Electro-Anatomical Approach to Membranous Septal Aneurysm: Potential as a Focus of Critical Ventricular Arrhythmias

doi:10.4236/ss.2013.412105

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Surgical Science, 2013, 4, 543-546

Published Online December 2013 (http://www.scirp.org/journal/ss)

http://dx.doi.org/10.4236/ss.2013.412105

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Electro-Anatomical Approach to Membranous Septal

Aneurysm: Potential as a Focus of Critical

Ventricular Arrhythmias*

Hajime Imura1, Hiroshige Murata2, Masami Ochi1

1Department of Cardiovascular Surgery, Nippon Medical School Hospital, Tokyo, Japan

2Department of Cardiology, Nippon Medical School Hospital, Tokyo, Japan

Email: [email protected]

Received November 8, 2013; revised November 28, 2013; accepted December 5, 2013

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In accor-

ABSTRACT

Membranous septal aneurysm (MSA) is a rare anomaly and known to cause ventricular tachycardia and atrioventricular

block. However, underlying mechanisms have not been addressed in its long history. We report first 3-D electro-ana-

tomical mapping of MSA during and three years following the surgery. An elderly patient underwent a surgery for

MSA. In the map ping, we located the His b undle near MSA and observed delayed potentials arou nd MSA. Our report

showed that electrophysiological character of myocardium was changed around MSA and this change might be a reason

for ventricular tachycardia and atrioventricular block. An ordinary surgery for MSA might not resolve this problem

since we still observed delayed potentials three years after the surgery.

Keywords: Membranous Septal Aneurysm; Electro-Anatomical Mapping; Ventricular Tachycardia; Atrioventricular

Block

1. Introduction

The interventricular septum consists of muscular and

membranous components. Aneurysm of the membranous

portion, which was first described in 1826, is a cong enit-

al structure protruding into the right ventricle and can be

associated with various pathologies such as rupture, ob-

struction in the right ventricle and arrhythmias [1]. Ven-

tricular tachycardia (VT) and complete atrioventricular

block (AVB) were presented as complications of mem-

branous septal aneurysm (MSA) in old reports [2] and

still described as crucial problems in current literatures

[3,4], however, only few studies performed electrophy-

siological investigation for MSA in its long history. To

address the underlying mechanisms of such arrhythmias,

both anatomical and electrophysiological approaches are

indispensable, however, they have not been implemented

due to the rarity and difficulty to approach.

A 3-D electroanatomical mapping system (CARTO)

constructs a 3-D structure of the heart and draws a col-

or-coded map of impulse propagation and voltage on the

figure using electromagnetic technology. The system has

been well-established in describing the arrhythmogenic

substrate during open-heart surgery as well as catheter

ablation for VT. Here we report the first CARTO map-

ping during and three years following surgery for a case

of this rare pathology.

2. Case Presentation and Scientific Findings

An elderly patient was referred to our hosp ital for surgic-

al treatment of MSA. Because MSA’s size significantly

increased and she became symptomatic (chest discomfort

and palpitation), she elected to undergo surgical treat-

ment. She had no other medical history. In preoperative

examinations, her resting electrocardiogram showed

normal sinus rhythm with no abnormalities. No signifi-

cant ventricular or other arrhythmias were observed dur-

ing 24 hours of electrocardiogram monitoring. Also,

blood examination yielded no abnormal data. An echo-

cardiogram disclosed a large MSA (3.5 cm in height)

while ventricular septal defect was absent. Her coronary

*Conflict of interest: none declared.

H. IMURA ET AL.

544

angiogram showed no stenotic lesions.

Because ventricular septal defect was absent, we per-

formed CARTO mapping (CARTO-XP, Biosense Web-

ster, Diamond Bar, CA, USA) prior to arresting the heart

under cardiopulmonary bypass in surgery (Figure 1). In

the mapping (Figure 2) MSA exhibited a small amount

of electrical activity (fractionated potential), which was

obviously from the far field because there were no mus-

cular cells in a histopathological examination (Figure 3).

More significantly, we observed delayed potential around

MSA (Figure 2). After the mapping, the aneurysm was

resected and the defect was closed with a patch. The pa-

tient showed uneventful postoperative course and her

Figure 1. (A) Membranous septal aneurysm (MSA) with the

heart beating. The MSA was extremely large between the

anterior and septal leaflets of the tricuspid valve and bulges

into the right ventricle. A catheter was placed near the His

bundle. (B) MSA under cardiac arrest. A chordae-like

structure was seen.

symptoms were improved, however, the delayed poten-

tial was still observed three years after the surgery (Fig-

ure 4).

3. Discussion

This report is the first to show a 3-D voltage mapping

and approach the mechanism of arrhythmias in MSA. We

observed delayed potential around MSA, indicating that

MSA could be a focus of VT [5]. The evaluation became

possible by placing a catheter all around MSA without

any restrictions under cardiopulmonary bypass, and we

for the first time recorded delayed potentials around

MSA. The cause of delayed potentials was unclear. It is

well known that left ventricular apical aneurysm is

sometimes accompanied by delayed potentials in the

myocardium around it and can be a focus of VT [6].

Because of the structural resemblance between MSA and

left ventricular apical aneurysm, similar mechanisms can

Figure 2. (Upper Panel): A schematic representation of the

electro-anatomical mapping during surgery (anterior view).

The color changes according to electrical potential (red-blue:

0.5 - 1.5 mV). Blue tags identify points where the delayed

potential was observed and yellow tags shows the His bun-

dle. (Lower Panel): Electrical activities observed in II lead,

at the yellow tag (a), and blue tags (b). FP: fractionated

potential. DP: delayed potential.

Open Access SS

H. IMURA ET AL.

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545

Figure 3. (A) Light microscopy examination stained with toluidine blue. An elastic lamina-like structure is visible along the

right margin. The tissue mainly consists of myxoid matrix. Areas where elastic fibers are abundant are partially observable.

(B) An electron microscopy examination of tissue indicated by an arrow. Smooth muscle cells, collagen fibers and elastic

microfilaments are seen underneath the e ndocar dial cells. A muscular c omponent was not seen in both (A) and (B).

Figure 4. A schematic representation of the electro-anato-

mical mapping three years after the surgery. The schema

presents a right lateral view of the mapping. Blue tags iden-

tify points where the delayed potential was observed and

black tags shows the patch. Delayed potentials were still

be at work for MSA. Thus

observed around the patch.

, we speculate that stretching

urysm

rgery for large MSA, which was

force due to left ventricular pressure around MSA may

be a primary reason of these delayed potentials and can

cause VT for MSA. The force may also be the cause of

AVB because the His bundle was near MSA.

As previous studies recommended [7], the ane

as resected and the defect was closed with a patch for

this case. We placed all the sutures on the myocardium

(except near the His bundle and tricuspid annulus) to

reduce the stretching force, nevertheless, the delayed

potential was still observed three years after the surgery.

Persistent stretching force over the long term may cause

irreversible changes in the electrophysiological character

of the myocardium around MSA

4. Conclusion

We experienced a su

known as potential causes of critical arrhythmias such as

VT and AVB. Although the patient had not shown such

arrhythmias, for the first time, we observed changes in the

electrophysiological character of the myocardium around

MSA. These changes can be an evidence of predisposi-

tion to VT and AVB for MSA. Thus, we approached to

the mechanisms of critical ventricular arrhythmias in

MSA, which have not been addressed since this pathol-

ogy was first presented. Persistent stretching force over

the long-term may cause irreversible changes in the elec-

trophysiological character of the myocardium around

H. IMURA ET AL.

546

MSA because the delayed potential was still observed

three years after the surgery.

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