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Clinical Electrophysiology

Editor-in-Chief

Dr. David J. Wilber.

J A C C : C L I N I C A L E L E C T R O P H Y S I O L O G Y V O L . 2 , N O . 1 , 2 0 1 6

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Peri-Mitral Atrial Tachycardia Using theMarshall Bundle Epicardial Connections

Takekuni Hayashi, MD,a Seiji Fukamizu, MD,b Takeshi Mitsuhashi, MD, PHD,a Takeshi Kitamura, MD,b

Yuya Aoyama, MD,b Rintaro Hojo, MD,b Yoshitaka Sugawara, MD,a Harumizu Sakurada, MD, PHD,c

Masayasu Hiraoka, MD, PHD,d Hideo Fujita, MD, PHD,a Shin-ichi Momomura, MD, PHDa

ABSTRACT

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OBJECTIVES The aim of this study was to determine whether re-entrant circuits were associated with the ligament of

Marshall (LOM).

BACKGROUND Peri-mitral atrial tachycardias (PMATs) following pulmonary vein isolation (PVI) or mitral valve surgery

are common.

METHODS Six PMATs involving epicardial circuits were identified from 38 patients. Of these, 4 PMATs involved the LOM

(PMAT-LOM, mean cycle length 308 � 53 ms), as confirmed by the insertion of a 2-F electrode in the vein of Marshall

(VOM). All patients underwent PVI and mitral isthmus ablation. The PMAT-LOMs were diagnosed based on left atrium

(LA) activation maps that covered <90% of tachycardia cycle length (TCL), and a difference between the post-pacing

interval and TCL that was: 1)#20 ms at the VOM, the ridge between the left pulmonary vein and appendage, the anterior

wall of the LA, and along the 6 to 11 o’clock direction of the mitral annulus; and 2) >20 ms at the distal coronary sinus

(CS), the posterior wall of the LA, and the mitral isthmus ablation line (or noncapture). Catheter ablation was performed

at the ridge for all PMAT-LOMs.

RESULTS Three tachycardias were successfully terminated at the ridge, which showed continuous fractionated

potential lasting >100 ms, confirming the bidirectional block of Marshall bundle (MB)–LA connections. The

remaining tachycardia required ablation for the CS-MB connections, confirming bidirectional block of CS-MB

connections.

CONCLUSIONS PMAT-LOMs following PVI or valve surgery accounted for up to 11% of PMATs. The bidirectional

block of either MB-LA or CS-MB connections is required to eliminate PMAT-LOMs. (J Am Coll Cardiol EP 2016;2:27–35)

© 2016 by the American College of Cardiology Foundation.

T he ligament of Marshall (LOM) is an epicar-dial vestigial fold that contains the vein ofMarshall (VOM) and a myocardial sleeve

called the Marshall bundle (MB). The LOM has previ-ously been implicated as a source of focal activityinitiating atrial fibrillation (AF) (1–3). Radiofrequencycatheter ablation (RFCA) has emerged as an effectivetherapy for patients with AF (4–6). Peri-mitral atrialtachycardia (PMAT) commonly develops after pulmo-nary vein isolation (PVI) or mitral valve surgery (7).The creation of a linear lesion from the mitral annulus

m the aDivision of Cardiovascular Medicine, Saitama Medical Center, Jich

rdiology, Tokyo Metropolitan Hiroo Hospital, Tokyo, Japan; cDepartme

dical Treatment Corporation Ohkubo Hospital, Tokyo, Japan; and the d

an. The authors have reported that they have no relationships relevant t

nuscript received July 14, 2015; accepted August 13, 2015.

(MA) to the left inferior PV, in the so-called mitralisthmus (MI), is the most common ablation strategyfor PMAT. Achieving a complete ablation line(defined by a bidirectional conduction block acrossthe MI line) is critical to eliminate PMAT, but doingso can be technically difficult and can require coro-nary sinus (CS) ablation of up to 70% (8). In rare cases,re-entrant circuits of PMAT involve an epicardialconnection (9). This study was conducted to clarifythe characteristics of PMATs that use epicardial con-nections, especially the LOM (PMAT-LOMs).

i Medical University, Saitama, Japan; bDepartment of

nt of Cardiology, Tokyo Metropolitan Health and

Toride Kitasohma Medical Center Hospital, Ibaraki,

o the contents of this paper to disclose.

ABBR EV I A T I ON S

AND ACRONYMS

AF = atrial fibrillation

AT = atrial tachycardia

CFAE = complex fractionated

atrial electrogram

CS = coronary sinus

LA = left atrial/atrium

LAA = left atrial appendage

LOM = ligament of Marshall

MA = mitral annulus

MB = Marshall bundle

MI = mitral isthmus

PMAT = peri-mitral atrial

tachycardia

PPI = post-pacing interval

PVI = pulmonary vein isolation

RFCA = radiofrequency

catheter ablation

TCL = tachycardia cycle length

VOM = vein of Marshall

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METHODS

STUDY POPULATION. This study consistedof 38 consecutive patients with PMAT whounderwent PVI for AF or mitral valve surgeryin the Saitama Medical Center of Jichi Medi-cal University and Tokyo Metropolitan HirooHospital from March 2009 to September2014. Of these patients, 28 underwent abla-tion for AF (paroxysmal AF n ¼ 12; persistentAF lasting #1 year n ¼ 2; long-standingpersistent AF lasting >1 year n ¼ 14) and 10underwent mitral valve surgery (replacementn ¼ 7; plasty n ¼ 3). All patients gave signedinformed consent before the procedure.

ELECTROPHYSIOLOGICAL STUDY ANDABLATION

PROCEDURE. Antiarrhythmic drugs, exclu-ding amiodarone, were discontinued $5half-lives prior to ablation. The electrophy-siological study was performed duringcontinuous intravenous administration ofpropofol (3 to 6 mg/kg/min). A decapolar or

multipolar catheter (Inquiry Luma-Cath, St. JudeMedical, Tokyo, Japan, or BeeAT, Japan Lifeline Co.,Ltd., Tokyo, Japan) was inserted via the right sub-clavian vein to the CS. The left atrium (LA) and PVwere explored via transseptal catheterization with 2or 3 long sheaths. PV mapping was performed using acircular mapping catheter (Inquiry Optima, St. JudeMedical or Lasso, Biosense Webster, Inc., South Dia-mond Bar, California). A 3.5-mm irrigated-tip catheter(ThermoCool Navistar, Biosense Webster or CoolPath, St. Jude Medical) and a 3-dimensional anatomicmapping system (CARTO, Biosense Webster or EnSiteNavX and Velocity, St. Jude Medical) were used formapping and ablation.

AF ABLATION STRATEGY. Ablation for AF was per-formed as previously described (10). Briefly, in pa-tients with paroxysmal AF and persistent AFlasting #1 year, circumferential PVI was performed. IfAF was present, sinus rhythm was restored by inter-nal or external cardioversion. The target in this phasewas the elimination of all PV potentials; once thetarget was attained, continuous intravenous isopro-terenol (4 mg/min) was administered, a 20- to 40-mgbolus of adenosine triphosphate was injected, andfurther RFCA was performed to eliminate any recon-duction of PV potentials or adenosine triphosphate–provoked acute dormant PV conduction. The end-point of PVI was the establishment of a bidirectionalconduction block between the LA and PV. If repro-ducible non-PV foci–initiated AF was identified, RFCAwas attempted to eliminate the non-PV foci.

In the patients with long-lasting persistent AFlasting >1 year, PVI was performed during AF, fol-lowed by mapping of complex fractionated atrialelectrograms (CFAEs) of the LA. CFAEs were definedas previously reported (11). Subsequently, linearablation of a roof and MI line was performed. If AFpersisted after linear ablation, LA CFAE ablation wasperformed. If the AF still persisted in this phase, in-ternal or external cardioversion was performed. If theAF converted to atrial tachycardia (AT) after eitherlinear or CFAE ablation, or both, mapping and abla-tion were performed.

DIAGNOSIS AND ABLATION OF PMAT. Linear abla-tion of the MI was performed for induced or spon-taneously occurring PMAT. PMAT was diagnosedusing a 3-dimensional anatomic mapping systemwith the entrainment pacing technique. A differencebetween the post-pacing interval (PPI) and tachy-cardia cycle length (TCL) of #20 ms from the 4, 8,and 12 o’clock positions in the LA or CS along MA.Left-side PVI was performed in patients without AF.Subsequently, RFCA was applied from the 4 o’clockposition of the MA to the bottom left-side PV with 25to 35 W. If endocardial ablation was unable to suc-cessfully achieve a complete MI conduction block(defined by bidirectional conduction block across theMI line), further RFCA application was deliveredwithin the CS opposite of the endocardial MI linewith 20 to 25 W.

DIAGNOSIS OF PMAT USING LOM. PMATs usingepicardial connections were diagnosed with a 3-dimensional anatomic mapping system with theentrainment pacing technique. PMATs using epi-cardial connections were diagnosed based on: 1) anLA activation map of a 3-dimensional anatomicmapping system that covered <90% of the TCL; 2) adifference between PPI and TCL from the LA 6 to 11o’clock positions of the MA that was #20 ms; 3) adifference between PPI and TCL from the LA 4o’clock position of the MA or prior MI line that was>20 ms or noncapture with high-output pacing(20 mA � 2 ms); and 4) a difference between PPIand TCL from the multiple sites of CS that was #20ms. Added to these observations, PMAT-LOM wasdiagnosed based on: 1) a difference between PPIand TCL from the 2-F octopolar electrodes (EPstarFix, Japan Lifeline) inserted into the VOM thatwas #20 ms; 2) a difference between PPI and TCLfrom the CS distal beyond the bifurcation of VOMthat was >20 ms; and 3) a difference between PPIand TCL from the ridge (defined as the area be-tween the left-side PVs and left atrial appendage[LAA]) that was #20 ms.

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ABLATION OF PMAT USING LOM. Theoretically,creating either a bidirectional block of MB-LA or CS-MB connections without MI ablation can eliminatePMAT-LOM. Furthermore, the evaluation of differ-ential pacing from the CS can be misleading when theexisting MB epicardial connections bypass the MI. Forexample, when the bidirectional block of MI isincomplete, conduction time from the CS pacing site(pacing from the CS distal over VOM) to the LAA maybe longer than from the CS proximal site, resulting ina pseudo-conduction block that may be mis-interpreted as a complete MI block (Figure 1).

For the reasons stated above, RFCA was applied atthe ridge (i.e., MB-LA connections site) with 30 to 35W.

FIGURE 1 Pseudo-Conduction Block of the MI With MB Epicardial Co

The activation sequence of coronary sinus (CS) during left atrial append

distal CS (CS 1 to 2) to the LAA during the CS 1 to 2 pacing was longer

8 pacing (B), suggesting complete mitral isthmus (MI) block. However,

sequence during CS 7 to 8 pacing, which suggested 2 or more pathways

from the CS to the LAA during CS pacing (i.e., incomplete MI block) (B an

proximal CS pacing site to the LAA, which can be misleading and misint

successfully disconnected the connections between the MB and LA, wh

proximal to proximal to distal (A, left panel). After ridge ablation, the con

of the LAA during CS 1 to 2 pacing changed to match the CS 7 to 8 pac

LAA during CS pacing (i.e., there was a complete MI block) (D). ABL ¼

Ablation endpoint was a complete block of MB-LAconnections (defined by bidirectional conductionblock across the MB-LA connections). If endocardialablation was unable to successfully achieve an MB-LAblock, further RFCA was delivered to the bifurcationof the CS and VOM with 20 to 25 W. In such cases, theablation endpoint was a complete block of CS-MBconnections.

RESULTS

PMATs using epicardial connections were identifiedin 6 patients. The baseline characteristics of thesepatients are listed in Table 1. Of these cases, 2 PMATs

nnections

age (LAA) pacing is proximal to distal (A, left panel). The conduction time (115 ms) from the

than the conduction time (90 ms) from the proximal CS (CS 7 to 8) to the LAA during CS 7 to

the LAA activation sequence during CS 1 to 2 pacing was different than the LAA activation

(via the mitral annulus [MA] and Marshall bundle [MB] epicardial connections) for propagation

d C). The conduction time from the distal CS pacing site to the LAA can be longer than from the

erpreted as a complete MI block. Radiofrequency ablation was attempted at the ridge and

ich was demonstrated by changing the VOM sequences during the LAA pacing from distal to

duction times from the CS pacing site to the LAA were prolonged, and the activation sequences

ing, which indicated the presence of a single conduction pathway via MA from the CS to the

ablation catheter; RAO ¼ right anterior oblique; VOM ¼ vein of Marshall.

TABLE 1 Patient Characteristics

Case Sex Age, yrs SHD AF Type Session TCL, ms Direction Applied Ablation

1 M 65 Post–right atrialmyxoma surgery/OMI

PAF 2 270 CW PVI

2 M 64 Post-MVP PerAF 2 285 CW PVI, LA CFAEs, roof line, MI, CTI

3 M 41 None LPerAF 4 310 CW PVI, LA CFAEs, roof line, MI, CTI

4 F 78 None LPerAF 3 280 CCW PVI, LA CFAEs, roof line, MI

5 M 49 None LPerAF 1 280 CCW PVI, LA CFAEs, roof line, MI

6 M 77 OMI PAF 1 380 CCW Left-side PVI, roof line, LA anterior ablation

AF ¼ atrial fibrillation; CFAE ¼ continuous fractionated atrial electrogram; CCW ¼ counterclockwise; CTI ¼ cavotricuspid isthmus; CW ¼ clockwise; LA ¼ left atrium;LPerAF ¼ long-standing persistent atrial fibrillation; MI ¼ mitral isthmus; MVP ¼ mitral valve plasty; OMI ¼ old myocardial infarction; PAF ¼ paroxysmal atrial fibrillation;PerAF ¼ persistent atrial fibrillation; PVI ¼ pulmonary vein isolation; SHD ¼ structural heart disease; TCL ¼ tachycardia cycle length.

FIGURE 2 The 3-D

AP ¼ anteroposterio

PPI ¼ post-pacing in

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involved the CS, which bypassed the LA endocardiumscar area of the MI line. RFCA was applied in the CSwithout LA endocardium ablation, and tachycardiawas successfully terminated (cases 1 and 2).

CHARACTERISTICS OF PMAT USING LOM. FourPMAT-LOMs were identified in the remaining 4

imensional Anatomic Activation Mapping of PMAT Using LOM in 4 Differe

r; CFAE ¼ complex fractionated atrial electrogram; LPO ¼ left posterior obliq

terval; PVI ¼ pulmonary vein isolation; other abbreviations as in Figure 1.

patients. The mean TCL was 308 � 53 ms (range 260 to380 ms). Three patients underwent catheter ablationfor long-standing persistent AF. Of these patients, 2patients underwent prior catheter ablation (PVI, roofline, MI, and LA CFAE ablation; cases 3 and 4) and 1patient had no prior ablation. In the 2 patients withprior ablation, PMAT-LOM lasted from the beginning

nt Cases

ue; PMAT-LOM ¼ peri-mitral atrial tachycardia–ligament of Marshall;

FIGURE 3 Examples of PMAT Using LOM

(A) The tachycardia activation sequences of the VOM and CS were distal to proximal, which indicated the presence of MB-LA connections and MB–distal CS connections

(case 3) (left panel). The PPI was equal to the tachycardia cycle length (TCL) from the VOM pacing during tachycardia. The difference between PPI and TCL from the

CS 1 to 2 was 35 ms (i.e., out of re-entrant circuits) (right panel). (B) In case 3, the potentials of the ablation catheter at the ridge showed fractionated potentials

that lasted 170 ms. Radiofrequency was applied at this site during tachycardia, and the tachycardia was successfully terminated. At the beginning of the ablation, the

activation sequences of CS were distal to proximal. During the ablation, the wave fronts changed to activate from CS 3 to 4 to CS 1 to 2 and CS 5 to 8. These observations

indicated that ridge ablation had disconnected the MB–distal CS connections as well as the MB-LA connections. (C) The fluoroscopic catheter positioning in case 3.

The bifurcation of CS and VOM is positioned at CS 3 to 4. (D) The tachycardia activation sequences of cases 4 and 5 were the reverse of case 3. The potentials of the

ablation catheter at the ridge also showed fractionated continuous potentials that lasted 155 ms (case 4) and 120 ms (case 5). The PPI was equal to the TCL from

the ablation catheter pacing during tachycardia. In both cases, tachycardia was terminated by radiofrequency ablation at these sites. LAO ¼ left anterior oblique;

RA ¼ right atrium; other abbreviations as in Figures 1 and 2.

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of the procedure. In the patient with long-standingpersistent AF without prior ablation (case 5), AF wasconverted to PMAT-LOM after PVI, roof line, and MIablation (including CS ablation). The remaining pa-tient had a prior myocardial infarction with a historyof paroxysmal AF and underwent catheter ablationfor multiple AT (case 6). The macro–re-entrant AT(TCL 260 ms) originating from the anterior wall of theLA at the beginning of the procedure changed to roof-dependent AT (TCL 380 ms) after LA anterior abla-tion. Subsequently, AT changed to PMAT-LOM (TCL

380 ms) after roof and MI line ablation following left-side PV isolation (no PV potential in right-side PV).

The 3-dimensional anatomic activation mapshowed either clockwise or counterclockwise PMATpattern (Figure 2). However, only 79 � 1% (range 78%to 81%) of the TCL was covered by the activation map.This finding suggested the existence of epicardialcircuits. Using both the 3-dimensional anatomicactivation map and PPI technique revealed the cir-cuits of PMAT-LOM (Figures 2 and 3). The circuits ofclockwise PMAT-LOM were as follows: 1) the wave

FIGURE 4 Example of Bidirectional Blocks Between the MB and LA Connections in Case 3

(A) Both activation sequences of the CS and VOM were proximal to distal during LAA pacing. (B)With the differential pacing site method, the conduction time from VOM

1 to 2 to LAA (175 ms) during VOM 1 to 2 pacing was longer than the conduction time from VOM 5 to 6 to LAA (165 ms) during VOM 5 to 6 pacing. These observations

were evidence of complete bidirectional block of MB-LA connections. Note: The earliest activation site of the CS during VOM pacing was CS 3 to 4, which indicated

disconnection of the MB–distal CS connections. Abbreviations as in Figure 1.

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front propagated from the 5 to 11 o’clock positions ofthe LA endocardium around the mitral valve andproceeded vertically across the anterior wall of the LAfrom bottom to roof; 2) the activation was unable toproceed across the posterior wall of the LA due to theblocked line of the roof, and it moved to the ridge;and 3) the wave front proceeded across the epicar-dium via MB bridging the endocardium over the MI,and it broke out from the 5 to 6 o’clock positions ofthe LA endocardium around the mitral valve via theCS. The counterclockwise PMAT-LOMs followed thereversed circuit of the clockwise PMAT-LOMs.CATHETER ABLATION OF PMAT USING LOM. RFCAwas applied at the ridge in which the difference be-tween PPI and TCL was #20 ms in all patients. ThreePMAT-LOMs were terminated by the ridge ablation.Local electrograms of tachycardia termination sitesshowed continuous fractionated potential in thediastole phase during AT in 3 cases (cases 3 to 5)

(Figure 3). Further RFCA was applied at the ridge tocreate a block in the MB-LA connections, and bidi-rectional conduction block across the MB-LAconnection was confirmed in these cases (Figure 4).Bidirectional block of MI line was confirmed in these 3cases after bidirectional block of the MB-LA connec-tions. The tachycardia was not terminated by ridgeablation in the remaining patient. RFCA was deliv-ered to the bifurcation of the CS and VOM, and PMAT-LOM was successfully terminated. Further RFCA wasapplied to this area to create a block in the CS-MBconnections, and bidirectional block of CS-MB con-nections was confirmed (Figure 5). Interestingly,in this case, incomplete MI block was demonstratedafter bidirectional block of the CS-MB connectionswas created. Furthermore, MB-LA connections stillremained.

In the patients with PMAT-LOM, 1 case had recur-rence of paroxysmal AF within 1 month after the

FIGURE 5 Bidirectional Block Between CS and MB Connections

(A) The activation sequences of the VOM were distal to proximal during the CS pacing. With the differential pacing site method, the conduction time from CS 3 to 4 to

VOM 1 to 2 (270 ms) during the CS 3 to 4 pacing was longer than the conduction time from CS 7 to 8 to VOM 1 to 2 (255 ms) during the CS 7 to 8 pacing. (B) The activation

sequences of CS were proximal to distal during VOM pacing. The conduction time from VOM 3 to 4 to CS 7 to 8 (255 ms) during VOM 3 to 4 pacing was longer than the

conduction time from VOM 1 to 2 to CS 7 to 8 (245 ms) during VOM 1 to 2 pacing. These observations were evidence of complete bidirectional block of the CS-MB

connections. Note: The conduction time from VOM 1 to 2 to LAA (160 ms) during VOM 1 to 2 pacing was shorter than the conduction time from VOM 3 to 4 to LAA (170

ms) during VOM 3 to 4 pacing. This observation suggested residual connections between the MB and LA. Furthermore, incomplete mitral isthmus block was demon-

strated by the conduction time from CS 3 to 4 to LAA (145 ms) during the CS 3 to 4 pacing that was shorter than the conduction time from CS 7 to 8 to LAA (165 ms)

during the CS 7 to 8 pacing. Abbreviations as in Figure 1.

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procedure during a mean follow-up period of 15 � 6months. No patients had recurrence of AT.

DISCUSSION

MAIN FINDINGS. The present study demonstratedthat:

1. The re-entrant circuits of PMATs following PVI forAF or mitral valve surgery involved epicardialconnections bypassing the MI in 16% of patients (6of 38); the majority of these (4 of 38) involved theMB epicardial connection.

2. The local electrograms of PMAT-LOM terminationsites of the ridge showed fractionated potentiallasting >100 ms in 3 of 4 patients.

3. Bidirectional blocks of either MB-LA connectionsor CS-MB connections are feasible and effectivelycure PMAT-LOMs.

RE-ENTRANT CIRCUITS OF PMAT USING LOM. The3-dimensional activation mapping showed a non-centrifugal pattern, and the activation of LA endo-cardium covered only 79% of the TCL. The remaining21% of noncovered re-entrant circuits presented inthe LOM of the epicardium. Although the local elec-trograms of PMAT-LOM termination sites of theridge showed fractionated potential at the early- tomid-diastole phase in 3 of 4 patients, the tachy-cardia was clearly distinguished from localized re-entry originating from the ridge by the entrainmentpacing technique. In cases 3 and 4, small fractionated

PERSPECTIVES

COMPETENCY IN MEDICAL KNOWLEDGE: The

re-entrant circuits of PMATs following PVI for AF or

mitral valve surgery involved epicardial connections

bypassing the MI in 16% of patients, the majority of

which involved MB epicardial connections. Bidirec-

tional block of either the MB-LA or CS-MB connec-

tions is feasible and effectively cures PMAT-LOMs.

TRANSLATIONAL OUTLOOK: Prospective clinical

trials are needed to assess the real percentage of

PMAT-LOM prevalence.

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continuous potentials following the large spiky po-tentials were recorded in the distal site of theVOM (VOM 1 to 2), whereas only large spiky potentialswere recorded in the proximal VOM. These findingsindicated that the area of slow conduction wasnot the main body of MB but the connection siteof MB-LA. There was a possibility that previousleft-side PVI line including ridge ablation led tothe slow conduction zone in the connection siteof MB-LA.

ABLATION STRATEGY OF PMAT USING LOM. Pre-vious reports showed that PMAT-LOM, which in-cludes the MB epicardial connections bypassingprevious endocardial MI lines, was terminated by thecreation of a bidirectional block of MI using ethanolinfusion into the VOM; however, the previous reportsdid not evaluate bidirectional blocks of either the MB-LA or CS-MB connections (12,13). In the present study,3 of 4 PMAT-LOMs were terminated by the creation ofa bidirectional block of the MB-LA connections.The remaining case of tachycardia was terminated bythe creation of a bidirectional block of the CS-MBconnection without MI block. Our data indicate thatit is not always necessary to create bidirectionalblocks of MI for terminating PMAT-LOM. Further-more, evaluation of the MI block may be misleadingwhen MB epicardial connections bypass the MI. Ac-curate evaluations of the MB connections are neces-sary to eliminate PMAT-LOM. Bidirectional block ofeither the MB-LA or CS-MB connections is necessaryto eliminate PMAT-LOM. Han et al. (14) reported 3electrophysiological types of MB-LA connections:single, double, and multiple connections. Creating abidirectional block of the MB-LA connections in pa-tients with multiple connections is technically diffi-cult. However, ablation should be initially attemptedat the ridge for creating blocks in the MB-LA con-nections because creating CS-MB blocks has potentialcomplications, such as coronary occlusion. CreatingCS-MB connections block is an alternative strategyin cases in which blocking MB-LA connections isdifficult.

CLINICAL IMPLICATIONS. PMATs using epicardialconnections including the LOM can develop after AFablation or mitral valve surgery. When the differencebetween PPI and TCL is >20 ms at the ablation site ofendocardial MI lines, the possibility of PMAT is easyto exclude. However, in this situation, PPI mappingshould be undertaken at the CS, including the VOM.For accurate diagnosis of PMAT-LOM, a 2-F electrodeneeds to be inserted in the VOM. However, when it istechnically difficult to insert the 2-F electrode in the

VOM or when the VOM is absent in cases ofsuspected PMAT-LOM, RFCA should be attempted atthe ridge in which the difference between PPI andTCL is #20 ms.

STUDY LIMITATIONS. First, the ridge ablation wasperformed during left-side PVI in all patients. Theridge ablation naturally led to the disconnection of theMB-LA connections. Furthermore, the majority ofpatients underwent RFCA in the CS for the creation ofMI block, and CS ablation can disconnect CS-MB con-nections. Procedures of PVI and MI ablation, includingCS, both carry the possibility of disconnecting the MBepicardial connections that bypass the MI. Further-more, a 2-F electrode was not inserted in all patients,and we were unable to insert it in patients withoutVOM. Finally, because these patients underwentextensive previous LA ablation, a long PPI could beobtained due to delayed conduction with misleadingentrainment results. Therefore, the real percentage ofPMAT-LOM may not be accurate.

CONCLUSIONS

The re-entrant circuits of PMATs following PVI for AFor mitral valve surgery involved epicardial connec-tions bypassing the MI in 16% of patients, the ma-jority of which involved MB epicardial connections.Bidirectional block of either the MB-LA or CS-MBconnections was feasible and effectively curedPMAT-LOMs.

REPRINT REQUESTS AND CORRESPONDENCE: Dr.Takekuni Hayashi, Division of Cardiovascular Medi-cine, Saitama Medical Center, Jichi Medical Univer-sity, 1-847, Amanuma, Oomiya-ku, Saitama 330-8503,Japan. E-mail: hayahsi1979@yahoo.co.jp.

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KEY WORDS atrial fibrillation, epicardialmapping, Marshall bundle, peri-mitral atrialtachycardia, radiofrequency catheterablation