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Archives of cardiovascular diseases
Volume 111, n° 5
pages 340-348 (mai 2018)
Doi : 10.1016/j.acvd.2017.07.002
Received : 31 January 2017 ;  accepted : 29 July 2017
Clinical research

A novel method for localization and ablation of conduction gaps after wide antral circumferential ablation of pulmonary veins
Nouvelle méthode de localisation des gaps de conduction après ablation circonférentielle des veines pulmonaires
 

Raoul Bacquelin a, b, c, Raphaël P. Martins a, b, c, , Nathalie Behar a, b, c, Vincent Galand a, b, c, Baptiste Polin a, b, c, Jonathan Lacaze a, b, c, Frédéric Sebag a, b, c, Christophe Leclercq a, b, c, Jean-Claude Daubert a, b, c, Philippe Mabo a, b, c, Dominique Pavin a, b, c
a CHU de Rennes, service de cardiologie et maladies vasculaires, 35000 Rennes, France 
b Université de Rennes 1, LTSI, 35000 Rennes, France 
c Inserm, U1099, 35000 Rennes, France 

Corresponding author at: Service de cardiologie, CHU de Rennes, rue Henri-Le-Guilloux, 35000 Rennes, France.Service de cardiologie, CHU de Rennes, rue Henri-Le-Guilloux, 35000 Rennes, France.
Summary
Background

Atrial fibrillation ablation is often performed by achieving pulmonary vein isolation using the “wide antral circumferential ablation” (WACA) technique, but many pulmonary veins remain connected because of conduction gaps in the ablation line.

Aim

To analyse the efficacy of a novel technique based on pacing manoeuvres to detect gaps in an initial WACA lesion.

Methods

Patients referred for radiofrequency atrial fibrillation ablation were enrolled prospectively. A WACA lesion set was performed, isolating ipsilateral pulmonary veins together. If pulmonary vein isolation was not achieved, the atria were paced using an ablation catheter. For each pacing site, “activation delay” and “activation sequence” were analysed using a circular mapping catheter positioned at the pulmonary vein ostium.

Results

Twenty-one patients were included. A total of 25 non-isolated WACA lesion sets were studied. Three patterns were identified: (1) the activation delays converged towards one point with the shortest delay; no modification of the activation sequence (indicating one gap); (2) the activation delays converged towards at least two close locations; no change in the activation sequence (indicating at least two close gaps); (3) the activation delays converged towards at least two remote locations; modification of the activation sequence (indicating at least two remote gaps). Pacing manoeuvres and effect of ablation allowed precise localization of gaps, ultimately leading to pulmonary vein isolation in all patients.

Conclusion

This simple pacing method accurately detected the location of residual connections after WACA lesion sets performed for atrial fibrillation ablation, allowing pulmonary vein isolation to be achieved.

The full text of this article is available in PDF format.
Résumé
Rappels

L’ablation de la fibrillation atriale (FA) repose sur l’isolation des veines pulmonaires (IVP) qui est très souvent réalisée en faisant des lésions linéaires circonférentielles larges (LLCL). Cependant, des gaps de conduction sont parfois présents après avoir réalisé les lésions.

But de l’étude

Nous avons analysé l’efficacité d’une nouvelle méthode basée sur des manœuvres de stimulation pour détecter des gaps de conduction sur des LLCL.

Méthodes

Les patients adressés pour une ablation de FA par radiofréquence ont été inclus de façon prospective. Des LLCL étaient réalisées autour des VP homolatérales. SI l’IVP n’était pas obtenue, l’oreillette était stimulée par le cathéter d’ablation. À chaque site de stimulation, le « délai d’activation » et la « séquence d’activation » enregistrés sur le cathéter circulaire positionné à l’ostium des veines pulmonaires étaient analysés.

Résultats

Vingt et un patients ont été inclus. Au total, 25 LLCL non isolées ont été étudiées. Trois réponses à la stimulation ont été identifiées : (A) les délais d’activation convergeaient vers un point unique où le délai était le plus court, sans modification de la séquence d’activation (indiquant la présence d’un gap unique) ; (B) les délais d’activation convergeaient vers2 zones proches, sans modification de la séquence d’activation (indiquant la présence de2 gaps proches) ; (C) les délais d’activation convergeaient vers2 zones éloignées, avec modification de la séquence d’activation (indiquant la présence de2 gaps éloignés). Les manœuvres de stimulation décrites ont permis de localiser de façon précise lalocalisation des gaps de conduction et d’en effectuer l’ablation, menant à une IVP chez tous les patients.

Conclusion

Cette méthode de stimulation simple permet de localiser de façon précise des gaps de conduction résiduels sur des LLCL, permettant d’obtenir une IVP en fin de procédure.

The full text of this article is available in PDF format.

Keywords : Atrial fibrillation, Ablation, Pulmonary vein isolation, Conduction gap, Recurrence

Mots clés : Fibrillation atriale, Ablation, Isolation veineuse pulmonaire, Gaps de conduction, Récurrence

Abbreviations : AF, CMC, PV, PVI, WACA


Background

Pulmonary vein (PV) isolation (PVI) is the cornerstone of most atrial fibrillation (AF) ablation procedures, as PVs play a critical role in AF initiation and maintenance [1, 2]. The so-called “wide antral circumferential ablation” (WACA) technique, using radiofrequency ablation to perform circular lesions encompassing the ipsilateral PV away from the ostia, is used frequently, and has been shown to be more effective than ostial PVI [3, 4]. However, after point-by-point anatomical ablation, zones of residual connections can persist along the ablation lines, which can be difficult to identify precisely. Moreover, a high percentage of patients may have AF recurrences after an initial ablation, mostly as a result of PV reconnections, and will require a redo procedure to achieve complete and long-lasting PVI. Detection of the conduction gaps in the initial lesion set is sometimes challenging; a few techniques have been described to find these gaps/reconnections, all of which have some drawbacks [5, 6, 7]. Localization of a residual connection on the line, based solely on the analysis of the activation sequence in the circular mapping catheter (CMC) positioned at the PV ostium, gives only a rough estimation of its precise location. This technique may be imprecise, especially in case of large circular lesions, where the activation within the isolated PV antra may not propagate along a straight course. Activation mapping inside the PV antra with the ablation catheter may be challenging because of fibrosis and difficulties in identifying far-field potentials or because of synchronous activation at different levels in relation to multiple gaps. Lastly, the “pace-and-ablate” technique may overestimate the presence of residual connections, resulting in unnecessary delivery of radiofrequency.

Complementary techniques may be useful in helping to find these connection gaps. In this study, we describe a novel and efficient technique to detect gaps precisely in the initial ablation lines, based on pacing manoeuvres around WACA lines.

Methods
Study population

Patients referred to our tertiary centre for a first radiofrequency ablation of paroxysmal or persistent AF were enrolled prospectively. Patients were included if PVI was not achieved after performing the WACA around the ipsilateral PV ostia, as the aim of the study was to determine the position of conduction gaps in such patients. Patients with complete PVI after performing the WACA lesion were excluded.

This study was performed according to local institutional regulations. All patients provided written informed consent.

Ablation procedure

Antiarrhythmic drugs were discontinued before the procedure (1 month for amiodarone; 5 half-lives for other drugs). Three catheters were inserted via the femoral route: one quadripolar coronary sinus catheter (Xtrem®, Sorin Group, Clamart, France) or decapolar coronary sinus catheter (Inquiry™ St. Jude Medical/Irvine Biomedical, Inc., Irvine, CA, USA); one duodecapolar CMC (Reflexion Spiral™, St. Jude Medical, St. Paul, MN, USA; or Lasso®, Biosense Webster, Diamond Bar, CA) and an irrigated tip electrode ablation catheter (Cool Path™ Duo, St. Jude Medical or ThermoCool™, Biosense Webster). The WACA lesion set was performed anatomically at the antral level, using a three-dimensional mapping system (EnSite™ Velocity™ NavX™ System, St. Jude Medical or CARTO3® System, Biosense Webster),>1cm away from the PV ostia. Radiofrequency energy was delivered during a 20–45 second period using a point-by-point technique with a maximal power of 30W, except for the posterior wall, where 20–25W were used. Ipsilateral PVs were isolated together, and no intervenous lines were performed. Once WACA lesions were performed, PVI was validated in sinus rhythm (after direct cardioversion, if needed) by verifying the absence or dissociation of PV potentials in the CMC located in the PV ostia. If PVI was not achieved by WACA, gaps were located using the technique described below.

Gap localization
First step: positioning the CMC

The first step was to choose the PV (superior or inferior) where the CMC was to be positioned, determined as the one with the shortest atrio-PV activation time. To do so, the CMC was placed consecutively in the ipsilateral non-isolated superior and inferior PVs. Atrio-PV activation time was assessed: in case of non-isolated right PVs (in sinus rhythm, from the onset of the P wave in lead II to the earliest PV potential recorded in the CMC); and in case of non-isolated left PVs (during coronary sinus pacing at a 600ms cycle length, from the pacing spike to the earliest PV potential). The CMC was then placed in the PV ostium (superior or inferior) with the shortest atrio-PV activation time, in a stable position, and the pacing manoeuvres were started.

Second step: localization of the gap(s)

The right and left WACA lines were divided into eight zones (Figure 1A). The atrium was then paced, using the ablation catheter, 5mm away from the ablation line in each zone (bipolar stimulation; 600ms pacing cycle length; output at twice the pacing threshold). For each site, the following variables were analysed: the atrio-PV delay between the pacing spike and the earliest PV potential recorded in the CMC, called the “activation delay”; and the pattern of “activation sequence” recorded on the CMC. These two variables (“activation delay” and “activation sequence”) were determined for each of the eight zones around the WACA line.



Figure 1


Figure 1. 

Schemes showing different responses to pacing around the circumferential ablation lesions, and assumptions of gap localization. A. Superior and inferior pulmonary veins (PVs) were arbitrarily separated into eight different zones (1–8). The circular mapping catheter (CMC) was positioned in the PV with the shortest atrio-PV activation time (see “First step: positioning the CMC” for details). In this example, the CMC was positioned in a superior PV. For the following panels, pacing applied around the lesions (red dots) and responses to pacing (activation delays and sequences) for each point are shown. B. Pattern A: the activation delays converge towards a single point where the delay is the shortest (49ms), without any modification of the activation sequence; the presence of a single residual connection, in front of this pacing site, was assumed. C. Pattern B: the shortest activation delays converge towards two locations (41 and 51ms), without any change in the activation sequence, indicating the presence of two close gaps. D. Pattern C: the activation delays converge towards two remote locations (38 and 36ms), with a clear modification of the activation sequence recorded on the CMC, indicating the presence of two remote gaps. Inf: inferior; Sup: superior; WACA: wide antral circumferential ablation.

Zoom

Third step: ablation of the gaps and validation of the technique

After determining the zone with the shortest activation delay, multiple pacing points were performed in this zone, to carefully determine the exact location of the area with the shortest activation delay. This area was assumed to be the position of the conduction gap in the ablation line. Radiofrequency energy was then delivered at this location. If PVI was achieved, the presence of one single gap in the WACA lesion was established. If PVI was not achieved, the effect of radiofrequency delivery on atrio-PV activation time and sequence was analysed, to determine if residual gap(s) were present. Pacing manoeuvres as described above were repeated, and ablation was delivered in the presumed location of the other gaps until PVI was achieved.

Statistical analyses

Continuous variables are expressed as means±standard deviations; categorical variables are expressed as numbers and/or percentages. Variables with non-normal distributions are expressed as medians (ranges). The analyses were performed with SPSS software, version 11.0 (SPSS Inc., Chicago, IL, USA).

Results
Patient characteristics

Patient characteristics are described in Table 1. Twenty-one patients were prospectively included in the study (mean age 59.1±10.6 years; 17 men). Most patients had paroxysmal AF (13 patients, 61.9%) and a moderately dilated left atrium (24.2±4.1cm2).

Gap localization

Based on the strategy defined in the Methods section, three distinct patterns were identified (Figure 1B–D).

In pattern A (Figure 1B), the activation delays converged towards a single point where the delay was shortest, without change in the activation sequence recorded on the CMC. We hypothesized that this situation indicated the presence of a single gap in the WACA line, in front of the location of the shortest activation delay.

In pattern B (Figure 1C), the shortest activation delays converged towards two or more close locations, without change in the activation sequence. We assumed that this situation indicated the presence of multiple gaps located close to each other.

In pattern C (Figure 1D), the activation delays converged towards two or more remote locations, with a modification of the activation sequence recorded on the CMC. We hypothesized that this situation indicated the presence of multiple remote gaps.

Once a gap was identified, radiofrequency ablation was performed, and three different responses were encountered: occurrence of PVI (in case of a single gap) (Figure 2A); abrupt lengthening (≥15–20ms) of the atrio-PV activation time, without modification of the activation sequence in the CMC, suggesting the presence of a close residual gap (Figure 2B); abrupt lengthening of the atrio-PV activation time, with modification of the activation sequence in the CMC, suggesting the presence of a residual remote gap (Figure 2C).



Figure 2


Figure 2. 

Different responses to ablation of connection gaps. Tracings from top to bottom are surface electrocardiogram leads (I, II and V1) and intracardiac electrograms recorded from the catheter inside the coronary sinus (CS 1,2 to 9,10), the circular mapping catheter (CMC) (Lasso 1,2 to 19,20) and the ablation catheter (ABL 1–2 and 3–4). A. Presence of a single PV residual gap; the ablation to the targeted site resulted in complete PVI (arrows). B. Presence of two close PV gaps; an abrupt lengthening of the atrio-PV activation time from beat-to-beat (from 125 to 167ms), without any change in the activation sequence, was observed during ablation. In this example, the second connection was found to be 2cm away from the initial connection. C. Presence of two remote PV gaps; an abrupt lengthening of the atrio-PV activation time from beat-to-beat (from 139 to 154ms), with a change to the activation sequence in the CMC, was observed.

Zoom

Among the 25 WACA lesion sets with at least one gap, pattern A was initially found in 20 cases, while patterns B and C were found in three and two cases, respectively (Figure 3).



Figure 3


Figure 3. 

Flowchart showing the different patterns found when using the pacing method in the study. EP: electrophysiological; PVI: pulmonary vein isolation; WACA: wide antral circumferential ablation.

Zoom

Pattern A

Among the 20 cases with activation delays converging towards a single point with the shortest delay (Figure 4), a unique connection was found in 16 of them, leading to PVI after ablation at the precise location of the residual connection (Figure 2A). For the remaining four cases, a second connection, close to the first one, was found after ablation of the first connection, responsible for an abrupt lengthening (≥20ms) of the atrio-PV delay during ablation of the first gap, without modification of the activation sequence in the CMC. Ablation of the remaining connection led to PVI in all cases.



Figure 4


Figure 4. 

Example of the patternA. Posterior (panel A) and right anterior oblique (panel B) views of a three-dimensional shell of the left atrium reconstructed with the EnSite™ NavX™ System, in a patient referred for a redo ablation of atrial fibrillation. The wide antral circumferential ablation (WACA) lesion is depicted as the black line around the pulmonary veins (PVs). Electrograms recorded on the circular mapping catheter (located in the right inferior PV in this case) during pacing around the WACA lesion are shown in the boxes. Colour coding (from white to purple, i.e. early to late activation) was used to visualize the activation delays. One can appreciate the convergence of the activation delays, without any change in the activation sequence, towards a unique point in the posterosuperior region of the right WACA lesion. A unique residual connection was found and ablated (orange dots in panel A) to achieve PV isolation.

Zoom

Pattern B

A pattern combining shortest activation delays converging towards two or more locations with no change in the activation sequence was found in three patients. Two of these patients had two close gaps; ablation of the first connection led to an abrupt lengthening of the atrio-PV delay (25ms for one patient, 42ms for the other; Figure 2B), without modification of the CMC activation sequence. The remaining patient had three connections in a right-sided WACA line, including two close gaps and one remote gap; the last of these was only unmasked after ablation of the two initial connections.

Pattern C

A pattern combining convergence of the activation delays towards two remote locations with modification of the activation sequence recorded on the CMC was found in two patients. Connections were separated by at least three zones: roof and floor on the left WACA line for one patient; and anterior and posterior on the right WACA line for the other. Ablation of the first gap (with the shortest activation delay) led to an abrupt lengthening and modification of the atrio-PV delay. The remaining gap was then found by repeating the pacing protocol, which was consistent with pattern A.

Concordance between the shortest activation delay and gap locations

Using the pacing technique, 36 gaps were found and ablated to achieve complete PVI in the study population study: 14 and 22 located on the left and right WACA lines, respectively. Afterwards, we aimed to compare the exact position of these connections with the zone with the earliest PV activation recorded on the CMC before radiofrequency energy delivery. These zones were concordant in 23 of the 36 gaps (63.9%). The concordance was similar for left and right WACA lesions (9/14 gaps [64.3%] and 14/22 [63.6%], respectively). Consequently, in around one-third of the cases, gaps were located in a zone other than the one presumed by the area with the earliest activation recorded on the CMC. Among the 13 non-concordant gaps, seven were in contiguous zones, while six were in distant zones. Therefore, the supposed location of the conduction gaps assumed by analysing the activation sequence of the CMC in these patients was inaccurate compared with their exact position.

Discussion

The main results of this study are as follows: gap localization on WACA lines can be found using a careful pacing method; activation delays and sequences recorded on the CMC, while pacing all around the linear lesions, allow the reliable detection of single or multiple conduction gaps; and the earliest activation recorded on the CMC predicts the position of the gap on the lesion line in only two-thirds of cases, stressing the need for more accurate methods of detection.

Methods in the literature for gap localization

PVI using WACA is safer (avoiding PV stenosis) and more effective than using smaller isolation areas around the PVs [3, 4]. However, finding gaps after an initial WACA procedure is sometimes challenging, particularly when large WACA linear lesions are performed, often exceeding 10cm of the circumference. Many groups have tried to develop methods to facilitate the localization of residual PV connections during an initial procedure or during a redo procedure when PVs are reconnected [5, 6, 7, 8].

The usual method used to localize residual connection gaps is based on the activation sequence recorded on the CMC or on activation mapping at the PV antra while steering the ablation catheter inside the lesion set. However, the activation sequence in the CMC gives only a rough estimation of its precise location. Indeed, in our study, only two-thirds of the connections were located in the region of the primoactivated dipole of the CMC. In a recent study by Salas et al. [8], concordance between gap location and the earliest PV electrogram in the circular catheter during pacing was only found in 25% of cases, with an average distance between the gap and the site in front of the earliest PV electrogram of 20.4±9.6mm. The anatomy of muscle sleeves may explain such discrepancies, as they are often composed of circular or spirally orientated bundles of myocytes with additional longitudinal or obliquely orientated ones, forming a mesh-like structure [9]. Furthermore, the CMC often does not fit perfectly inside PV ostia because of their oval shape. This technique is therefore imprecise, especially in case of large circular lesions, where the activation within the isolated PV antra may not propagate along a straight course.

Miyamoto et al. [7] used the activation sequence inside the PV ablation line to localize PV connection sites. An activation map was performed inside the line, and the conduction gap was defined as the site where the activation proceeded toward the entire PV. However, this method is time consuming, and requires detailed mapping inside the WACA lesion. Moreover, activation mapping inside the ablation lines may also be challenging, especially in case of large circular lesions encompassing a wide antral area, because of: difficulties in identifying low-voltage or fractionated atrial/PV potentials related to previous ablation or fibrosis, and separating them from far-field potentials; and synchronous activation at different levels in relation to multiple distant gaps. An equivalent technique using atrial mapping during PV pacing, called the “pace and map” manoeuvre, focusing on the atrial rather than the PV side of the line, has been described by Salas et al. [8].

Another commonly used technique for gap localization is the so-called “pace-and-ablate” approach [6]. Pacing applied along the inner aspect of the WACA line aims to find viable tissue. In case of left atrial capture, a gap is suspected and radiofrequency energy is delivered. However, high-output pacing may induce atrial far-field capture, thus overestimating the presence of residual connections, and resulting in unnecessary delivery of radiofrequency energy.

When PVI is not obtained, despite residual connection search and repeated radiofrequency delivery, the major downside is that a segmental and sometimes more distal ablation may be performed by electrophysiologists in order to obtain PVI, increasing the risk of PV stenosis and decreasing the efficacy of ablation, as a significant amount of antral tissue remains connected to the atria. The electroanatomical approach used in this study provides an efficient means of identifying and ablating conduction gaps strictly on the previous WACA lines.

Important characteristics of the method

Pacing has to be delivered outside the ablation line, while being close enough (5mm) to avoid the capture of muscle strands parallel to the ablation line, which would not enter the PVs, as described in anatomical studies [10] and/or because of conduction anisotropy [11].

In 5 of 25 cases, a discrepancy existed between the numbers of gaps assumed and found, i.e. two close gaps were found when the pacing manoeuvre indicated the presence of one (in four cases) and two close gaps associated with one remote conduction gap were found when the technique hypothesized the presence of two close gaps. These cases can be explained by a low density of pacing locations tested around WACA lesions. Indeed, when two close locations are present, a lenient mapping with few pacing points may indicate the presence of a unique gap, while a more thorough density of pacing points would have shown a convergence towards two different, but close, points. We therefore recommend performing a pacing manoeuvre each centimetre around WACA lesions in order to avoid this pitfall. A second explanation may be the different conduction velocities between various connections. Indeed, a close or remote connection can be “masked” if the conduction through it is slower than the initial “obvious” connection, where conduction velocity is faster. The presence of a second connection is then unmasked after ablation of the initial connection (Figure 5).



Figure 5


Figure 5. 

Typical example of a pitfall of the technique, initially assuming the presence of two close gaps, whereas three gaps were eventually found. Posterior (panels A and B) and right anterior oblique (panel C) views of a three-dimensional shell of the left atrium reconstructed with the EnSite™ NavX™ System. The wide antral circumferential ablation (WACA) lesion is represented by the red dots. The circular mapping catheter (CMC) was placed in the right superior pulmonary vein (PV) (not shown in the three-dimensional map). Electrograms shown in boxes are recorded in the CMC where activation delays are the shortest. A. The electrogram recorded before ablation of the residual first connection. B. Before ablation of the residual second connection. C. Before ablation of the residual third connection. Pacing manoeuvres initially located gaps in the posterosuperior and posterior part of the WACA lesion. Ablating the more rapid connection () (shortest activation delay of 73ms in panel A), resulted in an abrupt lengthening of the activation delay, without any change in the activation sequence of the PV recorded in the CMC, confirming the presence of the close second gap. Pacing manoeuvres were then performed again to precisely locate the residual gap. Surprisingly, two different activation sequences were observed, one similar to the initial activation sequence with a longer delay at the site of the second connection, when pacing posteriorly to the WACA lesion (panel B, activation delay 100ms, bottom traces), and the second one more delayed when pacing anteriorly to the WACA lesion (panel B, top traces). This pattern is a typical response to the presence of two remote gaps. Ablating the posterior connection (, close to the first one) again resulted in an abrupt lengthening of the activation delay, with a change in the activation sequence of the PV recorded in the CMC. The last connection () was localized and ablated in the anterior part of the circular lesion, in a position diametrically opposed to the second gap (panel C). This last connection was probably masked because of its extremely slow conduction (207 vs. 73ms) and its relative proximity to the first connection compared with the second one, explaining how it was unmasked after removal of the first faster connection.

Zoom

This is a reason why the analysis of the activation sequence on the CMC while ablating a connection gap is crucial, because it shows the clinician if a remaining connection is present, and if it is close or not. Indeed, when a sudden lengthening of the activation delay is observed without any change in the activation sequence, one can assume the presence of a close remaining connection. Conversely, a modification of the activation sequence combined with a lengthening of the atrio-PV delay is the hallmark of the presence of a remote remaining gap.

Study limitations

This technique allows the precise localization of a unique gap or two residual gaps after PVI using WACA. The efficacy of the technique to accurately detect and localize three or more gaps was not evaluated precisely in our study, as only two patients had more than two gaps; this would therefore require further studies. However, this may not be necessary, as the number of gaps is decreasing with the development of new technologies, such as ablation catheters that measure the contact force [12].

Only one CMC was inserted into the atria to analyse the activation sequence inside the PV, and was placed inside the PV antra with the shortest atrio-PV delay. Using two CMCs (one in each ipsilateral PV) could have helped to accurately detect residual connections [13], but cannot be recommended because of higher costs and a possible increased risk of complications.

Conclusions

The detection of conduction gaps strictly on WACA lines is sometimes challenging. We describe here a simple pacing method for accurately detecting the precise location of residual connections after a WACA lesion is performed for AF ablation, based on the activation delays and sequences in the CMC after pacing manoeuvres performed around the ablation lesion.

Sources of funding

None.

Disclosure of interest

The authors declare that they have no competing interest.


Acknowledgments

Jenny Lloyd (MedLink Healthcare Communications Ltd.) provided editorial assistance on the final version of the manuscript, and was funded by the authors.

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