Radiofrequency Catheter Ablation of Supraventricular Tachycardia in Children and Adolescents

Radiofrequency Catheter Ablation ofSupraventricular Tachycardia SubstratesAfter Mustard and Senning Operationsfor d-Transposition of the Great ArteriesRonald J. Kanter, MD, FACC,* John Papagiannis, MD,§ Michael P. Carboni, MD,*Ross M. Ungerleider, MD, FACC,† William E. Sanders, MD, FACC,\ J. Marcus Wharton, MD, FACC‡Durham and Chapel Hill, North Carolina, and Athens, Greece

OBJECTIVES The purpose of this study was to determine the efficacy and risks of radiofrequency ablationof various forms of supraventricular tachycardia after Mustard and Senning operations ford-transposition of the great arteries.

BACKGROUND In this patient group, the reported success rate of catheter ablation of intraatrial reentrytachycardia is about 70% with a negligible complication rate. There are no reports of the useof radiofrequency ablation to treat other types of supraventricular tachycardia.

METHODS Standard diagnostic criteria were used to determine supraventricular tachycardia type.Appropriate sites for attempted ablation included 1) intraatrial reentry tachycardia: presenceof concealed entrainment with a postpacing interval similar to tachycardia cycle length; 2)focal atrial tachycardia: a P-A interval #220 ms; and 3) typical variety of atrioventricular(AV) node reentry tachycardia: combined electrographic and radiographic features.

RESULTS Nine Mustard and two Senning patients underwent 13 studies to successfully ablate allsupraventricular tachycardia substrates in eight (73%) patients. Eight of eleven (73%) patientshaving intraatrial reentry tachycardia, 3/3 having typical AV node reentry tachycardia, and2/2 having focal atrial reentry tachycardia were successfully ablated. Among five patientshaving intraatrial reentry tachycardia (IART) and not having ventriculoatrial (V-A) conduc-tion, two suffered high-grade AV block when ablation of the systemic venous portion of themedial tricuspid valve/inferior vena cava isthmus was attempted.

CONCLUSIONS Radiofrequency catheter ablation can be effectively and safely performed for certain supraven-tricular tachycardia types in addition to intraatrial reentry. A novel catheter course is requiredfor slow pathway modification. High-grade AV block is a potential risk of lesions placed inthe systemic venous medial isthmus. (J Am Coll Cardiol 2000;35:428–41) © 2000 by theAmerican College of Cardiology

The Mustard and Senning operations were developed assurgical treatments for transposition of the great arteries.These operations fell into disfavor in part owing to a highincidence of arrhythmias at long-term follow-up. Intraatrialrentry tachycardia (IART) has been reported to occur in 2%to 10% of Mustard and Senning patients at 4 to 10 years’follow-up (1–5). Sudden cardiac death has been reported tooccur late after these operations in 3% to 15% of patients(1,2,6,7), and a rapid ventricular response to paroxysmalatrial tachycardias has been thought to be the cause of death

in many instances. Such morbidity and mortality hasprompted an aggressive treatment philosophy. Older ther-apies have been far from perfect; antiarrhythmic drugs arefraught with proarrhythmic and noncardiac complicationsand with incomplete efficacy; antitachycardia pacing is onlyeffective for slower tachycardias and may accelerate them tomore dangerous, faster ones; and bradycardia pacing isadjunctive therapy, at best (8).

Based upon the high efficacy of radiofrequency catheterablation to treat adults with typical atrial flutter (9,10),several investigators have reported a favorable early experiencein Mustard and Senning patients having IART (11–14). Theseresearchers utilized principles of concealed entrainmentmapping (11–13), identification of nonconducting anatomicbarriers (11,14) and presence of split potentials (13) toablate IART circuits successfully in 70% to 80% of patients(11–13).

From the Departments of *Pediatrics, †Surgery, and ‡Internal Medicine, DukeUniversity School of Medicine, Durham, North Carolina; the §Department ofPediatric Cardiology, Onassis Cardiac Surgery Center, Athens, Greece; and the\Department of Internal Medicine, University of North Carolina at Chapel HillSchool of Medicine, Chapel Hill, North Carolina.

Manuscript received November 17, 1998; revised manuscript received September 3,1999, accepted October 18, 1999.

Journal of the American College of Cardiology Vol. 35, No. 2, 2000© 2000 by the American College of Cardiology ISSN 0735-1097/00/$20.00Published by Elsevier Science Inc. PII S0735-1097(99)00557-4

Although these reports only described experience withIART, other supraventricular tachycardias may occur inpatients with transposition. This report presents a singleinstitution’s experience with radiofrequency catheter abla-tion for various supraventricular tachycardias in patientswho had undergone Mustard or Senning operations.

METHODS

Patient selection. All patients referred to Duke UniversityMedical Center from January 1994 to March 1998 forelectrophysiologic study and radiofrequency catheter abla-tion following Mustard or Senning operations were in-cluded (n 5 10). An eleventh patient (patient 10) under-went his procedure at the University of North CarolinaMemorial Hospital, where the first author (R.J.K.) partici-pated. Patient demographic, surgical, and clinical arrhyth-mia data appear in Table 1. Supraventricular tachycardiahad been documented in all patients, except patient 9, inwhom the history suggested the diagnosis. Informed con-sent was obtained using a protocol approved by the DukeUniversity Institutional Review Board for the first sevenpatients. A standard consent for electrophysiologic studyand catheter ablation was obtained from the last fourpatients.

Anatomic descriptions. All operative reports were re-viewed by a pediatric cardiac surgeon (R.M.U.) with atten-tion to the locations of all incisions and the ultimatelocation of the coronary sinus with respect to the inferiorsuture line of the atrial baffle. Specific handling of thecoronary sinus was described for 10 of the 11 patients (Fig.1). If the baffle suture line kept the coronary sinus ostium inthe systemic venous atrium, the medial isthmus between thetricuspid valve annulus and inferior vena cava was necessar-ily bisected, perhaps with the majority on the systemicvenous side (Fig. 1c). Superiorly, this suture line alwaysdeviates from the tricuspid annulus to avoid the atrioven-tricular (AV) node. Hence, at least part of the medialisthmus would remain on the pulmonary venous side. If thecoronary sinus was incised or other efforts made to redirectthe ostium into the systemic venous atrium surgically, it wasconcluded that the great majority of the isthmus remainedin the pulmonary venous atrium (Fig. 1b). Likewise, if theostium was kept in the pulmonary venous atrium, themedial isthmus remained there as well (Fig. 1a).

The isthmus between the tricuspid valve annulus and theinferior vena cava orifice was arbitrarily divided into medial,

mid, and lateral portions. If the tricuspid annulus were theface of a clock in a left anterior oblique projection, theanterior aspect of the medial isthmus would range from 4:00to 5:00 o’clock, the mid isthmus from 5:00 to 7:00 o’clock,and the lateral isthmus from 7:00 to 8:00 o’clock, with eachportion extending as a wedge posteriorly to the inferior venacava orifice. The relationship of the isthmus subdivisions tothe eustachian ridge was not considered, because the oper-ative reports never mentioned this structure.

Definitions of tachycardia types. Tachycardia types weredetermined by a combination of surface electrocardio-graphic features and intracardiac electrophysiologic charac-teristics.

Intraatrial reentry tachycardia was paroxysmal in onset andtermination and had a regular nonsinus P-wave morphol-ogy. It was inducible by atrial programmed stimulation oratrial burst pacing and had periods of second-degree AVblock with a constant atrial cycle length. The mechanism ofmacroreentry was supported by demonstration of manifestentrainment.

Focal atrial tachycardia (FAT) was different from IART inits surface electrocardiographic appearance and intracardiacelectrogram features. The P waves were discrete, with a clearisoelectric inter-P-wave interval in all leads. Split andfractionated electrograms were not present in regions ofearliest atrial activation, including successful ablation sites.Unlike IART, manifest entrainment could not be demon-strated.

Typical variety of AV node reentry tachycardia was diag-nosed when a regular, narrow-complex tachycardia could beinduced by atrial or ventricular programmed stimulation inassociation with a 1:1 AV relationship, a ventriculoatrial(V-A) interval #70 ms, and concentric atrial activation.Because a His bundle recording could not be consistentlyobtained, standard maneuvers to dissociate ventricular oratrial electrograms from the tachycardia circuit were notpossible. Additional findings supporting the diagnosis in-cluded 1) initiation of tachycardia during atrial extrastimu-lus testing following an AV interval increase of $50 msduring a decrease in atrial prematurity of 10 ms; 2) theobservation that a single atrial extrastimulus initiates tachy-cardia following a double ventricular response; or 3) theability of adenosine to terminate tachycardia following anatrial electrogram.

Technique of electrophysiologic study. Antiarrhythmicmedications were discontinued at least four half-lives beforeeach study. Intravenous propofol was used as a generalanesthetic agent (15), except in Patients 2 and 6, who werestudied under conscious sedation. Hemodynamic measure-ments were obtained in all patients, except Patients 6 and10, in whom echocardiographic evaluation was performed.Diagnostic electrode catheters with close spacing (2 to10 mm) were placed in the left ventricle, systemic venousatrium, and the inferior portion of the systemic venousremnant of the atrial septum in the region of the coronary

Abbreviations and AcronymsAV 5 atrioventricularFAT 5 focal atrial tachycardiaIART 5 intraatrial reentry tachycardiaV-A 5 ventriculoatrial

429JACC Vol. 35, No. 2, 2000 Kanter et al.February 2000:428–41 Tachycardia Ablation in Mustard and Senning Patients

Tabl

e1.

Pat

ient

Dem

ogra

phic

san

dSu

rgic

alan

dA

rrhy

thm

iaH

isto

ry

Pat

ient

Gen

der

Typ

eof

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ial

Swit

ch

Age

atA

tria

lSw

itch

(mon

ths)

Loc

atio

nof

Med

ial

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mus

Fro

mF

igur

e1

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erC

ardi

acD

iagn

oses

Pri

orO

pera

tion

s

Clin

ical

Arr

hyth

mia

s(M

etho

dof

Doc

umen

tati

on)

Fai

led

Ant

iarr

hyth

mic

Dru

gs

Dur

atio

nF

rom

Fir

stT

achy

card

iaSy

mpt

oms

toR

FA

(yrs

)

1M

Mus

tard

761b

VSD

;sev

ere

PS

BA

S(1

day)

;BT

S(4

mos

);V

SDcl

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ean

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t(6

yrs)

with

Mus

tard

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T(E

Rvi

sit)

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7

2M

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tard

251a

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AS

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atch

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rgem

ent

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omy

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supe

rior

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rior

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430 Kanter et al. JACC Vol. 35, No. 2, 2000Tachycardia Ablation in Mustard and Senning Patients February 2000:428–41

sinus ostium. A His bundle recording was only obtainedduring ablation for AV node reentry tachycardia. A fourthdiagnostic catheter, consisting of 5 to 10 bipoles, was placedwithin the systemic venous atrium from the inferior to thesuperior vena cava. In the Mustard patients, signals from theinferior-most bipoles recorded signals from the medialisthmus or right side of the inferior remnant of the atrialseptum, the middle bipoles from the posterior wall of thenative left atrium, and the superior-most bipoles from theright side of the superior remnant of the atrial septum (Fig.2). In the two Senning patients, this catheter mapped theposterior length of the systemic venous tube—inferiorly,from the right side of the atrial septal remnant (due tosurgical septectomy) adjacent to the IVC; then along the

atrial septal flap; and superiorly, to the right side of the atrialseptal remnant adjacent to the superior vena cava (Fig. 2).Patient 11 required transhepatic venous access, becausethere was bilateral iliofemoral venous thrombosis. Eachpatient was heparinized and the activated clotting timemaintained at 250 to 300 s.

Standard pacing maneuvers were performed at baselineand under the influence of isoproterenol at 0.03 to 0.07mg/kg/min. A 4-mm tip ablation catheter (EP Technol-ogies, Sunnyvale, California; or Cordis-Webster, Bald-win Park, California) was then used for mapping pur-poses. Surface lead gains were increased to permitidentification of the P-wave onset, and atria were mappedduring tachycardia for presystolic activity and for splitpotentials. When 1:1 or 2:1 AV conduction was present,adenosine was used to identify P-wave onset. Regions inwhich there was electrical activity preceding P-waveonset were paced at cycle lengths 20 to 40 ms shorter thanthe atrial tachycardia cycle length to determine thepresence of concealed entrainment.

Selection of sites for radiofrequency ablation. IART. Anisthmus of atrial tissue was selected for creation of linearlesions based upon electrophysiologic characteristics andknowledge of the adjacent lines of conduction block, bothnatural and surgical. The presence of atrial presystolicactivity was felt to be necessary, and was accompanied bysplit potentials if the site was adjacent to a suture line.Entrainment with concealed fusion proved that a site wascritical to the IART circuit, if the atrial activation sequencewas identical to that of tachycardia and if the postpacinginterval was #30 ms longer than the IART cycle length(13). Natural barriers to conduction included the superiorand inferior vena cava orifices and the tricuspid and mitralvalve annuli. In Mustard patients, the baffle suture line andthe right atriotomy were also potential lines of conductionblock (Fig. 2). In Senning patients, the surgical anatomy ismore complex, and there were several potential surgical linesof conduction block: 1) the suture line where the atrial septalflap forms a roof over the pulmonary veins; 2) the edge ofthe atrial septal remnant; 3) the suture line where the rightatrial freewall attaches to the atrial septal remnant to formthe roof over the systemic venous tube (Fig. 2, bottom:A–C); and 4) the suture line where the rightward mostsection of the pulmonary venous atrium is attached to theremaining right atrial freewall (Fig. 2, bottom: D–F).

FAT. Foci of earliest atrial activation were sought. Basedupon published data from patients having atrial ectopictachycardia (16), sites activated at least 20 ms prior to theP-wave onset were considered starting points for detailedmapping.

In cases of IART and FAT, radiofrequency ablation wasconsidered successful if energy delivery during the tachycar-dia terminated the tachycardia, and if it could not be

Figure 1. Diagrams of the pulmonary venous atrium followingMustard (a– c) and Senning (d) operations as viewed from a rightanterior oblique projection. They illustrate the variations of surgi-cal handling of the coronary sinus and medial isthmus between theinferior vena cava orifice and the tricuspid valve. (a) Inferior atrialbaffle suture line is placed posterior to the coronary sinus ostium,keeping it and nearly all of the medial isthmus on the pulmonaryvenous side (Patients 2, 10). (b) Suture line is in approximately thesame location as in (a), but the ostium is surgically redirectedposteriorly into the systemic venous atrium (Patients 1, 3, 6, 8). (c)Suture line is placed anterior to the coronary sinus ostium, keepingit and a large portion of the medial isthmus on the systemic venousside (Patients 4, 5). (d) Right atrial freewall edge (arrows), whichserves as a roof over the systemic venous tube, is sutured posteriorto the coronary sinus ostium, similar in location to (a) (Patients 9,11). AVN 5 compact AV node; CSO 5 coronary sinus ostium;TV 5 septal leaflet of tricuspid valve; cross-hatched area 5medial isthmus; shaded area 5 region of “slow” inputs into AVnode; stippled area 5 region of “fast” inputs into AV node.


reinduced for at least 60 min, at baseline and under theinfluence of isoproterenol.

ATRIOVENTRICULAR NODE REENTRY TACHYCARDIA. Ra-diofrequency modification of the slow inputs to the AVnode was attempted using established principles publishedfrom patients having normal hearts (17,18). Access to thetricuspid annulus was possible only using an arterial cathe-ter, which was retroflexed across the tricuspid valve into thepulmonary venous atrium. The catheter was pulled back androtated clockwise until there was a dominant ventricularsignal. Subtle flexion or extension was performed until a His

bundle electrogram was obtained (Fig. 3, left). The catheterwas further extended inferiorly until this electrogram disap-peared (Fig. 3, right). Radiofrequency energy was deliveredat this site during sinus rhythm. Accelerated junctionalrhythm was considered a sensitive indicator of the appro-priateness of the ablation site, and inability to reinduce AVnode reentry tachycardia after 60 min was considered aspecific indicator of successful ablation.

Statistical analysis. Descriptive data are presented as themean 6 SD, or, when appropriate, with 95% confidenceintervals (CI). The Fisher exact test was used to analyze dataon a nominal scale. Data obtained on a continuous scale

Figure 2. Diagrams of surgical anatomy with suture lines and of typical electrode catheter placement in Mustard and Senning patients.All important structures posterior to the level of the tricuspid valve are shown. The pulmonary venous atrium and the systemic venous baffle(cutaway) are illustrated in the Mustard diagram. The circle representing the coronary sinus ostium (CS os) is broken to emphasize itsinconstant relationship with the adjacent portion of the baffle’s suture line. In the Senning diagram, only the systemic venous atrium andthe anterior atrial septal remnant portion of the pulmonary venous atrium are shown. See text for details. LA 5 left atrial catheter; LAA 5left atrial appendage; LV 5 left ventricular catheter; MV 5 direction of mitral valve location; RAA 5 right atrial appendage.


were analyzed using the Student t test. A p value ,0.05 wasconsidered statistically significant.

RESULTS

Patient characteristics. Eleven patients, ranging in agefrom 11 to 29 years, underwent 13 electrophysiologicprocedures 10 to 27 years following their atrial switchoperation (Tables 1 and 2). They had been symptomatic fortwo months to 19 years. Two patients had experiencedsyncope, two patients had symptomatic sustained IARTrequiring cardioversion, five patients had symptomatic non-

sustained palpitations, and two patients had asymptomaticIART on Holter monitoring.

The patients had undergone Mustard or Senning opera-tions ranging from 2 to 76 months of age (Table 1). Basedupon the operative notes, the medial portion of the isthmusof tissue between the tricuspid valve and inferior vena cavalorifice was almost exclusively left in the pulmonary venousatrium in eight patients (Fig. 1a,b,d) and was bisectedbetween systemic and pulmonary venous atria in two pa-tients (Fig. 1c). In patient 7 the operative note did notprovide sufficient detail to determine this information. Sixpatients had coexisting structural cardiac defects, which are

Figure 3. Posteroanterior (PA) and lateral (Lat) radiographs and electrograms during mapping for and ablation of the typical variety ofAV node reentry tachycardia in Patient 9. (Bottom Left) The ablation catheter (Abl) was first used to identify the region of the His bundleusing the retrograde aortic approach. (Bottom Right) The successful ablation site (Abl) of the “slow” inputs to the AV node. Radiographson the left are lower magnification than those on the right. Baff 5 systemic venous baffle multipole catheter. Bipole 4 is most superior andbipole 7 most inferior; HLA 5 high anatomic left atrial catheter; LV 5 left ventricular catheter; PSRA 5 posteroseptal right atrialcatheter. The electrograms are from the most proximal bipole. See text for details.


Tabl

e2.

Car

diac

Cat

hete

riza

tion

and

Ele

ctro

phys

iolo

gySt

udy

Res

ults

Pat

ient

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(yrs

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thm

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BC

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(ms)

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duce

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116

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plet

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stru

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all

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223

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329

Non

eV

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pace

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nduc

tion

IAR

T24

54

11M

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(32

mm

Hg)

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512

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mal

sinu

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tion

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T22

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515

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nus

440

No

cond

uctio

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250

629

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stud

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med

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430

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280

390

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No

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T(is

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(30

mm

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(300

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911

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supe

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260

690

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AV

NR

T31

0

1021

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60be

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min

400

500

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ical

AV

NR

T52

0IA

RT

(iso)

250

1113

Unr

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eV

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arte

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ratio

n—91

%;

seve

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(80

mm

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Nor

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sinu

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#123

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(iso)

200

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n6

SD19

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6.6

yrs

365

ms

(95%

CI

532

8–40

2)IA

RT

524

4m

s(9

5%C

I5

229–

257)

FAT

536

5m

s(9

5%C

I5

280–

446)

AV

NR

T5

387

ms

(95%

CI

525

6–51

8)

AV

BC

L5

atri

oven

tric

ular

bloc

kcy

cle

leng

th;A

VN

RT

5A

Vno

dere

entr

yta

chyc

ardi

a;FA

T5

foca

latr

ialt

achy

card

ia;I

AR

T5

intr

aatr

ialr

eent

ryta

chyc

ardi

a;is

o5

isop

rote

reno

l;L

VO

TO

5le

ftve

ntri

cula

rou

tflow

trac

tobs

truc

tion;

RV

ED

P5

righ

tve

ntri

cula

ren

d-di

asto

licpr

essu

re;S

VC

5su

peri

orve

naca

va;V

AB

CL

5ve

ntri

culo

atri

albl

ock

cycl

ele

ngth

;VSD

5ve

ntri

cula

rse

ptal

defe

ct.


listed in Table 2. Three patients had undergone rate-adaptive, single chamber, ventricular pacing for “sick sinussyndrome,” and none had undergone implantation of anatrial pacing lead.

Electrophysiologic study and radiofrequency ablation.Baseline hemodynamic and electrophysiologic data appearin Table 2. Antegrade AV conduction was present anddecremental in every case. Because a stable His bundlerecording was not obtained in every patient, the anatomiclocation of AV and V-A block was not always available.Ventriculoatrial conduction was present in six of the eightpatients in whom the medial isthmus was known to bemostly on the pulmonary venous side, but was absent in thetwo patients in whom the native coronary sinus ostium wasleft on the systemic venous side (p 5 NS). Atrioventricularnode reentry tachycardia was not inducible in any patientlacking V-A conduction. It was inducible in three patientshaving V-A conduction (50%) (p 5 NS).

IART. This tachycardia was inducible in all patients, andtwo patients had two apparently different circuits. Theirmean cycle length was 244 6 13 ms (range: 200–280 ms).A tachycardia thought to represent a circuit reversal of apreviously identified circuit was counted as a single tachy-cardia. Radiofrequency energy was applied to the so-calledcritical zones of conduction as a series of stepwise connectedburns creating linear lesions. Focal lesions were neversuccessful for interrupting any IART. Overall, IART cir-cuits were successfully ablated in 8 of 11 (73%) patients(95% CI for failure rate: 2% to 52%).

Mustard patients. Among nine Mustard patients, 10apparently different IART circuits were identified. Theisthmus of tissue between the tricuspid valve and inferiorvena caval orifice was identified as a critical zone ofconduction for nine of these circuits, and the region be-tween the orifice of the superior vena cava and the supero-posterior remnant of the atrial septum was a critical zone forone circuit (Fig. 4). In all five patients in whom it wasattempted, concealed entrainment with a short postpacinginterval could be demonstrated on both systemic and pul-monary venous sides of the inferior baffle.

All IART circuits were successfully ablated in six (67%)patients (95% CI for failure rate: 2% to 64%). Of the ninecircuits involving the isthmus between the tricuspid valveand inferior vena caval orifice, only the medial isthmus couldbe negotiated from the systemic venous side due to thesurgical anatomy; the inferior/anterior portion of the bafflealways seemed to be very near the inferior vena caval orifice,leaving the entire mid- and lateral isthmus on the pulmo-nary venous side. Linear lesions were always attempted fromthe systemic venous side first, except in patient 2, due to thepresence of an intravascular stent. In the other eight, thisapproach was successful in one, abandoned in two becauseof increasing AV block, and unsuccessful in five. When thesystemic venous approach was unsuccessful, the retrograde,right ventricular approach to this region required prolapsing

the flexed catheter across the tricuspid valve into thepulmonary venous atrium. Interruption of IART was usu-ally only accomplished once the catheter tip was pulled backto the tricuspid valve annulus. In Patient 10, interruption ofthe IART circuit required that the linear lesion be extendedmore posteriorly to what was probably the right atriotomyscar. These pullbacks engaged the mid- or lateral isthmus,well away from the medial isthmus.

Senning patients. The two Senning patients had threeseemingly separate IART circuits (Fig. 4). In both patients,a critical zone of conduction was identified in the supero-posterior remnant of the atrial septum below the superiorvena caval orifice, but IART interruption did not occur untilthe linear lesions were continued inferiorly and posteriorlyto the uppermost suture line where the atrial septal flapforms the roof over the pulmonary veins (Fig. 4). Thecatheter could be felt to “hop” over the cut edge of the atrialseptal remnant to engage the more posterior structure. Inpatient 11, brief recurrences of this IART persisted untiladditional linear lesions were created posteriorly, from thesuperior-most portion of the native left atrium inferiorly tothis same suture line (Fig. 4, broken black rectangle). Thethird IART circuit had as a critical zone of conduction themid-isthmus, which had been entirely segregated from the

Figure 4. Locations of radiofrequency ablation attempts in Mus-tard and Senning patients. Illustrated are lesion locations forsupraventricular tachycardias successfully and unsuccessfully ab-lated. In patients whose tachycardias were successfully ablated,unsuccessful locations are not illustrated. In the Mustard diagram,the solid gray area represents the systemic venous atrium, and thestippled area, the isthmus between the tricuspid valve and inferiorvena cava. In the Senning diagram, the systemic venous atrium isopened, approximating the anatomy from Figure 2. The rightatrial freewall flap comprising the roof over the systemic venous(intercaval) atrium is also removed, revealing the entire atrial septalremnant. The portion remaining on the pulmonary venous atrial(PVA) side includes the tricuspid valve/inferior vena cava isthmus.See text for details. MV 5 mitral valve; SVA 5 systemic venousatrium; TV 5 tricuspid valve.


systemic venous atrium by the inferior portion of thesuperoinferior suture line attaching the right atrial freewallonto the inferior remnant of the atrial septum, posterior tothe coronary sinus ostium (Fig. 4). Therefore, this couldonly be negotiated by using a retrograde arterial catheter andpulling back from this suture line to approximately “6o’clock” of the tricuspid valve annulus. Both patients hadsuccessful ablation of IART circuits.

FAT. There were two FATs, each in Mustard patients(Tables 2 and 3). Both were inducible with atrial pro-grammed stimulation. The cycle lengths of these tachycar-dias tended to be longer than those of the IARTs (363 6 60vs. 244 6 13 ms, p 5 0.2). The cycle length of the FATfrom patient 7 varied from 360 to 450 ms and was markedlyinfluenced by autonomic tone. It could also be terminatedby adenosine. Sites of earliest atrial activation were in thepulmonary venous atrium in one and the systemic venousatrium in the other. Both foci were immediately adjacent tosuture lines (Fig. 4) and were successfully ablated.

TYPICAL VARIETY OF AV NODE REENTRY TACHYCARDIA.

This tachycardia was inducible in two Mustard patients andone Senning patient, but prior to delivery of radiofrequencyenergy only in patient 10. The cycle lengths of thesetachycardias tended to be longer than those of the IARTs(387 6 116 vs. 244 6 13 ms, p 5 0.16). The V-A intervalsduring tachycardia were 27 to 65 ms.

These three patients were successfully treated by applyingradiofrequency energy along the tricuspid annulus below thelocation where a His bundle electrogram was observed(Figs. 3 and 4). Accelerated junctional rhythm was observedduring radiofrequency energy in each. The PR intervals andthe existence of V-A conduction were unaffected by theseablations.

Procedural issues and complications. These were lengthyprocedures, in part due to the inclusion of hemodynamicstudies. The total fluoroscopy times per patient (80 min;95% CI: 62–99 min) and procedure times (8.8 h; 95% CI:8.0 to 9.6 h) were longer than those reported from thePediatric Radiofrequency Registry (19).

Two patients suffered second- or third-degree AV blockduring delivery of radiofrequency energy from the systemicvenous side of the medial isthmus, and in one, it waspermanent. These were the only two patients in whom thecoronary sinus ostium was kept on the systemic venous sidewith no attempt at surgical redirection or incision of thecoronary sinus (p 5 0.02) (Fig. 1). These two patients weretwo of the five not having V-A conduction (p 5 NS).Among the eight patients whose medial isthmus was leftalmost exclusively on the pulmonary venous side, nonesuffered any degree of AV block (p 5 NS).

Follow-up. At 28 months’ mean follow-up (range: 4 to 54months), all 11 patients are alive (Table 4). Of those threewhose ablations were not thought to be successful, one hasa dual-chamber pacemaker for permanent second-degree

atrioventricular block, and the other two receive class Iantiarrhythmic drugs. All remain asymptomatic.

Among the eight patients whose ablations were thoughtto be successful, three receive digoxin, and one (Patient 10)atenolol. Digoxin had not been efficacious in those patientspreprocedure. Patient 10 suffered IART recurrences, begin-ning two months following his procedure, but he is nowcompletely controlled with atenolol. He had many recur-rences prior to the procedure while receiving atenolol.Patient 4 has episodes lasting ,3 s of a junctional tachy-cardia during exertion. All other patients remain asymptom-atic. In summary, seven of the eight patients (88%; 95% CIfor recurrence rate: 0% to 36%) whose procedures weresuccessful have had no supraventricular tachycardia recur-rences.

DISCUSSION

Radiofrequency ablation of FAT and atrioventricularnode reentry tachycardia. The principal new informationin this report is a description of radiofrequency catheterablation of other supraventricular tachycardias in addition toIART following the Mustard and Senning operations. Sitesof focal atrial tachycardias on either systemic or pulmonaryvenous sides of the surgical baffles can be mapped andablated. These sites seemed to be immediately adjacent tobaffle suture lines. Criteria previously described for accuratelocalization of atrial ectopic tachycardia foci (16) were usefulin these two patients.

The typical variety of AV node reentry tachycardia wasinducible in three patients; however, in two it was only seenfollowing application of radiofrequency lesions to the me-dial isthmus for IART. These two cases could thereforehave been caused by alteration of conduction properties ofthe slow inputs to the AV node, and, hence, could beiatrogenic. Irrespective of the etiology, application of radio-frequency energy along the tricuspid valve on the pulmonaryvenous side, probably corresponding to M1 and M2 zones(20), resulted in accelerated junctional rhythm (21) andrendered the tachycardia as noninducible. Well-establishedcatheter ablation techniques (17,18,21) for the typical vari-ety of AV node reentry tachycardia, then, proved efficaciousin this patient group. The catheter course was similar to thatrequired for isthmus ablation from the pulmonary venousside. However, more clockwise torque was required torender the tip medial and against the anteroseptal tricuspidannulus. To avoid damage to the compact AV node, webelieve that it is critical to obtain a His bundle electrogramfirst. Flexion on the catheter may then be relaxed slightlyuntil the His bundle signal no longer is present and thereremain small atrial and large ventricular electrograms. Insummary, we found both electrographic and fluoroscopicinformation to be necessary for safe and successful manage-ment of the typical variety of AV node reentry tachycardia.


Tabl

e3.

Rad

iofr

eque

ncy

Abl

atio

nof

Supr

aven

tric

ular

Tac

hyca

rdia

san

dO

ther

Pro

cedu

ralI

ssue

s

Pat

ient

Dat

eof

Stud

yT

achy

card

ia

Cri

teri

afo

rL

ocat

ion

ofR

FE

nerg

yD

eliv

ery

Succ

essf

ul(y

es/n

o)M

ain

Site

ofSu

cces

sful

RF

AM

ain

Site

ofU

nsuc

cess

ful

RF

AN

o.of

RF

App

licat

ions

Flu

oros

copy

Tim

e(m

in)

Pro

cedu

reT

ime

(h)

Com

plic

atio

ns

11/

94IA

RT

CE

M;p

resy

stol

icpo

tent

ials

No

Med

iali

sthm

us(S

VA

linea

r;P

VA

foca

l)

2311

011

Upp

erbo

dyed

ema

(24

h)

28/

94IA

RT

CE

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resy

stol

icpo

tent

ials

No

Mid

-an

dla

tera

lis

thm

us(P

VA

linea

ran

dfo

cal)

750

9.5

Non

e

33/

95IA

RT

CE

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stol

icpo

tent

ials

Yes

Med

iali

sthm

us(S

VA

linea

r)10

358.

5N

one

412

/95

IAR

TC

EM

;pre

syst

olic

pote

ntia

lsY

esM

id-i

sthm

us(P

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edia

list

hmus

(SV

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ear)

2065

9T

rans

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seco

nd-

degr

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pote

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340

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thir

d-de

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bloc

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seco

nd-

degr

eeA

Vbl

ock

62/

96FA

TE

arlie

stat

rial

elec

trog

ram

(A-P

inte

rval

535

ms)

Yes

PV

A-l

eft

ofL

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s(f

ocal

)N

one

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stol

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tent

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Yes

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sept

alre

mna

nt(S

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linea

r)

2775

12

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CE

M;p

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stol

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Yes

Med

iali

sthm

us(S

VA

linea

r)4/

96IA

RT

#2C

EM

;pre

syst

olic

pote

ntia

lsY

esM

id-i

sthm

us(P

VA

linea

r)M

id-i

sthm

us(S

VA

linea

r)11

408

Non

e

74/

94FA

TE

arlie

stat

rial

elec

trog

ram

(A-P

inte

rval

561

ms)

Yes

Mid

-sep

tal

rem

nant

(SV

Afo

cal)

1775

10N

one

5/96

IAR

TC

EM

;pre

syst

olic

pote

ntia

lsY

esM

id-i

sthm

us(P

VA

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r)M

id-i

sthm

us(S

VA

linea

r)8

356.

5N

one

811

/96

IAR

TC

EM

;pre

syst

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pote

ntia

lsY

esM

id-i

sthm

us(P

VA

linea

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edia

list

hmus

(SV

Alin

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111

8N

one

Typ

ical

AV

NR

TA

nato

mic

loca

tion

of“s

low

inpu

ts”

toA

Vno

de;

acce

lera

ted

junc

tiona

lrh

ythm

Yes

Mid

-ist

hmus

TV

A(P

VA

foca

l)

20

(con

tinue

d)

{ }

}{

}{

}{


Tabl

e3.

(con

tinue

d)

95/

97IA

RT

CE

M;p

resy

stol

icpo

tent

ials

Yes

SVC3

sutu

relin

eof

sept

alfla

p(S

VA

linea

r)

Mid

-ist

hmus

(PV

Alin

ear)

;med

ial

isth

mus

(SV

Alin

ear)

1788

7N

one

Typ

ical

AV

NR

TA

nato

mic

loca

tion

of“s

low

inpu

ts”

toA

Vno

de;

acce

lera

ted

junc

tiona

lrh

ythm

Yes

Mid

-sep

talT

VA

(PV

Afo

cal)

10

106/

97T

ypic

alA

VN

RT

Ana

tom

iclo

catio

nof

“slo

win

puts

”to

AV

node

;ac

cele

rate

dju

nctio

nal

rhyt

hm

Yes

Mid

-sep

talT

VA

(PV

Afo

cal)

710

28

Non

e

IAR

TC

EM

;pre

syst

olic

pote

ntia

lsY

esR

t.A

trio

tom

ysc

ar3

TV

A(P

VA

linea

r)

Med

iali

sthm

us(S

VA

linea

r)36

113/

98IA

RT

#1C

EM

;pre

syst

olic

pote

ntia

lsY

esL

ater

alis

thm

us(P

VA

linea

r)M

id-i

sthm

us(S

VA

linea

r)9

579

Non

e

IAR

T#2

CE

M;p

resy

stol

icpo

tent

ials

Yes

SVC

/sup

erio

rle

ftat

rium3

sutu

relin

eof

sept

alfla

p(S

VA

linea

r)

8

Mea

n6

SD21

/pt

(95%

CI:

14–2

8)80

min

/pt

(95%

CI:

62–9

9)8.

8h/

proc

edur

e(9

5%C

I:8.

0–9.

6)

AV

NR

T5

atri

oven

tric

ular

noda

lree

ntry

tach

ycar

dia;

CE

M5

conc

eale

den

trai

nmen

tm

appi

ng;F

AT

5fo

cala

tria

ltac

hyca

rdia

;IA

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5in

traa

tria

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tach

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dia;

LP

Vs

5le

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lmon

ary

vein

s;P

VA

5pu

lmon

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veno

usat

rium

;R

FA5

radi

ofre

quen

cyab

latio

n;SV

A5

syst

emic

veno

usat

rium

;SD

5st

anda

rdde

viat

ion;

SVC

5su

peri

orve

naca

va;T

VA

5tr

icus

pid

valv

ean

nulu

s.


Radiofrequency ablation of IART. Our overall acutesuccess rate for ablation of IART circuits (77% of circuits;73% of patients) compares favorably with that described inprevious reports (78% of circuits; 79% of patients) (11–13).Among Mustard patients having isthmus-dependent IART,Van Hare et al. (11) reported a relationship between thesurgically determined location of the coronary sinus ostiumand the location of successful radiofrequency ablation–pulmonary venous versus systemic venous side of the bafflesuture line. When the ostium was on the systemic venousside, ablation on the same side was required for successfulinterruption of IART, and vice versa (11). Our findings didnot agree with theirs.

Although the nomenclature in Table 1 is different fromthat used in the report by Van Hare et al., the “location ofthe medial isthmus” from Table 1 was similarly deducedfrom the description of the surgical handling of the coronarysinus. Whenever the coronary sinus was kept on thepulmonary venous side, or whenever it was surgically incisedto permit redirection into the systemic venous atrium, weconcluded that the medial isthmus was almost entirelypulmonary venous. Hence, a medial isthmus with bothsystemic and pulmonary venous components would corre-spond to a systemic venous coronary sinus in the Van Harestudy (11). With that explanation, in only three of fiveMustard patients in our series, in whom surgical proceduraldata were available, was the location of the coronary sinuspredictive of the site of successful ablation IART; in three offour patients in whom the coronary sinus was left on thepulmonary venous side, ablation was successful on that side,having first been unsuccessful on the systemic venous side.In the other patient (Patient 3), ablation was successful fromthe systemic venous side. Among the two patients in whom

the coronary sinus remained on the systemic venous side, inpatient 4 the ablation was successful from the pulmonaryvenous side, having failed from the systemic venous side.

There are several possible explanations for the discrep-ancy in these findings. The small numbers of patients inboth series make statistically based conclusions difficult.Second, with respect to the surgical handling of the coro-nary sinus, there may not be a fair comparison of patients inthe two experiences. For example, in several patients in ourseries, we concluded that the medial isthmus was kept onthe pulmonary venous side, when the coronary sinus ostiumwas surgically redirected to systemic venous atrium. If suchsurgical redirection was performed in the patients in theVan Hare series (11), then the expression “systemic venouscoronary sinus ostium” would not have equivalence. Third,because of our experience with AV block in two patientsduring application of radiofrequency energy to the systemicvenous side of the medial isthmus, we did not perform morethan two linear lesions in this region in any subsequentpatient before switching to the pulmonary venous approach.Hence, we became less aggressive.

Sites for delivery of radiofrequency ablation energy de-pended upon the tachycardia mechanism. For focal atrialtachycardia and AV node reentry tachycardia, the criteriaused are discussed above. For IART, various maneuverswere used: 1) identification of fractionated atrial electro-grams prior to the P-wave onset, preferably with splitpotentials, during tachycardia; 2) characterization of theanatomy based upon fluoroscopic location of the ablationcatheter during mapping; and 3) proof of participation ofthat region in the tachycardia circuit, using entrainmentwith concealed fusion. In agreement with previous reports(11–13), when concealed entrainment was accompanied by

Table 4. Current Patient Status at Last Follow-up

Patient

DurationSince Last RFA

(mos)

CurrentAntiarrhythmic

MedicationsCurrent

Rhythm Status

ClinicalTachycardiaRecurrences

1 54 Dg Normal sinus None2 47 Pr; Q AAICP paced None3 40 None VVIR paced None4 32 Dg Normal sinus None5 28 Diso DDD paced None6 27 None VVIR paced None7 26 Dg Normal sinus None8 20 None Normal sinus None9 14 Dg Junctional Brief palpitation

(,5 s runs,junctionaltachycardia)

10 13 At Junctional/sinus IART11 4 None Normal sinus None

Mean 6 SD 28 6 15 months(4–54 mos)

At 5 atenolol; Dg 5 digoxin; Diso 5 disopyramide; IART 5 intraatrial reentry tachycardia; Pr 5 propranolol; Q 5 quinidine;RFA 5 radiofrequency ablation.


a postpacing interval #20 ms longer than the tachycardiacycle length, that location was considered to be a critical partof the tachycardia circuit. Knowledge of the anatomicboundaries of that portion of the circuit was then necessaryto permit successful radiofrequency ablation.

The observation in Mustard patients that entrainmentwith concealed fusion and a short postpacing interval couldbe demonstrated on both systemic and pulmonary venoussides of the lower atrial baffle suggested to us that the entireisthmus participates in the reentrant circuit and must betransected. As the baffle extends anteriorly, to encircle theinferior vena caval orifice, catheter manipulation suggestedthat no portion of the mid- or lateral isthmus remained onthe systemic venous side (Fig. 4). Except in patients inwhom a large portion of the medial isthmus remains on thesystemic venous side, the best opportunity for transectingthe entire isthmus is from the pulmonary venous side at thelevel of the mid- or lateral isthmus.

AV block during radiofrequency ablation. This is the firstreport of damage to AV conduction during radiofrequencyablation of the medial isthmus from the systemic venousside following the Mustard procedure. To understand howthis might have occurred, precise knowledge of the originalsurgical procedure is necessary. Essential components of theMustard operation include a subtotal atrial septectomyfollowed by placement of a complex baffle of pericardium orprosthetic material, described as “pant legs” in shape.Damage to anterior or “fast” inputs to the AV node mightbe expected by the septectomy, although there are nointraoperative mapping data that precisely address thisanatomic region. Electrocardiographic evidence for thiswould include first-degree AV block; however, prolongationof the PR interval is frequently seen after this procedure dueto severe intraatrial conduction delay (22). Confounding ourability to discriminate the anatomic level of PR intervalprolongation was an inability to obtain a reliable Hisrecording. Based upon our knowledge of AV node conduc-tion in the normal heart, we considered the presence ofintact V-A conduction as suggestive of at least adequatefunction of the “fast” inputs to the AV node.

With respect to posterior or “slow” inputs to the AVnode, conduction block to the entire posteroseptal regionhas been demonstrated during intraoperative mapping,when the coronary sinus was kept on the systemic venousside of the inferior baffle suture line (23). A portion of the“slow” inputs to the AV node are thought to exist in thisregion (Fig. 1). The two patients in our series suffering atleast transient second- or third-degree AV block wereamong the six in whom the coronary sinus ostium drainedinto the systemic venous side and the only two in whom ithad not been surgically redirected or incised. Therefore, thecombination of the original surgical technique plus ablationcatheter access to the medial isthmus from the systemicvenous side (Fig. 1c) may have caused “slow pathway”damage. If the absence of V-A conduction observed in these

two patients represents prior loss of “fast pathway” conduc-tion, then overall impairment of AV node conduction mightbe expected.

Study limitations. There are several limitations of thisstudy. Anatomic detail was inferred from the fluoroscopiclocation of catheters coupled with prior echocardiographicand angiographic information. Real-time transesophagealechocardiographic or intracardiac echographic (24) tech-niques would provide new and potentially more accurateinformation regarding anatomy and catheter contact. Map-ping IART in such complex structures may also benefitfrom new magnetic electroanatomic mapping techniquessuch as those described by Marchlinski et al. (25) and byDorostkar et al. (26). In our patients, no attempts weremade to demonstrate creation of bidirectional block toconduction, either during or following radiofrequency en-ergy delivery to IART circuits. This will require novelcatheter placement in future patients. The absence of areliable His bundle electrogram throughout all studiesprevented meaningful evaluation of AV node function. Thiswould have been most important in the two patientssuffering AV node damage. Follow-up longer than 28months will be necessary to determine the long-term effi-cacy of radiofrequency ablation for supraventricular tachy-cardias in these patients. In particular, it is hoped that therecurrence rate of IART will be as low as that seen in adultswith normal hearts and not as high as that seen in Fontanpatients. We speculate that the relatively normal atrial sizeand pressure in our patients—in distinction from thatobserved in Fontan patients—will predict this to be so.

Clinical implications. As the population of patients whohad undergone the Mustard or Senning operation ages,paroxysmal tachycardias remain their most significant clin-ical problem. The majority of these tachycardias are su-praventricular in origin, predominantly IART. Other thanatrial fibrillation, there appears to be no supraventriculartachycardia that should be considered exempt from candi-dacy for radiofrequency ablation following these operations.As in patients having normal cardiac anatomy and commonatrial flutter, risk of damage to the AV node should bediscussed with patients, as ablation of inputs to the AV nodemay occur.

AcknowledgmentsWe gratefully acknowledge Phyllis Bason for manuscriptpreparation and the Pediatric Catheterization Laboratoryand Electrophysiology Laboratory staffs for providing su-perb patient care. We also thank our referring physicianswho trusted us with the care of their patients.

Reprint requests and correspondence: Dr. Ronald J. Kanter,Duke University Medical Center, Box 3090, Durham, NC 27710.E-mail: [email protected].


REFERENCES

1. Hayes CJ, Gersony WM. Arrhythmias after the Mustard operation fortransposition of the great arteries: a long-term study. J Am CollCardiol 1986;7:133–7.

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Radiofrequency Catheter Ablation of Supraventricular Tachycardia in Children and Adolescents

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