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ONLINE APPENDIX
Methods
Study Design
This study was approved by the Human Investigations Committee of Yale University. All
consecutive patients who admitted between 1999 and 2015 to Yale-New Haven Hospital with the
diagnosis of aortic dissection, either Type A or Type B, either acute or chronic, were
retrospectively screened. Date of onset of symptoms was classified as onset of disease, and
patients without an unequivocally defined onset were excluded.
Our goal was to characterize the natural history of a traditional flap dissection from acuteto chronic. Therefore, besides the inclusion criteria specifically assigned for each observation tool
(described within each paragraph separately), the following additional exclusion criteria were
applied: intramural hematoma, penetrating aortic ulcer, localized or focal dissection (e.g.,
dissection limited to the arch), and dissection limited to the abdominal aorta.
The temporal states were defined in relation to the onset of disease as follows: acute = day
0 to 14, subacute day 15 to week 6, and chronic = after week 6 (11). Computed tomography (CT)
imaging, transesophageal echocardiographic (TEE) studies and intra-operative pathologic
specimens were temporally ordered and sequenced according to their time difference from the
onset, named Δtime.
Study population
In total, 414 patients were admitted during the time period with the diagnosis of aortic
dissection and fulfilled the inclusion criteria. 192 of those were classified as Stanford Type A and
222 as Stanford Type B dissections. While 172 (91%) of the Type A dissections were operated
within the acute state, 46 (20.7%), 19 (8.6%) and 54 (24.3%) of the Type B dissection underwent
surgical or interventional repair at the acute, subacute and chronic state, respectively. One
hundred and four patients (46.8%) with Type B dissection were solely treated medically during
follow-up period.
Online Table 1 presents the demographic characteristics and follow-up information
categorized by each assessment tool – CT, echocardiography and histopathology. Due to different
selection criteria regarding each tool, demographic data may differ in characteristics and followup duration between categories.
Radiographic Imaging
To examine the natural anatomic changes from acute to chronic, only patients who
naturally transitioned into the chronic state (> 6 weeks) without intervention within the earlier
stages were included (Online Table 1) (11). The analysis of progress over time per se requires at
least two imaging studies (inclusion criterion) during follow-up; images after any kind of
intervention (e.g. fenestration, surgery) were categorically excluded, assuming that this might
change the flow properties and natural remodeling of the dissected aorta. Of note, only 7 patients
(3.6%) of the Type A dissection had serial images and consequently, no serious analysis could be
performed.
The measurements of the ascending and descending aorta were evaluated at the bifurcation of the
pulmonary artery. Thereby, the following measures were taken:

Absolute aortic diameter: Maximum inner diameter – including true and false lumen – of
the aorta, including thrombus, but excluding wall hematoma. The inner diameter was
taken to permit incorporation of contrast CTs.

Flap thickness: Maximum thickness of the flap within the middle third of the flap, but
without adherent thrombus.

Longitudinal extent and supply of abdominal branch vessels.
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
Patency of the false lumen: Thrombosis grade of false lumen, classified as none, partial,
and complete thrombosis.
Beyond these basic measurements, the following rates and changes were calculated/estimated:

Dynamic of the dilatation: The interval growth rates (diameter2-diameter1/Δtime2-Δtime1)
for all serial images were obtained and used to create a best-fit graph describing the
dynamics/changes of aortic diameter dilation over time. The upper 95 percentiles within
each temporal stage (acute-subacute-chronic) were considered outliers. The best-fit model
was that of exponential decay with plateau phase. The Δtimes from onset were estimated
at which the growth rate change over time decelerated/stabilized (plateau + 95%
confidence interval) and plateaued.

Dynamic of flap changes: The dynamic of changes in flap thickness over time were
similarly estimated as dynamic of dilatation.
Echocardiographic Imaging
The intra-operative transesophageal echocardiographic images (TEE) were reviewed in
order to evaluate flap mobility. Therefore, patients who were operated at different Δtimes (acute,
subacute and chronic) from onset were randomly selected and intra-operative TEEs were
analyzed (taken before cannulation to initiate cardiopulmonary bypass) (Online Table 2). These
were only evaluated if an appropriate quality of short and long-axis aortic views demonstrating
the flap was available.
Of note, only 27% of the Type B dissection patients had an intra-operative TEE adequate
for inclusion. Therefore, both Type A and Type B dissections were analyzed together for this
parameter and a best-fit graph estimated.
Regression Model
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As described previously by our group (50), we analyzed the growth rate and the changes
of flap thickness by performing a multivariate regression analysis. Defining ST and ST-1 as
sequential imaging studies of size/thickness performed at time T and T-1, respectively, for each
patient, and TIME as the time interval in months between ST and ST-1 , the equation defining
aneurysm growth may be written as:
(1)
ST = ST-1exp α *TIME,
where exp denotes the exponential function and α is a coefficient to be estimated.
To test whether growth of the aortic root is affected by acuity stage, we amend equation (1):
(2)
ST = ST-1exp(α + β*subacute)*TIME,
where subacute is a binary variable, α and β are coefficients to be estimated, and other terms are
as defined above. For estimation purposes, we take natural logarithms of equations (1) and (2),
and rearrange terms, yielding:
(3.1)
ln(ST/ST-1) = α*TIME + µ,
(3.2)
ln(ST/ST-1) = α*TIME + β*subacute*TIME + µ,
where µ denotes an independent and identically distributed (iid) normal error term. Equations
(3.1 and 3.2) are estimated by ordinary least squares regression. Note that equations (3.1 and 3.2)
include no intercept term, since when T=0 we must have ST=ST-1. The smearing method is used to
correct for the biases associated with retransformation of the logarithmic equation.
Histopathologic Analysis
Surgical pathology randomly received specimens from the operating rooms for 95 of the
above-mentioned patients according to each temporal stage (Online Table 2), and the specimens
were grossly examined. Representative sections were submitted for formalin fixation and paraffin
embedding. All cut sections were stained with hematoxylin and eosin, with representative
sections stained with Masson trichrome (to highlight fibrosis) and/or elastic van Gieson (EVG, to
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highlight elastin). Sections were reviewed by two Pathologists (AJA and JAR) for the presence or
absence of atheroma, intimal hyperplasia, subadventitial fibrosis, inflammation, and fibrosis of
vasa vasorum; measured for medial atrophy (in millimeters, mm); and examined for cystic medial
necrosis (pooling of basophilic ground substance), medionecrosis (loss of smooth muscle nuclei),
elastin fragmentation (disruption of elastic fibers), and fibrosis (increase in collagen deposition)
and graded according to Schlatmann and Becker’s grading system (see Appendix 2 for definition
of classification categories and grades) (70).
The parameters were divided into 4 groups for Type B (day 1-14, week 2-6, week 6-year
1 and >year 1) and 3 groups for Type A dissection (day 1-2, day 2-14, >week 2) according to
Δtime to onset and adjusted to the definition of acute, subacute and chronic (11). For each
variable, the statistical difference between these time-dependent groups was tested. Variables
with a grading system (grade I-III) were first converted into binary variables (grades I-II = “0”,
grade III = “1”), and analyzed using crosstabs and performing the chi-square test. Continuous
variables were compared using the ANOVA test.
Statistical Analysis
Categorical variables were reported as number of cases with percentages. Continuous
variables were reported as mean ± standard deviation and/or median and range. The analyses
were conducted in XLSTAT-Pro® (Version 2015.2.01, Addinsoft, Paris, France) and GraphPad
Prism® (Version 6.0f, GraphPad Software Inc., La Jolla, CA). Statistical significance level was
set a priori at p < 0.05.
Limitations of the Methodology
It should be emphasized that the comparisons we make of aortic histopathology and flap
mobility evaluation at different time points are from different patients – not from the same patient
at different times (impossible in the clinical setting).
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Online Table 1: Demographic characteristics and follow-up of patients assigned
for radiographic studies (only Type B dissection)
Computed Tomography
n=
68
No. of imaging studies
294
Δtime to first image
Median (days)
1 (range 0-2517)
Mean (days)
105 ± 372
Absolute diameter
Mean (mm)
38.5 ± 8.2
Flap Thickness
Mean (mm)
2.3 ± 2.1
Δtime to recent image
Median (years)
0.8 (range 0.01-13.7)
Mean (years)
2.2 ± 2.9
Absolute diameter
Mean (mm)
43.6 ± 9.6
Flap Thickness
Mean (mm)
2.6 ± 0.6
59 ± 13
Mean age (years)
44 (65%)
Male gender
29 ± 7
BMI
Co-Morbidities
Medication at discharge
Marfan
Smoking
29 (43%)
COPD
10 (15%)
Chronic renal failure
9 (13%)
Hypertension
66 (97%)
β-blocker
64 (94%)
α-blocker
8 (12%)
ACE-I / ARB
40 (59%)
CCB
38(56%)
multiple
63 (93%)
29 (43%)
Surgical Intervention
Δtime from onset
3 (4%)
Median (days)
390 (range 45-3577)
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Type of intervention
Mean (days)
781 ± 879
Graft replacement
21 (31%)
Elephant trunk II
7 (10%)
TEVAR
1 (1%)
Data are shown as median (range), mean ± standard deviation, or number (percentage).
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Online Table 2: Demographic characteristics and follow-up of patients assigned for
TEE and Pathology analysis
TEE
Histopathology
32
44
63 ± 11
62 ± 12
23 (72%)
23 (52%)
1 (range 0-79)
2 (range 0-184)
6 ± 15
19 ± 40
15
50
Mean age
56 ± 14
57 ± 14
Male gender
9 (60%)
33 (66%)
0.2 (range 0.0-5.3)
0.2 (range 0.0-13.7)
1.1 ± 1.6
1.8 ± 3.1
Type A dissection
n=
Mean age (years)
Male gender
Median Δtime to image/specimen (days)
Mean Δtime to image/specimen (days)
Type B dissection
n=
Median Δtime to image/specimen (years)
Mean Δtime to image/specimen (years)
Data are shown as median (range), mean ± standard deviation, or number (percentage).
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Online Table 3: Results of the Regression Models
Measure
Sub-Sample
Aortic size
acute/subacute
Variable
Adjusted R2
F
TIME
.41
24.03
TIME*subacute
Flap
Coefficient (mean/95% CI)
T-Statistic
p value
.2068065
.1228638 - .2907491
4.96
<.001
-.1795578
-.2666887 - -.092427
-4.15
<.001
chronic
TIME
.31
46.13
.0013704
.0009623 - .0017785
6.79
<.001
acute/subacute
TIME
.32
11.20
.4330813
.2007184 - .6654443
3,76
.001
-.2657542
-.5048604 - -.0266479
-2.24
.030
.0007298
-.0014079 - .0028675
.69
.493
TIME*subacute
chronic
TIME
.001
.048
Interaction terms between growth rate, time and stage. CI: confidence interval.
Online Table 4: Histopathology Grading
Grade I
Grade II
Grade III
Cystic medial
Minute cyst present within a
Increased cyst size and
Large cyst extending over
necrosis
single lamellar unit
number in total width of one
more than one lamellar unit
lamellar unit
Elastin
Fewer than 5 foci in one
5 or more foci fragmented in
Foci with elastin
fragmentation
micro field (x200), smooth
one field (x200), confluent or
fragmentation in 5+ elastic
muscle orientation preserved
scattered media, smooth
lamellae, regardless of micro
muscle orientation preserved
field, smooth muscle cells
altered in orientation
Fibrosis
Increase in collagen in area
Increase in collagen between
Increase collagen in area
(increased collagen)
compromising less than 1/3rd
1/3rd and 2/3rds of total width
compromising > 2/3rd total
of total width of media
of media
width of media
Medionecrosis
Area compromising less than
Area compromising between
Area compromising greater
(focal loss of nuclei in
1/3rd of total width of media
1/3rd and 2/3rds of total width
than 2/3rd of total width of
of media
media
the media)
Atheroma
Vasa vasorum
Atheroma present
Fibrosis present
fibrosis
Inflammation
Intimal
Inflammation present
Hyperplasia present
hyperplasia
Medial atrophy
Measured in mm
Grading according to Schlatmann and Becker (70).
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