Magnetic Electroanatomical Mapping for Ablation of Focal Atrial Tachycardias

Magnetic Electroanatomical Mapping forAblation of Focal Atrial Tachycardias

FRANCIS MARCHLINSKI. DAVID CALLANS, CHARLES GOTTLIEB,ENRIQUE RODRIGUEZ, ROBERT COYNE, and DAVID KLEINMAN

From the Electrophysiology Section, Allegheny University Hospitals and the Philadelphia HeartInstitute and Sidney Kimmel Research Center, Philadelphia, Pennsylvania

MARCHLINSKI, F., ET AL.: Magnetic Electroanatomical Mapping for Ablation of Focal Atrial Tachycar-dias. Uniform success for ablation of focal athaJ tachycardias has been difficult to achieve using standardcatheter mapping and ablation techniques. In addition, our understanding of the complex relationship he-tween atrial anatomy, electrophysiology. and surface ECG P wave morphology remains primitive. Themagnetic electroanatomical mapping and display system (CARTO) offers an on-line display of electricalactivation and/or signal amplitude related to the anatomical location of the recorded sites in the mappedchamber. A window of electrical interest is established based on signals timed from an electrical referencethat usually represents a fixed electrogram recording from the coronary sinus or the atrial appendage.This window of electrical interest is established to include atria! activation prior to the onset of the P waveactivity associated with the site of origin of a focal atrial tachycardia. Anatomical and electrical land-marks are defined with limited fluoroscopic imaging support and more detailed global chamber and morefocal atrial mapping can be performed with minimal fluoroscopic guidance. A three-dimensional colormap representing atrial activation or voltage amplitude at the magnetically defined anatomical sites isdisplayed with on-line data acquisition. This display can be manipulated to facilitate viewing from anyangle. Altering the zoom control, triangle fill threshold, clipping plane, or color range can all enhance thedisplay of a more focal area of interest. We documented the feasibility of using this single mappingcatheter technique for localizing and ablating focal atrial tachycardias. In a consecutive series of 8 pa-tients with 9 focal atrial tachycardias, the use of the single catheter CARTO mapping system was associ-ated with ablation success in all but one patient who had a left atrial tachycardia localized to the medialaspect of the orifice of the left atria! appendage. Only !ow power energy deHvery was used in this patientbecause of the unavaHahiHty of temperature monitoring in the early version of the Navistar catheter, thelocation of the arrhythmia, and the history of arrhythmia control with f!ecainide. No attempt was madeto Umit fluoroscopy time in our study population. Nevertheless, despite data acquisition from 120-320anatomically distinct sites during global and more detaHed focal atrial mapping, total fluoroscopy expo-sure was typically < 30 minutes and was as !itt!e as 12 minutes. The detailed display capabilities of theCARTO system appear to offer the potential of enhancing our understanding of atrial anatomy, atrial ac-tivation, and their relationship to surface ECC P wave morphology during focal atrial tachycardias. (PACE1998: 21:1621-1635)

atrial tachycardia, catheter ablation, catheter mapping

Introduction

The success of catheter ablation for focalatrial tachycardias has been iimitod by tbe inher-ent difficulty of localizing the arrhythmia site of

Address for reprints: Francis Marchlinski, M.D., AlleghenyUniversity Hospitals Cardiac Electrophysiology Section, MailStop 471. Broad and Vine Streets. Philadelphia, PA 19102. Fax:(215) 991-4881: e-mail: fmphilapaCy home.net

origin within the complex three-dimensionalstructures of the right and left atria. Not uncom-monly, despite hours of catheter manipulation, ra-diofrequency ablation for atrial tachycardiasguided by fluoroscopy alone may be unsuccessful.Success rates only in the 70%-85% range havebeen reported.^^ These results contrast markedlyto the near uniform success of these same standardcatheter ablative techniques directed at treatingatrioventricular (AV) nodal reentry and eliminat-

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MARCHLINSKI, ETAL.

ing accessory pathways.^ ^ Three-dimensionalnonfluoroscopic magnetic field spatial electro-gram mapping (CARTO '̂̂ ', Biosense Ltd., Israel)offers the potential to facilitate localization of ab-lation of focal atrial tachycardias.

The magnetic sensor in the catheter tip can belocalized accurately in the three-dimensionalspace using the magnetic field generator placedunder the fluoroscopic tahle. Electrogram datarecorded from the same catheter tip and placed atdifferent endocardiai locations can be collectedrapidly and shown in three dimensions on a rotat-ahle computer display.'̂ "^^ The ability to return tothe same anatomical location is easily docu-mented. This article will describe our preliminaryresults using this technique to localize and elimi-nate focal atrial tachycardias. Emphasis will beplaced on techniques that: (1) enhance the record-ing and nonflnoroscopic localization process; and(2) enhance display of the data collected. We willconclude by describing how this magnetic map-ping technique can be used to enhance our under-standing of the relationship between atrial elec-trophysiology and anatomy.

Background and Rationale for the Useof the Biosense—CARTO System

The standard approach to the ablation of focalatrial tachycardia has evolved rapidly over the last5 years. It was recognized early in the ablation expe-rience that localization of focal atrial arrhythmiasin the complex three-dimensional structures of theright and left atrium would he difficult. Efforts to fa-cilitate regionalization of the origin of the atrial ar-rhythmia evolved rapidly. The use of multiple, mul-tipolar recording catheters in the form of secondablation catheter, Crista™ catheters, HALO'̂ '̂catheter, and hasket catheters has been advocated asan important tool for establishing electrical andanatomical references to facilitate the site of originlocalization and ablation.'^"^•' Indeed, identificationof the most common regions of origin of atrial ar-rhythmias was facilitated using the described, multi-polar catheters. It is now firmly estahlished that mostatrial tachycardias originate from well-definedanatomical regions.̂ ^"^^ These regions in the rightatrium include the crista terminalis, the tricuspid an-nulus, and right atrial appendage. In the left atriumthese regions include the atria surrounding and

involving the pulmonic veins, the mitral annulus.and the left atrial appendage.^""^''

Twelve-lead surface electrocardiographic Pwave analysis also provides important clues to thelocalization of atrial foci in these described re-gions/**"^" Despite these important advances indata collection and advances in techniques forsuccessfully regionalizing the site of origin, uni-form success of atrial tachycardia ablation hasbeen difficult to achieve.^"^'^^'^^ Admittedly, thedifficulty in initiating some atrial tachycardiasand the frequency of multiple atrial tachycardiamorphologies make the near uniform success ofahlation seen with accessory pathway and AVnodal reentry unlikely. Nevertheless, there existsome technical and recording limitations that canbe obviated by the magnetic field electroanatomi-cal mapping technique. For example, data on Pwave morphology may not he availahle in everypatient because the P wave location may be withintbe QRS interval or ST segment and the inherentdifficulty in establishing high grade AV block insome patients. In addition, the use of multiple.multipolar catheters requires complex display ca-pabilities and skill in interpretation of simultane-ously recorded signals if they are to be used for on-line arrhythmia localization. Finally, exceptionsexist to well-established rules with respect to"typical" atrial tachycardia locations and their as-sociated characteristic 12-lead FCG P wave mor-phologies. Chamber enlargement or rotation andthe presence of prior cardiac surgery or congenitalheart disease certainly can confound surface ECGP wave analysis in selected patients. Hence, rapidregionalization of atrial tachycardias based onnoninvasive 12-lead ECG analysis of the P wavemorphology may not always be possible. Thus, atechnique that can create a rapid on-line elec-troanatomical display for localizing the site of ori-gin using a single mapping catheter should expe-dite and simplify arrhythmia localization.

Magnetic Electroanatomical MappingTechnology and Recording Techniques

Reference Electrogram

An electrical reference is necessary to estab-lish a window of interest during which mappedelectrogram signals can be assessed. Optimally,the electrical reference should: [1) represent a

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recording of, or from, the chamber targeted formore detailed mapping or a recording that at leastmaintains a fixed relationship to the tachycardiaof interest; and (2) maintain a stable recordingthroughout the mapping process. The surface Pwave, which is frequently small and may occur intiming coincident with a larger amplitude QRScomplex or ST segment, is usually not a satisfac-tory electrical reference when attempting to local-ize the site of origin of an atrial tachycardia. Anelectrical recording from a catheter placed in a sta-ble position in the right atrial appendage or coro-nary sinus typically serves as the optimal electri-cal reference for an atrial tachycardia localization.

Window of Interest

Once the reference is established, a time win-dow of interest is created (Fig. 1). The window ofinterest should be initially set to encompass thecycle length ofthe atrial tachycardia and excludeventricular activation. This very wide window ofinterest is critical if a macroreentrant atrial tachy-cardia is suspected. In the absence of structuralheart disease or previous atrial surgery, a narrowerfield of interest can be set to decrease the likeli-hood of overlap with far-field ventricular electro-gram recordings. The presystolic activation timefor focal atrial tachycardias at the site of effectiveablation typically ranges from approximately —30to -120 ms. The window of interest must at min-imum, therefore encompass a duration of at least120 ms before the onset of the P wave and extendto the end of the surface ECG P wave or just priorto the QRS complex. This interval or window ofinterest as shown in Figure 1 is established in re-lationship to the stable intracardiac referencechannel and will demonstrate only atrial electro-gram recordings.

Recording from the Mapping Catheter

Bipolar tip to ring and unipolar tip and/orring recordings are available from the mappingcatheter. Unipolar recordings eliminate the inher-ent difficulty in identifying local activation timewith bipolar recordings. However, sniall ampli-tude multicomponent bipolar electrograms fre-quently characterize the presystolic activity ofthesite of origin of many focal atrial tachycardias, andat these sites a specific activation time based on

Backward

Figure 1. Establishing tlie time window of interest(Windows Setting) for focal atria! tachycardia prior tomapping. The time window of interest is established inrespect to a fixed electrical reference. A recording froma stable catheter position in the coronary sinus (CS 7-8}was used as the electrical reference in the exampleshown. The time window of interest for an atrial tachy-cardia should approximate the cycle length of thetachycardia and exclude the QRS duration. The dura-tion of the time window of interest should be at least 120ms before the onset ofthe P wave for a focal atrial tachv-cardia (220 ms before the electrical reference in the ex-ample shown) and extends to the onset ofthe QRS com-plex (37 ms after the electrical reference in the exampleshown).

unipolar recordings from these areas may be diffi-cult to assess. We recommend the operator takeadvantage ofthe fact that both unipolar and bipo-lar recordings are available for analysis. Further-more, during mapping and data acquisition theoperator should confirm the automatic annotationof local activation and manually adjust the anno-tation of activation after assessing both bipolarand unipolar electrograms when confusion exists.

Designation of Anatomical Landmarks andMapping Setup for Different Rhythms

The designation of important anatomical andelectrophysiological landmarks at the beginningofthe mapping process: (1) facilitates orientationon the three-dimensional computers display; (2)helps identify important anatomical boundariesto facilitate limiting fluoroscopic support; and (3)identifies early in the study important sites whichshould be avoided during any subsequent energyapplication, such as the His-bundle region. Werecommend identifying and tagging the inferior


MARCHLINSKI, ET AL.

vena cava, the superior vena cava, the os of thocoronary sinus, the tricuspid annulus, and theHis-hundle region when mapping the right atrium,and the pulmonic veins and the mitral annuluswhen mapping the left atrium.

There are several important electroanatomi-cal considerations to keep in mind when estab-lishing these anatomical designations. Atrial my-ocardium appears to form the endovascularsurface of the superior vena cava up to the level ofthe azygos vein, which inserts approximately 3-5cm above the superior vena cava and high rightatrial junction.^^ In marked contrast, the atrial my-ocardium appears to terminate abruptly at thelevel of the inferior cava and right atrial junction.Penetration of atrial myocardium for variable dis-tances into the pulmonic veins and the coronarysinus has also been documented.^^ In attemptingto identify the portion of the superior vena cavathat approximates the right atrium, the mappingcatheter should be withdrawn 2-3 cm below the

level at which atrial olectrograms are lost. A simi-lar approach can be used for identifying the ori-fices of the pulmonary veins. Loss of electrogramsas one pulls hack from the atrium will allow forthe superior margin of the inferior vena cava to bedesignated. Activation of the junction between theinferior vena cava and low right atrial junction canbe estahlished. Catheter placement just inside thecoronary sinus may be difficult even with a steer-able catheter. Nevertheless, an attempt should hemade so the proximal boundaries of this structurecan be designated. By manipulating the catheterslightly and flexing the tip several points can beohtained that can help to actually identify and dis-play the anatomical boundaries and the orienta-tion of the various sites of atrial ingress. The re-gion of the His bundle is estabhshed based on theelectrogram recording and tagged appropriately.The remaining mitral and triscuspid annulus des-ignations should be established only whenmapped recordings demonstrate large amplitude

Figure 2. Computer monitor display of detailed right atrial maps representing over 150 recordings from the rightatrium during atrial tachycardia. The atrial tachycardia originated from the posterokiteral right atrium in the regionof the crista terminalis (arrow). Panel (A) Activation map in right anterior oblique projection with the earliest activa-tion represented by red color recorded 83 ms before reference electrogram recorded from catheter in tbe coronary si-nus and the latest activation indicated by purple. The color range for the activation times is displayed in the top rightof panel A. Panel (B): Isopotential or voltage map of tbe recorded bipolar signals in the right anterior oblique projec-tion with tbe lowest amplitude signals designated by tbe red color. Tbe color range for the signal amplitudes is shownin tbe top right of panel B. Note the low amplitude signals recorded along the tricuspid annulus (TA). Tbe approxi-mate location of tbe superior vena cava (SVC) and inferior vena cava (IVC) are designated on each panel. The totalfluoroscopy time required to obtain detailed activation map and perform successful ablation was 12 minutes in thispatient.

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ventricular electrograms coupled with low ampli-tude atrial electrograms in an amplitude ratio of atleast 2:1. At least three to four anatomical sites onthe medial and lateral sides of the tricuspid andmitral annulus should be designated in order tobetter characterize and permit more accurate dis-play of the three-dimensional location of the valveplanes.

Importantly, we have found that the identifi-cation arid designation of the descrihed land-marks facilitates subsequent nonfluoroscopiccatheter manipulation. In fact, much of the re-maining mapping and site of origin localizationcan be performed with limited fluoroscopic sup-port (Fig. 2). After an initial learning curve, wenow find that we can perform detailed right or leftatrial mapping using consistently < 15 minutes oftluoroscopy time. Importantly, the ability to de-fine these key anatomical boundaries helps pre-vent unrecognized catheter manipulation in theventricular chanihers and radiofrequency energydelivery in the described vascular structures orHis-bundle region. Because anatomical shifts mayoccur with the onset of different arrhythmias, adesignation of the location of an anatomical ori-fice should he considered arrhythmia specific. Anew map or a new chamber designation must beselected and the entire map repeated when map-ping the same chamber during different rhythms,such as sinus rhythm, the targeted arrhythmiaand/or the pacemapped rhythm.

Global Atrial and Focal Atrial Mapping

Global mapping of the designated atrialchamber may be helpful in regionalizing the siteof origin for a focal atrial tachycardia (Fig. 3)Global mapping may he of greater importancewhen one cannot identify a body surface P wavemorphology to help regionalize the arrhythmia,Data is displayed in three dimensions with eachtriangle of three data points within a designatedanatomical distance-(triangle fill threshold) filledby a computer generated color. The global activa-tion or the isopotential/voltage map will nomi-nally display earliest to latest activation or small-est to largest signal amplitude as a color rangewith red representing earliest or smallest signalsand purple representing the latest or largest am-plitude signals for activation and isopotential

maps respectively. Global mapping of the rightatrium and coronary sinus can help identify aright or left atrial site of origin for tachycardiasdemonstrating a P wave morphology consistentwith an inferoseptal origin (Fig. 4). It also serves arole in confirming the presence of isthmus blockand distinguishes recurrent, albeit slowed atrialflutter versus atrial tachycardia in patients withsymptomatic tachycardia after prior isthmus abla-tion for atrial flutter (Fig. 5). Identification of im-portant landmarks and global mapping of eachchamber in sufficient detail to satisfy the nominaltriangle fill threshold and have all of the atria rep-

GLOBAL MAP - RIGHT LATERAL GLOBAL MAP AP

Figure 3. Right atrial global (top panels) and detailed(bottom panel) activation maps during focal atrialtachycardia. In the top panels global activation mapssboivn in tbe right lateral and left anterior oblique pro-jections demonstrate earliest activation in tbe region ofthe mid- and anterolateral rigbt atrium. The color dis-play as indicated in the top right of eacb panel showsearliest activation designated by color red. After tbeglobal map more detailed mapping was performed fo-cusing on tbe lateral rigbt atrium. Tbis detailed mapidentified a focal early area (arrow) surrounded by sitesactivated later consistent with a focal atrial tachycar-dia. Note the preferential spread of activation antero-laterally through tbe trabeculated atrium from this fo-cal site.


MARCHLINSKI, ET AL.

LA TACHYCARDIA FROM MITRAL ANNULUS

BOTTOM VIEW LAO VIEW

Figure 4. Atria! tachycardia with ECG P wave morphol-ogy consistent with posterior paroseptal site of origin lo-calized to the mitral annulus. Note on 12-lead ECG pos-itive P wave in VI, and inverted P wave in leads 2, 3.and avE. Activation map of the right atrium and thecoronary sinus arc displayed and suggested an origin ofthe tachycardia along the medial mitral annulus. Be-cause of a history of a prior cerebral vascular accidentand extensive calcific rheumatic mitral disease, leftatrial mapping and ablation were not performed.

resented by a color takes from 20-30 minutes peratrial chamber in our experience.

After global chamber mapping confirms oridentifies a region of interest, more detailed map-ping in a small area of the atrium to preciselylocalize an arrhythmia prior to ablation is indicated(Fig. 3). In selected patients with an easily identifi-able site of origin based on analysis of the P wavemorphology one can forego global mapping andafter establishing important landmarks target amore specific area for more detailed mapping.During the learning curve of using the CARTOsystem, it is advisable to perform the more globalchamber mapping. The global mapping not onlywill confirm the region of interest but will alsoserve to increase the operator's utiderstandingof the complexities of the atrial anatomy. Before en-ergy application, it is advisable to identify later ac-tivation times surrounding the site of earliest

activation to confirm a focal origin of the tachy-cardia and hopefully limit the number of energy ap-plications (Fig. 3).

The CARTO system allows for mapping andthe individual or simultaneous display of multi-ple chambers. Display of multiple chamberssimultaneously is appropriate when all recordingsin each chamher have been obtained during thesame rhythm. In fact, when trying to assess rightatrial activation that is chamber specific, it isbest to designate points recorded in the coronarysinus as recordings from another chamber. Thiswill result in the color display along the in-feromedial right atrium more accurately reflect-ing true atrial activation with the triangle fillcolors representing only right atrial points. Mapscreated of the same chamber during differ-ent rhythms should be designated as a new mapand not a new chamber to avoid subsequent con-fusion when attempting to display required in-formation.

Figure 5. Eocal atrial tachvcardia after atria! flutter ab-lation confirmed with mapping using GARTO. Activa-tion map of supraventricular tachycardia after atrialflutter ablation confirmed the presence of isthmus block(broken line) during the tachycardia and during pacingfrom the coronary sinus (not shown). A focal atrialtachycardia originating from the low right atria! septumwas identified with spread of activation (arrows) fromthis point source to the isthmus inferiorly and up theseptum superiorly.


MAGNETIC ELECTROANATOMICAL MAPPINC

Display Options and Utility

The unique feature ofthe CARTO system is itsability to display in three dimensions elec-troanatomical information as on-line point by pointelectrogram data acquisition is performed. With thesimple manipulation of the computer mouse thethree-dimensional computer display can be rotatedin X, Y, or Z plane to permit viewing from any an-gle. Across the task bar just above the three-dimen-sional image are eight selection buttons wbich al-low for rapid sequential viewing at fixed anglesthat correspond to standard fluoroscopic imagingand also include PA, coronal, and caudal imagesthat are not obtainable with conventional fluoro-scopic imaging tecbniques [Fig. 6). The main three-dimensional image can be viewed in fixed projec-tions that correspond to standard fluoroscopicimage projections, such as right anterior ohlique orleft anterior oblique views. Up to two additionalprojections can be simultaneously displayed as in-serts on the screen to allow for multiplane on-lineviewing [Fig. 7). This ahility to manipulate thethree-dimensional image and/or simultaneouslyview multiple image angles facilitate nonfluoro-scopic localization of the catheter tip and permitsconstant visualization of specific areas of interest.

Clipping Plane

These areas of interest may become obscuredin selected views by a plane of myocardium whencolor designation of myocardium to represent volt-age or activation has been applied to fill each threedata points or triangles tbat are within a designatedanatomical distance [triangle fill threshold]. To en-hance viewing of obscured areas of interest,recorded information can be removed or clipped intbe X, Y, or Z plane for a variable and pro-grammable anatomical distance (Figs. 8 and 9).Tbis may help unveil anatomical relationships thatare best appreciated when viewed from a specificangle. In addition, use ofthe "clipping plane" facil-itates an understanding ofthe relationship betweenthe two-dimensional fluoroscopic image and theCARTO computerized electroanatomical display.

Zoom Display

There are several other display techniquesthat can be used to enhance the focus of attention

to a smaller area ofthe atrium and permit more fo-cused detailed mapping. The simplest displaytechnique to enhance the focus of attention andfacilitate more detailed mapping is the use of thezoom feature. The zoom display should be used tomaximize the size ofthe chamber display withoutlosing the boundaries that enhance safe, nonfluo-roscopic mapping (Fig. 10).

Triangle Fill Threshold

The triangle fill threshold represents thelongest distance in millimeters between tbreepoints above which the triangle is not filled by acolor in isopotential or activation mapping dis-plays. This feature is typically used to ensure ad-equate point sampling when performing moreglobal cardiac chamber mapping. The nominalvalue is set to 40 mm. Areas of the atrium will notbe represented by a color until points within 4 cmof each other are sampled. By setting tbe value toa lower number [20-30 mm) after more detailedfocused mapping has begun, the atrium repre-sented by the color display will be tbe area of in-terest with a more "real" anatomical contourwhile a three-dimensional mesh will representmost of the rest of atrium. This manipulation ofthe triangle fill threshold allows one to focus at-tention to the area targeted for continued detailedpoint acquisition to define later points surround-ing the earliest site while the transparent meshdisplay does not ohscure the view of this areafrom multiple angles [Fig. 11).

Altering the Color Range

Another tool for focusing attention to an areaof interest is to alter the color range or the limits ofactivation times or voltages over which a completerange of colors will be applied. For example, onecan identify the time coincident witb the onset ofthe P wave and designate all activation times afterthis point as being late and therefore representedby the purple color. By narrowing the color rangein this fashion, the full range of color will be dis-played only for the area ofthe atrium activated be-fore the onset of the P wave. As illustrated in Fig-ures 11 and 12, this focuses the operator'sattention on the area requiring the more detailedmapping. Tbe color range can also be narrowed onthe lower end of an isopotential or voltage map to


MARCHLINSKI, ET AL.

RAO LAO

RIGHT LATERAL LEFT LATERAL

Figure 6. Focal right atria! tachycardia originating from the right atrial appendage displayed using the eight standardfixed viewing display options for any map ohtained by CARTO system. Note that site of earliest activation (arrow! canhe identified in only 4 ofthe 8 views. By rapidly toggling through the standard display options one can quickiv iden-tify the best view to select for monitoring during more detailed mapping to identify a focal site of origin.



RIGHT ATRIAL TACHYCARDIA AT THE OS OF THEATRIAL APPENDAGE

DETAILED MAP - RIGHT LATERAL

Figure 7. Focal atria! tachycardia originating from theright atria! appendage demonstrating the ability of theCARTO system to display 3 views simultaneously dur-ing mapping. The primary view can be rotated in the X,Y, or Z planes. In the centra! display the right atrium isshown as viewed from the bottom ofthe atrium with aleft anterior oblique (LAO) angulation to optimize theview of the right atrial site of origin of the focal atrialtachycardia. The inserts display the right atrium in theanterior posterior (AP) and LAO views.

X PLANE CLIPPED

DETAILED MAP - AP DETAILED MAP - LEFT LATERAL

Figure 9. Use of clipping plane to view site of origin offocal atria! tachycardia. Top panel shows site of origin(arrow) of right atrial tachycardia viewed in right lateralview bottom left pane! shows detailed activation mapwith the medial right atrium clipped or eliminated inthe anterior posterior (APj plane. By rotating the"clipped" image to a left lateral plane the activation ofthe right atrial free wall can be identified. Site of origin(arrow) was along the crista terminalis with spread ofactivation preferentially into the trabeculated atrium.

RIGHT LATERAL

RIGHT LATERAL X PLANE CLIPPED BY ISmin AP

Figure 8. Use of dipping p!ane to view site of origin offocal atrial tachycardia ohscured by atriai anatomy.Top panels show right lateral and AP view of activationmap of atria! tachycardia originating from the os ofright atrial appendage. Note that earliest site of atrialactivation is obscured by activation ofthe lateral rightatria! free wall. Bottom panels demonstrates the sametwo views after eHminating or dipping 15 mm of acti-vation map in the X p!ane. By eliminating or dippingthe !atera! right atria! free waH the site of origin at theOS ofthe atria! appendage (arrow) is readily visualizedin the right lateral view (bottom left).


MARCHLINSKI, ET AL.

STANDARD ZOOM

Figure 10. Use of zoom control to enhance focal area of interest when mapping focal atriai tachy-cardia. Left panel: Standard display in a modified coronal -AP projection. Right pand: Zoom fea-ture used to enlarge display and facilitate identification of the origin of focal atrial tachycardiafrom the right atrial appendage indicated hy red color at site of earliest presystolic activity.

better define a diffuse area associated with low am-plitude signals. In the example shown in Figure 13,a large area of the lateral free wall of the rightatrium associated with the origin of a tachycardiais represented hy signals with an amplitude < 1.0mV. Presumably these low amplitude signals arebeing recorded from abnormal myocardium.which serve as an arrhythmogenic suhstrate.

Propagation Map

The last display tool used when assessing fo-cal atrial tachycardia that will be discussed is thepropagatioamap. The propagation of electrical ac-tivity in the atrial chamber or chamhers is dis-played as a video sequence of red activation on ahlue chamber background (Fig. 14). The steps inthe display can be adjusted [the nominal value isequal to a step of 30 ms). The display is very help-ful in obtaining another visual image of spread ofatrial activation from a focal location. This hasalso been helpful in identifying the likely locationof anatomical harriers such as the crista terminalisand for visnally displaying patterns of simultane-ous atrial activation over a short time period.

Results of Focal Atrial TachycardiaAblation Using CARTO

We now have experience with mapping andattempted ablation of six consecutive patients

with six focal right atrial tachycardias and two pa-tients with three focal left atrial tachycardias.Mapping and ahlation appeared to be successfulin all hut one patient. This latter patient had a leftatrial tachycardia, which appeared to originate inproximity to the medial aspect of the os of the leftatrial appendage. Because of the patient's clinicalhistory of heing responsive to flecainide therapyand the lack of temperature monitoring only lowpower was used for ablation dnring her ahlationattempt. It was not clear whether successfnl ahla-tion was nnable to be achieved because of inade-quate power titration or be of technical difficultyof performing the detailed activation map of theOS of the left atrial appendage with the then avail-able 8 Fr Navistar catheter (a 7 Fr size is nowavailable).

In the eight patients, no attempt was made tosystematically try to limit fluoroscopy time andindeed the initial experience tended to result inthe operators desire to demonstrate fluoroscopi-cally the anatomically designated sites by theCARTO system. Nevertheless, despite detailedglobal activation maps (between 100 and 320atrial sites mapped), the total flnoroscopic timeexceeded 60 minutes in only one patient [90 min).Of note, in three of the patients, detailed mappingand ablation procedures required < 15 minutes oftotal fluorosGopy time [Figs. 2 and 6). The CARTOsystem proved especially helpful in two patients.



Figure 11. Standard display ofthe site of origin ofutrialtachycardia originating from the right atrial appendage(left panel) enhanced hy altering the display color range(top right) or triangle fill threshold (hottom right). Seetext for details.

In the first patient, a supraventricular tachycardiaoccurred 2 months after atrial flutter ablation withisthmus block. It was not clear based on the Pwave morphology and the tachycardia ratewhether the arrhythmia represented a recurrence,albeit slow, of atrial flutter or the occurrence of anatrial tachycardia. Detailed mapping during coro-nary sinus pacing confirmed the presence of isth-mus hlock. Detailed mapping near the septumwith the same catheter during the tachycardiaconfirmed the presence of a focal arrhythmia withspread of activation both superiorly along the sep-tum and inferiorly toward the isthmus [Fig. 5).Thus, with the single mapping catheter isthmusblock could he established and a focal atrial tachy-cardia mapped and ablated. In the second patientthe atrial tachycardia appeared to have an inferi-orly directed P wave. Yet, the tachycardia wassuccessfully localized and ablated when targetingthe lower annular region of the lateral tricuspidannulus (Fig. 13). A voltage map of the lateralright atrium defined a large area of low amplitudeatrial activity. This large area of decreased voltageamplitude was felt to explain the hasis for the sur-face P wave origin that presumably originatednear the upper border ofthe "scarred" atrium. The

Inappropriate Sinus Tachycardia

LAO RIGHT LATERAL WITHCORONAL TILT

Figure 12. Display of the site of origin of inappropriate sinus tachycardia. The color range hasbeen altered such that everything that is activated coincident with the surface ECG P wave is dis-played in purple. This change in the color range enhances the detail and display of the pre-Pwave activation. Note the origin of the focus responsible for the inappropriately fast sinus rate(displayed in red) is consistent anatomically with the superolateral crista terminalis.


MARCHLINSKI, ET AL.

A TACH P WAVE SITE OE ORIGIN

RIGHT ATRIAL TACHYCARDIA

ACTIVATION MAP -RAO MAX VOLTAGE MAP

Figure 13. Focal right atria! tachycardia originating from a zone of low ampHtude atria! e!ectrograms. Top pane!sshow atria! tachycardia P wave morpho!ogy (left) and site of origin activation time relative to electrical reference(right) for right atrial tachycardia originating from the apical mid-right atrial free waU (arrow-bottom left panel). Thepatient had no Icnown stractura! heart disease. The activation map in the right anterior obUque view identified thesite of origin of the focal atrial tachycardia along the free wall of the right atrium approaching the tricuspid annu!us.The !ocation of the atrial taclwcardia was lower than anticipated given the P wave morpho!ogy in leads II. III. andaVF (top left panel). The voltage map (bottom right panel} identified low amplitude atrial electrograms over an ex-tensive area of the lateral right atria! free wall. The low amplitude signa!s probaMy accounted for the absence of anyidentifiab!e surface P wave activity unti! the more superior part of the atria was activated, thus creating inferiorly di-rect F waves. The voltage map helped explain the observed ECG phenomenology.



INAPPROPRIATE SINUS S/P SINUS ABLATION

Figure 14. Propagation maps showing first two 10-20ms activation windows (top and bottom) during inap-propriate sinus tachycardia (left panels) and duringrhythm generated from focus hwer down on the crista(right panels) after ablation of focus responsible for in-appropriate sinus tachycardia. Note rapid spread of ac-tivation medially and inferiorly along the crista on thebottom left panel during inappropriate sinus tachycar-dia. The activation following the ablation spreads su-periorly and inferiorly along the crista. Alt panels showviews in a modified left anterior oblique (LAO) pro-jection.

information acquired from the CARTO displaywas useful in helping to explain and clarify thisunanticipated surface ECG finding.

Magnetic Electroanatomical Mappingas a Research and Teaching Tool

The Carto magnetic electroanatomical map-ping system and display couples three-dimen-sional anatomical information with electrical in-formation related to signal amplitude andactivation time. As such, this display will un-douhtedly enhance our understanding of the rela-tionship of atrial activation to surface ECC P wavemorphology and atrial anatomy. The CARTO sys-tem will also more accurately confirm the anatom-ical location of sites of origin of atrial tachycardiasthan can be established with fluoroscopy alone,Intra right and left atrial activation and transatrialactivation patterns during sinus rhythm (Fig. 15)and with atrial tachycardias will be defined.Anatomical structures supporting preferentialconduction or associated with block will be iden-tified. Investigators will likely revisit in more de-tailed fashion much of the initial studies that at-tempted to relate the complexities of the right andleft atrial anatomy to its electrophysiology inhealth and disease. We anticipate that due to itsunique capabilities, additional major research andteaching roles of the magnetic electroanatomicalmapping system will be rapidly identified.


MARGHLINSKI, ET AL,

RIGHT ATRIUM

LEFT ATRIUM

Figure 15, Detailed propagation maps during .si'nu.s- rhythm in left anterior oblique (LAO) (toppanels) and right anterior oblique (RAO) (bottom panels) projection for both right atrium and leftatrium.

1634 August 1998 PACE, Vol, 21

MAGNETIC ELECTROANATOMICAL MAPPINC

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Magnetic Electroanatomical Mapping for Ablation of Focal Atrial Tachycardias