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Contact force threshold for permanent lesion formation in atrial fibrillation ablation: A cardiac magnetic resonance–based study to detect ablation gaps
Author's Accepted Manuscript
Contact Force Threshold for Permanent Lesion Formation in Atrial Fibrillation Ablation: A Cardiac Magnetic Resonance-based Study to Detect Ablation Gaps David Andreu MSc, PhD, Federico Gomez-Pulido MD, Mireia Calvo MSc, Alicia Carlosena-Remírez BSc, Felipe Bisbal MD, Roger Borràs BSc, Eva Benito MD, Eduard Guasch MD, PhD, Sussanna Prat-Gonzalez MD, PhD, Rosario J. Perea MD, PhD, Josep Brugada MD, PhD, Antonio Berruezo MD, PhD, Lluís Mont MD, PhD
PII: DOI: Reference:
S1547-5271(15)01024-3 http://dx.doi.org/10.1016/j.hrthm.2015.08.010 HRTHM6391
To appear in:
Heart Rhythm
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Cite this article as: David Andreu MSc, PhD, Federico Gomez-Pulido MD, Mireia Calvo MSc, Alicia Carlosena-Remírez BSc, Felipe Bisbal MD, Roger Borràs BSc, Eva Benito MD, Eduard Guasch MD, PhD, Sussanna Prat-Gonzalez MD, PhD, Rosario J. Perea MD, PhD, Josep Brugada MD, PhD, Antonio Berruezo MD, PhD, Lluís Mont MD, PhD, Contact Force Threshold for Permanent Lesion Formation in Atrial Fibrillation Ablation: A Cardiac Magnetic Resonance-based Study to Detect Ablation Gaps, Heart Rhythm, http://dx.doi.org/10.1016/j.hrthm.2015.08.010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Contact Force Threshold for Permanent Lesion Formation in Atrial Fibrillation Ablation: A Cardiac Magnetic Resonancebased Study to Detect Ablation Gaps David Andreu, MSc, PhD*; Federico Gomez-Pulido, MD*; Mireia Calvo, MSc; Alicia Carlosena-Remírez, BSc; Felipe Bisbal, MD; Roger Borràs, BSc; Eva Benito, MD; Eduard Guasch, MD, PhD; Sussanna Prat-Gonzalez, MD, PhD; Rosario J Perea, MD, PhD; Josep Brugada, MD, PhD; Antonio Berruezo, MD, PhD and Lluís Mont, MD, PhD
Unitat de Fibril·lació Auricular (UFA) Hospital Clinic, Universitat de Barcelona, Catalonia, Spain. Institut d’Investigacions Biomèdiques August Pi i Sunye IDIBAPS) Barcelona, Catalonia, Spain. * Both authors contributed equally to this work.
Short Title: Contact force threshold for permanent lesion formation
Address for correspondence: Lluís Mont, MD, PhD Cardiology Dept, Hospital Clinic C/ Villarroel 170 08036 Barcelona Phone: 0034-93-2275551 Fax: 0034-93-4513045 Email: [email protected]
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ABSTRACT Background Catheter contact force (CF) has a strong correlation with lesion formation during radiofrequency ablation. Delayed-enhancement cardiac magnetic resonance (DE-CMR) provides lesion information in patients with a prior atrial fibrillation (AF) ablation. Objective The aim of this study was to determine the CF threshold to create permanent lesions detected by DE-CMR. Methods A total of 36 patients referred for AF ablation were included. A CF catheter was used during the ablation procedure and DE-CMR was performed at three months postablation. Eighteen pulmonary vein (PV) segments were defined and 3D reconstructions of the left atrium (LA) derived from the DE-CMR images were obtained. One observer evaluated the presence of any discontinuity of previous ablation lesions (gap) in the 3D LA reconstructions and another observer (blinded to the gap findings) determined the minimum CF value in each PV segment. Results The PV segments where a gap was observed had a lower maximal CF than the segments without gap in the 3D LA reconstructions (6.7±4.4 g vs 12.2±4.7 g; p<0.001). In ROC analysis, a CF threshold >8 g provided 73% sensitivity and 81% specificity in the prediction of a complete PV lesion (Positive Predictive Value [PPV] =84%). A CF threshold >12 g had a specificity of 94% and increased the PPV to 91% in creating a complete lesion in the LA wall (area under the curve=0.834). Conclusion A CF threshold >12 g predicts a complete lesion with high specificity and PPV when a dragging ablation strategy is used in AF ablation.
KEYWORDS: Cardiac Magnetic Resonance, Atrial Fibrillation Ablation, Contact Force, Gaps, Delayed-Enhancement, Pulmonary Vein, Ablation Lesion.
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ABBREVIATIONS AF: atrial fibrillation CF: contact force DE-CMR: delayed-enhancement cardiac magnetic resonance PV: pulmonary vein CF-min: minimum contact force INTRODUCTION Circumferential pulmonary vein (PV) isolation is a well-established therapy for atrial fibrillation (AF).1 Nonetheless, a significant number of these patients experience postablation recurrence,2,
3
which has been shown to be closely related with PV re-
connection through gaps in the ablation lines around the PVs.4 New technological developments in ablation catheters may improve acute and long-term results by ensuring transmural and permanent lesion formation. The contact between the catheter tip and the tissue during ablation has a strong correlation with lesion formation. Clinical implementation of real-time contact force (CF) sensing at the catheter tip has been shown to be a useful tool for AF ablation, with improved outcomes.5-8 Delayed-enhancement cardiac magnetic resonance (DE-CMR) can identify myocardial scarring after ablation.9,
10
Recent studies showed that DE-CMR is a reliable tool to
precisely depict gaps in prior ablation and also to guide re-ablation procedures targeting the ablation line gaps.11 The correlation between delayed-enhancement cardiac magnetic resonance (DE-CMR) signal intensity and CF has been described recently.12 However, a CF threshold for lesion formation during circumferential RF ablation has not been yet established. The aim of the study was to define a CF threshold to ensure permanent scar formation and to determine if CF maps can predict the presence of gaps on postprocedural DE-CMR (CMR gaps).
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METHODS Patient Sample Between July 2012 and July 2014, consecutive patients referred for a first ablation of AF in which a CF sensing catheter was used were prospectively included. Inclusion criteria were age ≥18 years with symptomatic and drug-refractory AF. Patients with any treatable cause of AF, contraindication for anticoagulation or left atrial (LA) thrombus, LA anteroposterior diameter >50 mm, severe mitral valve disease, prosthetic mitral valve, left ventricular (LV) ejection fraction (LVEF) <30% and/or contraindication for DE-CMR were excluded. Written informed consent was obtained and the hospital’s Ethics Committee approved the study protocol. Electrophysiological Study Previously described institutional standard protocols of sedation and anticoagulation were applied. A 3D reconstruction of the left atrium was performed with an electroanatomic mapping system (CARTO, Biosense Webster, Diamond Bar, CA, USA) and merged with a 3D reconstruction derived from DE-CMR or CT images when available. Ipsilateral RF lesions were deployed in the antrum using a catheter dragging strategy. A 3.5-mm open-irrigated catheter with CF sensor (Navistar Thermocool Smart Touch, Biosense Webster) was used in all cases. The ablation settings were the usual in our center (40 W, 45º C). The endpoint was the absence or dissociation of a local electrogram in the entire surrounded region, together with exit block by pacing within the PV ostia. Real-time CF information, but not CF mapping, was visible to the operator during the procedure. The CF maps were analyzed off-line. Image Acquisition Three months after the ablation procedure, a DE-CMR study was performed in sinus rhythm using a 3T scanner (Magnetom Trio®, Siemens Healthcare, Erlangen, Germany) and 32-channel cardiac coil. If AF was present before DE-CMR, electrical cardioversion was performed under deep sedation (propofol 1 mg/kg). After 25-30 minutes of intravenous 0.2 mmol/kg gadobutrol (Gadovist®, BayerSchering, Berlin, Germany), a free-breathing 3D navigator and electrocardiographically gated inversionrecovery gradient-echo sequence were applied in the axial orientation. The acquired voxel size was 1.25x1.25x2.5 mm. Other typical sequence parameters were as follows: 4
repetition time/echo time, 2.3/1.4 ms; flip angle, 11°; bandwidth, 460 Hz/pixel; inversion time, 280 to 380 ms; and parallel imaging with GRAPPA technique, with reference lines of R=2 and R=72. A scout sequence was used to nullify the LV myocardial signal and determine optimal inversion time. Patients were instructed to maintain steady, shallow breathing during image acquisition. Typical scan time for a DE-CMR sequence was 15 minutes (11-18 min), depending on heart rate and breathing patterns. DE-CMR Gap Analysis The DE-CMR images were analyzed using a previously described technique.11 Briefly, full LA volume was reconstructed in the axial orientation and the resulting images were manually segmented and processed with ADAS software.13 Five concentric surface layers were created automatically, from endocardium to epicardium, at 10%, 25%, 50%, 75%, and 90% of LA wall thickness. A 3D shell was obtained for each layer. Pixel signal intensity maps obtained from DE-CMR were projected to each shell and colorcoded. To identify the prior ablation lesions and gaps, a pixel signal intensity-based algorithm was applied to characterize the hyperenhanced area as scar core or border zone, using 40±5% and 60±5% of the maximum intensity as thresholds. To minimize errors in the LA wall segmentation, the 50% surface layer was used to identify gaps in the previous ablation procedure, as in previous studies by our group.11 Both left and right PV ostium were divided into 9 segments (Figure 1). In cases with a common PV ostium, the 9th segments were not analyzed. A CMR gap in a PV segment was defined as any discontinuity of previous ablation lesions (scar core). Border zone was not taken into account for gap definition (Figure 2). Contact Force Analysis Contact force maps were created from the CF information at the ablation points. During the procedure, an ablation point was acquired every 10-15 seconds. If more than one ablation point was obtained in the same place during the procedure, the ablation point with lower CF was deleted in order to obtain legible maps (as the point with higher CF produced a larger lesion, more visible in the 3D DE-CMR reconstruction). Two different operators were involved in the acquisition of ablation points.
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Off-line analysis of CF maps was performed by a second operator, blinded to the DECMR data. Contact force color thresholds (maximum and minimum) were adjusted sequentially (starting from 1 g and increasing in 1-g increments until the maximum force) and a CF scan was performed to identify the minimum CF (CF-min) from the several RF points in each segment (Figure 1). Electrical Reconnection in Pulmonary Veins In the reablation procedures, the electrical reconnection location was identified in each PV according to the segment model described above. This electrical reconnection was then correlated with the presence or absence of gap in the DE-CMR reconstruction. Statistical Analysis Analysis was performed using SPSS 17.0 software (SPSS Inc, Chicago, Illinois). Continuous variables are presented as mean±SD, unless otherwise specified. Comparisons of the CF threshold between the PV segments with and without CMR gap were assessed using Student t test. The optimum CF threshold to determine a complete RF lesion was determined using ROC analysis. Additionally, due to the hierarchical model of the data, a generalized mixed model was fitted for binary response with random intercept and random slope of the regression. The Odds Ratio (OR) computed in our data with this model and the AUC from this hierarchical model were obtained. A random forest analysis was performed to obtain the best cutoff value to stratify the risk of AF recurrence according to the number of segments with a gap in the DE-CMR reconstruction. A P value <0.05 was considered significant.
RESULTS A cohort of 36 patients fulfilled the inclusion criteria; baseline characteristics are shown in Table 1. Acute PV isolation was attempted in all cases and was achieved in 99.3% of cases. Additional LA roofline was performed in 12 (33.3%) cases. The mean procedural time was 154.5±35.7 minutes, mean fluoroscopy time was 23.9±9.4 minutes, and mean RF time was 33.3±11.2 minutes. No complications were observed in this series of patients. DE-CMR was performed at a mean of 114.4±33.4 days after the procedure.
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DE-CMR gap analysis In total, 638 PV segments were included in the analysis. A left common PV ostium was present in five patients (13.9%) and a right common PV ostium in one case (2.8%). In two cases (5.6%), both left and right common PV ostia were present. Only two patients (5.6%) had no gaps on the DE-CMR. A total of 251 PV segments (39.3%) presented one or more gaps in the DE-CMR reconstruction, 103 (41.0%) in left-sided PVs (LPV) and 148 (59.0%) in right-sided PVs (RPV) (p<0.001). Segment 3 and 4 of the LPV had a lower proportion of gaps (3 cases, 8.3%). In contrast, segment 9 of the RPV presented a gap in 26 cases (78.8%). Figure 3 shows the frequency of gaps for all PV segments. See Supplemental Material for further information. Contact Force Analysis The mean CF-min value for all PV segments was 10.0±5.3 g (9.8±5.4 g in LPV vs 10.3±5.3 g in RPV; p=0.225). The PV segments with a gap in the DE-CMR reconstruction had a lower CF-min than the segments without a gap (6.7±4.4 g vs 12.2±4.7 g, respectively; p<0.001). The CF-min distribution varied along the PV segments. The mean lowest CF-min value was observed in the carina of both PVs (5.4±4.6 g left and 6.3±4.3 g right). These regions were also associated with a high presence of gaps in the DE-CMR analysis (62.1% and 78.8%, respectively). Figure 3 shows the mean CF-min values and the percentage of gaps for each PV segment in the DE-CMR analysis. There were no differences in the mean CF-min values acquired by the two different operators. The ROC analysis showed that a CF threshold >8 g provided a sensitivity of 73% (95% confidence interval (CI) [65-78]) and a specificity of 81% (95%CI [77-85]) to predict complete lesions in the DE-CMR images, with a positive predictive value (PPV) of 84% (95%CI [80-88]. On the other hand, a CF threshold > 12 g had a sensitivity of 59% (95%CI [55-64]) and a specificity of 94% (95%CI [90-98]). In this case the PPV increased to 91% (95%CI [87-95]). The ROC curve is shown in Figure 4 (AUC = 0.834). Using a generalized mixed model for binary response, the OR calculated with our data was 0.67 (95%CI [0.59-0.74], p<0.001). The AUC obtained with this hierarchical model was 0.890. See Supplemental Material for further information.
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Electrical Reconnection Five (13.9%) patients underwent a second ablation procedure. Four (22.2%) of 18 mapped PVs remained isolated. A total of 88 PV segments were analyzed. Table 2 shows the matching between the gap observed in each segment of the DE-CMR reconstruction and the location of the electrical gap. Fifty-three (60.2%) segments presented a gap in the DE-CMR reconstruction, whereas an electrical gap was observed in 36 (40.9%) segments. The PPV of the DE-CMR reconstruction to detect an electrical gap was 41.5% and the NPV was 85.7%. The sensitivity and specificity of the DE-CMR to predict an electrical gap were 86.1% and 57.7%, respectively. Follow-Up Analysis The mean follow-up was 13.1±8.9 months. Fourteen (38.9%) patients presented with LA arrhythmia during follow-up, of which 8 (57.1%) had AF recurrence and 6 (42.8%) had atypical flutter. Another patient presented with atrial tachycardia that originated in the posterior wall of the right atrium. All 14 patients with LA arrhythmia recurrence had 5 or more PV segments with a DE-CMR gap (Log-Rank test =0.023). The KaplanMeier graph is shown in Figure 5. Of these 14 patients with LA arrhythmia recurrence, 6 (42.9%) refused a redo procedure and/or underwent antiarrhythmic drugs therapy, 6 (42.9%) had a second ablation procedure (one in another center), and 2 (14.2%) were scheduled for a reablation procedure. DISCUSSION New CF technology contributes to better results of AF ablation.14, 15 Furthermore, some complications, such as cardiac perforation, are strongly related to high CF when mapping or ablating; the use of real-time CF sensing catheters may also improve safety.14 A randomized trial using CF technology found that CF reduces procedure and fluoroscopy time, as well as the number of CMR gaps.8 Furthermore, in the EFFICAS study, a low CF during the index procedure led to a higher rate of PV reconnection detected in a second procedure 3 months after.7 However, the optimal CF to create permanent lesions has not been established. In the present study, we found that PV segments with a CMR gap had a lower CF-min value than those without CMR gaps,
8
which provides new evidence on the relationship between the CF at the moment of ablation and the persistence of a definitive tissue lesion formation (Figure 6). Better outcomes have been reported when “ideal” CF was achieved6, grams).
6, 7
14
(10 to 40
In the TOCCATA study, CF of 20 g was associated with better outcomes,
while CF under 10 g was associated with a higher recurrence rate.7 However, this wide range could result in procedural complications. In the present study, a CF >8 g predicted a complete lesion when using a dragging ablation strategy, with good sensitivity and specificity (73% and 81%, respectively; PPV=84%), while a CF threshold >12 g increased the PPV to 91%. When comparing these results with the results from the TOCCATA study, differences could be explained by the different ablation techniques used. A dragging strategy with a high power output of 40 W was used in the present study, compared with a point-by-point RF delivery strategy with 25-30 W used in previous studies, in the anterior and posterior wall, respectively. Previous studies have demonstrated that DE-CMR can accurately characterize the scar formation after RF ablation,10-12 and accurately define postablation gap size and location, with good concordance with PV electrical reconnection sites.10 Moreover, DECMR has been successfully used to guide a second ablation procedure, achieving PV reisolation of 95.6%.11, 16, 17 In contrast, other studies have stated that gaps in the 3D CMR-derived shells do not correlate with the site of electrical reconnection.18,
19
Besides differences in the image processing methodologies used to determine a DECMR gap, the concept of distribution and orientation of myocardial fibers at the PV-LA junction could also explain part of the conflicting results. Several histological studies have demonstrated that the orientation of myocardial fibers at the PV antrum and inside the PV do not follow a straight trajectory.20-22 Besides, these myocardial fibers have not had a homogeneous distribution along all the PV ostia, and segmental ablation can eliminate the electrograms inside PV.21, 23, 24 Those facts explains why DE-CMR may lead to a false positive (DE-CMR gaps observed in isolated PV) or why DE-CMR gaps are sometimes not located in the same segment as the gap in the circular mapping (usually located inside the PV).11 Gap Analysis At three months postablation, the RPV carina had the highest probability of gap; the lowest probability was observed in the posterior aspect of the LPV antrum. A previous 9
study by Makimoto et al that included 30 patients found the lowest median CF in the anterior wall of the left PV.25 The data were similar for three different operators; no information was provided for carina regions. The areas with low CF-min observed in our study agree with those results (Figure 4). In our study, the inferior and anterior areas of the left PV as well as inferior and postero-inferior areas of the right PV had the lowest CF-min value of the 18 PV segments. In our study, fewer than 5 PV segments with a gap in a 3D reconstruction (DE-CMR model) best predicted freedom from clinical AF recurrences. Consistent with these results, Willems et al. reported that patients with clinical AF recurrences presented with more electrically reconnected PV segments than those without AF recurrence.26 In a previous study, our group observed DE-CMR gaps in almost all participants (94.4%).12 That very high rate of DE-CMR gap sharply contrasts with the 65% prevalence of electrical PV reconnection in the EFFICAS study7 and a 43% reconnection in Willems et al. 26 Some CMR-detected gaps might not correspond to electrical reconnection sites, as we previously demonstrated.12 Indeed, complete isolation, observed in 22.2% of the PV in the present study, resulted in a low PPV of the DE-CMR to identify electrical PV reconnection. Our findings suggest that a complete circumferential lesion around all PVs prompts a low AF recurrence rate after PV ablation. Nonetheless, our study was not designed to address this issue and the small number of patients and the short followup limit the strength of our conclusions. Multicenter studies with a higher number of patients are necessary to evaluate the usefulness of DE-CMR to stratify the risk of AF recurrences. Limitations Several limitations should be acknowledged. The main study limitation is that the variable catheter stability was not directly quantified in the analysis (tools to quantify this variable were not available when the data were acquired). As the catheter operator was not blinded to the CF information during the ablation procedure, the possibility exists of unintentional delivery of longer RF time in areas with higher CF. In addition, the point acquisition was not automatic and acquisition time may differ as a result. Both effects could add a bias to the study results. In an effort to maintain maximum homogeneity in the RF delivery technique, all RF ablation points were acquired in the CARTO system by only two expert operators. New tools available in the navigation
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system that store and integrate data such as power, force, impedance, and RF time at each location could minimize dependence on operator criteria. Another limitation was the hierarchical structure of the data. The provided CF threshold was calculated without taking this issue into account. From a clinical point of view, however, the reported CF threshold is justified by its clear interpretable value. Finally, logistic difficulties in the DE-CMR schedule, catheter supply problems, and competing studies greatly prolonged the enrollment period. CONCLUSIONS Using a CF threshold >12 predicts a complete lesion. DE-CMR detected lesions with high specificity and PPV when a dragging ablation strategy was used in AF ablation. ACKNOWLEDGEMENTS The authors thank Neus Portella for research assistance and Elaine Lilly for editorial assistance.
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Table 1. Baseline patient characteristics
Patient data
N=36
Age (years)
56.3±11.6
Men
28 (77.8%)
Hypertension
22 (61.1%)
Diabetes mellitus
4 (11.1%)
OSAS
2 (5.7%)
Paroxysmal atrial fibrillation
17 (47.2%)
Cardiomyopathy
3 (8.3%)
Procedure data Procedural time (minutes)
154.5±35.7
Fluoroscopy time (minutes)
23.9±9.4
Radiofrequency ablation time (minutes)
33.3±11.2
Prior image study (CT / MRI)
15 (41.7%) / 21 (58.3%)
Echocardiography data LA anteroposterior diameter (mm)
43.3±5.2
LV ejection fraction (%)
60.0±3.8
LV end-diastolic diameter (mm)
50.7±3.8
LV end-systolic diameter (mm)
31.4±6.1
OSAS: obstructive sleep apnea syndrome CT/MRI: computed tomography/magnetic resonance imaging LV: left ventricular LA: left atrial
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Table 2. Observed gap in each segment of the DE-CMR reconstruction matched to the presence of electrical gap
No electrical gap
Electrical gap
No DE-CMR gap
30
5
DE-CMR gap
22
31
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CLINICAL PERSPECTIVE Contact force (CF) catheters provide useful information during atrial fibrillation ablation procedures. Several studies have demonstrated a positive correlation between increasing CF values during RF application and pulmonary vein (PV) isolation success rate. However, very high CF values may lead to severe complications, as myocardial perforation and cardiac tamponade. Up to date the minimum CF value to achieve a complete lesion remained unclear. In this study we have determined the minimum CF that predicts a complete lesion as observed in a cardiac magnetic resonance study. Specifically, we found that a CF higher that 12 g has a predictive positive value of 91%. Using this CF threshold as a CF target during ablation can improve PV isolation success rate, and therefore may minimize the recurrence of AF after ablation. Prospective studies are necessary to demonstrate an improvement in the clinical outcomes of atrial fibrillation ablation when a higher CF of 12 g is applied around the PV.
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FIGURE LEGENDS Figure 1. Panel A. Eighteen-segment division of the pulmonary veins. Panel B. Contact Force (CF) electroanatomic map of the radiofrequency applications. In the left panel, no gap is visible when a minimum CF (CF-min) value is set to 7 g (red color <7 g, purple color >7 g). When using a CF-min value of 9 g (red color <9 g, purple color >9 g), a gap can be observed in segments 2, 3, and 5 of the left pulmonary veins (right panel-white arrows). In these segments the CF-min value was 9 g. Figure 2. Two examples of three-dimensional delayed-enhancement cardiac magnetic resonance (DE-CMR) reconstruction of the left atrium, three months after the ablation procedure. In the left panel, there is a CMR reconstruction without
B In the right panel, ablation gaps (purple-white C arrows) can be observed in the DEgaps. CMR reconstruction from another patient. Figure 3. Panel A: Mean minimum contact force gap value (CF-min) and ablation gaps observed in the 3D delayed-enhancement cardiac magnetic resonance (DECMR gap) reconstruction for each pulmonary vein segment. In the majority of segments, a strong correlation was observed between the number of gaps and the mean CF-min. Panel B: Mean CF-min value in the pulmonary vein segments with DECMR gap. Panel C: Mean CF-min value in the pulmonary vein segments without DE-CMR gap. Figure 4. Receiver operating characteristic (ROC) analysis of the contact force (CF) threshold as a predictor of complete ablation line. A CF >8 g has a sensitivity of 72.9% and a specificity of 80.9%. Using a CF threshold >12 g, the sensitivity decreases to 58.7% but the specificity rises to 94.0%. Area under the curve =0.834 Figure 5. Analysis of arrhythmia-free left atrium of the studied population compared to the number of gaps observed in the 3D cardiac magnetic resonance reconstruction of the left atrium. A statistically significant difference can be observed between the two groups. Figure 6. Side-by-side comparison of a contact force electroanatomic map and a 3D delayed-enhancement cardiac magnetic resonance (DE-CMR) reconstruction. Panel A: Posterior-anterior view. Panel B: Anterior-posterior view. A strong correlation between the ablation lesions observed in the DE-CMR reconstruction can 16
also be observed in the contact force electroanatomic map (white arrows). In some areas, no lesion appears in the CMR reconstruction even though a high contact force is achieved (blue arrow).
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Contact Force Threshold for Permanent Lesion Formation in Atrial Fibrillation Ablation: A Cardiac Magnetic Resonance-based Study to Detect Ablation Gaps David Andreu MSc, PhD, Federico Gomez-Pulido MD, Mireia Calvo MSc, Alicia Carlosena-Remírez BSc, Felipe Bisbal MD, Roger Borràs BSc, Eva Benito MD, Eduard Guasch MD, PhD, Sussanna Prat-Gonzalez MD, PhD, Rosario J. Perea MD, PhD, Josep Brugada MD, PhD, Antonio Berruezo MD, PhD, Lluís Mont MD, PhD
PII: DOI: Reference:
S1547-5271(15)01024-3 http://dx.doi.org/10.1016/j.hrthm.2015.08.010 HRTHM6391
To appear in:
Heart Rhythm
www.elsevier.com/locate/buildenv
Cite this article as: David Andreu MSc, PhD, Federico Gomez-Pulido MD, Mireia Calvo MSc, Alicia Carlosena-Remírez BSc, Felipe Bisbal MD, Roger Borràs BSc, Eva Benito MD, Eduard Guasch MD, PhD, Sussanna Prat-Gonzalez MD, PhD, Rosario J. Perea MD, PhD, Josep Brugada MD, PhD, Antonio Berruezo MD, PhD, Lluís Mont MD, PhD, Contact Force Threshold for Permanent Lesion Formation in Atrial Fibrillation Ablation: A Cardiac Magnetic Resonance-based Study to Detect Ablation Gaps, Heart Rhythm, http://dx.doi.org/10.1016/j.hrthm.2015.08.010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Contact Force Threshold for Permanent Lesion Formation in Atrial Fibrillation Ablation: A Cardiac Magnetic Resonancebased Study to Detect Ablation Gaps David Andreu, MSc, PhD*; Federico Gomez-Pulido, MD*; Mireia Calvo, MSc; Alicia Carlosena-Remírez, BSc; Felipe Bisbal, MD; Roger Borràs, BSc; Eva Benito, MD; Eduard Guasch, MD, PhD; Sussanna Prat-Gonzalez, MD, PhD; Rosario J Perea, MD, PhD; Josep Brugada, MD, PhD; Antonio Berruezo, MD, PhD and Lluís Mont, MD, PhD
Unitat de Fibril·lació Auricular (UFA) Hospital Clinic, Universitat de Barcelona, Catalonia, Spain. Institut d’Investigacions Biomèdiques August Pi i Sunye IDIBAPS) Barcelona, Catalonia, Spain. * Both authors contributed equally to this work.
Short Title: Contact force threshold for permanent lesion formation
Address for correspondence: Lluís Mont, MD, PhD Cardiology Dept, Hospital Clinic C/ Villarroel 170 08036 Barcelona Phone: 0034-93-2275551 Fax: 0034-93-4513045 Email: [email protected]
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ABSTRACT Background Catheter contact force (CF) has a strong correlation with lesion formation during radiofrequency ablation. Delayed-enhancement cardiac magnetic resonance (DE-CMR) provides lesion information in patients with a prior atrial fibrillation (AF) ablation. Objective The aim of this study was to determine the CF threshold to create permanent lesions detected by DE-CMR. Methods A total of 36 patients referred for AF ablation were included. A CF catheter was used during the ablation procedure and DE-CMR was performed at three months postablation. Eighteen pulmonary vein (PV) segments were defined and 3D reconstructions of the left atrium (LA) derived from the DE-CMR images were obtained. One observer evaluated the presence of any discontinuity of previous ablation lesions (gap) in the 3D LA reconstructions and another observer (blinded to the gap findings) determined the minimum CF value in each PV segment. Results The PV segments where a gap was observed had a lower maximal CF than the segments without gap in the 3D LA reconstructions (6.7±4.4 g vs 12.2±4.7 g; p<0.001). In ROC analysis, a CF threshold >8 g provided 73% sensitivity and 81% specificity in the prediction of a complete PV lesion (Positive Predictive Value [PPV] =84%). A CF threshold >12 g had a specificity of 94% and increased the PPV to 91% in creating a complete lesion in the LA wall (area under the curve=0.834). Conclusion A CF threshold >12 g predicts a complete lesion with high specificity and PPV when a dragging ablation strategy is used in AF ablation.
KEYWORDS: Cardiac Magnetic Resonance, Atrial Fibrillation Ablation, Contact Force, Gaps, Delayed-Enhancement, Pulmonary Vein, Ablation Lesion.
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ABBREVIATIONS AF: atrial fibrillation CF: contact force DE-CMR: delayed-enhancement cardiac magnetic resonance PV: pulmonary vein CF-min: minimum contact force INTRODUCTION Circumferential pulmonary vein (PV) isolation is a well-established therapy for atrial fibrillation (AF).1 Nonetheless, a significant number of these patients experience postablation recurrence,2,
3
which has been shown to be closely related with PV re-
connection through gaps in the ablation lines around the PVs.4 New technological developments in ablation catheters may improve acute and long-term results by ensuring transmural and permanent lesion formation. The contact between the catheter tip and the tissue during ablation has a strong correlation with lesion formation. Clinical implementation of real-time contact force (CF) sensing at the catheter tip has been shown to be a useful tool for AF ablation, with improved outcomes.5-8 Delayed-enhancement cardiac magnetic resonance (DE-CMR) can identify myocardial scarring after ablation.9,
10
Recent studies showed that DE-CMR is a reliable tool to
precisely depict gaps in prior ablation and also to guide re-ablation procedures targeting the ablation line gaps.11 The correlation between delayed-enhancement cardiac magnetic resonance (DE-CMR) signal intensity and CF has been described recently.12 However, a CF threshold for lesion formation during circumferential RF ablation has not been yet established. The aim of the study was to define a CF threshold to ensure permanent scar formation and to determine if CF maps can predict the presence of gaps on postprocedural DE-CMR (CMR gaps).
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METHODS Patient Sample Between July 2012 and July 2014, consecutive patients referred for a first ablation of AF in which a CF sensing catheter was used were prospectively included. Inclusion criteria were age ≥18 years with symptomatic and drug-refractory AF. Patients with any treatable cause of AF, contraindication for anticoagulation or left atrial (LA) thrombus, LA anteroposterior diameter >50 mm, severe mitral valve disease, prosthetic mitral valve, left ventricular (LV) ejection fraction (LVEF) <30% and/or contraindication for DE-CMR were excluded. Written informed consent was obtained and the hospital’s Ethics Committee approved the study protocol. Electrophysiological Study Previously described institutional standard protocols of sedation and anticoagulation were applied. A 3D reconstruction of the left atrium was performed with an electroanatomic mapping system (CARTO, Biosense Webster, Diamond Bar, CA, USA) and merged with a 3D reconstruction derived from DE-CMR or CT images when available. Ipsilateral RF lesions were deployed in the antrum using a catheter dragging strategy. A 3.5-mm open-irrigated catheter with CF sensor (Navistar Thermocool Smart Touch, Biosense Webster) was used in all cases. The ablation settings were the usual in our center (40 W, 45º C). The endpoint was the absence or dissociation of a local electrogram in the entire surrounded region, together with exit block by pacing within the PV ostia. Real-time CF information, but not CF mapping, was visible to the operator during the procedure. The CF maps were analyzed off-line. Image Acquisition Three months after the ablation procedure, a DE-CMR study was performed in sinus rhythm using a 3T scanner (Magnetom Trio®, Siemens Healthcare, Erlangen, Germany) and 32-channel cardiac coil. If AF was present before DE-CMR, electrical cardioversion was performed under deep sedation (propofol 1 mg/kg). After 25-30 minutes of intravenous 0.2 mmol/kg gadobutrol (Gadovist®, BayerSchering, Berlin, Germany), a free-breathing 3D navigator and electrocardiographically gated inversionrecovery gradient-echo sequence were applied in the axial orientation. The acquired voxel size was 1.25x1.25x2.5 mm. Other typical sequence parameters were as follows: 4
repetition time/echo time, 2.3/1.4 ms; flip angle, 11°; bandwidth, 460 Hz/pixel; inversion time, 280 to 380 ms; and parallel imaging with GRAPPA technique, with reference lines of R=2 and R=72. A scout sequence was used to nullify the LV myocardial signal and determine optimal inversion time. Patients were instructed to maintain steady, shallow breathing during image acquisition. Typical scan time for a DE-CMR sequence was 15 minutes (11-18 min), depending on heart rate and breathing patterns. DE-CMR Gap Analysis The DE-CMR images were analyzed using a previously described technique.11 Briefly, full LA volume was reconstructed in the axial orientation and the resulting images were manually segmented and processed with ADAS software.13 Five concentric surface layers were created automatically, from endocardium to epicardium, at 10%, 25%, 50%, 75%, and 90% of LA wall thickness. A 3D shell was obtained for each layer. Pixel signal intensity maps obtained from DE-CMR were projected to each shell and colorcoded. To identify the prior ablation lesions and gaps, a pixel signal intensity-based algorithm was applied to characterize the hyperenhanced area as scar core or border zone, using 40±5% and 60±5% of the maximum intensity as thresholds. To minimize errors in the LA wall segmentation, the 50% surface layer was used to identify gaps in the previous ablation procedure, as in previous studies by our group.11 Both left and right PV ostium were divided into 9 segments (Figure 1). In cases with a common PV ostium, the 9th segments were not analyzed. A CMR gap in a PV segment was defined as any discontinuity of previous ablation lesions (scar core). Border zone was not taken into account for gap definition (Figure 2). Contact Force Analysis Contact force maps were created from the CF information at the ablation points. During the procedure, an ablation point was acquired every 10-15 seconds. If more than one ablation point was obtained in the same place during the procedure, the ablation point with lower CF was deleted in order to obtain legible maps (as the point with higher CF produced a larger lesion, more visible in the 3D DE-CMR reconstruction). Two different operators were involved in the acquisition of ablation points.
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Off-line analysis of CF maps was performed by a second operator, blinded to the DECMR data. Contact force color thresholds (maximum and minimum) were adjusted sequentially (starting from 1 g and increasing in 1-g increments until the maximum force) and a CF scan was performed to identify the minimum CF (CF-min) from the several RF points in each segment (Figure 1). Electrical Reconnection in Pulmonary Veins In the reablation procedures, the electrical reconnection location was identified in each PV according to the segment model described above. This electrical reconnection was then correlated with the presence or absence of gap in the DE-CMR reconstruction. Statistical Analysis Analysis was performed using SPSS 17.0 software (SPSS Inc, Chicago, Illinois). Continuous variables are presented as mean±SD, unless otherwise specified. Comparisons of the CF threshold between the PV segments with and without CMR gap were assessed using Student t test. The optimum CF threshold to determine a complete RF lesion was determined using ROC analysis. Additionally, due to the hierarchical model of the data, a generalized mixed model was fitted for binary response with random intercept and random slope of the regression. The Odds Ratio (OR) computed in our data with this model and the AUC from this hierarchical model were obtained. A random forest analysis was performed to obtain the best cutoff value to stratify the risk of AF recurrence according to the number of segments with a gap in the DE-CMR reconstruction. A P value <0.05 was considered significant.
RESULTS A cohort of 36 patients fulfilled the inclusion criteria; baseline characteristics are shown in Table 1. Acute PV isolation was attempted in all cases and was achieved in 99.3% of cases. Additional LA roofline was performed in 12 (33.3%) cases. The mean procedural time was 154.5±35.7 minutes, mean fluoroscopy time was 23.9±9.4 minutes, and mean RF time was 33.3±11.2 minutes. No complications were observed in this series of patients. DE-CMR was performed at a mean of 114.4±33.4 days after the procedure.
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DE-CMR gap analysis In total, 638 PV segments were included in the analysis. A left common PV ostium was present in five patients (13.9%) and a right common PV ostium in one case (2.8%). In two cases (5.6%), both left and right common PV ostia were present. Only two patients (5.6%) had no gaps on the DE-CMR. A total of 251 PV segments (39.3%) presented one or more gaps in the DE-CMR reconstruction, 103 (41.0%) in left-sided PVs (LPV) and 148 (59.0%) in right-sided PVs (RPV) (p<0.001). Segment 3 and 4 of the LPV had a lower proportion of gaps (3 cases, 8.3%). In contrast, segment 9 of the RPV presented a gap in 26 cases (78.8%). Figure 3 shows the frequency of gaps for all PV segments. See Supplemental Material for further information. Contact Force Analysis The mean CF-min value for all PV segments was 10.0±5.3 g (9.8±5.4 g in LPV vs 10.3±5.3 g in RPV; p=0.225). The PV segments with a gap in the DE-CMR reconstruction had a lower CF-min than the segments without a gap (6.7±4.4 g vs 12.2±4.7 g, respectively; p<0.001). The CF-min distribution varied along the PV segments. The mean lowest CF-min value was observed in the carina of both PVs (5.4±4.6 g left and 6.3±4.3 g right). These regions were also associated with a high presence of gaps in the DE-CMR analysis (62.1% and 78.8%, respectively). Figure 3 shows the mean CF-min values and the percentage of gaps for each PV segment in the DE-CMR analysis. There were no differences in the mean CF-min values acquired by the two different operators. The ROC analysis showed that a CF threshold >8 g provided a sensitivity of 73% (95% confidence interval (CI) [65-78]) and a specificity of 81% (95%CI [77-85]) to predict complete lesions in the DE-CMR images, with a positive predictive value (PPV) of 84% (95%CI [80-88]. On the other hand, a CF threshold > 12 g had a sensitivity of 59% (95%CI [55-64]) and a specificity of 94% (95%CI [90-98]). In this case the PPV increased to 91% (95%CI [87-95]). The ROC curve is shown in Figure 4 (AUC = 0.834). Using a generalized mixed model for binary response, the OR calculated with our data was 0.67 (95%CI [0.59-0.74], p<0.001). The AUC obtained with this hierarchical model was 0.890. See Supplemental Material for further information.
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Electrical Reconnection Five (13.9%) patients underwent a second ablation procedure. Four (22.2%) of 18 mapped PVs remained isolated. A total of 88 PV segments were analyzed. Table 2 shows the matching between the gap observed in each segment of the DE-CMR reconstruction and the location of the electrical gap. Fifty-three (60.2%) segments presented a gap in the DE-CMR reconstruction, whereas an electrical gap was observed in 36 (40.9%) segments. The PPV of the DE-CMR reconstruction to detect an electrical gap was 41.5% and the NPV was 85.7%. The sensitivity and specificity of the DE-CMR to predict an electrical gap were 86.1% and 57.7%, respectively. Follow-Up Analysis The mean follow-up was 13.1±8.9 months. Fourteen (38.9%) patients presented with LA arrhythmia during follow-up, of which 8 (57.1%) had AF recurrence and 6 (42.8%) had atypical flutter. Another patient presented with atrial tachycardia that originated in the posterior wall of the right atrium. All 14 patients with LA arrhythmia recurrence had 5 or more PV segments with a DE-CMR gap (Log-Rank test =0.023). The KaplanMeier graph is shown in Figure 5. Of these 14 patients with LA arrhythmia recurrence, 6 (42.9%) refused a redo procedure and/or underwent antiarrhythmic drugs therapy, 6 (42.9%) had a second ablation procedure (one in another center), and 2 (14.2%) were scheduled for a reablation procedure. DISCUSSION New CF technology contributes to better results of AF ablation.14, 15 Furthermore, some complications, such as cardiac perforation, are strongly related to high CF when mapping or ablating; the use of real-time CF sensing catheters may also improve safety.14 A randomized trial using CF technology found that CF reduces procedure and fluoroscopy time, as well as the number of CMR gaps.8 Furthermore, in the EFFICAS study, a low CF during the index procedure led to a higher rate of PV reconnection detected in a second procedure 3 months after.7 However, the optimal CF to create permanent lesions has not been established. In the present study, we found that PV segments with a CMR gap had a lower CF-min value than those without CMR gaps,
8
which provides new evidence on the relationship between the CF at the moment of ablation and the persistence of a definitive tissue lesion formation (Figure 6). Better outcomes have been reported when “ideal” CF was achieved6, grams).
6, 7
14
(10 to 40
In the TOCCATA study, CF of 20 g was associated with better outcomes,
while CF under 10 g was associated with a higher recurrence rate.7 However, this wide range could result in procedural complications. In the present study, a CF >8 g predicted a complete lesion when using a dragging ablation strategy, with good sensitivity and specificity (73% and 81%, respectively; PPV=84%), while a CF threshold >12 g increased the PPV to 91%. When comparing these results with the results from the TOCCATA study, differences could be explained by the different ablation techniques used. A dragging strategy with a high power output of 40 W was used in the present study, compared with a point-by-point RF delivery strategy with 25-30 W used in previous studies, in the anterior and posterior wall, respectively. Previous studies have demonstrated that DE-CMR can accurately characterize the scar formation after RF ablation,10-12 and accurately define postablation gap size and location, with good concordance with PV electrical reconnection sites.10 Moreover, DECMR has been successfully used to guide a second ablation procedure, achieving PV reisolation of 95.6%.11, 16, 17 In contrast, other studies have stated that gaps in the 3D CMR-derived shells do not correlate with the site of electrical reconnection.18,
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Besides differences in the image processing methodologies used to determine a DECMR gap, the concept of distribution and orientation of myocardial fibers at the PV-LA junction could also explain part of the conflicting results. Several histological studies have demonstrated that the orientation of myocardial fibers at the PV antrum and inside the PV do not follow a straight trajectory.20-22 Besides, these myocardial fibers have not had a homogeneous distribution along all the PV ostia, and segmental ablation can eliminate the electrograms inside PV.21, 23, 24 Those facts explains why DE-CMR may lead to a false positive (DE-CMR gaps observed in isolated PV) or why DE-CMR gaps are sometimes not located in the same segment as the gap in the circular mapping (usually located inside the PV).11 Gap Analysis At three months postablation, the RPV carina had the highest probability of gap; the lowest probability was observed in the posterior aspect of the LPV antrum. A previous 9
study by Makimoto et al that included 30 patients found the lowest median CF in the anterior wall of the left PV.25 The data were similar for three different operators; no information was provided for carina regions. The areas with low CF-min observed in our study agree with those results (Figure 4). In our study, the inferior and anterior areas of the left PV as well as inferior and postero-inferior areas of the right PV had the lowest CF-min value of the 18 PV segments. In our study, fewer than 5 PV segments with a gap in a 3D reconstruction (DE-CMR model) best predicted freedom from clinical AF recurrences. Consistent with these results, Willems et al. reported that patients with clinical AF recurrences presented with more electrically reconnected PV segments than those without AF recurrence.26 In a previous study, our group observed DE-CMR gaps in almost all participants (94.4%).12 That very high rate of DE-CMR gap sharply contrasts with the 65% prevalence of electrical PV reconnection in the EFFICAS study7 and a 43% reconnection in Willems et al. 26 Some CMR-detected gaps might not correspond to electrical reconnection sites, as we previously demonstrated.12 Indeed, complete isolation, observed in 22.2% of the PV in the present study, resulted in a low PPV of the DE-CMR to identify electrical PV reconnection. Our findings suggest that a complete circumferential lesion around all PVs prompts a low AF recurrence rate after PV ablation. Nonetheless, our study was not designed to address this issue and the small number of patients and the short followup limit the strength of our conclusions. Multicenter studies with a higher number of patients are necessary to evaluate the usefulness of DE-CMR to stratify the risk of AF recurrences. Limitations Several limitations should be acknowledged. The main study limitation is that the variable catheter stability was not directly quantified in the analysis (tools to quantify this variable were not available when the data were acquired). As the catheter operator was not blinded to the CF information during the ablation procedure, the possibility exists of unintentional delivery of longer RF time in areas with higher CF. In addition, the point acquisition was not automatic and acquisition time may differ as a result. Both effects could add a bias to the study results. In an effort to maintain maximum homogeneity in the RF delivery technique, all RF ablation points were acquired in the CARTO system by only two expert operators. New tools available in the navigation
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system that store and integrate data such as power, force, impedance, and RF time at each location could minimize dependence on operator criteria. Another limitation was the hierarchical structure of the data. The provided CF threshold was calculated without taking this issue into account. From a clinical point of view, however, the reported CF threshold is justified by its clear interpretable value. Finally, logistic difficulties in the DE-CMR schedule, catheter supply problems, and competing studies greatly prolonged the enrollment period. CONCLUSIONS Using a CF threshold >12 predicts a complete lesion. DE-CMR detected lesions with high specificity and PPV when a dragging ablation strategy was used in AF ablation. ACKNOWLEDGEMENTS The authors thank Neus Portella for research assistance and Elaine Lilly for editorial assistance.
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Table 1. Baseline patient characteristics
Patient data
N=36
Age (years)
56.3±11.6
Men
28 (77.8%)
Hypertension
22 (61.1%)
Diabetes mellitus
4 (11.1%)
OSAS
2 (5.7%)
Paroxysmal atrial fibrillation
17 (47.2%)
Cardiomyopathy
3 (8.3%)
Procedure data Procedural time (minutes)
154.5±35.7
Fluoroscopy time (minutes)
23.9±9.4
Radiofrequency ablation time (minutes)
33.3±11.2
Prior image study (CT / MRI)
15 (41.7%) / 21 (58.3%)
Echocardiography data LA anteroposterior diameter (mm)
43.3±5.2
LV ejection fraction (%)
60.0±3.8
LV end-diastolic diameter (mm)
50.7±3.8
LV end-systolic diameter (mm)
31.4±6.1
OSAS: obstructive sleep apnea syndrome CT/MRI: computed tomography/magnetic resonance imaging LV: left ventricular LA: left atrial
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Table 2. Observed gap in each segment of the DE-CMR reconstruction matched to the presence of electrical gap
No electrical gap
Electrical gap
No DE-CMR gap
30
5
DE-CMR gap
22
31
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Sanchez JE, Plumb VJ, Epstein AE, Kay GN. Evidence for longitudinal and transverse fiber conduction in human pulmonary veins: relevance for catheter ablation. Circulation Aug 5 2003;108:590-597. Haissaguerre M, Shah DC, Jais P, Hocini M, Yamane T, Deisenhofer I, Chauvin M, Garrigue S, Clementy J. Electrophysiological breakthroughs from the left atrium to the pulmonary veins. Circulation Nov 14 2000;102:2463-2465. Ranjan R, Kato R, Zviman MM, Dickfeld TM, Roguin A, Berger RD, Tomaselli GF, Halperin HR. Gaps in the ablation line as a potential cause of recovery from electrical isolation and their visualization using MRI. Circ Arrhythm Electrophysiol Jun 2011;4:279-286. Makimoto H, Lin T, Rillig A, et al. In vivo contact force analysis and correlation with tissue impedance during left atrial mapping and catheter ablation of atrial fibrillation. Circ Arrhythm Electrophysiol Feb 2014;7:46-54. Willems S, Steven D, Servatius H, Hoffmann BA, Drewitz I, Mullerleile K, Aydin MA, Wegscheider K, Salukhe TV, Meinertz T, Rostock T. Persistence of pulmonary vein isolation after robotic remote-navigated ablation for atrial fibrillation and its relation to clinical outcome. J Cardiovasc Electrophysiol Oct 2010;21:1079-1084.
CLINICAL PERSPECTIVE Contact force (CF) catheters provide useful information during atrial fibrillation ablation procedures. Several studies have demonstrated a positive correlation between increasing CF values during RF application and pulmonary vein (PV) isolation success rate. However, very high CF values may lead to severe complications, as myocardial perforation and cardiac tamponade. Up to date the minimum CF value to achieve a complete lesion remained unclear. In this study we have determined the minimum CF that predicts a complete lesion as observed in a cardiac magnetic resonance study. Specifically, we found that a CF higher that 12 g has a predictive positive value of 91%. Using this CF threshold as a CF target during ablation can improve PV isolation success rate, and therefore may minimize the recurrence of AF after ablation. Prospective studies are necessary to demonstrate an improvement in the clinical outcomes of atrial fibrillation ablation when a higher CF of 12 g is applied around the PV.
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FIGURE LEGENDS Figure 1. Panel A. Eighteen-segment division of the pulmonary veins. Panel B. Contact Force (CF) electroanatomic map of the radiofrequency applications. In the left panel, no gap is visible when a minimum CF (CF-min) value is set to 7 g (red color <7 g, purple color >7 g). When using a CF-min value of 9 g (red color <9 g, purple color >9 g), a gap can be observed in segments 2, 3, and 5 of the left pulmonary veins (right panel-white arrows). In these segments the CF-min value was 9 g. Figure 2. Two examples of three-dimensional delayed-enhancement cardiac magnetic resonance (DE-CMR) reconstruction of the left atrium, three months after the ablation procedure. In the left panel, there is a CMR reconstruction without
B In the right panel, ablation gaps (purple-white C arrows) can be observed in the DEgaps. CMR reconstruction from another patient. Figure 3. Panel A: Mean minimum contact force gap value (CF-min) and ablation gaps observed in the 3D delayed-enhancement cardiac magnetic resonance (DECMR gap) reconstruction for each pulmonary vein segment. In the majority of segments, a strong correlation was observed between the number of gaps and the mean CF-min. Panel B: Mean CF-min value in the pulmonary vein segments with DECMR gap. Panel C: Mean CF-min value in the pulmonary vein segments without DE-CMR gap. Figure 4. Receiver operating characteristic (ROC) analysis of the contact force (CF) threshold as a predictor of complete ablation line. A CF >8 g has a sensitivity of 72.9% and a specificity of 80.9%. Using a CF threshold >12 g, the sensitivity decreases to 58.7% but the specificity rises to 94.0%. Area under the curve =0.834 Figure 5. Analysis of arrhythmia-free left atrium of the studied population compared to the number of gaps observed in the 3D cardiac magnetic resonance reconstruction of the left atrium. A statistically significant difference can be observed between the two groups. Figure 6. Side-by-side comparison of a contact force electroanatomic map and a 3D delayed-enhancement cardiac magnetic resonance (DE-CMR) reconstruction. Panel A: Posterior-anterior view. Panel B: Anterior-posterior view. A strong correlation between the ablation lesions observed in the DE-CMR reconstruction can 16
also be observed in the contact force electroanatomic map (white arrows). In some areas, no lesion appears in the CMR reconstruction even though a high contact force is achieved (blue arrow).
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