Dominant frequency (DF) mapping has been widely used to study the pathophysiology of atrial fibrillation (AF). In this study, a DF mapping system was developed to guide catheter ablation on electro-physiology (EP) procedures of persistent AF patients. The proposed platform has an automated graphical user interface (GUI) that processes non-contact unipolar electrograms (EGMs) recorded simultaneously by St. Jude Ensite Velocity System and provides 3D representation of the left atrium with DF behaviours and phase analysis

Almeida, TP

Chu, GS

Li, X

Ng, GA

Salinet, JL

Schlindwein, FS

Vanheusden, FJ

Nottingham Trent Institutional Repository (IRep)

A Platform to guide Catheter Ablation of Persistent Atrial Fibrillationusing Dominant Frequency MappingXin Li1, Joa˜o L. Salinet1,Tiago P. Almeida1, Frederique J. Vanheusden1,Gavin S. Chu2, G. Andre´ Ng2, Fernando S. Schlindwein11 University of Leicester, Leicester, UK2 Department of Cardiovascular Sciences, University of Leicester, Leicester, UKAbstractDominant frequency (DF) mapping has been widelyused to study the pathophysiology of atrial fibrillation(AF). In this study, a DF mapping system was developedto guide catheter ablation on electro-physiology (EP) pro-cedures of persistent AF patients. The proposed plat-form has an automated graphical user interface (GUI)that processes non-contact unipolar electrograms (EGMs)recorded simultaneously by St. Jude Ensite Velocity Sys-tem and provides 3D representation of the left atrium withDF behaviours and phase analysis.1. IntroductionAtrial fibrillation (AF) is the most common arrhythmiain clinical practice, affecting 0.4% of the general popula-tion, and 5%-10% of those over 60 years old [1, 2]. How-ever, the underlying pathophysiological mechanisms re-main unclear [3,4]. Recent work has shown that atrial siteshosting high DF might be important sites for the mainte-nance of AF [5]. In addition, targeting in maximal DFsites in the implementation of real-time DF mapping leadto elimination of left to right frequency gradients [6]. Thespatio-temporal behaviour of DF sites was further investi-gated and recently has been shown to be largely temporallyunstable, with transient episodes of stable DF for short seg-ments, as well as a degree of re-appearance of DF activ-ity over time [7]. In addition, organization index (OI) andRegularity index (RI) have been used in both basic andclinical to help in identifying possible AF arrhythmogenicsites [5, 7]. Recently, phase analysis has been shown as apromising additional tool to identify possible AF sites [8].Therefore, these studies may lead the potential importanceto access the DF and phase features during the EP proce-dures.The main objective of this study was to design and de-velop a near-real time graphical user interface (GUI) thatallows for DF mapping and for the DF spatio-temporal be-haviour assessment persistent AF ablation procedures. TheDF GUI has been developed to be used as an auxiliary toolwith the time-based domain system to target atrial sub-strate in patients with persistent AF.2. Method5 persistent AF patients undergoing left atrium (LA)catheter ablation were enrolled. A high density non-contact balloon array (St. Jude Ensite Velocity System)was introduced transeptally in the LA. 2048 channels ofunipolar EGMs(sampling frequency: 2034.5 Hz) were si-multaneously acquired for 30 seconds. During the EP pro-cedure, data were exported from the Ensite Velocity Sys-tem and investigated on the DF mapping platform hostedby a user-oriented GUI developed in the MATLAB envi-ronment (R2013b, Mathworks, MA, USA), running on ahigh-specification laptop (Intel Core i7-4800MQ proces-sor, 32Gb DDR3 RAM, 32Gb solid state drive).Figure 1. Screenshot of the main feature (DF plots) of theplatform. The first row is sequence of DF maps with fixedcolour range (4-10 Hz), while the second row is showingthe same sequence of DF maps with adaptive colour range.The data processing performed in the GUI (Figure 1) hasbeen divided into the steps as illustrated in Figure 2. Eachof the steps will be explained in the following subsections,ISSN 2325-8861   Computing in Cardiology 2014; 41:649-652.649Figure 2. The flow chart of the System of data processing,including both on-line analysis (left) and off-line analysis(right).and the processing time for each step was measured.2.1. Platform Supported FilesThe DF GUI (Figure 1) allows for on-line and off-line EP investigations, by reading either exported comma-separated data from Ensite Velocity System (.csv) orloading pre-saved Matlab format (.mat) by using theRead/Load buttons.As illustrated by Figure 2: 2048 virtual EGMs with 30seconds duration, mesh vertices and map labels locationsand surface ECGs are read to the memory, during the on-line analysis. Processed data is read during off-line anal-ysis, hence the following steps of data processing can beskipped.2.2. QRST SubtractionQRST subtraction ( previously described in [9]) of all2048 virtual EGMs was performed to remove the effectof ventricular far field. The user is allowed to select theECG lead, where a QRS onset and T end segmentationwill be performed and projected to the intra-cardiac signalsafter coherent delay adjustment. Then, the raw EGMs arereplaced by the atrial EGMs, stored in memory.2.3. DF CalculationFast Fourier transform (FFT) was performed on all 2048atrial EGMs (after QRST subtraction) with Hamming win-dow and zero padding factor of 5, resulting in a frequencystep of 0.05 Hz. DF was defined as the frequency peakfrom 4 Hz to 10 Hz of the power spectrum, and DF calcu-lation was performed on 4 seconds windows with 50%(2seconds) overlap. [7]Regularity Index ( RI) was defined as the ratio of area ofthe DF peak and the total area of the power spectrum. [5]Organisation Index ( OI) was defined as the ratio of areaof the DF peak and all the harmonics (up to 20 Hz) and thetotal area of the power spectrum.[2]2.4. High DF cloud and Trajectory of Cen-tres of gravity (CG)High DF areas (HDFA) were defined as regions with DFbetween the maximum DF and 0.25 Hz below during eachtime window. For each high DF area, the centre of gravity(CG) was found and the trajectory of the shorted path fromthe previous CG was also calculated.[7]2.5. Mesh TriangulationThe locations of 2048 (64 × 32) virtual electrodes pro-vided by the system can be easily manipulated to form amesh of rectangles. Nevertheless, this type of mesh wouldresult in steep CG trajectories. The atrium was thereforere-meshed to obtain a triangular structure in order to ob-tain smoother CG trajectories.2.6. Phase CalculationThe phase of each channel was generated as the inversetangent of the imaginary part of the Hilbert transform ofthe virtual EGMs [10]. Thus, the each sample of the EGMphase was limited between -pi and +pi.2.7. Saving Data for Off-line AnalysisThe processed data, which includes the measured DFs,trajectories, phase, CGs, labels positions, vertices and tri-angulations, was saved in .mat file for future off-line anal-ysis (Figure 2).3. ResultThe proposed tool has a user-oriented interface, whichcan be easily operated by the clinicians. The DF GUI hasembedded the following main features: Load/read data;map type selection; time window selection; rotation con-trol.3.1. Load/Read DataThe Read/Load buttons on the left upper corner of themain window are used as the analysis type selection. If650the user clicks on one of the buttons, a file selection win-dow will pop up. The Read button is used during on-lineinvestigations, while the Load button is used during off-line analyses. Once the data files are selected, the button ischanged to red showing the tool is processing the data andwill turn green when ready to show the results.3.2. Map type panelOn the right upper corner of the main page, a group ofbuttons were designed to allow the user to change the typeof parameters showing on the 3D mesh. One of these but-tons can be active, showing the current status of the plots,accordingly:(i) DF: By default, the button is set to DF, where a groupof sub-plots (2×3) are shown in the axis. Note that the first3 plots (first row) are 3 continuous windows of DF plotswith the fixed colour code range (4 Hz -10 Hz), while thesecond row shows the adaptive colour code range, whichranges from the minimum to the maximum of the threemaps. This provides a more detailed look of the landscapesand contours of the DF maps.(ii) OI/RI: Once the user changes the button to OI/RI,the 3 plots in the second row will change to OI/RI of thesame time window in adaptive colour code range.(iii) Phase: Like the previous options, the phase can alsobe shown in second row as 3 plots (Figure 3). In order torepresenting the phase, a slider was designed to play thephase movie in 3D. Pause and play back are available inthis section, the play speed can also be changed by enteringan integer number in the right lower corner as frames perstep.Figure 3. DF (upper graphs) and Phase animation plots(lower graphs), here the sliders at the bottom can be usedto control phase plot movie as described.(iv) Trajectory of CGs: Once the trajectory radio buttonis selected, 2 large plots of only the High DF clouds andCG of the first time window are shown. The ’Next’ buttoncan be operated to change the current window and all theCGs and trajectories/paths of how the CGs travel in on the3D mesh. As shown in Figure 4, the red area refers to thecurrent high DF cloud(s), where the CG is the white dotwith black edge in the middle of the cloud. The magentadots represents the previous CGs and the white dash line isthe shorted path between CGs on the mesh.Figure 4. Trajectory of CGs and current High DF cloud(v) Summary of CGs: The tool allows to shown onelarger plot of the CG dots on the mesh as a summary ofthe CGs clustering (Figure 5). In this section, the virtualEGMs of interested can be accessed by selecting the nodeson the mesh. As shown in Figure 5, the EGM signal isfrom the white circle on the heart mesh.Figure 5. Trajectory of CGs and current High DF cloud3.3. Window SelectionThe ’Page+’ and ’Page-’ buttons allow the user to goforward and backwards by three windows per step(or thenumber of windows available if fewer than three at begin-ning or the end of the segment). The ’Plot’ button is func-tioning like a ’reset’ or ’force to plot’, which can be usedwhen a reset of starting window is needed in the CG tra-jectory plot.3.4. Rotation Control and LabelsThe Link/Unlink button on the left upper corner is de-signed to link and unlink the rotation with all six plots.651Thus, the user can rotate the plots together or individuallyby ticking and un-ticking the radio button.As seen in Figure 1 3 4 and 5, the software also allowsto show the location references (position labels) and namescreated in Ensite Velosity system during the EP study.3.5. Processing TimeA processing time test was performed on the data on30 second data of each patient. The overall platform pro-cessing time (mean ± SD) per module for the 5 patients isshown on Figure 6 (total processing time 10.4 ± 1.5 min).It can be seen from Figure 6 that the main module caus-ing the variation of the processing time between patients isthe QRST subtraction. This is due to different heart-rate,as fewer or more QRST segments are included in the pat-tern. A strong correlation between the heart rate and QRSTsubtraction time has been noticed.Figure 6. The processing time of the key modules4. ConclusionThe proposed DF mapping platform is a fully automatedGUI that provides 3D representation of the left atrium withthe DF behaviour during the EP procedure with commer-cial available mapping system (St. Jude Ensite Velocity).This DF GUI has been successfully used to guide catheterablation on EP procedures in 5 persistent AF patients andthe clinical outcomes are currently being assessed.References[1] Nattel S. Atrial electrophysiology and mechanisms of atrialfibrillation. Journal of cardiovascular pharmacology andtherapeutics 2003;8 Suppl 1:S5–S11. ISSN 1074-2484.[2] Everett TH, Kok LC, Vaughn RH, Moorman JR, HainesDE. Frequency domain algorithm for quantifying atrialfibrillation organization to increase defibrillation effi-cacy. IEEE Transactions on Biomedical Engineering 2001;48:969–978. ISSN 00189294.[3] Nattel S. New ideas about atrial fibrillation 50 years on.Nature 2002;415:219–226. ISSN 00280836.[4] Jalife J, Berenfeld O, Mansour M. Mother rotors and fibril-latory conduction: A mechanism of atrial fibrillation, 2002.[5] Sanders P, Berenfeld O, Hocini M, Jaı¨s P, VaidyanathanR, Hsu LF, Garrigue S, Takahashi Y, Rotter M, Sacher F,Scave´e C, Ploutz-Snyder R, Jalife J, Haı¨ssaguerre M. Spec-tral analysis identifies sites of high-frequency activity main-taining atrial fibrillation in humans. Circulation August2005;112(6):789–97. ISSN 1524-4539.[6] Atienza F, Almendral J, Jalife J, Zlochiver S, Ploutz-SnyderR, Torrecilla EG, Arenal A, Kalifa J, Ferna´ndez-Avile´sF, Berenfeld O. Real-time dominant frequency mappingand ablation of dominant frequency sites in atrial fibril-lation with left-to-right frequency gradients predicts long-term maintenance of sinus rhythm. Heart rhythm the of-ficial journal of the Heart Rhythm Society January 2009;6(1):33–40. ISSN 1556-3871.[7] Salinet JL, Tuan JH, Sandilands AJ, Stafford PJ,Schlindwein FS, Andre´ Ng G. Distinctive patterns of domi-nant frequency trajectory behavior in drug-refractory per-sistent atrial fibrillation: preliminary characterization ofspatiotemporal instability. Journal of cardiovascular elec-trophysiology April 2014;25(4):371–9. ISSN 1540-8167.[8] Rodrigo M, Guillem MS, Climent AM, Pedro´n-Torrecilla J,Liberos A, Millet J, Ferna´ndez-Avile´s F, Atienza F, Beren-feld O. Body Surface Localization of Left and Right AtrialHigh Frequency Rotors in Atrial Fibrillation Patients: AClinical-Computational Study. Heart rhythm the officialjournal of the Heart Rhythm Society 2014;ISSN 1556-3871.[9] Salinet JL, Madeiro JPV, Cortez PC, Stafford PJ, Andre´Ng G, Schlindwein FS. Analysis of QRS-T subtraction inunipolar atrial fibrillation electrograms. Medical and Bi-ological Engineering and Computing 2013;51:1381–1391.ISSN 01400118.[10] Umapathy K, Nair K, Masse S, Krishnan S, Rogers J, NashMP, Nanthakumar K. Phase mapping of cardiac fibrilla-tion. Circulation Arrhythmia and electrophysiology Febru-ary 2010;3(1):105–14. ISSN 1941-3084.Address for correspondence:Xin LiDepartment of EngineeringUniversity of LeicesterLE1 7RHUKxl153@le.ac.uk652

A platform to guide catheter ablation of persistent atrial fibrillation using dominant frequency mapping

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A platform to guide catheter ablation of persistent atrial fibrillation using dominant frequency mapping

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