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teven M. Markowitz, MD, Bruce B. Lerman, MD

rom the Department of Medicine, Division of Cardiology, Cornell University Medical Center, New York, New York.

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Electroanatomic mapping refers to the acquisition andisplay of electrical information combined with spatialocalization. Technologies presently available includeoth contact and noncontact electroanatomic mapping.his review focuses on the creation and proper interpre-

ation of contact electroanatomic maps, which involveshe sequential recording of unipolar or bipolar electro-rams with a catheter in contact with the endocardium orpicardium and display of this information on a three-imensional navigation system. These techniques haveecome invaluable in the evaluation of complex arrhyth-ias by providing a spatial catalogue of electrical infor-ation. This allows the user to define an area of interestith greater resolution than is possible using fluoroscopy

lone and to revisit sites of interest that already have beenatalogued.

ontact electroanatomic mapping systems

he Biosense Webster CARTO system (Biosense Webster,nc., Diamond Bar, CA, USA) localizes catheter positionsing three ultra-low magnetic fields, which are generatedy coils within a locator beneath the patient.1 Sensorsoused within the mapping catheter detect the strengths ofhese magnetic fields and allow computation of catheterosition in three-dimensional space as well as catheter ori-ntation (pitch, roll, and yaw). This system requires a spatialeference, which may be external to the patient or an intra-ardiac catheter.

The Boston Scientific RPM (Realtime Position Manage-ent) system (Boston Scientific, Natick, MA, USA) uses an

EYWORDS Electroanatomic mapping; Supraventricular tachycardia; Ven-ricular tachycardia (Heart Rhythm 2006;3:240–246)

This work was supported in part by grants from the National Institutesf Health (RO1 HL-56139), the American Heart Association, Grant-in-AidNew York City Affiliate), the Maurice and Corinne Greenberg Arrhythmiaesearch Grant, the Raymond & Beverly Sackler Foundation, and theichael Wolk Foundation.

Address reprint requests and correspondence: Dr. Steven M.arkowitz, Division of Cardiology, Starr 4, Cornell University Medicalenter, 525 East 68th Street, New York, New York 10021.

E-mail address: smarkow@med.cornell.edu.

t(Received October 23, 2005.)

547-5271/$ -see front matter © 2006 Heart Rhythm Society. All rights reserved

ltrasound ranging technique with a transmitter/receivernit and two intracardiac reference catheters with ultra-ound transducers.2 The distance between transducers onhe reference catheters is calculated by measuring the delayetween departure and reception of the ultrasound pulse.nce the locations and orientations of reference catheters

re established, triangulation algorithms define the positionnd curve of a mapping catheter.

In the St. Jude EnSite NavX system (St. Jude Medical,t. Paul, MN, USA), electrical signals are transmitted be-

ween three orthogonal pairs of surface patch electrodes.3

he position in space of any catheter electrode (includingistal and proximal electrodes) can be calculated using thetrengths of these three electrical signals. An external orntracardiac reference electrode serves as the origin of theoordinate system.

efining chamber geometry

y sequentially moving a mapping catheter, the geometryf a chamber of interest can be constructed. Some systemsompute this contour using points manually acquired fromhe distal electrode of the mapping catheter, whereas othersontinuously update the position of a catheter or shaft andefine the chamber as the outermost extent of catheterxcursion. Anatomic structures such as the vena cava, AVnnuli, and pulmonary veins often are identified and dis-layed because these structures may behave as central ob-tacles for reentrant arrhythmias or as the sources of focalrrhythmias.4,5 During this process, it is necessary to dis-inguish internal locations from the endocardial surface.his is especially important in systems, such as CARTO,

hat use only the distal electrode and manually acquiredoints. It also is important to recognize structures that do notomprise the chamber proper, such as the great cardiaceins and the pulmonary veins. Including these “external”oints within an atrial map may obscure the detailed anat-my of the atrium by interpolating an anatomic shell be-ween neighboring points. Thus, the left atrial appendageay be joined to the left pulmonary veins if these are

ncluded in the same map, concealing the ridge betweenhese structures.

The spatial reference is important in maintaining in-

ernal consistency within the electroanatomic map. If the

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241Markowitz and Lerman How to Interpret Electroanatomic Maps

patial reference of a magnetic system is displaced duringstudy, the anatomic map may become grossly distorted.orizontal, vertical, or rotational movements may each

ffect the map to different degrees. The ultrasound rang-ng system (RPM) and cutaneous patch system (EnSiteavX) are capable of detecting displacement of the ref-

rence catheters and allow for repositioning in case ofislodgment.

Cardiac and respiratory movements may decrease theccuracy of catheter localization. Movement during the car-iac cycle will displace catheters between mechanical sys-ole and diastole, but this discrepancy is easily prevented byating the catheter location to a specific time in the cardiacycle. Changes in rhythm may complicate catheter localiza-ion; apparent shifts might occur if points are compared inifferent rhythms because of change in chamber geometrynd gating. Respiratory excursions also can cause signifi-ant shifts in apparent catheter location. This can be ad-ressed by visually selecting points during the same phasef the respiratory cycle. An intracardiac spatial referenceill largely reduce this problem but is more prone to dis-

igure 1 Reference and mapping electrograms from isthmus-deI, an intracardiac reference from the coronary sinus (R1-R2), andM1-M2) are shown. Activation time on the mapping catheter (yehosen as the peak negative amplitude in the coronary sinus electrs �6 ms relative to the reference. B: The reference is incorrectlyf its more negative voltage, resulting in a spurious activation tim

odgment. e

isplaying electrical information

lectrical information can be presented in the form ofctivation timing, voltage amplitude, or other user-de-ned measurements. These values are color coded andssigned to the spatial location of the mapping catheter.lectrical information is interpolated between neighbor-

ng points on the anatomic shell to provide a gradient ofeasured or user-defined values. Thus, the accuracy and

sefulness of electroanatomic maps depends largely onhe resolution of the map, and entire areas may be rep-esented by interpolated information if they are not thor-ughly interrogated.

An electrical reference is required for the selection andcceptance of points on the map. This electrical reference isf key importance for any study that measures activationiming, and stability of this reference is critical to avoidninterpretable maps. For maps of supraventricular tachy-ardia, an electrogram in the coronary sinus often is chosens a reference because of its stability. Care must be taken tonsure that automatic sensing of the reference is reproduc-ble and is not subject to oversensing in the case of annular

nt flutter are displayed in the CARTO system. Surface ECG leadolar electrogram from the distal electrodes of a mapping catheterine) is determined relative to the reference, which in this case is(red line). A: Activation time at this site is correctly determined

d as the ventricular component of an annular electrogram because30 ms.

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242 Heart Rhythm, Vol 3, No 2, February 2006

ia, a surface lead is commonly chosen as the electricaleference. Automated sensing of mapping and referencelectrograms is accomplished by detecting peak amplituder peak slope.

The most common type of maps used for practical clin-cal applications are activation maps and voltage maps.ctivation maps typically use bipolar recordings, which are

ssigned activation times based on their earliest deflectionr intrinsicoid deflection. These maps are useful for bothocal and macroreentrant tachycardias.

efining focal and macroreentrantachycardias

focal tachycardia should demonstrate a discrete area ofarly activation that precedes the surface P wave or QRS,nd there should be centrifugal spread of activation fromhis early site (Figures 2A and 3A).5 Focal tachycardias also

ay demonstrate areas of block and slow conduction, buthese are bystander sites, which are not critical for mainte-ance of the tachycardia. These arrhythmias typically dem-nstrate total activation times substantially less than theachycardia cycle length.

Electroanatomic maps may provide direct visualiza-ion of a macroreentrant circuit, which is defined as thehortest distance of continuous activation comprising theachycardia cycle length.4 Macroreentrant arrhythmiasemonstrate adjacent areas of early and late activation,onnected by sites with intermediate values of activationFigures 4A, 5, and 6). Commonly �90% of the tachy-ardia cycle length can be mapped within a reentrantircuit.

When mapping a tachycardia, the user must define notnly an electrical reference but a window for assigningctivation times on the mapping catheter. Within this win-ow, activation is considered “early” or “late” relative to theeference. For macroreentrant circuits, the sensing windowhould approximate the tachycardia cycle length, and des-gnating activation times in a circuit as “early” or “late” isrbitrary. In theory, a change in the window or referenceould not change a macroreentrant circuit but only result inphase shift of the map. Displaying information as an

sochronal map may clearly demonstrate the direction ofavefront propagation, which is perpendicular to the isoch-

onal lines (Figures 2, 4A, and 5C). Entrainment mapping isarticularly useful when combined with electroanatomicapping to define critical components of a reentrant circuit

nd identify bystander regions. This combined approachay be required in situations where the electroanatomicap is ambiguous.A useful feature of the mapping software includes an

lgorithm to detect “early-meets-late activation” (FiguresA, 5, and 6). By coding these adjacent regions a specificolor, it becomes apparent that conduction proceeds from

ate to early sites, as would be expected in a reentrant m

ircuit. This avoids the false impression generated by inter-olating between early and late activation. If an insufficientumber of points is obtained in this early-meets-late zone, it

igure 2 Right atrial isochronal map of a focal tachycardia arisingrom the posterolateral tricuspid annulus, displayed in the right ante-ior oblique view with caudal angulation. A: Early activation isresent at the posterolateral annulus with centrifugal activation of theest of atrium. The coronary sinus electrogram is chosen as theeference, and the sensing window is �140 and �100 ms relative tohe reference. The tachycardia cycle length is 325 ms, and totalctivation of the right atrium is 146 ms (45%). B: The sensingindow is manipulated to overlap two sequential beats of the focal

achycardia by expanding the window to the tachycardia cycle length�50 and �275 ms relative to the reference). This results in anninterpretable activation map where “early” sites from panel A nowre assigned “late” activation times because they are referenced to thereceding beat. This map shows a spurious rim of “early-meets-late”ctivation because adjacent sites arise from different beats (“head-eets-tail”; threshold 85%). The total activation time of 315 ms is

naccurate because the window overlaps two sequential beats.

ight be falsely concluded through the interpolation of

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243Markowitz and Lerman How to Interpret Electroanatomic Maps

ctivation times that the wavefront propagates in the wrongirection (Figure 4B).

ources of error when interpretinglectroanatomic maps

he following sources of error or “pitfalls” should be keptn mind when interpreting electroanatomic maps:

. Incomplete mapping and low resolution. If a map isincomplete, bystander sites may be mistakenly identifiedas part of the reentrant circuit. Regions that are poorlysampled will have activation interpolated betweenwidely separated points. This may give the appearance ofconduction, but critical features such as line of blockmight be missed (Figures 5 and 6). In addition, low-resolution mapping might obscure other interesting phe-nomena, such as the second loop of a dual-loop tachy-cardia. Some arrhythmias, such as complex reentrantcircuits, require more than 80 to 100 points to obtainadequate resolution. Other tachycardias can be mappedwith fewer points, including focal tachycardias and someless complex reentrant arrhythmias such as isthmus-de-pendent atrial flutter.

. Mapping a single chamber. If mapping is limited tothe right atrium, left atrial tachycardias may be mis-taken for focal arrhythmias originating in the region of

igure 3 Activation map of the right ventricular outflow tract ialve is depicted by a yellow ring. Note early activation of the sHead-meets-tail” criteria are applied. This results in the artifactnterpolated. Higher-density mapping in this region would correctecause the activation time of 66 ms is substantially less than the

the Bachmann bundle, the interatrial septum, or the

coronary sinus (Figure 5). This misinterpretation canbe avoided by recognizing broad areas of early acti-vation along the septum, which are indicative of septalbreakthrough. These tachycardias often demonstratefusion of wavefronts around the anterior and lateralwall of the right atrium. Mapping in the septum mayreveal double potentials, with the early componentcorrelating with earlier left atrial activation. Entrain-ment mapping is particularly useful in excluding theparticipation of the right atrium in left atrial macro-reentrant circuits.

. Fractionated electrograms. If highly fractionated andwide potentials are present, it may be difficult to assignan activation time. In some macroreentrant circuits, largepercentages of the tachycardia cycle length are occupiedby fractionated low-amplitude potentials. If these poten-tials are dismissed or assigned relatively late activationtimes, a macroreentrant tachycardia might mimic a focalarrhythmia, and it will appear as if substantially less than90% of the tachycardia cycle length is mapped (Figure4B).

. Central obstacles or conduction block. Failure toidentify areas of scar or central obstacles to conduc-tion may confuse an electroanatomic map becauseinterpolation of activation through areas of conductionblock may give the appearance of wavefront propaga-tion and confuse the reentrant circuit (Figures 5D and6). This occurrence precludes identification of a crit-

tient with focal idiopathic ventricular tachycardia. The pulmonicutflow tract with centrifugal activation of the right ventricle. B:taposition of “early” and “late” sites in a region that is highly

ror. Close inspection reveals this map could not be macroreentrycardia cycle length of 380 ms.

n a paeptal oual juxthis er

ical isthmus to target for ablation. A line of conduc-

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244 Heart Rhythm, Vol 3, No 2, February 2006

tion block can be inferred if there are adjacent regionswith wavefront propagation in opposite directions sep-arated by a line of double potentials or dense isoch-rones (arbitrarily �100-ms difference in activationover �2-cm distance).

. Inappropriate activation window. If the activation win-dow spans two adjacent beats of a focal arrhythmia, theresulting map may be ambiguous. This may occur with

igure 4 Right atrial isochronal map of isthmus-dependentounterclockwise atrial flutter, displayed in the left posteriorblique view. A: The tachycardia cycle length is 220 ms, andctivation times comprise 204 ms (93% of the tachycardia cycleength) based on a map of 60 points. Note adjacent areas of earlynd late activation around the tricuspid annulus, designated by aed zone signifying “head-meets-tail.” In this map, a fractionatedlectrogram depicted in panel A is assigned a late activation timeelative to the reference. B: The same fractionated potential isssigned an early activation time, which changes the map andonveys the misleading impression of a focal tachycardia. Notearge areas of interpolation due to low resolution of mapping in theeptal wall, which should serve as a clue to the inaccuracy of theap.

focal arrhythmias that demonstrate areas of slow passive m

conduction, possibly occupying substantial portions ofthe tachycardia cycle length. This type of inappropriatewindow gives rise to a spurious pattern of adjacent re-gions of “early” and “late” activation (Figure 2B). How-ever, the map lacks coherency, and the user is unable todefine a continuous path occupying the tachycardia cyclelength that uses both early and late adjacent regions withintervening values.

oltage mapping

t might not be possible to obtain complete electroana-omic maps for arrhythmias that are hemodynamicallynstable or nonsustained. These arrhythmias requiretrategies other than activation mapping. Voltage map-ing is an important tool for defining potential circuits inoth the atria and ventricles. In the left ventricle, aipolar voltage amplitude �1.5 mV is considered abnor-al, and “dense scar” can be inferred if amplitudes are0.5 mV.6 In the atria, scar is defined as an area with

ipolar voltage �0.05– 0.1 mV.7,8 However, areas of lowoltage may participate in reentrant— or even focal—rrhythmias. These areas with low voltage can be con-idered “diseased,” but they are not necessarily equatedo conduction block or scar.

ew uses for electroanatomic maps

ser-defined values might be used in a variety of situa-ions. One example is to record the results of entrainmentapping and code sites with numbers that reflect the

ostpacing interval.9 These values can give a sense of thextent of myocardium that lies within a tachycardia cir-uit as well as the distance of various sites from theircuit. It also has been proposed that sites can be taggedased on pacing threshold to identify electrically unex-itable tissue, which may be a more accurate way todentify dense scar.10

onclusion

lthough electroanatomic mapping is extremely valuableor understanding complex arrhythmias, these maps re-uire careful interpretation, editing, and review. It oftens useful to test various interpretations or hypothesesegarding the rhythm against the mapping data. The ten-ency to make a rapid diagnosis without reviewing thedequacy of each point and overall consistency of the

ap should be avoided.

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245Markowitz and Lerman How to Interpret Electroanatomic Maps

igure 5 Activation map of a left atrial macroreentrant tachycardia. A: Right atrial map in the left posterior oblique view shows a regionf early activation in the septum. Right atrial activation time of 116 ms is substantially less than the tachycardia cycle length of 315 ms37%). B: Biatrial map in a left anterior oblique view now clearly shows that the right atrium is no longer the “earliest” site of activation.he total activation time of the left atrium (275 ms) approximates the tachycardia cycle length (87%). This view also shows fusion ofavefronts in the lateral wall of the right atrium. C: Isochronal map of the left atrium in a posterior cranial view. An area of scar is identifiedith voltage �0.1 mV (gray points), and a reentrant circuit is present around this scar. D: The left atrial map is manipulated to reassign

scar” points with interpolated activation times (“location only” points). Failure to recognize the scar gives the impression of conduction

hrough this zone and obscures targets for ablation.

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246 Heart Rhythm, Vol 3, No 2, February 2006

eferences

1. Gepstein L, Hayam G, Ben-Haim SA. A novel method for nonfluo-roscopic catheter-based electroanatomical mapping of the heart: Invitro and in vivo accuracy results. Circulation 1997;95:1611–1622.

2. de Groot NM, Bootsma M, van der Velde ET, Schalij MJ. Three-dimensional catheter positioning during radiofrequency ablation inpatients: first application of a real-time position management system.J Cardiovasc Electrophysiol 2000;11:1183–1192.

3. Krum D, Goel A, Hauck J, Schweitzer J, Hare J, Attari M, Dhala A,Cooley R, Akhtar M, Sra J. Catheter location, tracking, cardiac cham-ber geometry creation, and ablation using cutaneous patches. J IntervCard Electrophysiol 2005;12:17–22.

4. Markowitz SM, Brodman RF, Stein KM, Mittal S, Slotwiner DJ, IwaiS, Das MK, Lerman BB. Lesional tachycardias related to mitral valvesurgery. J Am Coll Cardiol 2002;39:1973–1983.

5. Iwai S, Markowitz SM, Stein KM, Mittal S, Slotwiner DJ, Das MK,Cohen JD, Hao SC, Lerman BB. Response to adenosine differentiatesfocal from macroreentrant atrial tachycardia: validation using three-dimensional electroanatomic mapping. Circulation 2002;106:2793–2799.

6. Marchlinski FE, Callans DJ, Gottlieb CD, Zado E. Linear ablationlesions for control of unmappable ventricular tachycardia in patientswith ischemic and nonischemic cardiomyopathy. Circulation 2000;101:1288–1296.

7. Nakagawa H, Shah N, Matsudaira K, Overholt E, Chandrasekaran K,Beckman KJ, Spector P, Calame JD, Rao A, Hasdemir C, Otomo K,Wang Z, Lazzara R, Jackman WM. Characterization of reentrantcircuit in macroreentrant right atrial tachycardia after surgical repair ofcongenital heart disease: isolated channels between scars allow “focal”ablation. Circulation 2001;103:699–709.

8. de Groot NM, Schalij MJ, Zeppenfeld K, Blom NA, Van der VeldeET, Van der Wall EE. Voltage and activation mapping: how therecording technique affects the outcome of catheter ablation proce-dures in patients with congenital heart disease. Circulation 2003;108:2099–2106.

9. Triedman JK, Alexander ME, Berul CI, Bevilacqua LM, Walsh EP.Electroanatomic mapping of entrained and exit zones in patients withrepaired congenital heart disease and intra-atrial reentrant tachycardia.Circulation 2001;103:2060–2065.

0. Soejima K, Stevenson WG, Maisel WH, Sapp JL, Epstein LM. Elec-trically unexcitable scar mapping based on pacing threshold for iden-tification of the reentry circuit isthmus: feasibility for guiding ventric-

igure 6 Right atrial activation maps of a macroreentranttrial tachycardia in a patient with Ebstein anomaly and surgicalepair of an atrial septal defect. A line of conduction block cane inferred along the lateral wall based on two wavefrontsropagating in opposite directions. Interpolation of activationcross this line can be misinterpreted as conduction unless theine of block is recognized. The tachycardia is a dual-loopeentrant circuit around an atriotomy and around the tricuspidalve with a cycle length of 460 ms, of which 442 ms (96%) isapped. Gray tags represents “scar.” The tan tag identifies a

ite of concealed entrainment. Red tags are ablation points inhe critical isthmus. (Reproduced with permission from Iwai S,

arkowitz SM, Stein KM, Mittal S, Slotwiner DJ, Das MK,ohen JD, Hao SC, Lerman BB. Response to adenosine differ-ntiates focal from macroreentrant atrial tachycardia: validationsing three-dimensional electroanatomic mapping. Circulation

ular tachycardia ablation. Circulation 2002;106:1678–1683.