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
Open Access SS
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
Received November 8, 2013; revised November 28, 2013; accepted December 5, 2013
Copyright © 2013 Hajime Imura et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In accor-
dance of the Creative Commons Attribution License all Copyrights © 2013 are reserved for SCIRP and the owner of the intellectual
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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.
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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
w
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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