Keywords
Turner syndrome - aortic stiffness - pulse wave velocity - echocardiography - cardiovascular
magnetic resonance
Introduction
Turner syndrome (TS) is a genetic condition caused by partial or complete absence
of an X chromosome and occurs in 50 per 100,000 females at birth.[1] The main complication is aortic dissection, most often preceded by aortic dilatation,[2] which carries a substantial mortality risk.[3] To prevent acute aortic dissection, preventive surgery is advised when the aortic
diameter exceeds a diagnosis-specific cut-off value. Since patients with TS are known
for their short stature, correction for body size area using the aortic size index
is advised.[4] However, even patients with a normal aortic size index may develop aortic dissection.[5] Consequently, aortic dilatation alone is not sufficient for identifying patients
with TS at high risk of aortic dissection. Other clinical parameters identifying high-risk
patients are not very clear.[6]
It has been proposed that other more subtle changes such as increased stiffness of
the aortic wall, are present in patients with TS prior to dissection. Studies in patients
with hypertension, diabetes, or ischemic heart disease have shown aortic stiffness
to be an independent predictor of all-cause mortality and cardiovascular events.[7] Although previous literature showed an increased aortic stiffness in patients with
TS,[8]
[9]
[10] it remains unclear to what extent this is explained by the commonly found bicuspid
aortic valve (BAV) and coarctation of the aorta (CoA). Both BAV and CoA are also associated
with aortic stiffness,[11]
[12] and it is known that dissection may occur in the absence of BAV and CoA.[13] Differences in aortic stiffness between monosomy (45, X) and mosaicism have also
not yet been investigated.
In addition, histomorphological examination of aortic tissue from patients might also
be of help to identify possible pathological changes in the aortic wall and to interpret
aortic stiffness imaging parameters.
The aim of this current study was to investigate whether the aortic wall of patients
with TS is different from that of healthy control patients, and if this can be explained
solely by the bicuspid valve and/or aortic coarctation.
Materials and Methods
In this cross-sectional cohort study, we included all adult patients with TS who participated
between October 2014 and March 2016 in a study previously described.[14] Inclusion criteria for patients with TS were a 45, X or 45, X/46, and XX mosaic
karyotype. The patients were prospectively included and subjected to physical examination
(including height, weight, and systolic and diastolic blood pressure), electrocardiography,
two- and three-dimensional (2D and 3D, respectively) echocardiography, computed tomography
angiography (CTA), and magnetic resonance imaging (MRI), all on the same day.
Measurements of the aortic diameter were performed using the double-oblique technique
on CTA during systole, except for two patients. In those two patients, contrast-enhanced
magnetic resonance angiography (CEMRA) images were used, as CTA was not performed.
Scan parameters of the CT imaging can be found elsewhere.[14]
Two reference groups were selected: patients with BAV without TS and healthy control
women. We selected patients with BAV from the same prospective cohort study from which
the patients with TS were included. The inclusion criteria for BAV were age ≥18 years
and one of the following features: (1) aortic stenosis (gradient >2.5 m/sec), (2)
aortic regurgitation (at least moderate), or (3) ascending aortic diameter ≥40 mm
and/or aortic size index >2.1.
For carotid-femoral pulse wave velocity (CF-PWV) measurements, we included a statistically
age-matched control group. They did not undergo CTA or MRI and therefore aortic diameters
were measured during midsystole with echocardiography in this group of healthy patients
using the leading-edge-to-leading-edge technique.
The healthy control group for aortic distensibility and aortic arch pulse wave velocity
(AA-PWV) measurements were recruited from a previous MRI study on aortic stiffness
of patients with the same age.[15]
The study was approved by the medical ethical committee (MEC14–225). Written informed
consent was provided by all patients and controls.
A standard 2D transthoracic echocardiogram was performed by an experienced sonographer.
All studies were acquired using harmonic imaging on an iE33 or EPIQ7 ultrasound system
(Philips Medical Systems, Best, the Netherlands) equipped with an x5–1 matrix-array
transducer (composed of 3040 elements operating at 1–5 MHz). The aorta was measured
in the standard parasternal long axis view or on a more cranial view one intercostal
space higher which often improved the visualization of the ascending aorta.
PW Doppler signals were obtained consecutively at the common carotid artery and the
femoral artery ([Supplementary Fig. S1], panel A). PWV (expressed in m/s) was defined as: distance (in meters) between carotid
artery and femoral artery/delta time (in seconds). The distance was measured outside
the patient's body with a measuring tape. For both signals, the time interval was
measured between the onset of the QRS complex and the onset of the systolic PW Doppler
signal. Delta time was calculated as the difference between both time intervals. Validated
software was used to analyze the PWV (Curad Viewer version 3.5.3.0, Wijk bij Duurstede,
the Netherlands).
Image acquisition was performed using a 1.5-T scanner (Discovery MR450, GE Medical
Systems, Milwaukee, WI, USA) using a 32-channel phased-array cardiac surface coil.
A retrospectively echocardiography (ECG)-gated 2D balanced steady-state free precession
sequence during breath hold was obtained perpendicular to the ascending aorta at the
level of the pulmonary trunk to measure aortic distensibility. Typical scan parameters
were as follows: field of view (FOV) 420 mm (phase FOV 60%); matrix size, 256 × 192;
slice thickness, 6.5 mm; flip angle, 45 degrees; repetition time/echo time (TR/TE),
3.3/1.5 ms; and number of reconstructed phases, 24 per cardiac cycle. The contour
of the ascending aorta was manually traced in all phases (QMass analytical software
version 8.1, Medis, Leiden, the Netherlands). The minimum and maximum ascending aortic
cross-sectional areas were identified, and aortic distensibility (10–3 mm Hg−1) was calculated using the following calculation: (maximum area – minimum area)/(minimum
area × ΔP) × 1,000, where ΔP is the brachial pulse pressure in mmHg ([Supplementary Fig. S1], panel B).
A free-breathing, retrospectively ECG-gated 2D phase-contrast flow sequence was performed
to measure aortic PWV. The slice plane was positioned at the level of the pulmonary
artery perpendicular to the ascending and descending aorta. Typical scan parameters
were as follows: FOV, 350 mm (phase FOV 90%); matrix size, 192 × 160; slice thickness,
7.0 mm; flip angle, 20 degrees; number of averages, 3; TR/TE, 4.3/2.3 ms; views per
segment, 1; velocity encoding value, 200 cm/s; true temporal resolution, approximately
11 ms; and number of reconstructed phases, 100 per cardiac cycle. AA-PWV was defined
as distance between ascending and descending aorta/Δ time (expressed in m/s). Delta
time was measured with the same method explained by Devos et al[9] ([Supplementary Fig. S1], panel C). The onset of the systolic wave front was determined from the resulting
flow graph by the intersection point of the constant horizontal diastolic flow and
the upslope of the systolic wave front, the latter of which was modeled by linear
regression along the upslope from the flow values between 20 and 80% of the total
range. To determine the length of the aortic segment between the two aortic levels,
sagittal angulated T1-weighted black blood turbo spin echo images of the AA were acquired
during breath-hold. Typical scan parameters were FOV, 400 mm (phase FOV 100%); matrix,
256 × 256; slice thickness, 5.0 mm; and flip angle, 155 degrees. When the AA was not
properly visible on the black blood images a multiplanar reconstruction was made with
CEMRA images to measure the distance (n = 35, 47%). The CEMRA scan parameters are described elsewhere.[14] Qmass software was used for distensibility measurements and Qflow software was used
for PWV measurements (Medis, Leiden, the Netherlands).
We studied the histomorphology of formalin-fixed paraffin-embedded (FFPE) specimens
of the ascending aorta of five TS patients who underwent preventive replacement of
the ascending aorta because of dilatation. In one patient, we additionally performed
electron microscopy examination to ultrastructurally investigate medial elastin fiber
morphology and deposition of elastin. To clearly show the differences between aortic
tissue of patients with TS and healthy tissue, aortic tissue from a healthy woman
aged 45 years was obtained from the Heart Valve Bank in Rotterdam and investigated.
Routine staining with hematoxylin–eosin (HE), the elastica van Gieson (EvG), and alcian
blue (AB) stains was performed on 3 μm sections. The criteria as outlined in the recent
consensus statement on surgical pathology of the aorta[16] were used for scoring and classification of abnormalities. In addition, immunohistochemical
stains were performed on a Ventana Benchmark Ultra-automated staining platform (Roche
Diagnostics, Tucson, AZ) to assess the vessel wall expression of smooth muscle actin
(SMA), caldesmon, desmin, actin HHF-35, estrogen receptor (ER), and progesterone receptor
(PR), as well as the proliferation marker MIB-1. Immunohistochemical methods including
the antibody clones used are provided in the [Supplementary Material] ([Supplementary Appendix A]). For electron microscopy, representative samples of the media were isolated from
paraffin blocks and incubated with a mixture of 1% glutaraldehyde and 4% formaldehyde.
The sections were osmicated with 1% osmium in distilled water, dehydrated in 50 to
100% Acetone and embedded in a mixture of Embed-812, NMA, DDSA, and DMP-30 (EMS diasum,
Hatfield, Pennsylvania). Ultrathin sections (60–70 nm) were cut using an Ultramicrotome
UC7 (Leica, Germany), mounted on copper grids, and counterstained with uranyl acetate
0,5% for 30 minutes at 45°C and Ultrostain II (Leica, Germany) for 7 minutes at room
temperature in the Leica AC20. Elastin lamellae were visualized at magnifications
of ×2,800 and ×7,100 and analyzed under the electron microscope (Philips, Eindhoven,
the Netherlands).
All characteristics are presented as mean ± standard deviation when normally distributed,
and in case of nonnormal distribution, medians (interquartile ranges [IQR]) are provided.
Categorical variables are presented as frequencies with percentages. Comparison of
normally distributed continuous variables between two groups was done using the Student's
t-test or, in case of a skewed distribution, the Mann–Whitney test. Univariable linear
regression analysis was performed with patient characteristics as independent variables
and the measurement of aortic stiffness as dependent variable. In addition, multivariable
analysis was performed using the Enter method to adjust for age, aortic size index,
BAV, CoA, and hypertension. To assess interobserver variability, the intraclass correlation
coefficient (ICC) was calculated for all measurements using 25 randomly selected patients.
The IBM SPSS statistics 21.0 software was used to analyze the data. The statistical
tests were two sided and a p-value below 0.05 was considered significant.
Results
In total, 52 women with TS aged 35 ± 14 years were included: 40 with a tricuspid aortic
valve (TAV) and 12 patients with BAV. Twenty-five TS women had X chromosome monosomy
(45, X) and the other 25 TS women had X chromosome mosaicism (n = 2 missing). Renal function was normal in all. In 13 women (25%), the time between
the first and last investigation was ≥1 day (median, 7 days; IQR: 5–42 days) due to
technical or practical issues. We included 13 women with BAV without TS and 10 healthy
women for the control groups of CF-PWV. The control group for aortic distensibility
and AA-PWV measurements consisted of the same 13 women with BAV and an additional
38 healthy female patients. In [Fig. 1], a flowchart is presented with the number of measurements that could be performed
in the participants. [Table 1] shows the baseline patient characteristics of the TS women and control groups separately.
Surgical correction for CoA with end-to-end anastomosis was performed in three patients
with TS. Five patients with TS were treated for hypertension with β-blockers, angiotensin
receptor blockers, or angiotensin converting enzyme (ACE) inhibitors.
Fig. 1 Flow chart of the patients with aortic stiffness measurements. All three measurements
could be performed in 32 patients with Turner syndrome (25 TAV and 7 BAV) and in 8
control patients with BAV only. BAV, bicuspid aortic valve; PWV, pulse wave velocity;
TAV, tricuspid aortic valve.
Table 1
Baseline characteristics
|
Characteristics
|
Turner syndrome (n = 52)
|
Bicuspid aortic valve without Turner syndrome (n = 13)
|
Healthy controls echocardiography (n = 10)
|
Healthy controls MRI (n = 38)
|
|
Total (n = 52)
|
TAV (n = 40)
|
BAV (n = 12)
|
|
|
|
|
Age (y)
|
35 ± 14
|
36 ± 14
|
35 ± 13
|
34 ± 11
|
35 ± 15
|
34 ± 14
|
|
Height (cm)
|
156 ± 9
|
157 ± 9
|
154 ± 7
|
169 ± 11
|
187 ± 6
|
166 ± 8
|
|
Weight (kg)
|
66 ± 16
|
68 ± 17
|
61 ± 11
|
69 ± 11
|
83 ± 10
|
61 ± 11
|
|
Systolic blood pressure (mm Hg)
|
124 ± 17
|
124 ± 18
|
126 ± 16
|
116 ± 12
|
131 ± 10
|
118 ± 14
|
|
Diastolic blood pressure (mm Hg)
|
80 ± 13
|
80 ± 12
|
83 ± 14
|
77 ± 7
|
79 ± 7
|
70 ± 9
|
|
Hypertension
|
8 (15%)
|
7 (18%)
|
1 (8%)
|
3 (23%)
|
0 (0%)
|
0 (0%)
|
|
Surgical correction for aortic coarctation[a]
|
3 (6%)
|
0 (0%)
|
3 (25%)
|
2 (15%)
|
0 (0%)
|
0 (0%)
|
|
Aortic dilatation (>40 mm and/or ASI > 2.1 cm/cm2)
|
11 (21%)
|
6 (15%)
|
5 (42%)
|
9 (69%)
|
0 (0%)
|
1 (3%)[b]
|
|
Aortic stenosis (echo Vmax >2.5 m/s)
|
1 (2%)
|
0 (0%)
|
1 (8%)
|
11 (85%)
|
0 (0%)
|
0 (0%)
|
|
Aortic regurgitation (moderate or severe)
|
1 (2%)
|
0 (0%)
|
1 (8%)
|
5 (39%)
|
0 (0%)
|
0 (0%)
|
|
Absolute ascending aortic diameter (mm)
|
31 ± 5
|
30 ± 4
|
33 ± 6
|
40 ± 7
|
31 ± 3
|
27 ± 3
|
|
Aortic size index ascending aorta (mm/m2)
|
19 ± 4
|
18 ± 3
|
21 ± 3
|
22 ± 3
|
15 ± 2
|
16 ± 2
|
ASI, aortic size index (aortic diameter divided by body surface area); BAV, bicuspid
aortic valve; MRI, magnetic resonance imaging; TAV, tricuspid aortic valve; Vmax, maximum velocity.
Note: data are expressed as mean ± standard deviation or n (percentage).
Missing values were present for height (n = 1) and weight (n = 1), blood pressure (n = 6) and aortic size index (n = 1).
a One additional Turner patient has a coarctation of the aorta, but he did not undergo
surgical correction.
b One healthy woman with an aortic diameter of 29 mm, height of 151 cm and weight of
40 kg, which resulted in an ASI of 2.2 cm/m2.
[Figure 2] shows the comparison between patients with TS and controls for the CF-PWV, ascending
aortic distensibility and AA-PWV. We found no significant difference in CF-PWV between
the groups. Within the women with TS, patients with BAV (median = 7.0, IQR: 6.1–7.7
m/s) did not show a significantly different CF-PWV compared with the patients without
BAV (median = 6.7, IQR: 5.8–8.5 m/s). In all four TS women with CoA, the CF-PWV could
be measured (5.3, 6.9, 7.6, and 7.8 m/s) and was not statistically different from
TS women without CoA (median = 6.7, IQR: 5.9–8.4 m/s). Also, no statistical difference
was found between patients with monosomy (median = 6.5, IQR: 5.7–7.7 m/s) or mosaicism
(median = 6.9, IQR: 6.4–8.6 m/s). For CF-PWV measurements we found an ICC of 0.893
(0.772–0.951).
Fig. 2 Uncorrected results of carotid-femoral pulse wave velocity, ascending aortic distensibility,
and aortic arch pulse wave velocity divided into four groups. The median level in
each subgroup is indicated with the black line. BAV, bicuspid aortic valve; PWV, pulse
wave velocity; TAV, tricuspid aortic valve. * Significantly different from the healthy
group according to the Wilcoxon's one-sample test.
We found no significant difference in ascending aortic distensibility between the
groups. Within the women with TS, patients with BAV (median = 5.7, IQR: 2.5–8.3 mm
Hg−1) did not show a significantly different ascending aortic distensibility compared
with the patients without BAV (median = 5.3, IQR: 2.6–7.6 mm Hg−1). Only in two TS women with CoA, the ascending aortic distensibility could be measured
(1.5 and 6.2 × 10−3 mm Hg−1). No statistical difference was found between patients with monosomy (median = 5.2,
IQR: 3.9–7.1 mm Hg−1) or mosaicism (median = 5.6, IQR: 2.3–8.3 mm Hg−1). For ascending aortic distensibility measurements we found an ICC of 0.999 (0.996–0.999)
for the minimum area and 0.999 (0.998–1.000) for the maximum area.
Patients with TS showed significantly higher AA-PWV compared with healthy controls
([Fig. 2]). In the multivariable analysis ([Table 2]), the presence of TS remained significantly associated with higher AA-PWV (β = 1.08,
95% confidence interval [CI]: 0.54–1.62, p < 0.001). Within the patients with TS, patients with BAV (median = 4.8, IQR: 4.4–6.0
m/s) did not show a significantly different AA-PWV compared with the patients without
BAV (median = 5.3, IQR: 4.5–6.1 m/s). In three TS women with CoA, the AA-PWV could
be measured (4.4, 5.8, and 6.4 m/s), which was comparable to the median of TS women
without CoA (median = 4.9, IQR: 4.5–5.9 m/s). No statistical difference was found
between patients with monosomy (median = 4.7, IQR: 4.4–5.8 m/s) or mosaicism (median = 5.5,
IQR: 4.5–6.2 m/s). For AA-PWV measurements, we found an ICC of 0.970 (0.935–0.987)
for the distance measurements and 0.704 (0.437–0.857) for the time measurements.
Table 2
Univariable and multivariable analysis of aortic stiffness measurements in the total
group including patients with Turner syndrome, bicuspid aortic valve patients and
control patients
|
Characteristics
|
Univariable analysis
|
Multivariable analysis[a]
|
|
|
Beta (95% CI)
|
p-Value
|
Beta (95% CI)
|
p-Value
|
|
Carotid-femoral PWV (n = 69)
|
Turner Syndrome
|
0.54 (−0.34; 1.42)
|
0.223
|
0.03 (−0.65; 0.72)
|
0.924
|
|
Age
|
0.09 (0.06; 0.11)
|
<0.001
|
0.06 (0.04; 0.09)
|
<0.001
|
|
Baseline aortic size index
|
0.16 (0.05; 0.27)
|
0.004
|
0.14 (0.04; 0.25)
|
0.007
|
|
Bicuspid aortic valve
|
−0.67 (−1.54; 0.21)
|
0.132
|
−1.03 (−1.95; −0.12)
|
0.028
|
|
Aortic coarctation
|
−0.42 (−2.01; 1.16)
|
0.596
|
0.53 (−0.76; 1.82)
|
0.413
|
|
Hypertension
|
2.41 (1.26; 3.56)
|
<0.001
|
1.082 (0.13; 2.03)
|
0.027
|
|
Ascending aortic distensibility (n = 87[b])
|
Turner Syndrome
|
−1.01 (−2.5; 0.51)
|
0.191
|
−0.87 (−1.99; 0.25)
|
0.126
|
|
Age
|
−0.18 (−0.22; −0.14)
|
<0.001
|
−0.18 (−0.23; −0.14)
|
<0.001
|
|
Baseline aortic sixe index
|
−0.15 (−0.36; 0.07)
|
0.181
|
0.11 (−0.11; 0.32)
|
0.327
|
|
Bicuspid aortic valve
|
−0.09 (−1.97; 1.79)
|
0.926
|
−0.33 (−2.17; 1.52)
|
0.726
|
|
Aortic coarctation
|
−1.38 (−5.00; 2.24)
|
0.451
|
−1.86 (−4.79; 1.07)
|
0.210
|
|
Hypertension
|
−3.61 (−6.13; −1.09)
|
0.005
|
−1.25 (−3.35; 0.85)
|
0.238
|
|
Aortic arch PWV (n = 87[b])
|
Turner Syndrome
|
1.34 (0.72; 1.95)
|
<0.001
|
1.08 (0.54; 1.62)
|
<0.001
|
|
Age
|
0.06 (0.04; 0.08)
|
<0.001
|
0.05 (0.03; 0.07)
|
<0.001
|
|
Baseline aortic sixe index
|
0.14 (0.05; 0.24)
|
0.004
|
0.06 (−0.03; 0.16)
|
0.198
|
|
Bicuspid aortic valve
|
0.18 (−0.62; 0.99)
|
0.651
|
−0.35 (−1.17; 0.47)
|
0.395
|
|
Aortic coarctation
|
1.39 (0.27; 2.50)
|
0.015
|
0.66 (−0.35; 1.67)
|
0.195
|
|
Hypertension
|
2.47 (1.42; 3.52)
|
<0.001
|
0.80 (−0.24; 1.85)
|
0.131
|
Abbreviations: PWV, pulse wave velocity.
Note: bold = statistical significant in multivariabele analysis.
a Corrected for all other variables mentioned in this table.
b One patient had a missing value for weight.
The five patients with TS who underwent surgery had an age range of 11 to 47 years
at time of surgery. [Supplementary Table S1] shows a complete overview of the routine stains of each patient. Using the criteria
outlined in the recent consensus statement, the patients were found to show only mild
medial degeneration in four patients, and no medial degeneration in one patient, with
mostly intralamellar and focal, mucoid matrix accumulation ([Fig. 3]). In addition to these findings, we found compact smooth muscle cell layers and
a decrease in the intralamellar space, but only mild smooth muscle cell nuclei loss.
Also, conspicuous granular deposition of elastin adjacent to lamellae was found in
aortic tissue of women with TS when compared with healthy controls ([Fig. 3]). Additional electron microscopic images confirmed these granular structures by
showing “bulges” on the surface of elastin fibers ([Fig. 4]). The elastin fibers themselves were positioned closer together and were more irregular
and thinner compared with a healthy control. Immunohistochemically, the most striking
findings were seen in the middle section of the media with a complete lack of desmin
expression in all five patients, underexpression of caldesmon and progesterone receptor
in four out of five, and weak expression of HHF-35 in three out of five patients ([Fig. 5]). We observed apparent overexpression of estrogen receptor in the media of TS patients,
while SMA and MIB-1 were not differentially expressed.
Fig. 3 Routine stains of aortic tissue of patients with Turner syndrome and healthy controls.
Top row: (A) hematoxylin–eosin, (B) Elastica-van Gieson, and (C) alcian blue stains of a representative aortic explant of a Turner syndrome patient,
with essentially intact lamellation, and only minimal elastin fragmentation (B) and mucin deposition (C, arrow). Second row: (D) control case lacking significant degeneration in hematoxylin–eosin stains, (E) Elastica-van Gieson stains, or (F) alcian blue stains. Third row: (G) Turner case lacking significant degeneration in hematoxylin-eosin stains or (H, I) Elastica-van Gieson stains, but with decrease in smooth muscle cell volume. Bottom
row: (J) Elastica-van Gieson stains of two Turner patients with extensive and (K) focal granular deposition of elastin fibers (arrows) and (L) one healthy control (L).
Fig. 4 Representative electron microscopic images of the aortic media of a women with Turner
syndrome (A and B) and a healthy control (C and D). (A and C) ×2,800 magnification,
(B and D) ×7,100 magnification. This figure shows that the elastin lamellae of the
women with Turner syndrome are positioned closer together, more irregular and thinner,
and display numerous excrescences on the surface.
Fig. 5 Immunohistochemical stains of patient with Turner syndrome and healthy control. Top
row: (A) immunohistochemical caldesmon and (B) desmin stains of representative aortic explant of controls. Bottom row: (C) immunohistochemical caldesmon and (D) desmin stains of representative aortic explant of Turner syndrome patient, with
appreciable loss of staining in the media for both proteins.
Discussion
The results of our study show that women with TS have a stiffer AA compared with controls,
independent of the presence of BAV or CoA. Ascending aortic distensibility and CF-PWV
were not statistically different between patients with TS and controls. We also found
no effect of karyotype on aortic stiffness. Our imaging results confirm that the wall
of the aorta is indeed different in patients with TS, even in the absence of cardiovascular
pathology, such as a bicuspid valve, and this seems especially true for the AA and
ascending aorta. In addition, clear histomorphological changes are found in the ascending
aorta, pointing toward an inherent abnormal aortic wall.
The observed increased AA-PWV in our study was also observed by Devos et al[9]; however, Schäfer et al[8] did not find these results in the younger group of patients with TS. This may indicate
that aortic stiffness occurs later in the disease process. Besides increased aortic
stiffness, patients with TS also have a higher risk of AA abnormalities, such as elongation
of the AA.[17] It might be that anatomical abnormalities in the arch, including wall abnormalities
or anatomical variations influencing flow patterns, contribute to the occurrence of
dissection in the descending aorta. The majority (54%) of the patients with TS developed
dissection in the ascending aorta, while only 16.4% developed a dissection in the
descending aorta.[18] Further research is required to determine whether descending aortic dissection can
be a result of long-lasting abnormal flow patterns caused by AA abnormalities or increased
stiffness as in patients with TS. Consequently, these patients might benefit from
more intensive follow-up and earlier preventive surgery.
In addition, our histomorphological results showed abnormalities in the wall of the
patients with TS. A hitherto undescribed and striking pattern, which is not scored
in the current consensus statement,[16] was seen in most patients, with compact smooth muscle cell layers and granular deposition
of elastin adjacent to lamellae and in the intralamellar tissue. The described compact
smooth muscle cell layers and a decrease in the intralamellar space without strong
evidence of smooth muscle cell loss indicates a smooth muscle cell volume loss. This
finding is supported by contractile fiber attenuation demonstrated by a complete lack
of desmin expression, underexpression of caldesmon, and HHF-35, as well as weak expression
of PR. Our results are in line with a murine study[19] that showed decreased smooth muscle cell content and expression of smooth muscle
actin in mice with TS. Hinton et al[19] also found subtle smooth muscle cell misalignment abnormalities that were not present
in our patients. The phenomena of decreased smooth muscle cell volume with contractile
fiber attenuation and granular deposition of elastin may be key factors in medial
destabilization in TS patients. Because we only included patients who had undergone
surgery for aortic dilatation, these changes could also be a result of aortic dilatation.
However, it is not consistently present in aortic resection specimens from other types
of connective tissue disease (such as Marfan's disease or Loeys–Dietz syndrome [own
observation and Jain et al.[20]]). Based on our findings, we suggest that both smooth muscle cell volume and (patterns
of) elastin deposition should be included in future grading schemes to evaluate aortic
tissue, rather than solely focusing on smooth muscle cell loss and elastin degradation,
respectively.
Although histomorphological data confirms that the wall is different in patients with
TS, the elasticity measurement of the ascending aorta (ascending aortic distensibility)
was not statistically significant different between TS and controls. This might indicate
that elasticity measurements of the ascending aorta are impeded by nonoptimal diagnostic
power to determine these adverse structural changes within the aortic vessel wall
of individual patients with TS. If that is the case, hopefully new imaging developments
such as nuclear imaging[21] or computational fluid dynamics[22] will help to noninvasively visualize the changes in the aortic wall or the abnormal
blood flow as a result of abnormal aortic wall behavior. Another reason for our nonsignificantly
different ascending aortic distensibility between women with and without TS might
be the limited number of participants. Since there seemed to be a tendency to a reduced
ascending aortic distensibility in patients with TS, the size of the group might have
prevented us from finding a significant difference. Others have also investigated
whether the presence of BAV can explain the increased aortic stiffness in patients
with TS but the results are contradictory. Two studies[8]
[23] showed reduced ascending aortic distensibility and increased AA-PWV independently
of the presence of BAV, while Devos et al[9] showed that only patients with BAV have a reduced ascending aortic distensibility.
Our results are more in line with the first study, since we found no effect of BAV
on stiffness. The influence of CoA on aortic stiffness in patients with TS has been
investigated by Wen et al[10] who showed that the aortic distensibility of the descending aorta was only lower
among TS patients with CoA. A history of hypertension and specific medical treatment
and the effect of the treatment could have caused these ambiguous results in different
studies. Our own and former results should be interpreted with caution and verified
in a larger cohort of TS patients, taking into account the assumed factors which affect
the aortic elasticity.
The aortic stiffness over the entire aorta measured with CF-PWV showed no significant
difference between patients with TS and healthy controls, which is in line with previous
literature.[24] Important to acknowledge is that –CF-PWV uses a conventional measurement of the
distance on the body surface. Patients with TS are known to have a fairly abnormal
course of the larger vessels with unrolling and tortuosity.[9]
[25] Because of these aortic abnormalities, measurement of the aortic length on the outside
of the body is likely to fail in patients with TS. We probably underestimated the
length of the aorta, therefore, the value of the CF-PWV will be measured lower than
it actually is. The classic CF-PWV might not be efficient enough to identify abnormal
aortic elasticity with this measurement in patients with TS due to methodological
issues.
Conclusion
Women with TS show a stiffer AA independently of the presence of a BAV or CoA. No
differences were found in aortic stiffness between patients with monosomy or mosaicism.
In addition, histomorphological changes are found in the ascending aorta. Our histomorphological
investigation provided new insights into the structure of the aortic wall in patients
with TS. Further research should aim to investigate whether these structural changes
are indeed related to the markedly different elastic properties of the ascending aorta
in a larger cohort and how we can identify this difference in elastic properties more
accurately with the use of new imaging developments.
