UvA-DARE (Digital Academic Repository)
Hypoplastic aortic arch morphology pertinent to growth after surgical correction of
aortic coarctation
Machii, M.; Becker, A.E.
Published in:
The annals of thoracic surgery
DOI:
10.1016/S0003-4975(97)00444-X
Link to publication
Citation for published version (APA):
Machii, M., & Becker, A. E. (1997). Hypoplastic aortic arch morphology pertinent to growth after surgical
correction of aortic coarctation. The annals of thoracic surgery, 64, 516-520. DOI: 10.1016/S00034975(97)00444-X
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Download date: 18 Jun 2017
Hypoplastic Aortic Arch Morphology Pertinent to
Growth After Surgical Correction of
Aortic Coarctation
Masato Machii, MD, and Anton E. Becket, MD
Department of Cardiovascular Pathology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands
Background. Whether a hypoplastic transverse arch
will grow after successful coarctectomy remains controversial.
Methods. We studied 15 coarctation specimens with
hypoplastic transverse arch. Eight patients were less than
1 m o n t h old a n d 7 were b e t w e e n 1 and 3 months. The
diameter a n d length of the various segments of the aortic
arch were measured. The n u m b e r of elastin lamellae was
d e t e r m i n e d histologically. Collagen density was quantified with a microdensitophotometer. Using i m m u n o h i s tochemistry, we d e t e r m i n e d a - a c t i n - p o s i t i v e smooth
muscle cells in the media of the ascending aorta and the
hypoplastic transverse arch.
Results. Despite a hypoplastic transverse arch, the
ascending and descending aorta grew. The absolute n u m -
ber of elastin lamellae in the hypoplastic transverse arch
was low, b u t w h e n expressed as a ratio versus its diameter, this n u m b e r was high (p < 0.05). Collagen density
showed high absolute values in the descending aorta. In
the older group, 4 of 7 showed no staining for a-actin in
the hypoplastic transverse arch, whereas u n d e r 1 m o n t h
of age, only 2 of 8 cases were negative.
Conclusions. The hypoplastic transverse arch is characterized b y a relatively high n u m b e r of elastin lamellae.
Fewer a-actin-positive cells in the hypoplastic transverse
arch occur in older specimens, which could indicate a
d i m i n i s h e d potential growth.
he question of whether the hypoplastic transverse
arch will grow after successful relief of an associated
coarctation r e m a i n s controversial. It appears that in some
patients adequate growth can be obtained, but in others
this is not the case [1]. In recent years, extended end-toe n d anastomosis has b e e n p r o m o t e d as a surgical option
for hypoplastic transverse arch, with or without coarctation of the aorta [2, 3]. The indication for this procedure,
however, r e m a i n s controversial [4, 5]. It is clear that
growth of the hypoplastic s e g m e n t d e p e n d s on an adequate coarctectomy a n d on coexisting cardiac anomalies,
if present. In addition, the morphology of the hypoplastic
s e g m e n t at the time of operation may play a role. It has
b e e n reported that the hypoplastic s e g m e n t contains
fewer elastin lamellae than the comparable n o r m a l aortic
arch s e g m e n t [6]. The functional importance of this
observation r e m a i n s as yet hypothetical, in particular
because it has not b e e n put in the perspective of other
potential indices of growth, such as the presence or
absence of smooth muscle cells, the collagen density, a n d
the relation of these items compared with other segments
of the aorta.
We have e x a m i n e d the morphologic characteristics of
the thoracic aorta, taking into account d i m e n s i o n s as well
as histologic features, in specimens with t u b u l a r hypoplasia of the aortic arch.
T
Accepted for publicationFeb 8, 1997.
Address reprint requests to Dr Machii, Divisionof CardiovascularSurgery, Ebina General Hospital CardiovascularCenter, 1519 Kawaraguchi,
Ebina, Kanagawa24304,Japan.
© 1997 by The Society of Thoracic Surgeons
Published by Elsevier Science Inc
(Ann Thorac Surg 1997;64:516-20)
© 1997 b y The Society of Thoracic Surgeons
Material and Methods
Definitions
The aortic arch is divided into three parts: the proximal
transverse arch, the distal transverse arch, a n d the aortic
isthmus (Fig 1). We have applied the definitions of
hypoplasia set by Moulaert a n d colleagues [7], which are
based on m e a s u r e m e n t s from autopsy specimens. The
proximal transverse arch was thus considered hypoplastic w h e n the external diameter was 60% or less of that of
the ascending aorta. For the distal transverse arch a n d
the aortic isthmus, these figures were 50% or less a n d
40% or less, respectively. A hypoplastic s e g m e n t was
defined as t u b u l a r hypoplasia w h e n its length was 5 m m
or more.
Heart Specimens
Fifteen specimens with some type of t u b u l a r hypoplasia
of the transverse arch were obtained from mature neonates a n d infants. They ranged from I day to 3 m o n t h s of
age at the time of death. A division was made into cases
less than I m o n t h of age (n = 8) a n d cases b e t w e e n I a n d
3 m o n t h s of age (n = 7). All specimens had associated
coarctation of the aorta. Other associated intracardiac
abnormalities are shown in Table 1.
0003-4975/97/$17.00
PII S0003-4975(97)00444-X
Ann Thorac Surg
1997;64:516-20
MACHII AND BECKER
MORPHOLOGY OF HYPOPLAST1C AORTIC ARCH
Drnx
517
Gross M o r p h o l o g y
TA
T h e e x t e r n a l d i a m e t e r of t h e d i f f e r e n t s e g m e n t s w a s
m e a s u r e d i n t h e m i d d l e , a s i n d i c a t e d i n F i g u r e 1. T h e
d i a m e t e r of t h e d e s c e n d i n g t h o r a c i c a o r t a w a s m e a s u r e d
2.5 c m d i s t a l to t h e i n s e r t i o n of t h e a r t e r i a l d u c t , a n d t h e
aortic arch b r a n c h e s w e r e m e a s u r e d 5 m m distal f r o m
t h e i r o r i g i n ( s e e Fig 1).
T o c o m p e n s a t e for a g e a n d o t h e r d e v e l o p m e n t a l effects, w e d i v i d e d t h e d i a m e t e r of e a c h s e g m e n t b y t h a t of
t h e d e s c e n d i n g t h o r a c i c a o r t a a n d e x p r e s s e d it a s a ratio.
T h e l e n g t h (to t h e n e a r e s t 0.5 r a m ) w a s m e a s u r e d for t h e
proximal transverse arch, the distal transverse arch, and
t h e a o r t i c i s t h m u s ( s e e Fig 1).
Histology
Cross sections w e r e t a k e n f r o m the a s c e n d i n g aorta, the
d i s t a l t r a n s v e r s e a r c h , b o t h t h e r i g h t a n d left s u b c l a v i a n
a r t e r i e s , a n d t h e d e s c e n d i n g a o r t a at t h e s i t e s w h e r e t h e
m e a s u r e m e n t s h a d b e e n t a k e n . T h e s i t e of c o a r c t a t i o n
w a s n o t i n c l u d e d ( s e e Fig 1). T h e r i n g s of t i s s u e w e r e
r o u t i n e l y p r o c e s s e d , e m b e d d e d in p a r a f f i n , a n d c u t at
5 ~m thickness. They were stained with hematoxylin and
e o s i n , a n e l a s t i n t i s s u e s t a i n , a n d t h e p i c r o s i r i u s r e d F3BA
stain.
T h e n u m b e r of m e d i a l e l a s t i n l a m e l l a e w a s c o u n t e d at
t w o o p p o s i n g sites. T h e a v e r a g e of t h e t w o c o u n t s w a s
c a l c u l a t e d a n d c o n s i d e r e d to r e p r e s e n t t h e n u m b e r of
e l a s t i n l a m e l l a e . To c o m p e n s a t e for a g e a n d o t h e r d e v e l o p m e n t a l effects, t h e c a l c u l a t e d n u m b e r of e l a s t i n l a m e l l a e f o r e a c h s e g m e n t w a s d i v i d e d b y t h a t of t h e d e s c e n d -
Fig 1. Diagram of the thoracic aorta with hypoplastic arch segments
and the sites of measurements (dotted lines b e t w e e n arrowheads). (Dist. TA = distal transverse arch; ist = aortic isthmus;
prox. TA = proximal transverse arch.)
All s p e c i m e n s w e r e o b t a i n e d f r o m t h e C a r d i o v a s c u l a r
R e g i s t r y , a n d all h a d b e e n f i x e d i n 4% f o r m a l i n f o r a
c o n s i d e r a b l e l e n g t h of t i m e .
Table 1. Relevant Data Regarding the Heart Specimens and the Distal Transverse Arch for Group 1 (Less Than 1 Month qf
Age) and Group 2 (More Than 1 to 3 Months)
Size of Distal
Transverse Arch
(mm)
Case
No.
Group 1
1
2
3
4
5
6
7
8
Group 2
9
10
11
12
13
14
15
Age
Sex
Major Cardiac
Anomalies
LVOTO
Diameter
Length
No. of
Elastin
Lamellae
Collagen
Density
Smooth Muscle Cell
a-Actin
+
+
1
5
8
11
8
1
5
7
day
day
day
day
day
day
day
day
M
M
F
M
M
F
M
M
LV hypoplasia
LV hypoplasia
DILV
DILV
LV hypoplasia
LV hypoplasia
DILV
TGA, VSD
...
BAV
...
...
BAV
...
...
...
2.5
3.0
2.5
3.0
4.0
2.5
3.0
4.0
5.5
5.0
7.0
5.5
8.0
9.5
5.5
5.5
26
34
17
26
44
24
27
35
36.8
31.5
28.8
26.3
29.1
27.0
25.7
33.2
1
2
1
1
3
1
3
mo
mo
mo
mo
mo
mo
mo
F
M
M
M
M
M
F
...
VSD
DILV
DILV
DILV
VSD
DORV
SAS, BAV
...
...
...
...
SAS
...
5.0
3.5
3.5
3.0
3.0
3.5
3.5
8.0
14.5
11.5
6.0
6.5
11.0
12.0
33
27
22
31
23
27
29
25.7
45.3
27.6
35.6
23.1
35.3
22.1
++
+
~_
++
+
+
+
-
LV hypoplasia = small left ventricle
BAV bicuspid aortic valve;
D I L V= double-inlet left ventricle;
DORV = double-outlet right ventricle;
SAS = subaortic stenosis;
TGA =
with the ascending aorta more than 5.5 mm in diameter;
LVOTO left ventricular outflow tract obstruction;
+ = approximately half of cells
transposition of the great arteries;
VSD = ventricular septal defect;
++ = almost all cells positive;
positive;
-+ = a few cells positive;
negative.
518
MACHII AND BECKER
MORPHOLOGY OF HYPOPLASTIC AORTIC ARCH
Ann Thorac Surg
1997;64:516-20
Table 2. Morphometry of the Aorta and Main Branches in
the Two Age Groups a
Measurement
External diameter
Ascending aorta
Brachiocephalic artery
Right subclavian artery
Right common carotid
artery
Proximal transverse arch
Left common carotid
artery
Distal transverse arch
Left subclavian artery
Aortic isthmus
Descending aorta
Length
Proximal transverse arch
Distal transverse arch
Aortic isthmus
Group 1
(< 1 too)
Group 2
(1 mo to
< 3 too)
p
Values
6.8 -+ 0.9
(1.01 -+ 0.13)
5.5 -- 0.8
(0.82 ± 0.12)
3.1 -+ 0.7
(0.61 ± 0.10)
4.0 -+ 0.8
(0.60 -- 0.13)
8.4 -+ 1.1
(1.10 ± 0.11)
5.4 ± 0.4
(0.71 ± 0.08)
4.1 ± 0.5
(0.53 ± 0.06)
4.3 ± 0.3
(0.54 ± 0.08)
0.005
(0.161)
0.659
(0.049)
0.977
(0.123)
0.458
(0.312)
5.1
(0.74
3.8
(0.57
± 1.5
"- 0.17)
- 0.6
-+ 0.11)
5.9 ± 0.9
(0.78 --- 0.10)
4.1 + 0.5
(0.54 ± 0.06)
0.205
(0.670)
0.260
(0.555)
3.1
(0.46
3.5
(0.50
3.8
(0.55
6.8
= 0.6
= 0.10)
± 0.6
-+ 0.09)
± 0.7
-+ 0.09)
-+ 0.8
3.6 ±
(0.47 +
3.9 +
(0.50 ±
3.4 ±
(0.44 ±
7.6 ±
0.152
(0.790)
0.259
(0.978)
0.385
(0.099)
0.023
1.9 ± 0.8
6.4 ± 1.6
2.6 -+ 0.9
0.7
0.08)
0.4
0.06)
0.9
0.12)
0.5
1.9 ± 1.3
9.9 ± 3.2
2.7 ± 1.5
0.926
0.016
0.874
Results are expressed as mean value + standard deviation, together
with p values. The figures in parentheses refer to the mean value ±
standard deviation of the external diameter divided by that of the
descending aorta.
i n g a o r t a a n d e x p r e s s e d as a ratio. I n a d d i t i o n , t h e
c a l c u l a t e d n u m b e r of e l a s t i n l a m e l l a e w a s d i v i d e d b y t h e
d i a m e t e r for e a c h s e g m e n t a n d also e x p r e s s e d as a ratio.
Collagen Density
T h e a m o u n t of c o l l a g e n w a s q u a n t i f i e d u s i n g a m i c r o densitophotometric method after staining the sections
w i t h p i c r o s i r i u s r e d F3BA [8]. A r e f e r e n c e s e c t i o n w i t h a
k n o w n v a l u e w a s t a k e n as a c o n t r o l for e a c h b a t c h . T h e
m e a s u r e m e n t s w e r e p e r f o r m e d at 20 f r a m e s i n e a c h
s e c t i o n , c o v e r i n g t h e m i d d l e p a r t of t h e a o r t i c m e d i a . T h e
average obtained was considered the collagen density.
T h e v a l u e s w e r e t h e n e x p r e s s e d as a p e r c e n t a g e of t o t a l
p r o t e i n in t h e m e d i a .
r e s u l t s w e r e e x p r e s s e d as m e a n _+ s t a n d a r d deviation. A p
v a l u e of less t h a n 0.05 w a s c o n s i d e r e d significant.
Results
Morphologic Features
All c a s e s s h o w e d t u b u l a r h y p o p l a s i a of t h e d i s t a l t r a n s v e r s e a r c h . A s s o c i a t e d h y p o p l a s i a of t h e p r o x i m a l t r a n s v e r s e a r c h w a s p r e s e n t i n 2 s p e c i m e n s , a n d in 3 o t h e r
c a s e s t h e a o r t i c i s t h m u s w a s h y p o p l a s t i c also.
T h e m o r p h o m e t r i c d a t a a r e s u m m a r i z e d i n T a b l e 2.
T h e d i a m e t e r s of t h e a s c e n d i n g a n d d e s c e n d i n g a o r t a i n
s p e c i m e n s of 1 m o n t h of a g e or o l d e r w e r e s i g n i f i c a n t l y
l a r g e r t h a n t h o s e in t h e o n e s less t h a n 1 m o n t h of a g e
(p < 0.01 a n d p ~ 0.05, r e s p e c t i v e l y ) . T h e r e w e r e n o
significant changes in other segments. The hypoplastic
d i s t a l t r a n s v e r s e a r c h w a s s i g n i f i c a n t l y l o n g e r in t h e
o l d e r g r o u p t h a n i n c a s e s of less t h a n I m o n t h (p ~ 0.05).
T h e r a t i o of t h e d i a m e t e r of t h e v a r i o u s s e g m e n t s , div i d e d b y t h a t of t h e d e s c e n d i n g a o r t a , c h a n g e d o n l y i n
t h e b r a c h i o c e p h a l i c a r t e r y (p ~ 0.05), w h e r e it w a s d e c r e a s e d (see T a b l e 2).
Histologic Features
Between the age groups, there were no changes in either
t h e a b s o l u t e n u m b e r of e l a s t i n l a m e l l a e or t h e r a t i o s
o b t a i n e d b y d i v i d i n g t h e n u m b e r of e l a s t i n l a m e l l a e b y
t h a t of t h e d e s c e n d i n g a o r t a ( T a b l e 3). T h e r a t i o s o b t a i n e d b y d i v i d i n g t h e n u m b e r of e l a s t i n l a m e l l a e b y t h e
d i a m e t e r of t h e c o r r e s p o n d i n g s e g m e n t s d e c r e a s e d sign i f i c a n t l y i n t h e d i s t a l t r a n s v e r s e a r c h ( T a b l e 4); n o n e of
the other segments had a significant change. The distal
t r a n s v e r s e a r c h h a d a s i g n i f i c a n t l y l a r g e r v a l u e of t h i s
ratio than any other segment in the younger group or any
other segment but the right subclavian artery in the older
g r o u p . T h e left s u b c l a v i a n a r t e r y o t h e r w i s e h a d a s i g n i f icantly smaller value than any other segment throughout
the observed period.
Collagen Density
The collagen density showed no significant changes bet w e e n t h e age g r o u p s . T h e d e s c e n d i n g aorta h a d a g r e a t e r
Table 3. Absolute Number of Elastin Lamellae a
Vessel
Ascending aorta
Right subclavian artery
Immunocytochemistry
Group 1
( < 1 too)
Group 2
(1 mo to
-< 3 mo)
p
Values
48.3 ± 7.7
(1.08 ± 0.25)
25.0 +_ 5.3
(0.55 ± 0.10)
29.1 ± 8.3
(0.65 ± 0.20)
17.8 + 5.5
(0.39 + 0.12)
45.3 +_ 5.8
51.9 ± 6.5
(1.13 ± 0.17)
27.6 _+ 7.8
(0.60 -+ 0.14)
27.4 ± 4.0
(0.60 +- 0.11)
15.8 -+ 1.6
(0.35 ± 0.04)
46.0 ± 4.7
0.348
(0.663)
0.465
(0.479)
0.630
(0.590)
0.446
(0.479)
0.789
Sections from the ascending aorta and the hypoplastic
segment were stained immunocytochemically with a
m o n o c l o n a l a n t i b o d y for h u m a n s m o o t h m u s c l e c~-actin
( D A K O - s m o o t h m u s c l e actin, 1A4; D A K O C o r p o r a t i o n ,
C a r p i n t e r i a , CA).
Distal transverse arch
Statistical Analysis
a Results are expressed as mean -+ standard deviation and p values for
both age groups. The figures in parentheses refer to the mean ± standard
deviation of the ratio of the number of elastin lamellae divided by that of
the descending aorta.
Statistical a n a l y s i s w a s p e r f o r m e d u s i n g S t u d e n t ' s t test or
a n a l y s i s of v a r i a n c e w h i c h w a s s u i t a b l e for analysis. T h e
Left subclavian artery
Descending aorta
Ann Thorac Surg
1997;64:516-20
MACHI1 AND BECKER
MORPHOLOGY OF HYPOPLASTIC AORTIC ARCH
Table 4. Ratios Obtained by Dividing the Number of Elastin
Lamellae by the Diameter of the Corresponding Segmenl~
Vessel
Ascending aorta
Right subclavian artery
Distal transverse arch
Left subclavian artery
Descending aorta
Group 1
(< 1 mo)
7.17
6.54
9.44
5.06
6.82
_+ 0.83
± 1.38
_+ 1.47b
± 1.05a
_+ 1.39
Group 2
(1 mo to
< 3 too)
6.22
6.87
7.80
4.19
6.02
±
±
±
+
±
0.97
2.20
1.31c
0.57 a
0.47
p
Values
0.061
0.731
0.040
0.134
0.172
Results are expressed as mean + standard deviation and p
values,
b Significant differences (p < 0.05) with ascending aorta, right
and left subclavian artery, and descending aorta,
c Significant differences (p < 0.05) with ascending aorta, left subclavian artery, and descending aorta,
d Significant differences (p < 0.05) with ascending aorta,
right subclavian artery, distal transverse arch, and descending aorta.
density of collagen t h a n both the a s c e n d i n g aorta and the
distal transverse arch in y o u n g e r specimens, c o m p a r e d
w i t h the a s c e n d i n g aorta in older s p e c i m e n s (Table 5).
I m m u n o c y t o c h e m i c a l Features
Immunocytochemical staining revealed positive smooth
m u s c l e c~-actin cells in the a s c e n d i n g aorta in all cases b u t
1 ( c a s e 11). In the distal t r a n s v e r s e arch, c~-actin was
a b s e n t in 2 of 8 cases u n d e r I m o n t h of age a n d in 4 of 7
cases in t h e o l d e r g r o u p (Fig 2). T h e latter cases all h a d a
significantly l o n g e r distal t r a n s v e r s e a r c h t h a n the cases
f r o m the s a m e age g r o u p b u t w i t h p o s i t i v e s t a i n i n g for
t~-actin (p < 0.05) (see T a b l e 1).
Comment
This s t u d y r e v e a l s that t h e h y p o p l a s t i c t r a n s v e r s e arch is
n o t s i m p l y a m i n i a t u r e of the c o r r e s p o n d i n g s e g m e n t of
the n o r m a l aortic arch. It has b e e n r e p o r t e d t h a t t h e
h y p o p l a s t i c s e g m e n t has a l e s s e r n u m b e r of elastin
l a m e l l a e t h a n n o r m a l [6] a n d that the c o l l a g e n d e n s i t y in
the m e d i a p r o x i m a l a n d distal to a coarctation also differs
519
Table 5. Collagen Density ~
Vessel
Ascending aorta
Distal transverse arch
Descending aorta
Group 1
(< 1 mo)
Group 2
(1 mo to
-< 3 mo)
p
Values
30.7 ± 5.8
29.8 -+ 3.83
40.7 _+ 3.0 b
29.8 ± 4.7
30.7 ± 8.4
37.5 + 4.4 c
0.656
0.798
0.121
a Results are expressed as mean -+ standard deviation, as a percentage of
total protein, and p values,
b Significant differences (p < 0.05) with
ascending aorta and distal transverse arch.
c Significant differences
(p < 0.05) with ascending aorta.
[9]. H o w e v e r , w e are n o t a w a r e of a n y s t u d y c o r r e l a t i n g
m o r p h o m e t r i c data of t h e h y p o p l a s t i c s e g m e n t w i t h its
histologic features. T h e results of this s t u d y are i n t e r p r e t e d in light of t h e results o b t a i n e d in o u r p r e v i o u s
s t u d y of g r o w t h characteristics of n o r m a l aortas [10].
T h e p r e s e n t s t u d y c o n f i r m s that the h y p o p l a s t i c segm e n t has a significantly l o w e r n u m b e r of elastin l a m e l l a e
t h a n n o r m a l (p < 0.02) [10]. H o w e v e r , the ratio o b t a i n e d
b y d i v i d i n g t h e n u m b e r of elastin l a m e l l a e by the d i a m e t e r is significantly h i g h e r t h a n n o r m a l (p < 0.02). In
o t h e r w o r d s , this s e g m e n t has o n l y a f e w elastin lamellae,
b u t in r e l a t i o n to t h e d i a m e t e r , it has a h i g h n u m b e r of
l a m e l l a e . This in o u r o p i n i o n is characteristic of t u b u l a r
h y p o p l a s i a of the aortic arch. T h e possibility exists that
t h e h y p o p l a s t i c s e g m e n t r e c e i v e d a r e l a t i v e l y large v o l u m e of b l o o d d u r i n g early gestation, w h i c h m a y h a v e
d i m i n i s h e d g r a d u a l l y b e c a u s e of p r o g r e s s i o n of the coarctation lesion. This possibility is b a s e d o n t h e o b s e r v a tion of A l l a n a n d c o - w o r k e r s [11], u s i n g fetal e c h o c a r d i o g r a p h y f r o m 18 w e e k s ' g e s t a t i o n o n w a r d , t h a t t h e
coarctation g r a d u a l l y p r o g r e s s e d a n d e v e n t u a l l y also
p r o d u c e d aortic a r c h h y p o p l a s i a .
It is i m p o r t a n t to k n o w w h e t h e r the h y p o p l a s t i c segm e n t has t h e p o t e n t i a l to grow. In s o m e surgical p r o c e d u r e s , the h y p o p l a s t i c s e g m e n t is not t a k e n into f u r t h e r
c o n s i d e r a t i o n , a n d s i m p l e r e s e c t i o n of the coarctation
Fig 2. Immunocytochemical staining for
smooth muscle c¢-actin in the distal transverse aortic arch. (A) Positive staining in the
media between elastin lamellae (case 8; 7
days). (B) Negah've staining of cells in the
media, while the vasa vasorum stains positive
(case 11; 1 month). (1A4 stain: A, ×115; B,
×87; both before 38% reduction.)
520
MACHII A N D BECKER
M O R P H O L O G Y OF HYPOPLASTIC AORTIC A R C H
with e n d - t o - e n d anastomosis is p e r f o r m e d [4]. O t h e r
p r o c e d u r e s are tailored in such a w a y that the i m p a c t of
the hypoplastic s e g m e n t is minimized, eg, by p e r f o r m i n g
an e x t e n d e d e n d - t o - e n d anastomosis. In this operation,
the hypoplastic s e g m e n t is incised a n d reconstructed to
form the roof of the n e w aortic arch [3]. The indication for
the latter procedure, however, varies a m o n g centers, b u t
usually relates to the ratio o b t a i n e d b y dividing the
d i a m e t e r of the hypoplastic transverse arch b y that of
either the a s c e n d i n g aorta or the d e s c e n d i n g aorta. Some
w o u l d consider a ratio of 0.5 as an indication to p e r f o r m
an e x t e n d e d operation, w h e r e a s others take a ratio of less
than 0.25 [5]. However, it is of interest that neither one of
these a p p r o a c h e s considers the length of the hypoplastic
s e g m e n t [12]. This is s u r p r i s i n g b e c a u s e length has an
effect on the p r e s s u r e gradient, even after coarctectomy
[13]. Hence, one m a y speculate that a d e q u a t e growth
after " s i m p l e " e n d - t o - e n d anastomosis is achieved only
in cases with a short hypoplastic segment. Recently, a
6-month follow-up with g o o d results has b e e n r e p o r t e d
after e n d - t o - e n d anastomosis, b u t no m e n t i o n was m a d e
of the length of the hypoplastic s e g m e n t [4].
We i n c l u d e d length in our s t u d y a n d have r e v e a l e d
s o m e findings that m a y b e a r on the problem. First, the
hypoplastic s e g m e n t was longer in s p e c i m e n s of patients
over 1 m o n t h of age than in those less than 1 month.
Second, the older group contained a relatively large
n u m b e r (4 of 7) without c~-actin-positive cells in the
media, which indicates either absence of s m o o t h muscle
cells or a change in p h e n o t y p e . In these cases, moreover,
the hypoplastic s e g m e n t was significantly (p < 0.05)
longer than in the r e m a i n i n g cases with positive staining.
At the s a m e time, we also found that in the y o u n g age
group, 2 cases (cases 1 a n d 4) were negative for c~-actin.
Nevertheless, this observation is potentially i m p o r t a n t
b e c a u s e in the fetal aorta, smooth muscle a-actin increases a n d s m o o t h muscle ]3-actin decreases with gestational age [14]. This change is i n t e r p r e t e d as a differentiation p h e n o m e n o n in which s m o o t h muscle cells
g r a d u a l l y transform from the synthetic state (smooth
muscle /3-actin positive) to the contractile state (smooth
muscle a-actin positive). This could indicate, therefore,
that the absence of staining with the monoclonal m a r k e r
for smooth muscle a-actin relates to the state of differentiation of the cells, rather t h a n to an absence of cells. In
fact, routine staining with hematoxylin a n d eosin suggests the presence of smooth muscle cells within the
m e d i a in all instances. The p h e n o t y p i c characteristics of
these smooth muscle cells are i m p o r t a n t b e c a u s e the
synthetic cells are the ones that are capable of proliferation a n d p r o d u c t i o n of extracellular matrix c o m p o n e n t s .
In other words, this is the type of cell one m a y anticipate
to be actively involved in a process of growth.
An additional feature, albeit u n r e l a t e d to length, is the
fact that once we c o m p a r e d collagen density of the m e d i a
of the hypoplastic s e g m e n t with previously o b t a i n e d data
from n o r m a l aortas [10], the hypoplastic s e g m e n t h a d
significantly m o r e collagen than normal. This feature is
a l r e a d y evident at the time of birth. The a s c e n d i n g aorta
A n n Thorac S u r g
1997;64:516-20
also p r e s e n t s a significantly h i g h e r collagen density than
normal, although this b e c o m e s clear only after 1 m o n t h
of age. Nevertheless, an indication that morphologic
changes occur rapidly, affecting other parts of the thoracic aorta than only the hypoplastic segment. These
morphologic changes, moreover, have potential functional significance in having a negative effect on the
distensibility of the aorta.
The p r e s e n t s t u d y thus d o c u m e n t s that growth abnormalities in the thoracic aorta with a hypoplastic arch
s e g m e n t are not restricted to the area with t u b u l a r
hypoplasia. It seems likely that these differences also
relate to the h e m o d y n a m i c a b n o r m a l i t i e s created b y the
obstructed arch. From a morphologic point of view, this
study s u p p o r t s the concept of early coarctectomy soon
after birth, even in neonates without overt heart failure.
During this study, Dr Machii was a Research Fellow from the
Kitasato University, Faculty of Medicine, Kanagawa, Japan.
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