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Importance of Preexcited QRS MorphologyDuring Induced Atrial Fibrillation to theDiagnosis and Localization of Multiple

Accessory PathwaysLameh Fananapazir, MD, Lawrence D. German, MD, John J. Gallagher, MD,

James E. Lowe, MD, and Eric N. Prystowsky, MD

The present investigation evaluates the ability of several electrocardiographic (ECG) andelectrophysiologic methods to identify multiple accessory pathways in 47 patients in whom thepresence and sites of multiple accessory pathways were confirmed intraoperatively. To establishECG features that suggested the presence of multiple accessory pathways in these patients, weinitially studied the 12-lead ECG during maximal preexcitation in 101 patients with singleaccessory pathways. Distinctive 12-lead ECG patterns were noted for six defined anatomicareas around the right and left atrioventricular groove. Multiple preexcited QRS morphologies,each typical for a separate accessory pathway, and atypical preexcited QRS morphologies wererecorded during atrial fibrillation in 31 of 47 (66%) patients with multiple accessory pathways.By comparison, the ECG during sinus rhythm and rapid atrial pacing identified 14 (32%) and26 (55%) of the patients, respectively. In 12 (26%) patients in whom evidence for multipleaccessory pathways was absent from endocardial mapping data, atrial fibrillation provided thediagnosis. In five (11%) patients, atrial fibrillation was the only method that demonstrated thepresence of multiple accessory pathways. A combination of ECG findings during atrialfibrillation and rapid atrial pacing plus endocardial mapping data identified 43 (91%) of thepatients with multiple accessory pathways. There were two unique fusion patterns on the12-lead ECG that were characteristic of specific multiple accessory pathway combinations. Of20 patients with posteroseptal plus right free wall accessory pathways, 15 had markedlynegative A waves in leads II, III, and aVF and a QS or rS pattern in leads V1-V6, and two of fourpatients with left lateral plus left anterior accessory pathways had positive A waves in leads II,

III, and aVF, a negative A wave in aVL, an rR pattern in V1, and an R pattern in V2-V6.Induction of atrial fibrillation is valuable in detecting the presence and sites of multipleaccessory pathways and should be a standard part of the electrophysiologic study of patientswith ventricular preexcitation, especially when surgical ablation of the accessory pathway iscontemplated. (Circulation 1990;81:578-585)

A dvances in the nonpharmacologic managementof patients with the Wolff-Parkinson-Whitesyndrome require accurate determination of

the number of accessory pathways present and theircorrect anatomic locations. Multiple accessory path-ways occur in approximately 13% of patients withWolff-Parkinson-White syndrome,' yet few data areavailable regarding the relative merits of variouselectrophysiologic and electrocardiographic tech-

From the Division of Cardiology, Department of Medicine,Duke University Medical Center, Durham, North Carolina.Address for reprints: Eric N. Prystowsky, MD, Director, Clinical

Electrophysiology Lab., Northside Cardiology, 8402 HarcourtRoad, Indianapolis, IN 46260.

Received March 23, 1989; revision accepted October 12, 1989.

niques to uncover the presence or locations of thesepathways.The purpose of the present investigation was two-

fold. The first was to determine the contribution ofpreexcited QRS morphology during induced atrialfibrillation to the diagnosis of multiple accessorypathways and, second, to characterize the 12-leadQRS morphological features of specific combinationsof multiple accessory pathways.

MethodsThe aim of this study was to test the ability of the

12-lead electrocardiogram (ECG) to diagnose andlocate multiple accessory pathways. Therefore, we

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Fananapazir et al Multiple Accessory Pathway Localization 579

initially developed ECG criteria for the presence ofsingle accessory pathways in a group of patients(population A) with intraoperative confirmation ofpathway location. These ECG definitions were usedretrospectively to determine the frequency withwhich the ECG indicated the presence of multipleaccessory pathways in a separate group of consecu-tive patients with intraoperatively proven multipleaccessory pathways (population B).

Multiple accessory pathways were defined duringsurgery as two distinct areas of early activation of theatrium or ventricle separated by later activation timesin between. Although broad areas of early activationmay represent multiple accessory pathways, for thepurpose of this study, these patients were not included.Patients in whom the only evidence for multiple path-ways was earliest anterograde and retrograde activationsites that were separated by a few centimeters were alsonot included, since pathways may course diagonallyacross the atrioventricular groove.

Population APopulation A included 101 consecutive patients

(66 males; 32±15 years) with Wolff-Parkinson-Whitesyndrome who underwent epicardial mapping andsuccessful ablation of single accessory pathways atDuke University Medical Center since 1980. Patientswho had accessory pathways conducting only in theretrograde direction or congenital heart disease wereexcluded from this study.

Population BPopulation B included 47 consecutive patients with

multiple accessory pathways who underwent success-ful surgical mapping and ablation of multiple acces-sory pathways at Duke University Medical Centersince 1976. Their clinical characteristics are pre-sented in Table 1.

Electrocardiographic AnalysisTwelve-lead ECGs were recorded on a three-

channel ECG machine (Marquette 3050) at a paperspeed of 25 mm/sec during 1) normal sinus rhythm(at least two 12-lead ECGs were available for eachpatient before insertion of catheters at the electro-physiologic study); 2) right atrial and coronary sinuspacing at cycle lengths of 500 msec, 400 msec, and300 msec (to maximize preexcitation); and 3) atrialfibrillation. ECG leads I, II, III, V1, and V6 wererecorded simultaneously and continuously duringatrial fibrillation with intracardiac electrograms fromthe right atrium, coronary sinus, His bundle area, andright ventricle. Maximal preexcitation was defined asa QRS duration of 0.14 seconds or more.

Population A. Accessory pathways were localizedto 10 epicardial-mapped sites around the atrioven-tricular groove (Figure 1). There were no patients inthis series who had a left anterior accessory pathwayas the only pathway present. The 10 sites could begrouped into six anatomic areas based on similarECG features and the most frequently occurring

TABLE 1. Clinical Characteristics of Patients With MultipleAccessory Pathways (Population B)

47n

SexMalesFemales

Age (yr)Symptoms

PalpitationsSyncopeCardiac arrest/VF

Number of multiple accessorypathways per patientTwoThree

Associated cardiac abnormalitiesEbstein's anomalyAtrial septal defectMitral valve prolapseCardiomyopathy

2819

29±+13

475

12

443

9311

VF, ventricular fibrillation.

12-lead ECG morphology (present in >75% ofpatients) during maximal preexcitation was noted foreach accessory pathway area (Figure 1). The sponta-neous cycle length, PR interval, and QRS width weremeasured in normal sinus rhythm for each epicardialsite of accessory pathway. The PR interval and QRSduration were the shortest and longest determina-tions, respectively, in any 12-lead ECG lead.

Population B. The ECG was examined duringnormal sinus rhythm, rapid right atrial or coronarysinus pacing, and atrial fibrillation to determine thefrequency with which the following were recorded: 1)two or more preexcited QRS morphologies, eachtypical of a separate accessory pathway and 2) pre-excited QRS morphologies that were atypical of anysingle accessory pathway location and thus suggestedanterograde conduction with fusion over more thanone accessory pathway.

Electrophysiologic StudiesAs described previously,2,3 after informed con-

sent was obtained, all patients underwent detailedfour-catheter electrophysiologic investigationsbefore surgery, in the fasting, nonsedated, anddrug-free state. Endocardial mapping of retrogradeatrial activation near the right and left atrioventric-ular groove was performed during right ventricularpacing and reciprocating atrioventricular tachycar-dia using standard catheter techniques.3,4 Attemptswere made to induce sustained (>30-second dura-tion) atrial fibrillation in all patients using burstatrial pacing at cycle lengths of 180-220 msec if itdid not occur spontaneously.

Intraoperative Epicardial MappingDetails of our epicardial mapping techniques have

been described previously.5 The area of atrial inser-

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580 Circulation Vol 81, No 2, February 1990

V1V2,V3 V4,V5,V6

,M

V1,v2,v3 V4,v5,v6

AM*u

AJ LUA~

1

,vl,v2v v4.v5.v6,'3 4'u'

1

',

v1,v2,v3 V4,v5,v6

V1,v2,v3 v4,v5,v6

FIGURE 1. Diagrammatic representa-tion of ten epicardial single accessorypathway sites mapped at surgery and sixanatomic areas with distinctive electro-cardiographic pattems during maximalpreexcitation. RAS/RA, right anterosep-tal or right anterior accessorypathways;RAL/RL, right anterolateral or rightlateral accessory pathways; RP/RPL,right posterior or right posterolateralaccessory pathways; PS, posteroseptalaccessory pathways; LPL/LP, left pos-terolateral or left posterior accessorypathways; LL, left lateral accessorypathways; (+), positive A wave; (-),negative A wave; (±), isoelectric Awave.

ypikMA

tion of an accessory pathway was determined bylocating the earliest ventriculoatrial conduction timeduring right ventricular pacing and orthodromicreciprocating atrioventricular tachycardia, and theventricular insertion site was identified as the earliestsite of ventricular activation during atrial pacing inthe presence of preexcitation.

Statistical AnalysisStudent's t test was used for comparison of data. A

p value of less than 0.05 was regarded as showing a

significant difference.

ResultsPopulation A

There were no significant differences in sinus cyclelength between the various pathway locations. ThePR interval and QRS duration distinguished onlywidely separated accessory pathways; patients withleft lateral accessory pathways had significantly(p<0.01) longer PR intervals and shorter QRS dura-tions compared with patients with right-sided or

posteroseptal accessory pathways (Table 2). A PRinterval of >0.12 seconds was present in only 2 of 39(5%) patients with right-sided or posteroseptalaccessory pathways but occurred in 23 of 62 (37%)patients with left free-wall accessory pathways. Max-

imal preexcitation (QRS>0.14 seconds) was presentin 27 of 39 (69%) patients with right-sided andposteroseptal accessory pathways but was absent in52 of 62 (84%) patients with left posterolateral or leftlateral accessory pathways. The PR intervals andQRS durations of right-sided and posteroseptalaccessory pathways were not significantly different.Similarly, there were no significant differencesbetween the PR intervals and QRS durations of leftposterior or left posterolateral accessory pathwaysand left lateral accessory pathways.

Twelve-Lead ECG Characteristics of Single AccessoryPathways During Maximal Preexcitation

Although the 101 accessory pathways were locatedin 10 epicardial sites, distinctive maximally preex-cited 12-lead ECGs were recognized for only sixbroad areas around the atrioventricular groove,based on the A wave axis of the first 40 msec of theQRS duration (Figure 1 and Table 3).The ability of the maximally preexcited 12-lead

ECG to predict the sites of single atrioventricularpathways is shown in Table 3. The overall sensitivityand specificity of the 12-lead ECG for defining thelocation of accessory pathways were 89% and 93%,respectively. Of note is that in patients in whom themaximally preexcited 12-lead ECG failed to localize

f

1

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Fananapazir et al Multiple Accessory Pathway Localization 581

TABLE 2. Comparison of Electrocardiographic Data During Normal Sinus Rhythm in 101 Patients With Single Accessory Pathways(Population A)

Electrocardiographic intervals (sec) Number of patients withAP site n RR PR QRS PR>0.12 sec QRS<0.14 sec

RAS/RA 7 0.83+±0.21 0.09+0.02 0.14+0.03 0 (0%) 2 (29%)RAL/RL 9 0.84±0.20 0.09±0.02 0.14±0.03 1 (11%) 2 (22%)RPL/RP 12 0.90±0.21 0.10±0.03 0.14±0.03 1(8%) 3 (25%)PS 11 0.84±0.20 0.09±0.01 0.14±0.02 0 (0%) 5 (45%)LP/LPL 37 0.80±0.16 0.12+0.03* 0.11±0.02* 14 (38%) 32 (86%)LL 25 0.81±0.23 0.12±0.02* 0.12±0.02* 9 (36%) 20 (80%)

AP, accessory pathway; sec, second; RAS/RA, right anteroseptal or anterior; RAL/RL, right anterolateral or lateral; RPL/RP, rightposterolateral or posterior; PS, posteroseptal; LP/LPL, left posterior or posterolateral; LL, left lateral.

*p<0.05 compared with right-sided or posteroseptal accessory pathways.

correctly the accessory pathway site, the ECG fea-tures were those of an adjacent area.

Population BTwo ECG features suggested the presence of

multiple accessory pathways. The first was theappearance of more than one preexcited QRS mor-phology, each typical of a separate accessory path-way, that was recorded during 1) sinus rhythm,usually on different occasions, 2) atrial fibrillation(Figure 2), or 3) pacing from different right atrial orcoronary sinus sites (Figure 3). The second feature

was a 12-lead ECG pattern during normal sinusrhythm, rapid right atrial or coronary sinus pacing, oratrial fibrillation that was atypical of any of the sixcharacteristic patterns for single accessory pathways,indicating anterograde conduction with fusion overmore than one accessory pathway (Figures 4 and 5).In many instances, a fusion pattern diagnosed multi-ple accessory pathways but failed to localize individ-ual pathways. However, two unique fusion patternswere recognized (Figure 5).

Right free wall plus posteroseptal accessory path-ways had markedly negative A waves in leads II, III,

TABLE 3. Ability of Maximally Preexcited QRS Morphology to Predict Epicardial Sites of Single Accessory Atrioventricular Pathways

AP site n Maximal preexcited QRS morphology Sensitivity (%) Specificity (%)

RAS/RA 7 I, II, III, aVF; (+) A 100 99V1-V4; qS/rSV5-V6; R

RAL/RL 9 1, 11, aVF; (+) A 89 99III; (±)/(-)AtV1-V4; rSV5-V6; R

RPL/RP 12 I; (+) A 92 99II; (-)/(±)I(+) AaVF,III; (-)AV1-V4; rSV5-V6; R

11

37

25

I; (+) AII; (-)/(+)/(+) AaVF, III; (-) AV1; (±)/(-)V2-V6; RI, II; (-)/(±)/(+) AaVF, III; (-) AV1-V6; RaVL; qSI; rSII, aVF, III; (+) AV1-V6; R

91 99

78 95

100 100

PS

LP/LPL

LL

Total 101 89 93

AP, accessory pathway; (+), positive A wave in initial 40 msec of QRS; (-), negative A wave in initial 40 msec of QRS; (±), isoelectricA wave in initial 40 msec of QRS; RAS, right anteroseptal; RA, right anterior; RAL, right anterolateral; RL, right lateral; RPL, rightposterolateral; RP, right posterior; PS, posteroseptal; LP, left posterior; LPL, left posterolateral; LL, left lateral.

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582 Circulation Vol 81, No 2, February 1990

FIGURE 2. Tracings of the identification ofa left posterior and left lateral accessory path-way during induced atrial fibrillation at elec-trophysiologic study. Simultaneous tracingsfrom top to bottom are electrocardiographicleads I, II, III, V1. and V6 and intracardiacelectrograms from the high right atrium(HRA), His bundle area (HBE), right ventri-cle (RV), and proximal (PCS) and distal(DCS) coronary sinus. The first accessorypathway morphology (API) represents con-duction over a far left lateralpathway that canhave apredominant S wave in V6. The secondpathway (AP2) was located in a left posterorposition. N, normal QRS complex; H, Hisbundle deflection.

and aVF with a QS or rS pattern in leads V1-V6. Thisfusion pattern was present during atrial fibrillation in15 of 20 (75%) patients with this combination ofmultiple accessory pathways.

Left lateral plus left anterior accessory pathwaysdemonstrated an M-shaped R pattern in lead V1, anR pattern in V2-V6, and positive 1 waves in leads II,III, and aVF, with a negative A wave in aVL. Thispattern was present in two of four patients with thiscombination of multiple accessory pathways duringatrial fibrillation.

Endocardial Mapping in Patients With MultipleAccessory Pathways

The frequency with which endocardial mappingdata agreed with intraoperative epicardial mappingfindings are shown in Table 4 for the various combi-nations of multiple accessory pathways. Overall,endocardial mapping during electrophysiologic stud-ies correctly identified the sites and numbers of mul-tiple accessory pathways in 27 (57%) patients. The

I,1,111 AVR,AVL,AVF Vl V2 V3 V4,V5,V6

t~

FIGURE 3. Recordings of a 12-lead elec rc iogram

0t i>- t--l-+W.-, i1 :--;L--ti 1 htXia,'

H',fi 1;1 ,X

- .J=7 e eAL J-Af XJ1i1

FIGURE 3. Recordings of a 12-lead electrocardiogramrecorded during right atrialpacing showing two distinct preex-cited QRS morphologies with features indicating the presenceofalternate anterograde conduction over a posteroseptal and aleft lateral accessory pathway.

extra numbers of patients correctly identified by elec-trocardiographic findings are also shown in Table 4.

Contribution ofAtrial Fibrillation to the Diagnosis ofMultiple Accessory Pathways (Table 4)

Forty-two of the 47 patients with multiple acces-sory pathways were capable of anterograde conduc-tion over more than one accessory pathway. Of these,induction of atrial fibrillation was attempted in allpatients but was successful in 37. Analyzing all 47patients, atrial fibrillation indicated the presence ofmultiple accessory pathways in 31 of 47 (66%)patients compared with 14 of 47 (30%) patientsidentified during normal sinus rhythm and 26 of 47(55%) patients identified during rapid right atrial orcoronary sinus pacing. A combination of atrial fibril-lation plus rapid right atrial or coronary sinus pacingidentified 40 of 47 (85%) patients. The combinationof atrial fibrillation, rapid right atrial or coronarysinus pacing, and endocardial mapping identified 43

I, 1, AVR, AVL, AVF V,, V2, V3 V4, V5, V6

FIF ~ ~

T~~L

FIGURE 4. Recordings of a 12-lead electrocardiogramrecorded during atrialfibrillation showing abrupt alterations inA wave morphologies (see arrows) as well as a QRS pattemin some beats that is atypical for any single accessory pathwayin a patient with a right free wall accessory pathway plus aposteroseptal accessory pathway.

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Fananapazir et al Multiple Accessory Pathway Localization

LI,LM AVR,AVL,AVF VlYV2V3 V4,V5

:-1:g::+r~~A -i

o~~~~~~~~~~L~T14t

P S pius s

Ill,m AVR,AVL,AVF V, V2 V3 V4 V5s V6{ t I _ _ _ .~~~~~~~~~~~~~~~~~~~~~~~~~. .... . .....FIGURE 5. Recordings of 12-lead electrocardiographic fusion pattems characteristic of two combinations of multiple accessorypathways. A right free wallplus posteroseptal accessory pathway pattem is identified by markedly negative A waves in leads II, III,and aVF and poor progression ofR waves in leads V1-V6. A left lateral accessory pathway plus a left anterior accessory pathwaypattem is characterized by the presence of a preexcited M-shaped QRS in V,, an Rpattem in V2-V6, negative A waves in aVL, andpositive A waves in leads II, III, and aVF.

of 47 (91%) patients with multiple accessory path-ways. Atrial fibrillation provided the diagnosis ofmultiple accessory pathways in 12 of 47 (26%)patients who had one or more accessory pathwaysthat were not evident after detailed endocardialmapping, and in 5 of 47 (11%) patients atrial fibril-lation was the only means during the electrophysio-logic study by which the diagnosis of multiple acces-sory pathways was established.

DiscussionSurgical interruption6 or catheter ablation7 of

accessory pathways require a clear delineation of the

site or sites of all accessory pathways present. Vari-ous attempts2,8-13 have been made to correlate elec-trocardiographic findings in patients with Wolff-Parkinson-White syndrome with anatomicallocations of accessory pathways. This endeavour hasbeen largely confined to description of electrocardio-graphic features in patients with single accessory

pathways.Our findings indicate that analysis of the QRS axis

in the limb leads and the QRS morphology in theprecordial leads during maximal preexcitation can

predictably distinguish between six anatomic sites of

TABLE 4. Ability of Various Methods to Identify Multiple Accessory Pathways

NSR RAP AF AF+RAP

AP sites n F 2 F/2 F 2 F/2 F 2 F/2 AF+RAP EM AF+EM +EM

PS+RFW 20 7 1 8 12 1 12 15 5 15 17 12 17 19

PS+LFW 10 0 1 1 0 1 1 2 4 4 7 6 8 8

LP+LL 4 0 1 1 0 1 1 1 1 2 3 0 2 3

LL+LA 4 1 0 1 2 2 4 2 1 3 4 2 4 4

Others 9 3 1 3 7 3 8 7 4 7 9 7 8 9

Total 47 11 4 14 21 8 26 27 15 31 40 27 39 43

(30%) (55%) (66%) (85%) (57%) (83%) (91%)

AP, accessory pathway; F, fusion A wave morphology; 2, >2 A wave morphologies, each typical for an accessory pathway; F/2, fusion QRSpattern and/or .2 A wave morphologies; AF, atrial fibrillation; RAP, rapid right atrial or coronary sinus pacing; EM, endocardial mapping;PS, posteroseptal; RFW, right free wall; LFW, left free wall; LP, left posterior; LL, left lateral; LA, left anterior; NSR, normal sinus rhythm.

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584 Circulation Vol 81, No 2, February 1990

single accessory pathways with an overall sensitivityof 89% and specificity of 93%. Although electrocar-diograms in patients with right-sided or posteroseptalaccessory pathways often showed maximal preexcita-tion in sinus rhythm, induction of atrial fibrillation orright atrial or coronary sinus pacing was required toachieve maximal preexcitation in most patients withleft-sided pathways. Of note, our data also demon-strate that a PR interval of greater than 0.12 secondsalmost always identifies a left free wall accessorypathway.

Recognition of 12-lead electrocardiographic pat-terns that were typical for single accessory pathwaysprovided the basis for electrocardiographic identifi-cation of multiple accessory pathways.Two electrocardiographic features indicated the

presence and often the sites of multiple accessorypathways. These were the occurrence at varioustimes of more than one typical preexcited QRSmorphology, due to preferential or exclusive antero-grade conduction over one or another accessorypathway, and second, simultaneous preexcitation ofthe ventricle by anterograde conduction over morethan one accessory pathway resulting in a QRSpattern that was atypical for any single accessorypathway, but which characterized certain combina-tions of multiple accessory pathways. Our studyunderlines the usefulness of recording several 12-lead ectrocardiograms during normal sinus rhythmon different occasions during and at electrophysio-logic study as well as during pacing at various cyclelengths and from different atrial sites. Careful reviewof a patient's electrocardiograms taken over time notinfrequently demonstrates two distinct preexcitedQRS morphologies recorded on separate days.

Atrial fibrillation plays a key role in the diagnosisof multiple accessory pathways. Of all the techniquesavailable to identify and locate accessory pathways,analysis of electrocardiographic QRS morphologyduring atrial fibrillation was frequently more success-ful in uncovering the presence of multiple accessorypathways. In fact, atrial fibrillation was the onlymethod that diagnosed multiple accessory pathwaysin 11% of patients. Clearly, the longer the electro-cardiogram is recorded during atrial fibrillation, thegreater the chance of observing QRS morphologiesthat indicate multiple accessory pathways. We rou-tinely obtained several 12-lead electrocardiogramsduring atrial fibrillation as well as recorded continu-ous and simultaneous tracings from five surface elec-trocardiographic leads and multiple intracardiacleads. Since the QRS morphologies in V1 and V2 areoften critical to the differentiation of posteroseptalaccessory pathways from accessory pathways inneighboring sites, we suggest that these two leads berecorded throughout the study in addition to three tofour other leads. Further, we now routinely recordcontinuously long rhythm strips of all 12-lead elec-trocardiographic leads during atrial fibrillation at

The mechanisms by which multiple accessory path-ways become manifest during atrial fibrillation areunclear but probably relate to several factors includ-ing variable excitation wavefronts, alterations of con-duction and refractoriness of the accessory pathwaysand their atrial and ventricular connections, andpossibly supernormal and concealed conduction.1415Regarding the latter point, Chen and Prystowsky15recently demonstrated the effect of retrograde con-cealed conduction on subsequent anterograde acces-sory pathway conduction during atrial fibrillation.An important limitation of the use of atrial fibril-

lation in the diagnosis of multiple accessory pathwaysis the occurrence of bundle branch block and prema-ture ventricular complexes that may be confused withmultiple preexcited QRS complexes. However, thisproblem can be minimized by simultaneous recordingof a His bundle electrogram. Regarding differentia-tion of catheter-induced ventricular complexes frompreexcited complexes, it is important to determinefrequently and fluoroscopically that the intracardiaccatheters have not become displaced during atrialfibrillation. We also find it useful to compare QRScomplexes during atrial fibrillation with thoserecorded during right ventricular pacing with cathe-ter(s) in the same sites at both times. Further, wideQRS complexes that "suddenly" disappear withremoval of the ventricular catheters during continuedatrial fibrillation suggest a diagnosis of catheter-induced ventricular complexes.

Atrial fibrillation is also induced at electrophysio-logic studies in patients with Wolff-Parkinson-Whitesyndrome to determine the shortest preexcited RRinterval during this arrhythmia and to risk stratify foroccurrence of sudden cardiac death. In this context,it has been reported16 that the shortest preexcitedRR intervals are shorter in patients with multipleaccessory pathways compared with patients who hadsingle accessory pathways.

References1. Colovita PG, Packer DL, Pressley JC, Ellenbogen KA, O'Cal-

laghan WG, Gilbert MR, German LD: Frequency, diagnosisand clinical characteristics of patients with multiple atrioven-tricular accessory pathways. Am J Cardiol 1987;59:601-606

2. Gallagher JJ, Pritchett ELC, Sealy WC, Kasell J, Wallace AG:The pre-excitation syndromes. Prog Cardiovasc Dis 1978;22:285-327

3. Prystowsky EN: Diagnosis and management of the preexcita-tion syndromes. Curr Probl Cardiol 1988;13:231-310

4. Gallagher JJ, Pritchett ELC, Benditt DG, Tonkin AM, Camp-bell RWF, Dugan FA, Bashore TM, Tower A, Wallace AG:New catheter techniques for analysis of the sequence ofretrograde atrial activation in man. Eur J Cardiol 1977;6:1-14

5. Gallagher JJ, Kasell J, Sealy WC, Pritchett ELC, Wallace AG:Epicardial mapping in the Wolff-Parkinson-White syndrome.Circulation 1978;57:854-856

6. Sealy WC, Gallagher JJ: Surgical problems with multipleaccessory pathways of atrioventricular conduction. J ThoracCardiovasc Surg 1981;81:707-712

7. Morady F, Scheinman MM: Transvenous catheter ablation ofa posteroseptal accessory pathway in a patient with Wolff-Parkinson-White syndrome. N Engl J Med 1984;310:705-707

8. Rosenbaum FF, Hecht HH, Wilson FN: The potential varia-electrophysiologic study. tions of the thorax and esophagus in anomalous atrioventric-

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ular preexcitation (Wolff-Parkinson-White syndrome). AmHeart J 1945;29:281-326

9. Giraud G, Latour H, Puech P: Les troubles de rhythm dusyndrome du Wolff-Parkinson-White. Analyse electrocardio-graphic endocavitare. Arch Mal Coeur 1956;49:102-133

10. Tonkin AM, Wagner GS, Gallagher JJ, Cope CD, Kasell J,Wallace AG: Initial forces of ventricular depolarization in theWolff-Parkinson-White syndrome. Circulation 1975;52:1030-1036

11. Milstein S, Sharma AD, Guiraudon GM, Klein GJ: Analgorithm for the electrocardiographic localization of acces-sory pathways in the Wolff-Parkinson-White syndrome. PACE1987;10:555-563

12. Lindsay BD, Crossen K, Cain ME: Concordance of distin-guishing electrocardiographic features during sinus rhythmwith the location of accessory pathways in the Wolff-Parkinson-White syndrome. Am J Cardiol 1987;59:1093-1102

13. Lemery R, Hamill SC, Holms DR: The value of the resting12-lead electrocardiogram for localizing the site of pre-excitation in patients with Wolff-Parkinson-White syndrome -Discrepancy with previous observation. J Am Coll Cardiol1986;7:6A

14. Chang MS, Miles WM, Prystowsky EN: Supernormal conduc-tion in accessory atrioventricular connections: An electrophys-iologic study. Am J Cardiol 1987;59:852-856

15. Chen P-S, Prystowsky EN: Determinants of accessory pathwayconduction during atrial fibrillation in patients with preexcita-tion syndrome (abstract). Circulation 1988;78:II-23A

16. Klein GJ, Bashore TM, Sellers TD, Pritchett ELC, Smith WM,Gallagher JJ: Ventricular fibrillation in the Wolff-Parkinson-White syndrome. N Engl J Med 1979;301:1080-1085

KEY WORDS * atrial fibrillation * multiple accessory pathways* Wolff-Parkinson-White syndrome

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L Fananapazir, L D German, J J Gallagher, J E Lowe and E N Prystowskydiagnosis and localization of multiple accessory pathways.

Importance of preexcited QRS morphology during induced atrial fibrillation to the

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