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-, NO. -, 2019ª 2019 THE AUTHORS. PUBLISHED BY ELSEVIER ON BEHALF OF THE AMERICANCOLLEGE OF CARDIOLOGY FOUNDATION. THIS IS AN OPEN ACCESS ARTICLE UNDER
THE CC BY-NC-ND LICENSE (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Noninvasive Mapping of Premature
Ventricular Contractions by Merging
Magnetocardiography andComputed Tomography
Satoshi Aita, MD,a,* Kuniomi Ogata, MENG,c,* Kentaro Yoshida, MD,a,b Takeshi Inaba, RDCS,a Hisanori Kosuge, MD,a,d
Takeshi Machino, MD,a Yasuaki Tsumagari, MD,a Ai Hattori, MD,a Yoko Ito, MD,a Yuki Komatsu, MD,aKensuke Sekihara, PHD,e Hitoshi Horigome, MD,f Kazutaka Aonuma, MD,a Akihiko Nogami, MD,aAkihiko Kandori, PHD,c,y Masaki Ieda, MDa,y
ABSTRACTOBJECTIVES This study aimed to develop a novel premature ventricular contraction (PVC) mapping method to predict
PVC origins in whole ventricles by merging a magnetocardiography (MCG) image with a cardiac computed tomography(CT) image.
BACKGROUND MCG can noninvasively discriminate PVCs originating from the aortic sinus cusp from those originatingfrom the right ventricular outﬂow tract.
METHODS This study was composed of 22 candidates referred for catheter ablation of idiopathic PVCs. MCG and CT
were performed the same day before ablation. Estimated origins by MCG-CT imaging using the recursive null steering
spatial ﬁlter algorithm were compared with origins determined by electroanatomic mapping (CARTO, Biosense Webster,Inc., Diamond Bar, California) during the ablation procedure. Radiopaque acrylic markers for the CT scan and coil markers
generating a weak magnetic ﬁeld during MCG measurements were used as reference markers to merge the 2 images
3-dimensionally.
RESULTS PVC origins were determined by endocardial and epicardial mapping and ablation results in 18 (86%) patients(right ventricular outﬂow tract in 10 patients, aortic sinus cusp in 2 patients, interventricular septum in 1 patient, near His
bundle in 1 patient, right ventricular free wall in 1 patient, and left ventricular free wall in 3 patients). Estimated origins by
MCG-CT imaging matched the origins determined during the procedure in 94% (17 of 18) of patients, whereas theelectrocardiography algorithms were accurate in only 56% (10 of 18). Discrimination of an epicardium versus an
endocardium or right- versus left-sided septum was successful in 3 of 4 patients (75%).
CONCLUSIONS The diagnostic accuracy of noninvasive MCG-CT mapping was high enough to allow clinical use
to predict the site of PVC origins in the whole ventricles. (J Am Coll Cardiol EP 2019;-:-–-) © 2019 The Authors.
Published by Elsevier on behalf of the American College of Cardiology Foundation. This is an open access article under the
CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

From the aDepartment of Cardiology, University of Tsukuba, Tsukuba, Japan; bDepartment of Cardiology, Ibaraki Prefectural
Central Hospital, Kasama, Japan; cResearch and Development Group, Hitachi Ltd., Kokubunji, Japan; dTsukuba Advanced Imaging
Center, Tsukuba, Japan; eSignal Analysis Inc., Hachioji, Japan; and the fDepartment of Pediatrics, University of Tsukuba, Tsukuba,
Japan. *Drs. Aita and Ogata contributed equally to this work and are joint ﬁrst authors. yDrs. Kandori and Ieda contributed equallyto this work and are joint senior authors. This work was supported by JPS KAKENHI grant number JP17K09484. Dr. Aonuma hasreceived a research grant from Hitachi, Ltd. Dr. Nogami has received honoraria from Abbott and an endowment from Medtronic
and Johnson and Johnson. Mr. Ogata holds the patent JP6393173B, position estimation method, and position estimation system.
Dr. Kandori holds the patent JP6393173B, positional estimation method and positional estimation system. All other authors havereported that they have no relationships relevant to the contents of this paper to disclose.
The authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’
institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information,
visit the JACC: Clinical Electrophysiology author instructions page.
Manuscript received January 31, 2019; revised manuscript received May 14, 2019, accepted June 19, 2019.

ISSN 2405-500X

https://doi.org/10.1016/j.jacep.2019.06.010

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ABBREVIATIONS
AND ACRONYMS
3-D = 3-dimensional
CT = computed tomography
ECG = electrocardiography
ECGi = electrocardiographic
imaging

LV = left ventricular
MCG = magnetocardiography

RVOT = right ventricularquantum interference device magnetometer is used

contractions (PVCs) is an establishedas the magnetic sensor in MCG. Because the perme-treatment option to eliminate patient symp-

ability of the human body is constant, detection oftoms and prevent PVC-induced cardiomyop-

the heart’s magnetic ﬁeld is barely affected by otherathy

organs around the heart such as fat, bone, and lungs

and

heart

failure(1).

Althoughtechnologies such as 3-dimensional (3-D)(6–8).

mapping, irrigated-tip ablation catheters,

The entire study protocol is outlined in Figure 1 andand contact force monitoring help operators

the Central Illustration. CT examinations were per-toformed 1 week before catheter ablation with a 320-row
CT scanner (Aquilion ONE GENESIS Edition, Canonon the location of the arrhythmia origin (2).

Medical Systems, Otawara, Japan). Just before the CT

It is especially difﬁcult to eliminate PVCs

scan, 5 custom-made radiopaque spherical markers

with an origin near the His-bundle region or

fabricated with acryl and ﬁxed on an L-shaped board

in the left ventricular (LV) summit, the intra-

were placed on the patients’ chests to determine theirmural layer, or the epicardial aspect. Electro-

3-D location relative to the heart (Figure 1A). The pa-

cardiography (ECG) algorithms can identify

rameters for CT imaging were prospective ECG-gated

the area of origin of ventricular arrhythmias, but theiracquisitions, tube potential of 120 kVp, and detector

spatial resolution is fundamentally low and theirconﬁguration of 320  0.5 mm. Scanning was initiateddiagnostic accuracy can be impaired by the patient’s

after a threshold of 150 Hounsﬁeld units was reached

physical characteristics (e.g., obesity and cardiac

in the ascending aorta. The CT images were recon-rotation and offsets of ECG lead placement) (3).

structed at a 0.5-mm slice thickness in the diastolic

Although the utility of magnetocardiography (MCG)

phase (basically 75% to 77%) of the R-R interval. The

to discriminate PVCs originating from the right ven-

CT Digital Imaging and Communications in Medicine

tricular outﬂow tract (RVOT) from those originating

images were viewed and edited with Expert INTAGE

from the aortic sinus cusps was previously reported(CYBERNET SYSTEMS CO., Tokyo, Japan).

RENS = recursive null steering

outﬂow tract

estimated from the magnetic ﬁeld. A superconducting

catheterprocedural

contraction

catheter ablationR

ablation(RFCA) for premature ventricularadiofrequency

complexity, efﬁcacy, and safety still depend

PVC = premature ventricular

RFCA = radiofrequency-, NO. -, 2019
- 2019:-–-MCG-CT Mapping of PVCs

map

and

ablatePVCs,from our center (4,5), this system did not allow map-

Just after the CT scan, the patient was moved toping of the whole right and left ventricles and identi-

the magnetically shielded room to undergo MCG

ﬁcation by the absolute location (coordinates) of therecording. MCG methodology has been described inorigins. To overcome these limitations and increasedetail previously (4,5,9,10). An MCG system (MC-the clinical utility of the MCG system for arrhythmia

6400, Hitachi High-Technologies Corporation, Tokyo,

treatments, we developed a custom-made technology

Japan) with 64 magnetic sensors was used to measure

to merge MCG images with 3-D computed tomography

the MCG signal and the magnetic ﬁeld signal gener-(CT) images. The aim of this prospective study was toated from the marker coils. The magnetic sensors

validate this method by comparing the estimated PVC

were in an 8  8 matrix with a pitch of 25 mm and aorigin on the MCG-CT merged images with that on themeasurement area of 175  175 mm. The MCG signals

map depicted on a 3-D mapping system during cath-from each patient were recorded in the resting stateeter ablation.

in the anteroposterior direction for 2 min at a sampling rate of 1 kHz. The MCG signals were passed

METHODSSTUDY POPULATION. Twenty-two consecutive pa-

tients with PVCs refractory to antiarrhythmic drugs
referred for catheter ablation in our hospital between
March 2017 and February 2018 were prospectively
included in this study. All except 2 patients withcoronary artery disease were free of any structural
heart disease. The study protocol was approved by
the local Institutional Review Board, and all patientsprovided their informed written consent.

through a 0.1- to 50-Hz band-pass ﬁlter and a 50-Hz
power line noise ﬁlter. As during CT scanning, thepatients’ arms were toward their head during MCG
recording. Before MCG recording for PVCs, triaxial (xy-z axis) circular marker coils, which were ﬁxed on an
L-shaped board as the acrylic markers for the CT scan,were placed at the same position as that during the CT
scan (Figure 1B). A coil driver applied alternating
electric current (40 Hz) to each marker coil. The positions of the marker coils on the patient were estimated from the measured magnetic ﬁeld signals byusing an optimization method (Online Appendix).

MCG AND CT. MCG can noninvasively measure theThen, the coordinates of the coil markers for MCG

weak magnetic ﬁeld generated by the human heart.

were merged with those of the acrylic markers for CT

The electric current distributions in the heart are(Figure 1C). Finally, the MCG signals from the PVCs

JACC: CLINICAL ELECTROPHYSIOLOGY VOL.

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Aita et al.

- 2019:-–-MCG-CT Mapping of PVCsF I G U R E 1 Entire Study Protocol (See Text for Details)(A) X-ray CT measurement. (B) Coil magnetic ﬁeld measurement. (C) Coordinate transformation. (D) MCG measurement of PVCs. Acrylic
markers for computed tomography imaging (†) and marker coils for magnetocardiography recording (‡) are shown. CT ¼ computed
tomography; MCG ¼ magnetocardiography; PVC ¼ premature ventricular contraction.

were recorded for 2 min, averaged, and then used todeveloped analysis software in MATLAB (MathWorks,

reconstruct the 3-D current distribution by applying

Inc., Natick, Massachusetts) for estimating the posi-

the recursive null steering (RENS) spatial ﬁlter

tion of the marker coils and 3-D current distribution

algorithm (Figure 1D) (Online Appendix) (11). We

from the MCG measurement.

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- 2019:-–-MCG-CT Mapping of PVCsC E NT R AL IL L U STR AT IO N Noninvasive Mapping of PVCs by Merging MCG and CT Images

A

X-Ray CT Measurement

X-ray CTC

Coordinate Transformation

Position ofmarker coils

CT image

Position of CT
markers

CT markers
Heart

Position of CT markers

Transformation of CT coordinate
system to MCG coordinate system

Detection of positions of CT markers

BD

Coil Magnetic Field Measurement

MCG Measurement
MCG

MCG
Magnetic
sensorMagnetic
sensorCoil magnetic
fieldElectricalcurrent
Marker coils

Cardiacmagnetic field
Position of marker coils

3-D electrical current

Estimation of 3-D electrical current

Estimation of positions of marker coils

Ablation sites

LAO60°CRA20°

2-D image (Coronal)
3-D image
MCG-CT mapping

CARTO mapping

Aita, S. et al. J Am Coll Cardiol EP. 2019;-(-):-–-.
CT ¼ computed tomography; MCG ¼ magnetocardiography; PVC ¼ premature ventricular contraction.

ELECTROPHYSIOLOGICAL STUDY AND CATHETER

spacing; Inquiry Luma-Cath Fixed Diagnostic Cath-ABLATION. Afterob-eter, Abbott, Saint Paul, Minnesota) inserted from thetained, electrophysiological study and RFCA were

subclavian vein (2). A 7-F quadripolar 3.5-mm-tip

performed. Antiarrhythmic drugs were discontinued

open-irrigated ablation catheter (Navistar Thermo-

for at least 5 half-lives before the procedure. Elec-

Cool STSF, Biosense Webster, Inc.) was used fortrode catheters were placed near the His bundle,

mapping and ablation. A 3-D electroanatomic map-

coronary sinus, and right ventricular apex. When aping system (CARTO System Version 4.3.5, Biosense

target PVC was suspected to originate from the left

Webster, Inc.) was used to identify the earliest acti-

outﬂow tract, a 2-F mapping catheter (Japan Lifeline

vation site of the target PVC. The radiofrequency

Co., Ltd., Tokyo, Japan) was advanced into the great

energy was delivered at a maximum power of 50 W

cardiac vein through the inner lumen of the catheter

and a maximum temperature of 42  C. Pace mapping

placed at the coronary sinus (4-mm interelectrode

was also performed to search for optimal RFCA

informed

consent

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sites. Successful RFCA was deﬁned as complete
elimination of the clinical PVC and noninducibility by

F I G U R E 2 Segmentation of the Left and Right Ventricles

programmed ventricular stimulation or by a drug
provocation test (isoproterenol up to 0.06 mg/kg/min,
20 mg adenosine triphosphate, and 10 mg edrophonium). We deﬁned the site of successful RFCA as thesite of PVC origin.
COMPARISONBETWEEN

MCG-CT

MAP

AND

ELECTROANATOMIC MAP. The right and left ventri-

cles were divided into 9 and 11 segments, respectively, that were derived from schemas depicted in aprevious study (Figure 2) (12). The segment in which aprocedure-derived PVC origin was identiﬁed wasdetermined

based

on

the

electroanatomic

mapmerged with CT imaging by the CARTO system (redclosed dots in Figure 2). The operator judged thesegment of the procedure-derived origin, and then 2electrophysiology fellows blinded to the RFCA results
independently judged the segment of the MCG-CT–
derived origin. These fellows also judged whether the
MCG-CT–derived origin was considered endocardial
versus epicardial or a left- versus right-sided septum.
Discrepancies were resolved by consensus. Although
we prospectively included patients in this study, an

A ¼ inferoapical septum; B ¼ anteroapical septum; C ¼ anteroapical free wall;
D ¼ anterobasal free wall; E ¼ anterobasal and mid-septum; F ¼ inferobasal septum;
G ¼ inferomedial free wall; H ¼ inferolateral free wall; I ¼ mid-inferior wall;
J ¼ inferoapical free wall; K ¼ aortic sinus cusps; L-a ¼ anteroseptal outﬂow tract; Lm ¼ mid-septal outﬂow tract; L-p ¼ posteroseptal outﬂow tract; L-f ¼ outﬂow tract freeestimated PVC origin could not be determined before

wall; M ¼ basal septum; N ¼ mid-septum; O ¼ apical septum; P ¼ inferior wall; Q ¼ lateralcatheter ablation because data analysis took 3 tofree wall.

4 weeks.
FOLLOW-UP

PROTOCOL. ECG

wasactivation mapping. Pace mapping was mainly used

continued in all patients from the end of RFCA andin the remaining 7 patients. A correct diagnosis bythroughout hospital stay. After discharge, the pa-

MCG-CT mapping was obtained in 17 of the 18 pa-

tients were followed up at the outpatient clinic, withtients (94%). Patients with an epicardial origin in themonitoring

visits at 1, 3, and 6 months after RFCA, and elimina-

LV anterior wall (Patient #18) (Figure 3), an endocar-

tion of the PVCs was conﬁrmed by 12-lead and Holter

dial origin in the LV lateral wall (Patient #7), andECGs recorded at each follow-up visit.

right-sided ventricular septum origin (Patient #3)
were correctly diagnosed by MCG-CT mapping. In the
1 patient (Patient #16) with failed diagnosis, the cor-

RESULTSPATIENT

rect origin was the epicardial aspect of the LV posteCHARACTERISTICS. Eighteenpatientsrior wall, whereas the MCG diagnosis was thewere included for further analysis after 4 patientsendocardialwith failed ablation were excluded from the study.

Figure 1). Overall, diagnosis of an epicardium versus

aspectofthelateralwall(OnlinePatient details and PVC characteristics are presented

an endocardium and a right-sided versus left-sided

in Table 1. The mean patient age was 54  17 years,

septum was correctly discriminated by MCG-CT

and 12 (67%) women were included. The mean LV

mapping in 3 of 4 patients (75%).

ejection fraction was 65  6%. The QRS morphology

ACCURACY OF ECG ALGORITHMS. The ECG algo-of the PVC was a right bundle branch block pattern inrithms provided by previous studies were also

3 (17%) patients and a left bundle branch block

applied to our patients (13–15). They were accurate inpattern in 15 (83%) patients.

10 of the 18 patients (56%) as shown in Table 1.

PVC ORIGINS AND MCG-CT MAPPING ACCURACY. The

REPRESENTATIVE

distribution of procedure-derived PVC origins in all 18

year-old man had frequent PVCs originating fromCASES. P a t i e n t# 1 8 . This 57-

patients is shown in Table 1 and Figure 2. In 15 cases

the LV outﬂow tract. A 12-lead ECG of the PVCs is(68%), spontaneous PVC constantly occurred during

shown in Figure 3A. Figure 3B shows the MCG current

the procedure, and we could map the PVC origin bymaps merged with CT imaging in the horizontal,

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- 2019:-–-MCG-CT Mapping of PVCsT A B L E 1 All Patients’ Data

Patient #

Age,
yrs

Sex

BMI,
kg/m 2

BNP,
pg/ml

PVC
Burden, %EF,%

BBB Type þ
Axis

Trans.
Zone

V1
QRS

Coupl.,
ms

Analyzed
PVCs

Origin(ECG)

Origin(MCG)

Origin
(ABL)

Seg.

Area
Ablated, cm 2

MCG
vs. ABL

Successful ablation
1

29

F

22.4

19

19.2

65

LBBB
IA

V45

rS

451

76

RVOT
SEP

RVOT
SEP

RVOT
SEP

L-m

0.9

Match

2

30

F

18.5

5

5.0

62

LBBB
IA

V3

QS

400

1

RVOT
POST

RVOT
POST

RVOT
POST

L-p

1.0

Match

3

67

M

22.3

27

26.7

69

LBBB LAD

V3

QS

411

38

HB

SEP
(RV)

SEP
(RV)

N

1.9

Match

4

68

F

20.5

13

13.3

73

LBBB
SA

V5

QS

465

61

RV
INF

RV
INF

RV
INF

P

1.6

Match

5

69

M

25.7

27

27.0

69

LBBB
IA

V34

rS

506

21

ASC

ASC

ASC

K

0.8

Match

6

57

F

29.1

13

12.8

70

LBBB
IA

V4

rS

440

1

RVOT
POST

RVOT
AS

RVOT
AS

L-a

1.1

Match

7

80

M

25.6

11

11.0

60

RBBB RAD

V56

RR

471

4

LV
LAT

LV
LAT
(endo.)

LV
LAT(endo.)

I

0.9

Match

8

77

F

21.4

18

18.0

65

LBBB
IA

V23

qrS

451

38

ASC

ASC

ASC

K

0.9

Match

9

53

F

20.9

42

15.0

62

LBBB
IA

V23

rS

408

17

RVOT
AS

RVOT
AS

RVOT
AS

L-a

1.8

Match

10

34

F

22.2

85

33.7

53

LBBB
IA

V34

QS

451

38

RVOT
FW

RVOT
AS

RVOT
AS

L-a

1.3

Match

11

36

F

23.0

67

27.0

57

LBBB
IA

V34

rS

428

27

RVOT
FW

RVOT
FW

RVOT
FW

L-f

1.2

Match

12

52

M

25.1

12

11.0

68

LBBB
IA

V34

rS

627

15

RVOT
FW

RVOT
POST

RVOT
POST

L-p

1.4

Match

13

40

F

21.2

31

17.0

73

LBBB
IA

V45

rS

376

81

RVOT
FW

RVOT
AS

RVOT
AS

L-a

1.3

Match

14

43

F

22.7

42

16.8

69

LBBB
IA

V34

QS

484

8

RVOT
AS

RVOT
AS

RVOT
AS

L-a

2.5

Match

15

39

F

19.7

12

22.0

67

LBBB
IA

V34

rS

455

1

RVOT
SEP

RVOT
FW

RVOT
FW

L-f

1.5

Match

16

79

M

22.9

56

8.0

65

RBBB
SA

V56

RR

444

1

LV
INF

LV
LAT
(endo.)

LV
POST(epi.)

H

1.1

Mismatch

17

70

F

21.8

10

6.3

64

LBBB LAD

V12

QS

429

15

HB

HB

HB

M

0.7

Match

18

57

M

37.7

58

39.0

56

RBBB
IA

< V1

Rs

538

41

ASC

LV
ANT
(epi.)

LV
ANT(epi.)

D

1.0

Match

Failed ablation
19

69

F

25.3

35.9

13.7

62

LBBB
IA

V3

rS

440

5

RVOT
AS

LV
ANT
(epi.)

NA

NA

NA

NA

20

66

F

25.0

27.0

27.7

45

LBBB
IA

V23

qrS

437

26

RVOT
SEP

RVOT
SEP

NA

NA

NA

NA

21

56

M

21.7

42.7

15.8

73

LBBB LAD

V12

qrS

520

16

RVOT
SEP

LV
SEP

NA

NA

NA

NA

22

39

F

20.6

48.9

8.0

58

LBBB
LAD

V45

rS

556

2

RV
LAT

RV
SEP

NA

NA

NA

NA

ABL ¼ ablation; ANT ¼ anterior wall; AS ¼ anteroseptal; ASC ¼ aortic sinus cusp; BMI ¼ body mass index; BNP ¼ brain natriuretic peptide; Coupl. ¼ coupling interval; ECG ¼ electrocardiography; EF ¼ left
ventricular ejection fraction; endo. ¼ endocardium; epi. ¼ epicardium; F ¼ female; FW ¼ free wall; HB ¼ His bundle; IA ¼ inferior axis; INF ¼ inferior wall; LAD ¼ left axis deviation; LBBB ¼ left bundle branch
block; LAT ¼ lateral wall; LV ¼ left ventricle; M ¼ male; MCG ¼ magnetocardiography; NA ¼ not applicable; POST ¼ posterior wall; PVC ¼ premature ventricular contraction; RAD ¼ right axis deviation;
RBBB ¼ right bundle branch block; RV ¼ right ventricle; RVOT ¼ right ventricular outﬂow tract; SA ¼ superior axis; SEP ¼ septum; Seg. ¼ segment; other abbreviations as in Figure 2.

coronal, and sagittal planes where the maximum

dot). The results from CARTO and ﬂuoroscopic im-

current during the PVC is shown in red. Figure 3C

aging during the ablation procedure are shown inindicates the coordinates of PVC origin by the

Figure 3E. Based on the recording of the local elec-

crossed lines, and Figure 3D indicates them 3-

trograms (Figure 3F), the great cardiac vein was acti-

dimensionally on the CT map. Of note, the left coro-vated earlier than the LV endocardium and aortic

nary artery on the epicardial aspect (red dashedsinus cusps. First, we applied RFCA to the left coro-arrows) was adjacent to the PVC origin (red closed

nary cusp followed by the LV endocardium (left andJACC: CLINICAL ELECTROPHYSIOLOGY VOL.

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- 2019:-–-MCG-CT Mapping of PVCsF I G U R E 3 Patient #18 With PVCs Originating From the Left Ventricular Epicardium(A) Electrocardiography, (B) electrical current maps merged with CT imaging in the horizontal, coronal, and sagittal planes. (C) Coordinates of
PVC origin shown by the crossed lines. (D) 3D CT map, (E) ﬂuoroscopic imaging and CARTO mapping, and (F) intracardiac electrogram inPatient #18 with PVCs originating from the epicardial aspect of the left ventricular anterior wall. The blue dots in B correspond to the positionof the maximal current amplitude of the 3-D electrical current distribution reconstructed by the RENS ﬁlter. These dots were automaticallylocated based on the numerical data by the system. The yellow dots in E indicate the successful ablation sites in the great cardiac vein (GCV)(see text for details). ABL ¼ ablation; ASC ¼ aortic sinus cusp; CS ¼ coronary sinus; GCV ¼ great cardiac vein; LAO ¼ left anterior oblique view;
LCC ¼ left coronary cusp; LV endo. ¼ left ventricular endocardium; PVC ¼ premature ventricular contraction; RAO ¼ right anterior oblique view.

Continued on the next pagebottom panels of ﬂuoroscopic images in Figure 3E).

FAILED ABLATION. The details of failed ablation areTransient suppression of the PVCs during the appli-

described in Table 1. In Patient #19, MCG-CT mapping

cations was observed, but the PVCs immediately

estimated the origin in the epicardial aspect of therecurred. Next, we advanced the ablation catheter

anterior wall of the left ventricle. Although we tried

into the great cardiac vein (right panel of ﬂuoroscopic

to ablate it from the great cardiac vein, high imped-

imaging in Figure 3E). Its local activation time pre-ance did not allow delivery of radiofrequency appli-ceded QRS onset by 30 ms, and ablation in the vein

cations. In Patient #20, MCG-CT mapping estimatedeliminated the PVCs completely. It was notable thatthe origin in the septal aspect of the RVOT, but thethe successful ablation site matched the estimatedaortic sinus cusp was targeted for ablation. Because

origin by MCG-CT mapping.

the PVC was infrequently observed during the pro-P a t i e n t # 7 . The estimated origin by MCG-CT map-

cedure, it was difﬁcult to identify the correct origin.

ping (red closed dot) was the endocardial lateral

In Patient #21, MCG-CT mapping estimated the origin

wall in the left ventricle (Figures 4A to 4C, Table 1,

in the LV septum, but only the right ventricular

Online Figure 2). Ablation at the same site on the

septum was actually targeted for ablation and the LV

CARTO map (Figure 4D) successfully eliminated theseptum was not mapped. In Patient #22, MCG-CT

PVCs.

an

mapping estimated the origin in the right ventricu-

endocardial origin but not an epicardial origin inlar septum. Ablation was applied to the lateral wall of

this case.

the RV, but it did not eliminate the PVCs.

Notably,

MCG-CT

mapping

predicted

Patient #2, 10, and 11. Three patients with PVCs originating from the RVOT are shown in Figures 5A to 5C

DISCUSSION(Table 1, Online Figure 3). The red closed dots in
Figures 5A to 5C indicate the estimated origins by MCG-

The key observations of the present study are as fol-

CT mapping, and the ablation sites are shown by red

lows: 1) a novel method to merge the MCG map withtags on the respective CARTO maps. The posterior site

the CT image using custom-made markers workedof the RVOT (Figure 5A), anterior site of the RVOT

successfully and identiﬁed the sites of origin in pa-(Figure 5B), and free wall site of the RVOT (Figure 5C)tients with PVCs originating from both ventricles; 2)were correctly diagnosed by MCG-CT mapping. The

accuracy was 94% in patients who had PVCs suc-

PVCs in these patients were successfully eliminated by

cessfully eliminated by catheter ablation, whereas

ablation.

that of the ECG algorithm was lower as previously

P a t i e n t # 1 6 . The mismatch of results is described inreported (16); and 3) from the theoretical and math-detail in Online Figure 1.

ematical viewpoints, this technology may have the78Aita et al.

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- 2019:-–-F I G U R E 4 Patient #7 With PVCs Originating From the Left Ventricular Endocardium(A) Electrical current maps merged with CT imaging in the horizontal, coronal, and sagittal planes. (B) Coordinates of PVC origin shown by thecrossed lines. (C) 3D CT map and (D) CARTO map in Patient #7 with premature ventricular contractions originating from the endocardial side ofthe lateral wall of the left ventricle (see text for details). LAO ¼ left anterior oblique view; SUP ¼ superior view.

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MCG-CT Mapping of PVCsF I G U R E 5 Patients With PVCs Originating From the Right Ventricular Outﬂow Tract

Magnetocardiography–computed tomography (MCG-CT) mapping and CARTO mapping in Patients #2, #10, and #11 with PVCs originating from the right ventricular
outﬂow tract, (A) posterior site, (B) anterior site, and (C) free wall site, respectively (see text for details). CRA ¼ cranial view; LAO ¼ left anterior oblique view;
PVC ¼ premature ventricular contraction; RAO ¼ right anterior oblique view.

Continued on the next page

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potential to identify transmural distribution of sites

analyzed and averaged, and the distance between theof origin (epicardial vs. endocardial origin and right-

MCG sensors and PVC origin. However, most of thesesided vs. left-sided septal origin). Although thisnegative factors can be overcome. The respiratory

study provides only preliminary results, the ﬁndings

effect may be minimized by performing CT scanningfrom a few cases shown in the ﬁgures have encour-and CARTO mapping during the expiratory phase.

aged us to undertake additional study of more sub-

The end-diastolic phase was selected throughout thejects and update the merge function.

CT scan, MCG recording, and CARTO mapping. The

Fundamentally, MCG has higher spatial resolution

volume status was consistent throughout the mea-

than ECG because the magnetic ﬁeld is not distorted

surements because CT and MCG mapping wereby ﬂow through tissues such as lungs, bones, andconsecutively performed within a few hours of eachmuscles. The RENS spatial ﬁlter algorithm canother on the same day, and all measurements andreconstructtreatment were performed in the fasting state.

asourcedistribution

from

bio-

resolution

Although the PVC coupling intervals varied (Table 1),

conventional

accuracy did not appear to be affected in this patient

methods. The robustness of this method to the source

series. One possible negative contributor is the small

correlation was previously validated in our computer

number of PVCs analyzed or averaged. In the single

simulation and our experiments using auditory-

patient (Patient #16) with failed localization by MCG-

evoked magnetoencephalographic data (11). The pre-CT mapping and with PVCs originating from the LV

sent method to 3-dimensionally merge MCG and CT

posterior wall, only 1 PVC was recorded during theimages further enhanced these advantages and the

MCG measurement. This factor may be associatedclinical utility of the MCG system in arrhythmia

with a decreased signal-to-noise ratio. Another factor

treatments.

is the longer distance between the MCG sensors andelectromagnetic
considerably

data

with

a

spatialhigher

than

that

of

the origin of the PVCs. Importantly, the LV posterior
MERGING THE MCG MAP WITH THE CT IMAGE.

wall is further from the sensors than the RVOT area.

Although our mathematical evaluation of the MCG-CT

This could be 1 reason for failed localization because

merged method calculated its error to be withinmagnetic signals attenuate in proportion to the

3 mm, its accuracy may be impaired by several factors

distance.

in humans such as effects caused by the respiratory

Taken together, overall accuracy was ethicallyphase or cardiac cycle (systole or diastole), volume

acceptablestatus, PVC coupling intervals, number of PVCs

cohort in a manner that informs the operator of thetoconductaprospective

validation

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estimated PVC origin before catheter ablation. Also,

origins determined by MCG mapping on an original 3-

the overall accuracy of the ECG algorithms was lower

D CT image. In fact, our method could potentiallythan that of the MCG method, and, particularly, their

allow the accurate diagnosis of epicardial origins andaccuracy in the subdivision of the PVC region was

the side (right vs. left) of septal origin. Of note, a veryquite low, supporting the clinical value of MCG overrecent study reported negative results of ventricular

ECG (16).

mapping by the ECGi system, which questions many

PREVENTING

CORONARY

ARTERYINJURY. It

iswell-known that coronary artery injury can occur as adirect thermal effect of RFCA. Although the rightcoronary artery and left circumﬂex artery are likely tosuffer from such a complication in the ablation of
Wolff-Parkinson-White syndrome and mitral isthmus
ablation, the left anterior descending artery on theepicardial aspect is also at risk for thermal injury (17).
Although PVCs can potentially be treated by ablationfrom the coronary sinus and its branches (2), the riskof coronary artery injury should be assessed, ideallyby a noninvasive method, before the ablation procedure is performed. In this study, we noticed thatthe locations of the coronary arteries were helpful as
landmarks to recognize the detailed and exact location of sites of origin. Because the coronary arteries
were precisely depicted in our CT images without
processing such as smoothing, attenuation, and volume reconstruction, they provided important safety
information to physicians before the procedure andmay be 1 of the advantages of our mapping
technology.

of the conclusions previously drawn from ECGi
mapping. This study directly compared the ECGi map
and invasive epicardial contact map, and primary
epicardial breakthroughs imaged using both methods
resulted in very large mean absolute errors of over
70 mm (23).
STUDY LIMITATIONS. First, the study volume issmall. Only 2 epicardial origins and 2 aortic sinus cusp
origins were included. However, the wide distribution of origins other than those in the common
outﬂow tracts was helpful in evaluating the accuracyof this system in the whole ventricles.
Although we prospectively included patients inthis study, the estimated PVC origin could not be
determined before catheter ablation because data
analysis took 3 to 4 weeks. Currently, we haveestablished a method to analyze data and reconstructand merge the 3-D map within a few days and conducted a validation study in which the estimatedresult is informed to the operators before the ablation
procedure.
Although we attempted to minimize negative fac-

PRIOR STUDIES. Noninvasive body surface mapping

tors impairing the accuracy of this mapping system,

systems for the detection of PVCs, so-called electro-

respiratory and cardiac motion should particularly be

cardiographic imaging (ECGi) (CardioInsight Tech-taken into consideration to maximize the perfor-

nologies,

mance of this mapping technology in clinical practice.

Inc.,

Cleveland,Ohio)(16,18)andanoninvasive epicardial and endocardial electrophys-

This study was not a direct comparison of MCG andiology system (EP Solutions SA, Yverdon-les-Bains,technologies such as ECGi; it only investigated the

Switzerland) (19–22), were previously introduced.

system’s ability to detect arrhythmia origin (electrical

Jamil-Copley et al. (16) investigated 24 patients withonset). The ability of this technology in other types ofoutﬂow tract PVCs using ECGi (RVOT in 18 patientsarrhythmias remains to be evaluated in futureand LVOT in 6 patients). The accuracy for thestudies.

discrimination between RVOT versus LVOT was 96%.

A quantitative analysis that can provide the spatial

Wissner et al. (21) reported that in 18 (86%) of 21 pa-

resolution of this mapping system could not be con-tients with PVC/VT, the correct ventricular segment

ducted because MCG recording requires a magneti-

was diagnosed as a result of nonquantitative assess-cally shielded room, making it difﬁcult to perform

ment. Of note, these systems depend not on theduring pace mapping. Because our technology was

original but the mathematically reconstructed uni-completely custom-made, we could not load MCG-CT

polar electrograms and apply a method to project thedata into the commercially developed CARTO map-

location data on the simpliﬁed heart torso createdping system. Errors in merging the electroanatomic

from CT images. This may result in decreased accu-

map depicted by the ablation catheter and CT imaging

racy or an error in discriminating endocardial,(within the CARTOMERGE system, Biosense Webster,

epicardial, and intramural origins. Our novel methodInc.) cannot be ignored in the assessment of thiscan potentially overcome these limitations by notstudy. We are now conducting a new validation study

projecting but simply merging the coordinates ofto allow more accurate merging of the CT, MCG, and

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- 2019:-–-MCG-CT Mapping of PVCsCARTO maps. This upgrade will allow completequantitative analysis of the accuracy of this MCG-CT
mapping method in the near future.

PERSPECTIVESCOMPETENCY IN MEDICAL KNOWLEDGER:
adiofrequency catheter ablation for PVCs has become

CONCLUSIONS

an established treatment option. However, procedural

In this preliminary study, MCG-CT mapping could
identify sites of PVC origins in both ventricles
noninvasively and semiquantitatively. A validation
cohort including more patients and further updates tothe system are needed to justify the use of contrast
medium and radiation during CT scanning and toclarify whether this technology improves proceduraloutcomes, procedural efﬁciency, and the safety ofcatheter ablation for ventricular arrhythmias.

complexity, efﬁcacy, and safety still depend on thelocation of the PVC origin. Although electrocardiographic algorithms can identify the area of origin ofventricular arrhythmias, their accuracy is fundamentally limited due to the low spatial resolution. A
custom-made technology to merge magnetocardiography images with 3-D computed tomography images
could accurately identify sites of PVC origin
distributed in the whole ventricles (17 of 18, 94%).
TRANSLATIONAL OUTLOOK: This technology

ADDRESSFOR

CORRESPONDENCE:

Dr. Kentaro

Yoshida, Department of Cardiology, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba

may have the potential to improve proceduraloutcomes, procedural efﬁciency, and the safety ofcatheter ablation for ventricular arrhythmias.

305-8575, Japan. E-mail: kentaroyo@nifty.com.

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98ra84.

KEY WORDS catheter ablation, computed
tomography, magnetocardiography,
noninvasive mapping, premature ventricular
contraction

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A PP END IX For supplemental methods andﬁgures, please see the online version of thispaper.

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ventricular contractions. Europace 2017;19:843–9.

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