Contact force and force-time integral in atrial radiofrequency ablation predict transmurality of lesions

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1 Europace (214) 16, doi:1.193/europace/euu68 CLINICAL RESEARCH Ablation for atrial fibrillation Contact force and force-time integral in atrial radiofrequency ablation predict transmurality of lesions Fabien Squara 1,2, Decebal Gabriel Latcu 1 *, Youssef Massaad 1, Marouane Mahjoub 1, Sok-Sithikun Bun 1, and Nadir Saoudi 1 1 Cardiologie, Centre Hospitalier Princesse Grace, Avenue Pasteur, 98, Monaco; and 2 Cardiology Department, Pasteur University Hospital, 6 Nice, France Received 6 November 213; accepted after revision 1 March 214 Aims During radiofrequency (RF) delivery, lesion volume is highly dependent on contact force (CF). It has recently been shown that changes of bipolar electrogram (EGM) predict transmurality. We hypothesized that there is a correlation between CF and EGM criteria of transmural lesion (TL) during RF.... Methods We prospectively studied consecutive 512 RF applications from atrial fibrillation ablation procedures. A force-sensing and results ablation catheter (Tacticath w, Endosense) was used to continuously measure CF and force-time integral (FTI) during each RF application. Distal bipolar EGM was analysed before, during, and after each RF application. Depending on initial EGM morphology, transmurality of lesions was defined by: (i) disappearance of the positivity after RF when there was QR morphology, (ii) diminution.75% of the positivity when there was QRS morphology, or (iii) disappearance of the R positivity when there was RSR morphology. Electrogram criteria were validated by electrophysiologists blinded to force measurements. Force-time integral was higher in TL than in non-transmural lesions (NTLs): vs gs (P,.1). Mean CF per RF pulse was higher in TL than in NTL: vs g (P,.1). The best cut-off to predict TL was an FTI 392 gs [sensitivity.89, specificity (Sp).93, positive predictive value (PPV).98, and negative predictive value.67] and a higher FTI (.7 gs) warrants transmurality of RF atrial lesions (1% Sp and PPV).... Conclusion Contact force and FTI during RF are correlated with TL. During RF delivery, a target FTI. 392 gs can be used as an endpoint Keywords Ablation Atrial fibrillation Contact force Force-time integral Introduction State-of-the-art radiofrequency (RF) catheter ablation for atrial fibrillation (AF) implies complete and perennial electrical disconnection of the pulmonary veins (PVs). 1 The success of the ablation depends upon transmural lesion (TL) creation. 2,3 Experimental data show that the quality of the electrode tissue contact (the contact force; CF) is a major determinant of the depth/size of RF lesions. 4 6 Amplitude reduction of bipolar and unipolar electrograms (EGMs) during RF delivery help in assessing lesion transmurality. 7 9 A recent study 1 described in detail EGM morphological changes as being highly predictive of TL. Nevertheless, artefacts during RF delivery may render EGM morphological changes difficult to assess. We hypothesized that there is a correlation between electrode tissue contact parameters (CF and force-time integral; FTI) and bipolar EGM criteria of TL during RF. If correlated with transmurality, establishing cut-off values of CF and FTI may help in efficient lesion creation (i.e. transmural) without excessive energy delivery. Methods Consecutive patients ablated for AF using a force-sensing irrigated catheter (Tacticath w, Endosense) were included. All the procedures were performed at the Princess Grace Hospital in Monaco and all patients gave written informed consent. Ablation strategy consisted in circumferential PV ablation with an endpoint of lasso-proven PV isolation (PVI) for The first two authors contributed equally to this paper. * Corresponding author. Tel: ; fax: address: dglatcu@yahoo.com Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 214. For permissions please journals.permissions@oup.com.

2 Correlation between CF and EGM criteria of TL during RF 661 What s new? This is the first study to correlate the likelihood of lesion s transmurality as assessed by specific local electrogram modifications during radiofrequency ablation to parameters that are now known as being of prime importance during pulse delivery (contact force and its product with time: the force-time integral). The results have the potential to strongly impact our practice as using contact force and force-time integral allows some prediction of results. Besides the fact that these results reinforce the importance of contact force assessment, they can further support electrical modification as a good and simple assessment of lesion transmurality. paroxysmal AF patients. Additional lesions targeting fractionated EGMs as wellas the roof and the left isthmuslines were performed for persistent AF patients. Ablation procedures were performed in a fasting state, under local anaesthesia and mild intravenous sedation (midazolam 1 4 mg). During RF delivery, pain control was obtained by 1 2 mg intravenous nalbuphine. Heparin was administered to maintain activated clotting times of 3 35 s. Catheters were inserted via the right femoral vein. The Tacticath, a 7-French 3.5 mm open-irrigated tip catheter, has embedded three optical fibres which allow measurement of both the magnitude and direction of the CF; this information as well as the FTI for each RF application are displayed on a dedicated screen (Tactisys, Endosense). The Tacticath was inserted transseptally in the left atrium (LA) via a nonsteerable sheath (Fast-Cath SL1, St Jude Medical; SJM). A circular catheter (Lasso 255, Biosense-Webster Inc.; BW) was also inserted in the LA. A decapolar diagnostic catheter (Inquiry, Irvine Biomedical Inc.) was inserted in the coronary sinus. Electroanatomic mapping (EnSite NavX, SJM) with image integration was used for each procedure. Radiofrequency was delivered with a Stockert 7 generator (BW) with a 428C target temperature. Power setting was adjusted between 3 and 35 W for ostial PV ablation (ranging from 1 to 5 W for other locations). The catheter was continuously irrigated at 17 ml/min with.9% NaCl. Duration of each RF application was left to the operator s appreciation. Importantly, carewastaken to perform each ablation in a point-by-point manner for 2 3 s. For each of the RF pulses, the cardiac rhythm, the ablation site location, the delivered power, the pulse duration, the delivered endocardial energy, the mean CF, the total FTI, as well as the impedance at the beginning and at the end of RF delivery was recorded. Electrograms were acquired on a digital electrophysiological recording system (Prucka Engineering, Inc.), with a sampling rate of 1 khz. Bipolar signals were recorded with a 3 5 Hz filtering and a 5 Hz notch pass. Morphological analysis and measurements of the bipolar EGM on the distal poles of the ablation catheter were performed simultaneously after the procedure by two electrophysiologists blinded to force measurements. Amplification and display speed were optimized. Poor quality EGMs, mainly due to artefacts, were excluded from the final analysis. The first two major positive deflections were defined as R and R, and the first and second major negative deflections were defined as Q and S, respectively. All EGM were analysed before and after RF. Their predominant morphology was classified into one of the following patterns: QS, QR, QRS, RS, or RSR. Were inputted: EGM criteria of transmurality (satisfied/not satisfied), peak-to-peak amplitude, positivity amplitude and negativity amplitude, and R amplitude when RSR morphology. Depending on initial distal bipolar EGM morphology, transmurality was defined by the occurrence during RF, and the persistence after RF, of one of the following EGM criteria 1 : (i) complete disappearance of the positivity when there was initial QR morphology, (ii) diminution.75% of the positivity when there was initial QRS morphology, or (iii) complete disappearance of the R positivity when there was initial RSR morphology (Figure 1). For moderately fragmented potentials without obvious predominant morphology, complete disappearance of the positivity was considered as a transmurality criterion. We also considered the splitting of the EGM potential during RF as a criterion for TL. 11 Statistical analysis Statistical analysis was done with Stata 9.1 (Statacorp 25). All continuous variables are expressed as mean + SD. Median values are given in box plot diagrams. Two-tailed Wilcoxon t-test was used to compare numerical variables. Continuous variables were compared by analysis of variance and the Bonferroni correction for multiple-comparison test. Non-normal continuous variables were compared using the nonparametric Mann Whitney Wilcoxon test. Nominal variables were compared by use of the x 2 test. P,.5 was considered significant. The predictive values of different thresholds of CF and FTI for TL were assessed using sensitivity (Se), specificity (Sp), and the receiving operator characteristics (ROC) curves analysis. Results Seven patients (six males), aged years (median 62.5 years) underwent catheter ablation procedures for paroxysmal AF (five) and long-standing persistent AF (two). A total of 512 point-by-point atrial RF applications were performed (see Figure 2). Forty-eight sites (9%) with QS or RS morphology on the distal bipolar EGM before RF application (favouring pre-existing scar) were excluded from further analysis. We also excluded 42 RF applications with split potentials before RF, or very fragmented/low amplitude potentials in which EGM analysis could not be reliably performed. In addition, nine epicardial RF applications located in the coronary sinus were excluded. In total, 99 of the initial 512 RF pulses were excluded from subsequent analysis. Among the 413 RF applications (81%) suitable for EGM analysis, 388 were located in smooth atrial portions (LA except the appendage), 25 in pectinated portions (LA appendage). The rhythm was sinus rhythm in 285 (69%) of them, and AF in 128 (31%). Initial EGM morphology at the beginning of each RF application was classified as follows: QR in 55 (13.3%), QRS in 219 (53%), RSR in 97 (23.5%), and fragmented potentials in 42 (1.1%) cases, respectively. Radiofrequency pulse characteristics in transmural vs. non-transmural lesions Bipolar EGM criteria for TL were fulfilled for 332 RF applications (8%). Force-time integral was significantly higher for pulses resulting in TL than pulses resulting in non-transmural lesion (NTL) ( vs gs, P,.1, Figure 3A). Mean CF per RF pulse was also much higher in TL sites ( vs g,

3 662 F. Squara et al. A Initial Transmural Nontransmural 1) Disappearance of R when initial QR morphology QR RF QS QR 2) Decrease >75% of R when initial QRS morphology QRS RF QRS QS QRS 3) Disappearance of R when initial RSR morphology B Initial QRS morphology Initial RSR morphology RSR.53 mv P,.1, Figure 3B). In addition, mean duration of RF applications was slightly higher for pulses resulting in TL ( vs s, P,.1, Figure 3C). A higher energy per pulse was delivered when TL criteria were fulfilled ( vs J, P,.1, Figure 3D). In the TL group, mean delivered energy per lesion decreased with a higher CF (Figure 4). Below 1 g, mean delivered energy in TL was vs J with a CF of 1 15 g (P ¼.3); J with a CF of 15 2 g (P ¼.2 vs g); J with a CF of 2 25 g (P ¼.2 vs g); and J with a CF of 25 3 g (P ¼.3 vs g). However, differences in delivered power between TL and NTL sites did not reach significance ( W for TL pulses vs W for NTL pulses, P ¼.6). Impedance before RF was slightly higher in TL sites ( vs V, P ¼.1), but end-pulse impedance was not significantly different ( V for TL pulses vs V for NTL pulses, P ¼.46). The impedance drop was not discriminant for transmurality ( V for TL vs V for NTL, P ¼.14). RF RS After RF (transmural) After RF (transmural) RSR.11 mv Figure 1 (A) Distal bipolar EGM criteria of TL after RF, depending on initial morphology. (B) Examples of recorded EGMs before and after RF, with different initial morphologies, displayed at 2 mm/s. prediction Receiving operator characteristics curves were made for FTI, mean CF, RF pulse duration, and delivered energy (Figure 5), for determining the best thresholds to predict TL. Force-time integral had the best prediction value with an area under curve (AUC) of.95 (P,.1 vs. the other AUC). Mean CF, RF pulse duration, delivered energy, and power had an AUC of.87,.64,.62, and.43, respectively. The best threshold to predict transmurality (defined by the minimal distance from the left corner of the ROC space) on ROC curve of the FTI was 392 gs, with a Se of.89 and a Sp of.93. The positive predictive value (PPV) for TL of an FTI ¼ 392 gs was.98, and the negative predictive value (NPV) for TL was.67. A higher FTI threshold (7 gs) had 1% Sp and PPV for TL, but a decreased Se (.39) and NPV (.3; Figure 6). Smooth portions vs. pectinated portions Subgroup analysis of RF applications in smooth portions and in pectinated portions showed similar results. No significant differences

4 Correlation between CF and EGM criteria of TL during RF RF applications Were excluded from further analysis : 48 RF applications (9%) with QS or RS morphology on the distal bipolar EGM before RF application 413 RF applications (81%) for final EGM analysis QR 55 (13.3%) QRS 219 (53%) Figure 2 Flow-chart of EGM analysis of all RF pulses. existed between FTI and CF of TL and NTL, respectively, depending on the atrial wall type. In smooth portions (LA except the appendage), FTI and CF were greater in TL compared with NTL: vs gs for FTI (P,.1) and vs g for CF (P,.1), respectively. In pectinated portions (LA appendage), results were similar: vs gs for FTI (P,.1) and vs g for CF (P ¼.2), in TL vs. NTL, respectively. Bipolar electrogram amplitude changes after radiofrequency Regardless of EGM morphology, FTI was poorly (but significantly) correlated with EGM peak-to-peak amplitude reduction after RF (r ¼.16, P ¼.1), and with EGM positivity reduction (r ¼.36, P,.1), but not with EGM negativity reduction (P ¼.95). Mean CF was correlated only with EGM positivity reduction after RF (r ¼.18, P,.1). Considering only the 274 initial QR/ QRS morphologies, EGM positivity reduction had an improved correlation with FTI (r ¼.44, P,.1) and mean CF (r ¼.33, P,.1). For the 97 initial RSR morphologies, R wave reduction after RF had a significant correlation with FTI (r ¼.43, P,.1) and mean CF (r ¼.22, P ¼.4). For all morphologies, RF application duration and delivered endocardial energy were both correlated with EGM peak-to-peak amplitude reduction (r ¼.26, P,.1 and r ¼.25, P,.1, respectively), EGM positivity reduction (r ¼.17, P,.1 and r ¼.13, P,.1, respectively), and EGM negativity reduction (r ¼.13, P ¼.1 and r ¼.14, P,.1, respectively). Radiofrequency power was neither correlated with EGM global amplitude, RSR 97 (23.5%) 42 RF applications with: split potentials before RF very fragmented potentials low amplitude potentials in which EGM analysis could not be reliably performed 9 epicardial RF applications located in the coronary sinus positivity, or negativity reduction (P ¼.3, P ¼.9, and P ¼.14, respectively). Discussion Fragmented potentials 42 (1.1%) Our study shows the predictive value of catheter contact to obtain TL. At similar power delivered with an open-irrigated force-sensing catheter, CF and FTI are the best predictors of transmurality of atrial lesions, as defined by the changes of the bipolar EGM. Mean CF was much higher for RF pulses when transmurality criteria were satisfied (26 vs. 11 g); nevertheless, the intermittent character of the contact (as defined by an oscillating CF with the cardiac cycle), almost always present in a beating heart, is integrated in a more powerful index, the FTI. Experimental data show that an intermittent catheter contact creates equivalent ablation lesions when energy delivery duration is increased. 12 In our study, the FTI best predicted transmurality, with a cut-off of 392 gs. A higher cut-off (7 gs) had a 1% Sp for obtaining TL but had a low Se (39%), raising the risk of unnecessary longer RF applications. The clinical implication of this finding is, in our opinion, obvious: while using a force-sensing catheter, very good tissue contact (i.e..2 g) must be aimed, but does not warrant TL. Since during RF delivery artefacts make EGM changes difficult to assess, a target FTI.4 gs may help operators to guide the RF duration. The rationale for better RF lesions using higher CF is a larger electrode tissue contact area, allowing improved RF energy delivery to the myocardium. This point was also suggested in our study by a lower mean delivered energy in TL when using higher CF, reflecting the fact that lower energy is needed to create equivalent lesions when higher CF is applied. Interestingly, we found that above a CF of

5 664 F. Squara et al. A B Force-time integral (gs) Duration (s) C Average = 212 gs Median = 19 gs Average = 21.9 s Median = 21.5 s P <.1 P <.1 P <.1 Average = 652 gs Median = 623 gs Average = 28.6 s Median = 25 s Delivered energy (J) D Average = 11.3 g Median = 8.8 g Average = 739 J Median = 71 J P <.1 Average = 26.3 g Median = 24.8 g Average = 95 J Median = 81 J Figure 3 Box plot diagrams with median values for force-time integral(a), mean contact force (B), RF pulse duration (C), and delivered endocardial energy (D), for transmural and non-transmural lesions. Outside values are excluded. Mean delivered energy (J) Mean delivered energy in transmural lesions depending on CF 2 < Figure 4 Mean delivered energy per RF pulse in the TL group, depending on the contact force (CF). Dashed lines represent the 95% confidence interval. Mean delivered energy quickly decreases as the CF increases from,1 to 2 25 g. Between 2 25 and 35 4 g, mean delivered energy decreases slowly, whereas it remains stable above 4 g.

6 Correlation between CF and EGM criteria of TL during RF Best point on the ROC curve for FTI = 392 (Se.89, Sp.93).75 Sensitivity Specificity 35 4 g, there was no further decrease of the mean delivered energy in TL, suggesting an already optimal catheter tissue contact. Accordingly, CF higher than 4 g should probably be avoided because of a higher risk of complications without expected additional benefit. Advantages of CF monitoring during AF ablation are two-fold. First, it provides additional useful information for safe catheter manipulation. 13 In addition, arrhythmia control is best achieved when ablation lesions are delivered with an average CF of.2 g, clinical failure being universally noted for CF,1 g. 14 In our TL group, mean CF was 26 g, which supports the hypothesis that clinical results depends upon transmurality of lesions. In the first clinical evaluation of the CF use (the TOCCATA study 14 ), despite complete PVI in all, clinical recurrences were frequent (75%) in patients treated with FTI, 5 gs. In several single-centre evaluations, 15,16 use of CF reduced ablation and procedure times for PVI, with a trend towards a decline in acute PV reconnections. In the EFFICAS I study, 17 low FTI at first ablation (357 vs. 78 gs) was predictive of early gap occurrence following PVI; the authors interpreted this phenomenon as indicative of catheter instability and development of oedema. Both of these possible mechanisms translate into a NTL lesion. While human pathology data on transmurality of lesions are lacking, acute ablation lesions on T2-weighted (for oedema) and delayed-enhancement (for necrosis) magnetic resonance imaging following AF ablation were correlated with FTI maps in 3-case report. 18 First proof that use of CF and FTI information may optimize lesion creation was brought by the EFFICAS II study: 19 by performing ablations with a stable catheter position, a CF. 1 g and a FTI. 4 gs, as well as contiguous lesions creation, PVI at 3 months was significantly improved. All this figures are very similar to ours, suggesting once again the clinical importance of the transmurality of lesions. We obtained similar FTI cut-offs using local scar criteria instead of PVI durability or AF recurrence, which reinforces the legitimacy of our data and provides electrophysiologists a helpful tool in the everyday clinical setting of the electrophysiology lab. Moreover, in EFFICAS studies, reconduction gaps at 3 months after acute PVI have clinical impact, since one-third of the patients with gaps report symptoms, and the quality of life improves in the absence of gaps. 2 Since not only CF and time, but also delivered power is important for lesions creation, more complex indices, such as the force-power-time index (FPTI) 21 and the lesion size index (LSI) 22 have been proposed. Force-power-time index was highly correlated with lesion depth in canine beating heart and was predictive of steam pop. 21 Lesion size index best predicted reconnection after PVI in humans (EFFICAS I). 22 In our series, programmed power was always the same around PV ostia: 35 W on the anterior wall and 3 W for the posterior wall applications and there was only a trend towards a slightly higher power for TL. In our study, impedance drop was not predictive of transmurality. Recent experimental data support this finding: while reflecting tissue heating, 23 impedance drop was not correlated with lesions depth in an in vivo experimental study with ultrasound real-time visualization of lesion formation. 24 Limitations FTI ROC area:.95 Mean CF ROC area:.87 Duration ROC area:.64 Energy ROC area:.62 Reference Figure 5 Receiving operator characteristics curves for TL predictability. Force-time integral (FTI) is the best predictor of transmurality with the best area under the ROC curve (in teal) with the value of.95. Mean CF curve is in red, RF duration in green, and delivered energy in purple. Among all the curves, the best threshold to predict transmurality is an FTI ¼ 392 with the minimal distance to the best ROC point (Se.89, Sp.93). In Otomo s 1 study, another best discriminator (EGM criteria) for TL was, at the parallel sites, the complete abolition of the negative deflection in distal unipolar EGM (Se 1%, Sp 1%). Most of the unipolar EGM (using the Wilson central terminal as indifferent electrode) were of poor quality and therefore not assessed in our study. The bipolar EGM criteria have slightly smaller accuracy in case of QRS morphology (Se 85%, Sp 95%). One of the greatest limitations was possible catheter s instability. In some cases, this was suspected from illogical EGM changes

7 666 F. Squara et al. A Duration of RF pulse (s) C Duration of RF pulse (s) during the pulse, and those pulses were eliminated from further analysis. Moreover, care was taken to deliver unique lesions on one site, but in case of NTL some new applications were possible since operators aimed to reach the endpoint of PVI. Morphological EGM changes, as described in Otomo s paper, 1 also depend on catheter s orientation; we did not assess orientation (parallel/non-parallel to the atrial wall), but all EGM morphologies of the bipolar signal were analysed (QR in case of non-parallel orientation and QRS or RSR in case of parallel orientation). The transmurality criteria described in the Methods section combined all possibilities, and their accuracy is high: the Se and Sp to predict TL would be 1% for both QR and RSR morphology, and 85 and 95%, respectively, for QRS morphology. Otomo suggested that applying EGM criteria may help recognizing TL formation and may reduce thermal damage and shorten the ablation and procedure time. Nevertheless, analysing EGM changes during RF delivery is difficult since artefacts are almost always present. Radiofrequency delivery was performed in an irrigated mode; in this setting, there was a continuous linear increase of the delivered B Duration of RF pulse (s) power at the beginning of each pulse, with the programmed power being reached several seconds (up to 1 s) after the beginning of each pulse. Thus, post hoc calculations of FPTI/LSI were impossible. Finally, a small number (seven) of patients were included in our study. However, as we assessed numerous RF applications, the small number of patients may have only limited impact on the results. Conclusion FTI = 392 gs FTI = 7 gs Figure 6 Scatter plots showing duration of the RF pulse over mean contact force, for each non-transmural lesion (NTL) (A), transmural lesion (TL) (B), and both (C). NTL are displayed as red dots and TL as blue dots. The curves for FTI ¼ 392 (continuous line) and FTI ¼ 7 (dashed line) are displayed on each scatter plot. In (A), 93% of NTL dots are underneath the curve of FTI ¼ 392, and all NTL have an FTI, 7 (Sp ¼ 1). In (B), 89% of TL are above the FTI ¼ 392 gs curve. (C) shows both NTL and TL dots. Contact force and FTI are correlated with transmurality of lesions. Before RF delivery, good and stable tissue contact (i.e..2 g) must be aimed. During RF delivery, a target FTI. 392 gs (if possible 7 gs) can be used as anendpointforeach ablation site, warranting TL. Acknowledgements Preliminary results of this study have been presented at HRS annual meeting in May 212 in Boston, MA, USA (oral presentation, AB13-1).

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