(Circulation. 2001;103:393.)
© 2001 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Ahmanson/UCLA Adult Congenital Heart Disease Center, University of California, Los Angeles.
Correspondence to Joseph K. Perloff, MD, Division of Cardiology, Room 47-123, UCLA CHS, Los Angeles, CA 90095-1679. E-mail jperloff{at}mednet.ucla.edu
| Abstract |
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Methods and ResultsIntraoperative biopsies from ascending aorta, paracoarctation aorta, truncus arteriosus, and pulmonary trunk in 86 patients were supplemented by 16 necropsy specimens. The 102 patients were 3 weeks to 81 years old (average, 32±6 years). Biopsies were examined by light (LM) and electron (EM) microscopy; necropsy specimens by LM. Positive aortic controls were from 15 Marfan patients. Negative aortic controls were from 11 coronary artery disease patients and 1 transplant donor. Nine biopsies from acquired trileaflet aortic stenosis were compared with biopsies from bicuspid aortic stenosis. Negative pulmonary trunk controls were from 7 coronary artery disease patients. A grading system consisted of negative controls and grades 1, 2, and 3 (positive controls) based on LM and EM examination of medial constituents.
ConclusionsMedial abnormalities in ascending aorta, paracoarctation aorta, truncus arteriosus, and pulmonary trunk were prevalent in patients with a variety of forms of CHD encompassing a wide age range. Aortic abnormalities may predispose to dilatation, aneurysm, and rupture. Pulmonary trunk abnormalities may predispose to dilatation and aneurysm; hypertensive aneurysms may rupture. Pivotal questions are whether these abnormalities are inherent or acquired, whether CHD plays a causal or facilitating role, and whether genetic determinants are operative.
Key Words: aorta lung arteries heart defects, congenital
| Introduction |
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| Methods |
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Three categories of ascending aortic biopsy controls
consisted of (1) positive controls: 15 patients with Marfan syndrome or
annuloaortic
ectasia12 13 14 ;
and (2) negative controls: 11 patients undergoing CABG, 1 transplant
donor, and 10 patients with acquired trileaflet calcific aortic
stenosis. Seven pulmonary trunk negative controls were from patients
undergoing CABG. Ascending aortic biopsies from patients with bicuspid
aortic stenosis or regurgitation
(Table 1
) were compared with each other and with biopsies
from acquired calcific aortic stenosis of inherently normal trileaflet
valves.
No pregnancies occurred among 49 females with Marfan syndrome, annuloaortic ectasia, bicuspid aortic valve, or aortic coarctation. Systemic blood pressure (average of 3 sphygmomanometer determinations) in aortic biopsy patients without coarctation was systolic, 92 to 130 mm Hg (mean, 115±5 mm Hg) and diastolic, 60 to 82 mm Hg (mean, 72±4 mm Hg). All control subjects and all study patients except those with coarctation had normal systemic arterial pressure for age. Four biopsied infants and 3 necropsied adults with truncus arteriosus had systemic arterial pressure in the truncus; the infants had wide pulse pressures.
Aorta and Pulmonary Trunk
Preoperative ascending aortic, paracoarctation
aortic, and pulmonary trunk diameters were determined by 2D
echocardiography, CT, or MRI.
Techniques and Morphological Analyses
Biopsies were examined by LM and EM; necropsy
specimens by LM. LM specimens were fixed in formaldehyde, embedded in
paraffin, and stained with hematoxylin and eosin. Elastic van Gieson
stain (low power, x4; high power, x10) was used for examining elastic
fibers, trichrome stain for collagen, and Hales colloidal iron for
ground substance. Fresh EM tissue was fixed in 2.5% glutaraldehyde and
2% paraformaldehyde, postfixed with osmium tetroxide, and embedded in
an epoxy resin. Semithin sections were prepared with a polychromatic
stain for screening and selection. Ultrathin sections were stained with
uranyl acetate and lead citrate. Electron micrographs were prepared on
a Zeiss EM 109 microscope.
A grading system consisted of negative controls (presumed
normal) and grades 1, 2, and 3, the latter representing positive
controls from Marfan syndrome or annuloaortic ectasia. Grades were
based on LM and EM analyses of medial smooth muscle, elastic fibers,
collagen, and ground substance
(Figures 1 to 4![]()
![]()
![]()
) as described in the legends. All specimens
were interpreted by 1 histologist and electron microscopist (S.M.B.)
who was blinded to the clinical data.
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The UCLA Human Subjects Protection Committee approved the protocol. Surgical specimens were obtained after informed consent.
| Results |
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Ascending Aorta and Paracoarctation
Aorta
Media above a bicuspid aortic valve was consistently
abnormal and identical whether the valve was stenotic or incompetent
(Table 1
). Ascending aortic media associated with acquired
calcific stenosis of inherently normal trileaflet valves was identical
with negative controls. All paracoarctation biopsies had medial
abnormalities
(Table 1
), the degree of which was identical in proximal and
distal segments, including in a 3-week-old neonate. In Fallots
tetralogy with pulmonary stenosis or atresia, ascending aortic media
was grade 2 or 3
(Figures 1
, 2
, and 3
)
(Tables 1
and 3
). One such patient, 73 years old, had a
5.4-cm ascending aorta that fragmented during surgery and had an
abdominal aortic aneurysm that had previously been operated on.
Neonates with complete transposition of the great arteries (TGA) had
grade 2 to 3 medial abnormalities in normal-sized ascending aortas
(Table 1
). A 14-year-old boy with a restrictive
perimembranous ventricular septal defect (VSD) had a 5.6-cm ascending
aorta with grade 3 medial abnormalities
(Table 1
).
Necropsy specimens in adults with Fallots tetralogy and
dilated ascending aortas had grade 2 to 3 medial abnormalities
(Table 3
). A phenotypically normal female with an
Eisenmenger VSD ruptured a normal-sized ascending aorta that had grade
3 medial abnormalities
(Table 3
), which were also present in the hypertensive
pulmonary trunk
(Table 2
).
Pulmonary Trunk
Grade 3 medial abnormalities were found in biopsies of
aneurysmal pulmonary trunks in Fallots tetralogy with absent
pulmonary valve and in mobile pulmonary valve stenosis
(Table 2
). A patient with a single ventricle and pulmonary
atresia had grade 3 medial abnormalities in a focal right pulmonary
artery aneurysm
(Table 2
). One patient with an atrial septal defect had
grade 3 medial abnormalities in a dilated volume-overloaded
normotensive pulmonary
trunk.
Pulmonary trunk necropsy specimens disclosed grade 2 or 3
medial abnormalities in patients with pulmonary vascular disease (PVD)
and VSD or complete TGA
(Table 2
). Two such patients had pulmonary trunk aneurysms,
1 of which fatally ruptured
(Table 2
). One patient with Fallots tetralogy and PVD
induced by a large Blalock-Taussig shunt suffered a fatal rupture of an
aneurysmal pulmonary trunk with grade 3 medial abnormalities
(Table 2
).
Truncus Arteriosus
Biopsies at initial repair (infants 4 to 6 months
old) disclosed grade 2 or 3 medial abnormalities
(Table 1
); an additional patient had grade 3 medial
abnormalities at age 5 years (re-repair)
(Table 1
). Necropsy specimens in adults with truncus
arteriosus and PVD disclosed grade 3 medial abnormalities
(Table 3
).
| Discussion |
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Current interest has shifted to specific medial constituentssmooth muscle, and extracellular matrix that consists of ground substance, a hydrated gel composed of glycosaminoglycans, proteoglycans, and adhesive glycoproteins in which elastic fibers and collagen are embeddedand the role of these constituents in the structural and functional integrity of great arterial walls.17 18 19 Smooth muscle governs vasodilatation and constriction. Elastin, with its low elastic modulus,9 is readily deformable, permitting phasic distension and recoil in response to pulsatile flow. Collagen provides inert strength (stiffness).
The ultimate expression of great arterial medial
abnormalities is Marfan syndrome or annuloaortic ectasia, the
prototypical
extremes12 13 14
(positive controls). In 18 varieties of CHD
(Tables 1 to 3![]()
![]()
), abnormalities that were qualitatively
similar and occasionally quantitatively identical to the positive
controls were found in thoracic aortas and pulmonary trunks. Published
data on the proximal and distal paracoarctation
aorta2 and the ascending
aorta above a bicuspid aortic
valve1 were reexamined and
extended by use of EM and LM with special stains.
Paracoarctation Aorta
Medial abnormalities were identical proximal to the
coarctation (high-pressure, low-velocity zone) and distal
(low-pressure, high-velocity
zone)6
(Table 1
), implying that the abnormalities were not
hemodynamically determined. An inherent pathogenesis is also in accord
with observations that (1) in fetuses with a widely patent ductus
arteriosus, mechanical forces do not impinge on what is destined to
become the postnatal paracoarctation aorta and (2) grade 3 medial
abnormalities were present in the paracoarctation aorta in the third
week of life
(Table 1
) and have been reported within 24 hours
postpartum.2
Ascending Aortic Dilatation
Dilatation above stenotic aortic valves has been
attributed to poststenotic turbulence, but ascending aortic turbulence
generated by discrete congenital subaortic stenosis is accompanied by
no more than moderate aortic
dilatation,20 and acquired
calcific stenosis of inherently normal trileaflet aortic valves is
accompanied by normal media and no more than moderate dilatation,
discounting turbulence per se as the cause of dilatation. The ascending
aorta above a bicuspid valve is dilated whether the valve is stenotic,
incompetent, or functionally
normal.3 4 Medial
abnormalities are identical irrespective of the functional state of the
valve
(Table 1
), an observation favoring an inherent medial
fault.
In Fallots tetralogy, ascending aortic dilatation varies
inversely with the degree of right ventricular outflow tract
obstruction, being largest with pulmonary
atresia.21 Four variables
potentially influence ascending aortic size: (1) abnormal morphogenesis
that results in unequal division of the fetal truncus, favoring the
aorta; (2) volume overload implicit in the biventricular aorta; (3)
aortic regurgitation that augments volume overload and introduces
pulsatile flow that may facilitate
dilatation21 22 ;
and (4) an intrinsic medial fault
(Table 1
)
(Figure 5B
).
|
In double-outlet right or left ventricle, single ventricle,
or tricuspid atresia with pulmonary stenosis, the volume-overloaded
ascending aorta was dilated and contained grade 2 or 3 medial
abnormalities
(Table 1
). In double aortic arch, grade 2 medial
abnormalities in a dilated ascending aorta
(Table 1
) may have been inherent.
Normal-Sized Ascending Aorta
In VSD with the Eisenmenger syndrome, a normal-sized
ascending aorta may harbor inherent medial
abnormalities.5 In 1 such
patient, a normal-sized ascending aorta with grade 3 medial
abnormalities fatally ruptured
(Table 3
). A surprising variation on this theme was a
14-year-old boy with a restrictive VSD and a 5.6-cm ascending aorta
that contained grade 3 medial abnormalities without apparent cause
(Table 1
).
The ascending aorta in complete TGA is usually normal-sized.
However, 8 neonates had grade 2 to 3 ascending aortic medial
abnormalities
(Table 1
) similar to those
reported,6 observations
suggesting an inherent pathogenesis.
Independent Variables
Pregnancy, age, and systemic hypertension influence the
structure of aortic media. Pregnancy is accompanied by fragmentation of
elastic fibers, a decrease in mucopolysaccharides, and an increase in
smooth muscle.23 To what
extent these changes normalize after delivery is unknown. Because
increasing numbers of female patients with CHD now reach reproductive
age, it is appropriate to ask whether gestational changes are additive
to those described here in CHD. With advancing age, ascending aortic
elastic fibers fragment, smooth muscle cells decrease, collagen and
ground substance increase, distensibility declines, and circumference
increases,24 changes
influenced by but occurring independently of vasa vasorum
flow25 or intimal
atherosclerosis.24 In
systemic hypertension, abnormalities of elastin and collagen are
significantly more prevalent than in normotensive subjects of
comparable age.26
Experimentally induced systemic hypertension is accompanied by an
increase in synthesis and accumulation of thoracic aortic
collagen.10 Coarctation
hypertension is accompanied by an increase in ascending aortic medial
collagen and a decrease in smooth muscle (increased
stiffness)27 that may
persist after successful
repair28 and coincide with
ascending aortic abnormalities of a coexisting bicuspid aortic
valve.
Nonhypertensive Pulmonary Trunk
Dilatation
Mobile congenital pulmonary valve stenosis is
associated with conspicuous dilatation of the pulmonary trunk, but
dysplastic pulmonary valve stenosis is accompanied by relatively little
dilatation29 despite
equivalent poststenotic turbulence, discounting turbulence per se as a
pivotal factor in dilatation. Pulmonary trunk dilatation above a mobile
stenotic pulmonary valve may be related to the morphology of that
specific type of congenitally malformed valve rather than to its
functional state, analogous to the proposed relationship between a
bicuspid aortic valve and dilatation of the ascending aorta. Pulmonary
trunk aneurysms are occasionally associated with mobile pulmonary valve
stenosis,30 and
fragmentation of medial elastic fibers with mucoid degeneration has
been found in these aneurysms
(Table 2
).31 One
patient underwent pulmonary trunk aneurysmectomy with valve replacement
15 years after valvotomy for mobile congenital stenosis; there were
grade 3 medial abnormalities in the aneurysmal pulmonary trunk
(Table 2
).
When the Jatene arterial switch operation was preceded by a pulmonary artery band, grade 2 to 3 medial abnormalities were subsequently found in the pulmonary trunk (neoaorta).6 Assuming that the pulmonary trunks were initially normal, these postband medial abnormalities were probably acquired.
In Fallots tetralogy with absent pulmonary valve, the
pulmonary trunk and proximal branches dilate
massively.32 Regurgitant
volume in utero is returned to the pulmonary trunk during each right
ventricular systole, phasically distending the central pulmonary
arteries, more so when egress is curtailed by agenesis of the ductus
arteriosus.32 These
aneurysmal pulmonary trunks had grade 3 medial abnormalities
(Table 2
) attributed to abnormal flow patterns originating
in utero.
One patient with a large left-to-right shunt at the atrial level had grade 3 medial abnormalities in a dilated normotensive pulmonary trunk.
Hypertensive Pulmonary Trunk Dilatation
When pulmonary hypertension dates from birth, pulmonary
trunk histology is initially indistinguishable from that of the
ascending
aorta,5 33 but
when hypertension is acquired after birth, the pulmonary trunk differs
significantly from the ascending
aorta.33 Before 1 year of
age, medial abnormalities in hypertensive pulmonary trunks associated
with nonrestrictive VSDs are absent, but they are consistently present
after age 5 years.5 Patients
with VSD and the Eisenmenger syndrome had grade 3 medial abnormalities
in dilated hypertensive pulmonary trunks, 2 of which were aneurysmal
(Figure 5A
), 1 of which fatally ruptured
(Table 2
). Complete TGA with nonrestrictive VSD was
associated with grade 2 medial abnormalities in hypertensive pulmonary
trunks
(Table 2
). A patient with Fallots tetralogy and PVD
induced by an oversized Blalock-Taussig shunt suffered a rupture of a
hypertensive aneurysmal pulmonary trunk with grade 3 medial
abnormalities that may have been acquired
(Table 2
), although vulnerability might have been enhanced
by an inherent reduction in elastic
fibers.11 Pulmonary
hypertension with rheumatic mitral stenosis has occurred with
presumably acquired cystic medial necrosis in a ruptured, hypertensive
pulmonary trunk.34
Monocrotaline-induced pulmonary hypertension is associated with altered
elastin and collagen
synthesis.8
Truncus arteriosus is neither an aorta nor a pulmonary
trunk, differing from a large aorta with pulmonary atresia or a large
pulmonary trunk with aortic atresia, both of which have an
aortopulmonary
septum.35 36
Medial abnormalities in neonates and infants with truncus arteriosus
(Table 1
) may be inherent, albeit facilitated by systemic
arterial pressure, volume overload, and a wide pulse pressure. In
adults with truncus arteriosus and PVD
(Table 3
), medial abnormalities must be considered in light
of abnormalities in neonates and infants
(Table 1
).
Significance of the Observations
It is uncertain whether medial abnormalities, even in
neonates and young infants, are inherent or acquired, whether and to
what degree coexisting CHD plays a causal or facilitating role, or to
what extent the abnormalities are responses to dilatation per se.
Nevertheless, the range, prevalence, degree, and potential risks,
including cardiac surgical risks, posed by these abnormalities are
matters that warrant emphasis.
Pathogenesis
Assuming that some medial abnormalities in CHD are
inherent, do the abnormalities reflect 1 or more genetic
defects?3 7 Might
the neural crest be linked to medial abnormalities in conotruncal
malformations?7 Marfan
syndrome is characterized by a defect in the chromosome 15 gene that
codes for fibrillin-1, in the absence of which elastin is more readily
degraded by
metalloproteinases.12 The
genetic fault in Marfan syndrome seems to impair aortic medial elastic
fibers more extensively than the observed impairment in CHD, because
the incidence of ascending aortic dissection or rupture is higher in
Marfan syndrome or annuloaortic
ectasia13 14 than
in CHD patients with aortic root dilatation. Our data set the stage for
pathogenetic studies, including morphometric
analyses8 and
immunoreactivity for matrix metalloproteinases, which are etiologically
important in abdominal aortic
aneurysms17 18 19
and in certain thoracic aortic
aneurysms.13
Limitations
We had limited access to biopsies from dilated
pulmonary trunks accompanying lowresistance, high-flow atrial septal
defects, which are now closed via minithoracotomy, and limited access
to dilated pulmonary trunks associated with mobile pulmonary valve
stenosis, which is now treated by balloon
valvuloplasty.
Conclusions
A hitherto unrecognized prevalence of great arterial
medial abnormalities of smooth muscle, elastic fibers, collagen, and
ground substance was found in 18 types of CHD encompassing a wide age
range. Aortic medial abnormalities may be associated with or predispose
to dilatation, aneurysm, and rupture and are potential cardiac surgical
risks. Pulmonary trunk medial abnormalities may be associated with or
predispose to dilatation and aneurysm formation in mobile pulmonary
valve stenosis or Fallots tetralogy with absent pulmonary valve.
Aneurysmal hypertensive pulmonary trunks may rupture and are risks
during lung transplantation.
Three important questions remain: whether great arterial medial abnormalities are inherent or acquired, whether and to what extent CHD plays a causal or a facilitating role, and whether and to what extent genetic determinants are operative.
Received January 26, 2000; revision received August 7, 2000; accepted August 31, 2000.
| References |
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