DIAGNOSTIC METHODSELECTROPHYSIOLOGY

The value of catheter mapping duringsinus rhythm to localize site of originof ventricular tachycardiaDENNIS M. CASSIDY, M.D., JOSEPH A. VASSALLO, M.D., ALFRED E. BUXTON, M.D.,JOHN U. DOHERTY, M.D., FRANCIS E. MARCHLINSKI, M.D., AND MARK E. JOSEPHSON, M.D.

ABSTRACT We assessed the value of endocardial catheter mapping in 52 patients in sinus rhythmand with 102 morphologically distinct ventricular tachycardias. The local bipolar electrograms fromvarious regions of the left ventricle were assessed and quantitatively classified with respect to thecharacteristics of amplitude and duration. With the use of this assessment we found that electrogramsfrom the site of origin were of significantly lower amplitude and longer duration; however, becausesuch an overlap occurred with electrograms that were not from sites of origin, this does not serve as a

useful clinical marker. Various types of electrograms, including normal, abnormal, fractionated,abnormal late, fractionated late, and longest, were evaluated with respect to sensitivity, specificity, andpositive predictive value. None of these types possessed the ability to reliably localize the site of originof ventricular tachycardia. We therefore conclude that endocardial catheter mapping during sinusrhythm is not useful as a guide in localized surgical therapy of ventricular tachycardia. Surgery guidedonly by the results of mapping during sinus rhythm would result in a more extensive excision than thatdirected by maps obtained during ventricular tachycardia and in some cases would result in theexclusion of the area considered to be the site of origin of the tachycardia.Circulation 69, No. 6, 1103-1110, 1984.

THE MANAGEMENT of ventricular tachycardia hasbeen improved with the application of new surgicaltechniques. 1 Paramount to the success of surgery is theability to localize the site of origin of ventricular tachy-cardia by endocardial mapping procedures. 2, 3 Map-ping during ventricular tachycardia has been accom-plished both before surgery in the catheterizationlaboratory and during surgery. It is not, however, pos-sible to map all morphologically distinct tachycardiasin all patients. This is related either to an inability to

From the Clinical Electrophysiology Laboratory, Hospital of the Uni-versity of Pennsylvania, Cardiovascular Section, Department of Medi-cine, University of Pennsylvania School of Medicine, Philadelphia.

Supported in part by grants from The American.Heart Association,Southeastern Pennsylvania Chapter, Philadelphia; grant Nos. HL00361and HL24278 from the National Heart, Lung and Blood Institute, Be-thesda; and by The Fannie E. Ripple Foundation, Morristown, NJ.

Address for correspondence: Mark E. Josephson, M.D., Chief, Car-diovascular Section, Room 658 Ravdin Building, Hospital of the Uni-versity of Pennsylvania, 3400 Spruce St., Philadelphia, PA 19104.

Received Nov. 4, 1983; revision accepted March 8, 1984.Dr. Cassidy is supported by a Canadian Heart Foundation Research

Fellowship, Ottawa.Drs. Buxton and Marchlinski are supported by the University of

Pennsylvania Measey Foundation.Dr. Doherty is supported by a grant-in-aid from the American Heart

Association, Southeastern Pennsylvania Chapter.Dr. Josephson is the Robinette Foundation Associate Professor of

Medicine (Cardiovascular Diseases).

Vol. 69, No. 6, June 1984

induce ventricular tachycardia or an inducible ventric-ular tachycardia that is not tolerated hemodynamical-ly. This limitation could be overcome if endocardialmaps obtained during sinus rhythm could supply infor-mation that would be of predictive value in localizingthe site of origin of ventricular tachycardia. Althoughsuch an approach has been suggested,4' no data hasbeen available to test the usefulness of such tech-niques. Our study was therefore undertaken to critical-ly evaluate the role of endocardial mapping duringsinus rhythm to localize the site of origin of ventriculartachycardia. The specific aims were (1) to quantita-tively assess the amplitude and duration of local leftventricular endocardial electrograms in a population ofpatients with coronary artery disease and ventriculartachycardias, and (2) to determine if these or any otherqualitative electrographic property possessed charac-teristics that could localize the site of origin of ventric-ular tachycardia.

MethodsPatient population. Fifty-two patients referred to the hospi-

tal of the University of Pennsylvania for electrophysiologicevaluation of ventricular tachycardia underwent sinus rhythmendocardial catheter mapping during the course of their studies.

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There were 45 men and seven women with a mean age of 58years (range 34 to 75).

All patients had coronary artery disease and previous histo-ries of myocardial infarction. The electrocardiographic patternof infarction was anterior in 38, inferior in eight, and mixed insix. In all the patients coronary artery disease was assessed bycoronary angiography and left ventriculography. All patientshad left ventricular aneurysms and reduced left ventricular func-tion as determined by the finding of depressed ejection fraction(mean 29%, range 12% to 45%). All patients had histories anddocumentation of recurrent sustained ventricular tachycardia.

Electrophysiologic study. Studies were performed in pa-tients in nonsedated, postabsorptive state after informed writtenconsent had been obtained. Thirty-three patients were not onany antiarrhythmic therapy, while the remaining 19 were on oneantiarrhythmic drug each. The patients who were receivingdrugs underwent mapping both while in sinus rhythm and dur-ing ventricular tachycardia while on the same antiarrhythmicdrug. Whenever possible the two maps were obtained with thecatheter at the same site; this was accomplished by stopping andstarting the ventricular tachycardia. In other patients the mapduring sinus rhythm was obtained first, followed by the mapduring ventricular tachycardia. If more than one morphological-ly distinct ventricular tachycardia was induced it was alsomapped.One quadripolar catheter (No. 6F USCI) was inserted percu-

taneously into the femoral artery and advanced to the left ventri-cle of each patient under fluoroscopic guidance. One to twoquadripolar catheters were inserted percutaneously and wereadvanced to the right ventricular apex and right ventricularoutflow tract. Catheters had a 5 mm interelectrode distance.Heparin, 5000 units as a bolus, followed by 1000 units/hr, wasadministered after insertion of the arterial catheter in each of thepatients.The left ventricular mapping scheme used is illustrated in

figure 1. The 12 sites represent segmental areas of the heart ofapproximately 5 to 10 cm2. Eight to 32 electrograms were re-corded in each patient. The catheter sites were independentlyverified by multiple-plane fluoroscopy in the presence of twoexperienced physicians familiar with this mapping scheme. Thecatheter was repositioned to another site to confirm reproduc-ibility of recordings and only minimal morphologic differencesbetween local electrograms were noted. Stability was ensuredby recording from each site for a minimum of 5 to 30 sec.Electrograms were recorded with the use of a 10 mm interelec-trode distance. The intracardiac electrograms were recorded atvariable gain to achieve the best electrographic definition andwere accompanied by a 1 mV calibration signal. A 10 mmbipolar fixed-gain signal was also recorded at a 1 cm/mV ampli-fication at each site. Electrograms were filtered at 30 to 500 Hz.Intracardiac recordings were simultaneously displayed on amultichannel oscilloscope (Electronics for Medicine VR 16) andwere stored on analog magnetic tape (Honeywell 5600) andrecorded on a 16-channel Mingograf (Siemens Elema) at a paperspeed of 200 mm/sec.

Definitions. Electrographic amplitude (in mV) was definedas the peak-to-peak deflection measured in the 10 mm variable-gain bipolar electrogram.

Electrographic duration (in msec) was defined as the timefrom the earliest electrical activity that deviated from a stablebaseline to the onset of the amplification signal decay artifact(an artifact caused by electronic decay of an amplified filteredsignal) measured in the 10 mm fixed-gain bipolar electrogram(figure 2). The amplification and duration measurements werecombined to give an amplitude/duration ratio to allow equalemphasis to be placed on each of these values.

Local activation time at a site was defined as the timefrom the

FIGURE 1. Schema of mapping sites in left ventricle (see text fordiscussion).

onset of the surface QRS to the time at which the largest rapiddeflection of the local electrogram crossed the baseline. Thismeasurement was obtained from the 10 mm variable-gain bipo-lar electrogram.

Electrograms were defined as normal based on the measure-ments obtained from 112 electrograms in patients with normalleft ventricles. The normal values represent those from 95% ofall electrograms obtained in these patients.6 Normal amplitudewas defined as one of 3 mV or more and normal duration wasdefined as one of 70 msec or less. The normal amplitude/dura-tion ratio was defined as 0.046 or greater. In cases in which onlyone of the amplitude or duration measurements were abnormal,the amplitude/duration ratio was used to define normality.

Electrograms failing to satisfy the above criteria for normalitywere defined as abnormal. Basic statistical methods were thenused to define the mean and SD values for amplitude, duration,and amplitude/duration ratio for the electrograms of this popula-tion.The electrograms that were the most abnormal were defined

as fractionated and were characterized by low amplitude, highfrequency, multicomponent signals of prolonged duration. Thisgroup was quantitatively defined as consisting of those abnor-mal electrograms that were greater than 1 SD from the meanvalues of the abnormal electrograms as a group. Again, if onlyone parameter of amplitude or duration met the criteria forfractionation, then the amplitude/duration ratio was used todefine fractionation.

Late electrograms were defined as those in which a compo-nent was recorded after the inscription of the latest surface QRSactivity. This was a timing characteristic and hence it could beapplied to any of the three types of electrograms describedabove.

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TIMEFIGURE 2. Three surface electrocardiographic recordings (I, aVF, and

V,) accompanied by three local bipolar electrograms (normal, abnor-mal, and fractionated and late) recorded from different left ventricularendocardial sites. The dashed vertical line denotes the end of surfaceQRS activity. The arrows show the onset and offset (characterized bythe amplification signal decay artifact) of local electrical activity. Eachelectrogram is accompanied by 1 mV calibration signals.

The longest electrogram recorded in each patient was alsoanalyzed and was defined as the electrogram of the greatestduration.The site of origin of ventricular tachycardia was arbitrarily

defined as the earliest recorded electrical activity occurring inlate diastole before the surface QRS during ventricular tachycar-dia. This was determined by catheter and/or operative mapping.When a ventricular tachycardia was localized between two stan-dard sites, the electrogram from each of these sites was consid-ered in the analysis of site of origin. Induction of tachycardiawas performed by standard previously described methods.7 Allother sites were considered to be non-sites of origin.Data analysis. Electrographic amplitudes, durations, and ac-

tivation times were assessed at each site by at least two inde-pendent observers. A minimum of four to six complexes were

assessed at each site. The data were analyzed with the use ofevery electrogram recorded but, because we believed that thismight introduce a sampling bias, the data were also evaluatedwith the use of the mean of all the electrograms at a site whenmore than one electrogram was obtained at a given site. Anelectrographic signal that came from between two standard siteswas designated to one site based on its local activation time. Bythis technique a maximum of 12 electrograms from the leftventricle could be obtained. It is the mean data that are present-ed since analysis of both methods yielded similar results.

All results are expressed in terms of mean + SD. Student's ttest for unpaired data was used when comparing electrographiccharacteristics from sites of origin and those from areas thatwere not sites of origin. Calculation of sensitivity, specificity,and positive predictive value were done by standard methods, as

summarized in table 1.

Results

General. The 52 patients exhibited 102 morpholog-ically distinct ventricular tachycardias for analysis: 20

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patients had only one morphology, 17 had two mor-phologies, 13 had three morphologies, one had fourmorphologies, and one patient had five ventriculartachycardia morphologies. The total number of elec-trograms available for analysis was 546 (10.5 per pa-tient). Of these electrograms, 102 were from sites oforigin while the remaining 444 were from non-sites oforigin. The number of electrograms that met the nor-mal criteria was 234 (42%); the remaining 312 (58%)electrograms were considered abnormal.

Abnormal electrograms - quantitative analysis. Themean abnormal electrographic amplitude was 1.4 ±0.9 mV and the mean abnormal electrogram durationwas 93 ± 40 msec. The mean abnormal electrographicamplitude/duration ratio was 0.017 ± 0.012.The generation of these data allowed a quantitative

definition of fractionated electrograms. The quantita-tive criteria used to define fractionated electrogramsbased on values 1 SD from the mean became an ampli-tude of 0.5 mV or less, a duration of 133 msec or more,and/or an amplitude/duration ratio 0.005 or less.

Classification of electrograms. A distribution of eachtype of electrogram is seen in table 2. Of the 312abnormal electrograms, 47 were fractionated by thedescribed criteria. This represents 9% of all electro-grams. Eighty of the abnormal electrograms were clas-sified as late, representing 15% of all electrograms and26 (5%) were considered both fractionated and late.Examples of the various types of electrograms areshown in figure 2.

Analysis of sites of origin. Results of the quantitativecomparative analysis of site of origin and non-site oforigin is shown in table 3. The sites of origin had loweramplitudes (2.0 ± 2 vs 3.6 + 2.8 mV; p < .001),longer durations (88 ± 33 vs 75 ± 27 msec; p <

TABLE 1Definitions of sensitivity, specificity, and positive predictive value

True positive Electrographic typeA at site of originFalse positive Electrogram type, not site of originTrue negative - Nonelectrogram type,B not site of originFalse negative - Nonelectrogram type at site of origin

True positiveSensitivity =

True positive + False negativeTrue negative

Specificity =

True negative + False positiveTrue positive

Positive predictive value = --True positive + False positive

ADefined by one of the following: normal, abnormal, fractionated,abnormal late, fractionated late, or longest.

BDefined by all electrograms not exhibiting particular characteristicbeing analyzed.

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TABLE 2Distribution of the 546 electrograms

Total (%)Site of Non-site of all

Electrogram type origin of origin electrograms

Normal 14 220 234 (42)Abnormal 88 224 312 (58)Fractionated 10 37 47 (9)Abnormal late 26 54 80 (15)Fractionated late 8 18 26 (5)Longest 16 36 52 (10)

.001), and lower amplitude/duration ratios (0.027 ±0.03 vs 0.058 + 0.055; p < .001) than did the non-sites of origin. Although all values reached statisticalsignificance, much overlap between the groups wasnoted.

Value of electrographic types. The sensitivity, specific-ity, and positive predictive value of each type of elec-trogram is summarized in table 4.Of all the types, only abnormal electrograms pos-

sessed good sensitivity, at 86%. Normal electrogramswere not sensitive, being present 14% of the time. Lateabnormal electrograms had a sensitivity of 26%. Like-wise, the longest electrogram recorded only possesseda sensitivity for the site of origin of ventricular tachy-cardia of 16%. The least sensitive type of electrogramwas the fractionated, whether or not it was late (10%and 8%, respectively).The specificity of each type of electrogram was also

examined. Both normal and abnormal electrogramshad a specificity of 50%. The fractionated electro-grams had a 92% specificity. The characteristic of"lateness" also led to increased specificity, i.e., ab-normally late electrograms had an 88% specificity andfractionated late electrograms had a 96% specificity.The longest electrogram recorded was also quite spe-cific, at 92%.The ability to positively predict the site of origin of

ventricular tachycardia was also examined for eachelectrographic subtype. The positive predictive value

TABLE 3Comparison of electrograms of site of origin with those not of site oforigin

Site of Non-siteorigin of origin p value

Amplitude (mV) 2.0±2A 3.6+2.8 <.001Duration (msec) 88 ±33 75+27 <.001Amplitude/duration

ratio (mV/msec) 0.027±0.030 0.058±0.055 <.001

AMean + SD.

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of normal electrograms was 6%, and for abnormalelectrograms it was 29%. Fractionated electrogramsonly predicted site of origin 21% of the time. Thecharacteristic of lateness added little to the predictivevalue; abnormal late electrograms had a 33% predic-tive value while fractionated late electrograms posi-tively predicted the origin of tachycardia 31% of thetime. Similarly, the longest electrogram had a positivepredictive value of only 31%. Therefore, no electro-graphic type manifested a good positive predictivevalue.

Single ventricular tachycardia morphology analysis. Aseparate analysis was performed on data from the 20patients who had only one distinct ventricular tachy-cardia morphology. These results are summarized intable 5. The distribution and value of each of the typesof electrograms were similar to those in the entirepopulation. Abnormal electrograms were fairly sensi-tive (80%) but were not specific (65%) and were ofpoor positive predictive value (21%) for the site oforigin of ventricular tachycardia. The only differencenoted in this analysis was the lack of normal electro-grams at the site of origin of ventricular tachycardia.This most likely reflects the fewer number of morpho-logically distinct ventricular tachycardias analyzed (20vs 82).An analog map from one patient is shown in figure

3. This map shows the dispersion of various types ofelectrograms throughout the entire endocardial sur-face, regardless of site of origin.

Discussion

Mapping during ventricular tachycardia has beenestablished to be both safe and useful; however, it maybe associated with several potential problems.8 Thetime required to map during ventricular tachycardiacan result in unfavorable hemodynamics. Some ven-tricular tachycardias lead to rapid hemodynamic col-lapse and patients with these tachycardias are not suit-able candidates for endocardial mapping. Occasionallytachycardias are totally noninducible, are of differentmorphologies than spontaneously documented ventric-ular tachycardias, or have rapidly changing morpholo-gies that make them unsuitable for activation mapping.Finally, operative mapping leads to increased cardio-pulmonary bypass time and its inherent problems. Itwould therefore be beneficial to be able to predict thesite of origin of ventricular tachycardia from mappingduring sinus rhythm.

It has been demonstrated with both epicardial andendocardial mapping during sinus rhythm that patientswith recurrent sustained ventricular tachycardia have a

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TABLE 4Sensitivity, specificity, and positive predictive value of each electrogram type (entire population)

Positive predictiveSpecificity (for site value (for site of

Sensitivity other than site origin ofElectrogram type (for site of origin) of origin) electrogram type)

Normal 14/102 (14%) 224/444 (50%) 14/234 (6%)Abnormal 88/102 (86%) 220/444 (50%) 88/312 (29%)Fractionated 10/102 (10%) 407/444 (92%) 10/47 (21%)Abnormal late 26/102 (26%) 390/444 (88%) 26/80 (33%)Fractionated late 8/102 (8%) 426/444 (96%) 8/26 (31%)Longest 11/102 (16%) 408/444 (92%) 16/52 (31%)

variety of abnormal electrographic findings that are notpresent in patients without this arrhythmia.4' 9 Thismay well define an electrophysiologic substrate forventricular tachycardia. However, the mere presenceof such electrograms does not allow the conclusion thatmapping during sinus rhythm can be used to guidesurgical therapy of ventricular tachycardia. Thishypothesis can only be proved if such electrograms areshown to be sensitive, specific and, most importantly,to possess positive predictive value for the site oforigin of ventricular tachycardia. The goal of this studywas to evaluate the hypothesis that endocardial map-ping during sinus rhythm in patients is useful in guid-ing localized surgical therapy of ventricular tachy-cardia.

Classification of electrograms. The literature dealingwith mapping techniques is confusing with regard toelectrographic descriptions. The confusion has arisenbecause of a lack of a standardization with regard toamplifier and filter settings and interelectrode distanceof recording apparatus and most importantly becauseof a lack of quantitative electrographic description ofcharacteristics of amplitude and duration. This lastproblem can be partially attributed to the fact that therehas been no quantitative description of bipolar electro-graphic characteristics of normal left ventricles.

In a prior study6 we defined quantitative standardsfor normal bipolar electrograms based on the findingsin 10 subjects with normal left ventricles from whom112 bipolar electrograms were obtained for analysis.The description of abnormal electrograms is the resultof comparison with this data base.Of the electrograms recorded in patients in sinus

rhythm, the ones that are fractionated are the mostabnormal. Only recently have microelectrode tech-niques been used in attempts to define fractionatedactivity.'0 The qualitative description that is in generalagreement with results of clinical mapping is that of anelectrogram with high frequency, low amplitude, mul-ticomponent signals of prolonged duration. The quan-titative descriptions in the literature, however, havevaried from none to amplitudes less than 1 mV anddurations greater than 50 msec,11-1 without any detailsabout how these values were obtained. Our definitionof fractionation encompasses all previous definitionsand is in fact more rigid. We believed that the signifi-cance of this type of electrogram would be best judgedby analyzing the most abnormal (more than 1 SD fromthe mean) of the abnormal electrograms. To make surethese criteria were not too rigid abnormal electrogramswere also analyzed as a group.

Electrograms having late activation or exhibiting

TABLE 5Analysis of electrographic distribution, sensitivity, specificity, and positive predictive value in patients with one morpho-logically distinct ventricular tachycardia

Positive predictiveSpecificity (for site value (for site of

Sensitivity other than site origin ofElectrogram type Number (%) (for site of origin) of origin) electrogram type)

Normal 97 (49%) 0/20 (0%) 80/177 (45%) 0/97 (0%)Abnormal 78 (51%) 16/20 (80%) 115/177 (65%) 16/78 (21%)Fractionated 22 (11%) 4/20 (20%) 159/177 (90%) 4/22 (18%)Abnormal late 13 (7%) 4/20 (20%) 168/177 (95%) 4/13 (31%)Fractionated late 12 (6%) 2/20 (10%) 167/177 (94%) 2/12 (17%)Longest 20 (10%) 2/20 (10%) 159/177 (90%) 2120 (10%)

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NSR1

aVF

VJ

RVA

1 ,- FL

2- .A AL

3 g AA

5 ~~~~~N

6 it N

7 t AL

9 NN

9 ~~~~~~~FL

VT1

oVF

VARVA +h

8

A10- 1011 11

12 12

TIME. tIME

FIGURE 3. Analog map from a patient in sinus rhythm (left) and duringventricular tachycardia (right). Three surface leads (I, aVF, and Vj) areaccompanied by one right ventricular apical (RVA) recording and 12 (1to 12) left ventricular endocardial recordings. Time line is on the bot-tom. The dotted vertical line denotes the onset of surface QRS activity.The asterisk at site 2 during sinus rhythm denotes the site of origin ofventricular tachycardia (arrow, site 2 ventricular tachycardia). The let-ters at the end of the sinus rhythm electrograms denote the type ofelectrogram (N = normal; A = abnormal; F = fractionated; and L =late).

late potentials are believed by some investigators to besignificant.5' 16-1 Previous work from our laboratoryhas demonstrated that normal endocardial bipolar elec-trograms do not extend beyond the first 50% of thesurface QRS complex.6 We therefore elected to defineas late any electrogram that extended beyond the sur-face QRS complex. Again the intent was to best deter-mine the significance of this finding.The last type of electrogram analyzed was the long-

est electrogram recorded by endocardial mapping.Long electrograms may represent slow conduction,which is one of the requirements for reentry andreentry is presumed to be the mechanism of sustainedventricular tachycardia. It is conceivable that the siteof origin exists near this area, but an obvious limitationexists in the use of this electrographic characteristic inpatients who have tachycardias of more than one mor-phologic type originating from nonadjacent sites.

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Another electrogram reported to be a useful markerfor ventricular tachycardia is the "split" or "doublepotential"5 electrogram.3 1'17,18 This electrographicfinding was observed so rarely during endocardialcatheter mapping that it was not suitable for use in theanalysis. This may be a function of the interelectrodedistance used in this investigation or of the number ofsampling sites available.

Analysis of sites of origin. The electrograms from thesites of origin were characterized by lower amplitudeand longer duration. However, considerable overlapexisted with the other electrograms so that this findingalone would not be helpful in distinguishing betweenrecordings from sites of origin and those from othersites.The electrograms from the sites of origin were gen-

erally abnormal (86%). This is in accord with whatprevious investigators have characterized the left ven-tricular electrograms in this patient population.4'9Two findings were striking in the analysis of the site

of origin. First, a completely normal electrogram wasobtained from the site of origin 14% of the time (14patients, 16 morphologically distinct ventriculartachycardias). This finding is not surprising since ven-tricular tachycardia can arise from normal left ventri-cles. Electrograms recorded from these normal leftventricles show no difference between the site of originvs non-site of origin. * The second important findingwas that the electrograms of the left ventricular endo-cardium that were not from sites of origin were abnor-mal 50% of the time. These two facts have to be con-sidered if the application of localized directed surgeryis being considered.

Predictive value. Mapping in patients during sinusrhythm, if it is to be clinically useful, must be able toaid in the localization of the site of origin of ventriculartachycardia. Although abnormal electrograms weresensitive (86%) they lacked specificity (50%). Thevarious other types of abnormal electrograms hadhigher specificity but very low sensitivity. None of thetypes of electrograms demonstrated a positive predic-tive value of greater than 33% and an attempt to com-bine the various types would still fail to give a positivepredictive value of greater than 40%.

There are a number of possible explanations for thefact that the mapping, during sinus rhythm, of endo-cardial electrograms does not predict site of origin ofventricular tachycardia. Our patient population had de-pressed left ventricular function (mean- ejection frac-tion of <30%) with diffuse mycocardial disease,

*Cassidy DM, et al: Unpublished observations.

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which typifies patients with recurrent sustained ven-tricular tachycardia. The electrograms recorded, re-gardless of type, may simply reflect this diffuse myo-cardial disease. The size and depth of the actualanatomical circuit has not been ascertained with thecurrently available techniques. Recordings obtainedduring endocardial catheter mapping may reflect activ-ity outside this circuit, thereby rendering such infor-mation less useful. Finally, conduction velocity andactivation patterns during sinus rhythm at the recordedsite of origin of ventricular tachycardia may not belinear, so that the assumption that such electrogramsare a marker of the slow conduction necessary forreentry may not be valid.

Limitations. A major limitation of this study is relatedto the number of points sampled. Although a maxi-mum of 12 sites were used for this analysis, thesevalues were derived from up to 32 samples in somepatients. This, however, may still not be enough. It isconceivable that if a much larger sample could beobtained the results would be different. However, alimited number of points can be sampled with endocar-dial catheter mapping during sinus rhythm, and it isthis method that must be used clinically. Also, prelimi-nary data obtained with intraoperative mapping underdirect visualization support our findings.'3A second limitation related to the technique of cath-

eter mapping involves precise localization of the cath-eter position, which can be difficult. Each location wasconfirmed in at least three fluoroscopic positions in thepresence of two independent physicians experiencedwith the endocardial mapping scheme. When possiblethe catheter was maintained in the same position forrecording of the sinus rhythm and ventricular tachycar-dia electrograms; this was accomplished by startingand stopping the tachycardia. Otherwise the catheterwas respositioned each time to the area from which arecording had previously been made. An earlier studyfrom this laboratory showed a good correlation be-tween results of catheter and operative mapping, sug-gesting reasonable reproducibility of this technique. '9Finally, when more than one electrogram was obtainedfrom an area the average value was used in the analy-sis. We therefore believe that adherence to these guide-lines has minimized the chance of an error that couldresult from catheter mispositioning.

It might be argued that the criteria selected for someof the types of electrogram were tbo rigid, but if sig-nificant differences are to be found, they should befound with the use of the most abnormal electrograms.It should be noted that if intermediate criteria had beenchosen some gain in sensitivity would have resulted,

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but at the expense of specificity and with no significantimprovement in positive predictive value.

This analysis was performed on a selected popula-tion. All patients had coronary artery disease and leftventricular aneurysms. The application of these resultsto other patient populations with ventricular tachycar-dia may not be justified.We conclude that surgical therapy of ventricular

tachycardia based on results of endocardial cathetermapping during sinus rhythm would lead to excision ofa larger area of endocardium than that based on resultsof mapping during ventricular tachycardia. In addi-tion, not all sites of origin would be excised if onlythose showing abnormality on the map during sinusrhythm were selectively removed.

References1. Josephson ME, Harken AH, Horowitz LN: Endocardial excision: a

new surgical technique for the treatment of recurrent ventriculartachycardia. Circulation 60: 1430, 1979

2. Josephson ME, Horowitz LN, Farshidi A, Spear JF, Kastor JA,Moore EN: Recurrent sustained ventricular tachycardia. 2. Endo-cardial mapping. Circulation 57: 440, 1978

3. Josephson ME, Horowitz LN, Spielman SR, Waxman HL, Green-span AM: Role of catheter mapping in the preoperative evaluationof ventricular tachycardia. Am J Cardiol 49: 207, 1982

4. Weiner I, Mindich B, Pitcon R: Determinants of ventricular tachy-cardia in patients with ventricular aneurysms: results of intraopera-tive epicardial and endocardial mapping. Circulation 65: 856, 1982

5. Klein H, Kard RB, Kouchoukos NT, Zorn GL Jr, James TN,Waldo AL: Intraoperative electrophysiologic mapping of the ven-tricles during sinus rhythm in patients with a previous myocardialinfarction. Circulation 66: 847, 1982

6. Cassidy DM, Vassallo JA, Marchlinski FE, Buxton AE, UnterekerWJ, Josephson ME: Endocardial mapping of sinus rhythm in hu-mans with normal left ventricles: activation patterns and character-istics of electrograms. Circulation (in press)

7. Josephson ME, Horowitz LN, Farshidi A, Kastor JA: Recurrentsustained ventricular tachycardia. I. Mechanisms. Circulation 57:431, 1978

8. Mason JW, Stinson EB, Winkle RA, Oyer PE, Griffin JC, RossDL: Relative efficacy of blind left ventricular aneurysm resectionfor the treatment of recurrent ventricular tachycardia. Am J Cardiol49: 241, 1982

9. Untereker WJ, Spielman SR, Laskey W, Greenspan AM, Hirsh-feld JW, Goldberg S, Horowitz LN, Kastor JA, Josephson ME:The endocardial electrogram as a predictor of wall motion. Circula-tion 62 (suppl II): 11-249, 1980

10. Gardner PI, Ursell PC, Fenoglio JJ, Wit AL: Anatomical andelectrophysiological basis for electrograms showing fractionatedactivity. Circulation 66 (suppl II): II-78, 1982

11. Waldo AL, Kaiser SGA: A study of ventricular arrhythmias associ-ated with acute myocardial infarction in the canine heart. Circula-tion 42: 1222, 1973

12. Boineau JP, Cox JL: Slow ventricular activation in acute myocardi-al infarction: a source of reentrant premature ventricular contrac-tions. Circulation 43: 702, 1973

13. Kienzle MG, Falcone RA, Kempf FC, Miller JM, Harken AH,Josephson ME: Intraoperative endocardial mapping: relation offractionated electrograms in sinus rhythm to endocardial activationin ventricular tachycardia -surgical implications. J Aol CollCardiol 1: 582, 1983

14. Waldo AL, Arciniegas JG, Klein H: Surgical treatment of life-threatening ventricular arrhythmias: the role of intraoperative map-ping and consideration of the presently available surgical tech-niques. Prog Cardiovasc Dis 23: 247, 1981

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D M Cassidy, J A Vassallo, A E Buxton, J U Doherty, F E Marchlinski and M E Josephsonventricular tachycardia.

The value of catheter mapping during sinus rhythm to localize site of origin of

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