entry and exit
blocks were confirmed (Figure B). Endocardially,
the pulmonary vein isolation was confirmed and
no further ablation was performed.
We hypothesize that, by isolating pulmonary
veins and posterior wall of the left atrium, the
appendage became the main atrial fibrillation
driver, marked by a new fractionation of the
local electrograms. Consequently, the effective
electric isolation of the appendage stopped the
arrhythmia and patient returned to sinus rhythm.
It is important to note that the epicardial appendage clipping might provide not only the functional occlusion but also the electrical isolation,
unlike the percutaneous devices that leave the arrhythmogenic potential of the appendage untouched.
The full-length version of this report can be viewed at: http://www.escardio.org/Guidelines-&-Education/E%E2%80%93learning/Clinicalcases/Electrophysiology/EP-Case-Reports.
Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2015. For permissions please email: [email protected].