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Objectives: Current risk assessment strategies in type B aortic dissection are focused on anatomic parameters, although haemodynamic abnormalities that result in false lumen (FL) pressurization are thought to play a significant role in aortic growth. The objective of this study was to evaluate blood flow of the FL using 4D flow magnetic resonance imaging (MRI) and identify haemodynamic and anatomic factors that independently predict the rate of aortic growth. Methods: Patients with dissection of the descending thoraco-abdominal aorta (n = 18) were enrolled in a prospective observational study and underwent 4D flow MRI for haemodynamic assessment of the entry tear and FL. Anatomic parameters were obtained by magnetic resonance angiography and baseline computed tomography. False lumen ejection fraction (FL EF) was defined the ratio of retrograde flow rate at the dominant entry tear during diastole over the antegrade systolic flow rate. Results: The median aortic growth rate was 3.5 mm/year (interquartile range 0.5-8.1 mm/year). Entry tear peak velocity was lower in patients with enlarging aortic dimensions (95.5 ± 24.1 vs 128.1 ± 37.4 cm/s, P = 0.039). After adjusting for co-variates FL EF (β = 0.15, P = 0.004), baseline maximal aortic diameter (β = 0.37, P = 0.001) and the entry tear distance from the left subclavian artery (β = 0.07, P = 0.016) were significant predictors of aortic growth rate. Conclusions: Beyond standard anatomic risk factors, FL EF is an independent predictor of aortic growth rate and may represent an intuitive, non-invasive method to estimate FL pressurization and improve patient-specific risk assessment in patients with type B aortic dissection.
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Cite this article as: Burris NS, Nordsletten DA, Sotelo JA, Grogan-Kaylor R, Houben IB, Figueroa CA et al. False lumen ejection fraction predicts growth in type B aortic
dissection: preliminary results. Eur J Cardiothorac Surg 2019; doi:10.1093/ejcts/ezz343.
False lumen ejection fraction predicts growth in type B aortic
dissection: preliminary results
Nicholas S. Burris
a,
*, David A. Nordsletten
b,c
,JulioA.Sotelo
d,e,f
, Ross Grogan-Kaylor
a
,
Ignas B. Houben
b
,C.AlbertoFigueroa
c,g
,SergioUribe
d,f,h
and Himanshu J. Patel
b
a
Department of Radiology, University of Michigan, Ann Arbor, MI, USA
b
Department of Cardiac Surgery, University of Michigan, Ann Arbor, MI, USA
c
Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
d
Biomedical Imaging Center, Pontificia Universidad Cato´lica de Chile, Santiago, Chile
e
Department of Electrical Engineering, Pontificia Universidad Cato´ lica de Chile, Santiago, Chile
f
Millennium Nucleus for Cardiovascular Magnetic Resonance, Santiago, Chile
g
Department of Surgery, University of Michigan, Ann Arbor, MI, USA
h
Department of Radiology, School of Medicine, Pontificia Universidad Cato´ lica de Chile, Santiago, Chile
* Corresponding author. Department of Radiology, University of Michigan, 1500 E. Medical Center Drive, Cardiovascular Center 5588, SPC-5030, Ann Arbor,
MI 48109-5030, USA. Tel: +1 734-763-7169; e-mail: nburris@med.umich.edu (N.S. Burris).
Received 16 September 2019; received in revised form 6 November 2019; accepted 13 November 2019
Abstract
OBJECTIVES: Current risk assessment strategies in type B aortic dissection are focused on anatomic parameters, although haemodynamic
abnormalities that result in false lumen (FL) pressurization are thought to play a significant role in aortic growth. The objective of this study
was to evaluate blood flow of the FL using 4D flow magnetic resonance imaging (MRI) and identify haemodynamic and anatomic factors
that independently predict the rate of aortic growth.
Presented at the 33rd Annual Meeting of the European Association for Cardio-Thoracic Surgery, Lisbon, Portugal, 3–5 October 2019.
CONVENTIONAL
AORTIC SURGERY
V
CThe Author(s) 2019. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.
European Journal of Cardio-Thoracic Surgery 0 (2019) 1–8 ORIGINAL ARTICLE
doi:10.1093/ejcts/ezz343
Downloaded from https://academic.oup.com/ejcts/advance-article-abstract/doi/10.1093/ejcts/ezz343/5671737 by University of Michigan, nburris@med.umich.edu on 16 December 2019
METHODS: Patients with dissection of the descending thoraco-abdominal aorta (n= 18) were enrolled in a prospective observational
study and underwent 4D flow MRI for haemodynamic assessment of the entry tear and FL. Anatomic parameters were obtained by mag-
netic resonance angiography and baseline computed tomography. False lumen ejection fraction (FL EF) was defined the ratio of retrograde
flow rate at the dominant entry tear during diastole over the antegrade systolic flow rate.
RESULTS: The median aortic growth rate was 3.5 mm/year (interquartile range 0.5–8.1 mm/year). Entry tear peak velocity was lower in
patients with enlarging aortic dimensions (95.5 ± 24.1 vs 128.1 ± 37.4 cm/s, P= 0.039). After adjusting for co-variates FL EF (b= 0.15,
P= 0.004), baseline maximal aortic diameter (b= 0.37, P=0.001) and the entry tear distance from the left subclavian artery (b= 0.07,
P= 0.016) were significant predictors of aortic growth rate.
CONCLUSIONS: Beyond standard anatomic risk factors, FL EF is an independent predictor of aortic growth rate and may represent an in-
tuitive, non-invasive method to estimate FL pressurization and improve patient-specific risk assessment in patients with type B aortic
dissection.
Keywords: Type B aortic dissection • False lumen • Computed tomography angiography • 4D flow magnetic resonance imaging •
Aneurysm
ABBREVIATIONS
CI Confidence interval
CT Computed tomography
FL EF False lumen ejection fraction
FL False lumen
LSC Left subclavian artery
MRA Magnetic resonance angiography
MRI Magnetic resonance imaging
SD Standard deviation
TBAD Type B aortic dissection
TEVAR Thoracic endovascular aortic repair
TL True lumen
vWERP Virtual work-energy relative pressure
INTRODUCTION
Aneurysmal degeneration of the false lumen (FL) is the most
common long-term complication in type B aortic dissection
(TBAD), occurring in 75% of patients who are medically man-
aged [1]. Prophylactic thoracic endovascular aortic repair
(TEVAR) has been shown to promote aortic remodelling, slow
disease progression and decrease long-term aorta-specific mor-
tality [2,3]. However, TEVAR for uncomplicated TBAD remains a
debated topic, given concerns of excess cost and procedural
complications. Thus, there remains a significant need for meth-
ods to better risk-stratify patients with TBAD to allow for a tar-
geted repair strategy. Existing methods for estimating the risk in
TBAD focus on anatomic variables measured on computed tom-
ography (CT) images, which are limited in their ability to capture
the complex and dynamic character of aortic dissection [46].
A recent CT-based risk prediction analysis showed that including
estimated FL outflow improved the model’s predictive power
from 0.55 to 0.7, further stressing the importance of FL haemo-
dynamic assessment of the FL [4].
Haemodynamic forces are thought to play a significant role in
the development of aneurysm in TBAD, and thus TEVAR exerts its
protective effects by decreasing the FL inflow and promoting
thrombosis. Unfortunately, haemodynamics of the FL are poorly
evaluated using standard CT images, and invasive catheter-based
measurements of FL pressure are rarely performed in clinical
practice. Studies using both computation modelling and flow
phantoms techniques have demonstrated that FL pressurization
occurs in the setting of excess inflow relative to outflow, resulting
in higher mean diastolic and pulse pressure in the FL [79].
Furthermore, in the setting of insufficient outflow, the degree of
retrograde flow increases in proportion to the degree of outflow
insufficiency [7,10].
Time-resolved 3-dimensional phase-contrast magnetic reson-
ance imaging (MRI) (4D flow) is an advanced MRI technique that
allows for volumetric assessment of blood flow in large vessels
[11]. 4D flow MRI studies in TBAD have identified a variety of ab-
normal blood flow characteristics in the FL that may relate to the
risk of future FL aneurysm formation, although the mechanisms
that link blood flow abnormalities and aortic growth remain
poorly defined [12,13]. Retrograde flow (or diastolic flow rever-
sal) may be an intuitive marker of FL pressurization that can be
easily identified by 4D flow MRI [14]. Specifically, the proportion
of FL flow exiting at the dominant entry tear in a retrograde fash-
ion during diastole, which in this manuscript will be referred to
as the ‘false lumen ejection fraction’ (FL EF), has been proposed
as surrogate maker of FL pressurization and has been shown to
be elevated among chronic TBAD patients with a history of pro-
gressive FL growth [13]. Despite the simplicity of the FL EF metric,
the haemodynamic environment of the FL is complex and influ-
enced by a variety of patient-specific factors such as anatomy
and age of the dissection, highlighting the need for a multivariate
analysis to control for the effects of confounding relationships
between variables.
The purpose of this study was to perform a comprehensive
analysis of FL haemodynamics in a cohort of patients with chron-
ic TBAD and to further evaluate the ability of a variety of haemo-
dynamic variables to independently predict aortic growth rate
during follow-up. We hypothesize that the degree of blood exit-
ing the FL through the dominant entry tear during diastole (FL
EF) will independently predict growth of the dissected descend-
ing thoraco-abdominal aorta.
MATERIALS AND METHODS
Patient identification and clinical characteristics
Between November 2014 and August 2019, a total of 18 adult
patients with unrepaired, chronic dissection of the descending
thoracic aorta (n= 15 type B; n= 3 repaired type A with
residual tear in the descending thoracic aorta) were
prospectively enrolled in an observational, IRB-approved study
2N.S. Burris et al. / European Journal of Cardio-Thoracic Surgery
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(HUM00120679) and underwent a single research MRI exam.
TBAD patients were identified through our Cardiac Surgery clinic
(n= 95) and were excluded for: (i) complete FL thrombosis (n= 7),
(ii) entry tear location in the abdominal aorta (n= 3), (iii) symp-
toms of chest pain or evidence of malperfusion (n= 3), (iv) claus-
trophobia or other contraindication to MRI (n= 22), (v) estimated
glomerular filtration rate <30 ml/min/1.73 m
2
(n= 8), and 28
patients declined participation. Patient information was collected
by a combination of research questionnaire and chart review.
Baseline anatomic data including maximal diameter (including
aortic wall), true lumen (TL) and FL size, distance of the entry tear
from the left subclavian artery (LSC), FL location and branch ves-
sel anatomy were measured on the baseline clinical CT scan
acquired at the time of aortic dissection diagnosis using clinical
image analysis software using a centreline approach (Vitrea, Vital
Images, Toshiba, Tokyo, Japan).
Magnetic resonance imaging technique and
imaging analysis
All MRI exams were performed on 3T MRI scanners (n=4: MR750,
GE Medical Systems, Milwaukee, WI, USA; n= 14: Ingenia, Philips,
Best, Netherlands). The research MRI examination included breath-
hold, contrast-enhanced magnetic resonance angiography (MRA),
reconstructed at 0.9 mm
3
isotropic resolution after the administra-
tion of an iron-based MRI contrast agent (ferumoxytol, 3 mg/kg) in
12 patients at 3 mg/kg dose or gadobenate dimeglumine
(Multihance
V
R
; Bracco, Milano, Italy) in 5 patients at 0.2ml/kg dose.
Following the MRA, 4D flow MRI was performed covering
the thoracic aorta. Briefly, 4D flow scan parameters included: flip
angle=15, reconstructed resolution = 1.5 mm 1.5 mm 2.5 mm,
acceleration factor = 2.0 2.0, views-per-segment = 3, average scan
time = 11 min, and average temporal resolution = 47 ms, velocity
encoding value = 200 cm/s. Raw 4D flow MRI data were uploaded
to a web-based software application (Arterys, San Francisco, CA,
USA) for data reconstruction, visualization and flow analysis.
Segmentations of the TL and FL were generated with dedicated
software (Mimics, Materialise, Leuven, Belgium) and additional 4D
flow haemodynamic analysis was performed in a computational
framework based on finite-elements developed in MATLAB
(MathWorks, Natick, MA, USA) [15,16]. Visualization of 4D flow
data was performed using ParaView (Kitware Inc., Clifton Park,
NY, USA).
Aortic growth rate was calculated as the difference in maximal
aortic diameter between the baseline CT angiography and the re-
search MRA over the time interval. Subjects were categorized as
‘stable’ if their aortic growth rate was <3 mm/year and ‘enlarging’ if
aortic growth rate was >_3 mm/year, based on the reported mean
growth rate in TBAD and known variability in diameter measure-
ments [17]. Dominant entry tear was defined as the tear with the
highest measured rate of inflow into the FL. FL EF (previously
termed entry tear regurgitant fraction) was calculated from 4D flow
MRI data by placing a flow analysis region of interest in the plane
and location of the dominant entry tear, and was defined as the
ratio of retrograde diastolic flow rate (l/min) over the antegrade
systolic flow rate (l/min) measured in the plane of dominant entry
tear as further illustrated in Fig. 1. Haemodynamics were also
assessed in planes orthogonal to the direction of flow in the prox-
imal TL and FL at 3 cm distal to the entry tear.
Statistical analysis
Patient characteristics were reported as mean ± standard devi-
ation (SD) for continuous variables, and frequencies for
Figure 1: 4D flow haemodynamic assessment. The FL EF was measured in the plane of the dominant entry tear and was defined as the proportion of retrograde flow
(l/min) exiting the FL during diastole over the systolic antegrade flow volume (l/min) at the dominant entry tear (A). Three-dimensional visualization of 4D flow mag-
netic resonance imaging data in a patient with type B aortic dissection demonstrating the flow analysis plane for the entry tear FL EF measurement (B, red line) and
the TL and FL analysis planes (B, grey line) measured 3 cm distal to the tear. Antegrade flow is depicted in the TL and FL during systole (black arrow, B), with retrograde
flow being ‘ejected’ from the FL during diastole (yellow arrow, B) in a representative case with measured FL EF of 57%. FL: false lumen; FL EF: false lumen ejection frac-
tion; LSC: left subclavian artery; TL: true lumen.
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categorical variables. Skewness and kurtosis were assessed (sktest
in Stata), and continuous variables are reported as mean ± SD if
normally distributed or median (interquartile range) if skewed.
Categorical values are reported as n(%). Pearson’s correlation
was used to determine associations between aortic growth rate,
anatomic and haemodynamic parameters. Comparison of con-
tinuous variables was performed with the unpaired t-tests or
non-parametric Mann–Whitney U-test, and a P-value of <0.05
was considered significant. Fisher’s exact test was used to evalu-
ate difference in frequency of categorical variables. Pairwise cor-
relation matrices were used to identify multicollinearity amongst
predictors. Subsequently, parsimonious multiple linear regression
models with Huber/White/sandwich robust variance estimator
were used to identify independent predictors of aortic growth
rate amongst a group of potential anatomic and haemodynamic
variables described in prior publications [6,12,13]. Statistical
analyses were performed using Stata 14.0 (StataCorp LP, College
Station, TX, USA).
RESULTS
Patient characteristics
The average patient age was 52.1 ± 9.5 years and the majority of
patients were male (13/18, 72%). The vast majority of patients
had a history of hypertension (16/18, 89%) and the minority had
an established history of connective tissue disease (3/18, 17%).
The average age of the dissection at the time of the research MRI
was 3.71 ± 3.17 years (range 0.24–8.01 years). The mean baseline
aortic diameter based on index CT was 39.4 ± 7.6 mm (range 29–
58 mm) and the maximal aortic diameter at the time of the re-
search MRI was 46.3 ± 8.6 mm (range 32–62 mm). The median
aortic growth rate between baseline CT and research MRI was
3.5 mm/year (interquartile range 0.5–8.1 mm/year, range 0–
22 mm/year). The median entry tear size was 16.2 mm (interquar-
tile range 10.8–20.0 mm, range 5–44 mm). Baseline aortic
diameter, entry tear size and distance of the entry tear from the
LSC were not significantly different between patients with stable
and enlarging aortic dimensions. These data are shown in greater
detail in Table 1.
Haemodynamic assessment
The average net flow rate in the TL was higher than the FL
(3.1 ± 1.1 vs 1.4 ± 1.3 l/min) as was the TL peak velocity
(87.3 ± 34.9 vs 64.5 ± 30.2 cm/s). Retrograde flow was common in
the FL with 16 (89%) of patients demonstrating measurable retro-
grade flow in the FL during diastole. Conversely, flow in the TL
was almost exclusively antegrade with only 5 (27%) patients dem-
onstrating any measurable TL retrograde flow with the highest
degree of retrograde flow in the TL being only 5% by volume vs
89% in the FL. The mean FL EF was 28.9 ± 24.4% (range 0–88%),
and FL EF did not correlate well with the FL retrograde flow frac-
tion measured 3 cm distal to the primary tear (r= 0.13, P= 0.607).
FL EF was significantly elevated in patients with enlarging vs sta-
ble aortic dimensions (43.8 ± 22.1% vs 10.3 ± 10.1%, P= 0.001).
Entry tear peak velocity was lower in patients with enlarging aor-
tic dimensions (95.5± 24.1 vs 128.1 ± 37.4 cm/s, P= 0.394).
Haemodynamic parameters are summarized in greater detail in
Table 2and 2representative cases are shown in Fig. 2.
Bivariate and multivariate analysis of aortic growth
FL EF demonstrated a moderate–strong correlation with aortic
growth rate (r= 0.71, P= 0.001) and baseline maximal aortic
diameter demonstrated a weak–moderate (r= 0.42, P= 0.081) but
non-significant correlation with aortic growth. Dominant entry
tear size (r= 0.01, P= 0.999), distance of the entry tear from the
LSC (r= 0.27, P= 0.286), FL peak velocity (r= -0.1, P= 0.731), FL
net flow (r= 0.36, P= 0.139) and FL retrograde flow fraction
(r= 0.31, P= 0.217) did not significantly correlate with aortic
growth rate on bivariate analysis. There was no significant
Table 1: Patient and anatomic characteristics
Characteristics Overall (n= 18) Stable (n= 8) Enlarging (n= 10) P-value
Patient age (years), mean ± SD 52.1 ± 9.5 (range 31–71) 47.5 ± 8.3 55.8 ± 9.2 0.064
Dissection type
Repaired type A, n(%) 3 (17) 3 (37) 0 (0)
Type B, n(%) 15 (83) 5 (63) 10 (100) 0.069
Sex (male/female), n13/5 6/2 7/3 1.000
Connective tissue disease, n(%) 3 (17) 2 (25) 1 (10) 0.559
Hypertension, n(%) 16 (89) 6 (75) 10 (100) 0.183
Smoking history, n(%) 9 (50) 5 (63) 4 (40%) 0.637
Age of dissection (years), mean ± SD 3.7 ± 3.2 (range 0.2–8.0) 5.7 ± 3.2 2.1 ± 2.1 0.013
Aortic growth rate (mm/year), median (IQR) 3.5 (0.5–8.1) (range 0–22) 0.3 (0–2.1) 7.9 (5.8–12.4) 0.001
a
Maximum diameter at MRI (mm), mean ± SD 46.3 ± 8.6 (range 32–62) 40.1 ± 7.1 50.7 ± 7.3 0.011
Dominant entry tear size by MRI (mm),
b
median (IQR) 16.2 (10.8–20.0) (range 5–44) 13.2 (10.1–24.3) 17.0 (12.3–20.0) 0.594
a
Baseline CT anatomic characteristics
Entry tear distance from LSC (mm), median (IQR) 20.0 (2.0–24.0) (range 0–130) 10.0 (2.0–45.0) 20.0 (19.0–34.0) 0.448
a
Inner curvature FL location, n(%) 5 (28) 2 (25) 3 (30) 1.000
Maximal aortic diameter (mm), mean ± SD 39.4 ± 7.6 (range 29–58) 38.1 ± 4.1 40.5 ± 9.6 0.524
Partial FL thrombus, n(%) 5 (28) 2 (25) 3 (30) 1.000
a
Mann–Whitney U-test.
b
Mean of maximal and minimal tear dimensions.
CT: computed tomography; FL: false lumen; IQR: interquartile range; LSC: left subclavian artery; MRI: magnetic resonance imaging; SD: standard deviation.
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correlation between FL EF and entry tear size (r= 0.01, P= 0.949).
Scatter plots of several of these correlations are shown in Fig. 3.
Multiple linear regression analysis models were performed to
identify independent predictors of aortic growth rate amongst a
group of anatomic and haemodynamic variables of interest. After
adjusting for co-variates, the variables that were independently
associated with aortic growth rate were FL EF [b= 0.15, 95% confi-
dence interval (CI) 0.07–0.23; P= 0.001], baseline maximal aortic
diameter (b= 0.37, 95% CI 0.18–0.56; P= 0.001), and the entry tear
distance from the LSC (b= 0.07, SE 0.02, 95% CI 0.02–0.12;
P= 0.016), with the overall model adjusted R
2
= 0.87 (Table 3). The
significance of predictors in the regression model did not change
when patients with connective tissue disease (Supplementary
Material, Table S1) or repaired type-A dissection and connective
tissue disease (Supplementary Material, Table S2) were excluded.
DISCUSSION
The key observations of this study can be summarized as follows:
(i) 4D flow MRI is a useful method for quantifying the complex
blood flow patterns in the FL of patients with chronic TBAD, (ii)
peak velocity at the entry tear jet is lower in patients with a history
of enlarging FL, likely due to obstructed or insufficient FL outflow,
(iii) FL EF, defined as the proportion of retrograde diastolic flow at
the entry tear, demonstrates a moderate–strong correlation with
aortic growth rate and (iv) after adjustment for co-variates, FL EF,
baseline maximal diameter and distance of the entry tear from the
LSC are independent predictors of aortic growth rate.
The results of our study are largely in agreement with prior lit-
erature on this topic. Specifically, baseline maximal diameter and
distance of the entry tear from the LSC are commonly reported
Table 2: 4D flow haemodynamic parameters
Characteristics Overall (n= 18) Stable (n= 8) Enlarging (n= 10) P-value
True lumen
a
Net flow (l/min), median (IQR) 2.6 (2.2–4.0) (range 2.0–5.5) 2.4 (2.1–2.8) 2.9 (2.5–4.4) 0.051
b
Peak velocity (cm/s), median (IQR) 87.1 (69.5–96.0) (range 37–169) 87.1 (77.6–89.6) 89.2 (54.0–99.7) 0.790
b
False lumen
a
Net flow (l/min), median (IQR) 1.1 (0.4–2.0) (range 0.1–4.6) 1.5 (0.4–3.5) 0.8 (0.4–1.9) 0.477
b
Peak velocity (cm/s), mean ± SD 64.5 ± 30.2 (range 16–120) 64.9± 34.5 64.2 ± 28.1 0.96
Retrograde flow fraction (%), mean ± SD 33.4 ± 31.9 (range 0–89) 24.2 ± 31.5 40.9 ± 31.9 0.28
Systolic flow eccentricity, mean ± SD 0.22 ± 0.7 (range 0.10–0.33) 0.22 ± 0.6 0.22 ± 0.9 0.97
Dominant entry tear
Net flow (l/min), median (IQR) 0.7 (0.4–0.9) (range 0.1–4.6) 0.8 (0.4–2.7) 0.6 (0.2–0.8) 0.168
b
Peak velocity (cm/s), mean ± SD 110.0 ± 34.1 (range 66–199) 128.1 ± 37.4 95.5 ± 24.1 0.04
False lumen ejection fraction (%) (retrograde flow fraction), mean ± SD 28.9± 24.4 (range 0–88) 10.3 ± 10.1 43.8 ± 22.1 0.001
a
Measured 3 cm distal to dominant entry tear.
b
Mann–Whitney U-test.
IQR: interquartile range; SD: standard deviation.
Figure 2: Representative case examples. A 52-year-old patient with type B aortic dissection and baseline maximal diameter of 42 mm that remained unchanged at 1-
year follow-up computed tomography exam, with a large proximal entry tear (32 mm), but similar-sized re-entry tear at the coeliac origin, and a measured FL EF of
0% (A). A 60-year-old man with type B aortic dissection and baseline maximal diameter of 50 mm that grew to 54 mm over a 4-month period, with a 20-mm proximal
entry tear just beyond the origin of the left subclavian artery with measured FL EF of 51% (B). FL EF: false lumen ejection fraction.
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as predictors of aortic growth and are widely recognized as risk
factors for aneurysmal degeneration and other adverse events [6].
Additionally, our observation that bi-phasic flow and retrograde/
regurgitant flow is common in the FL has also been well
described using a variety of imaging and computational model-
ling techniques [7,10,13,14,18,19]. Lastly, data from the
International Registry of Aortic Dissection (IRAD) have shown
that partial FL thrombosis is an independent predictor of mortal-
ity in TBAD patients and hypothesized that this was related to FL
pressurization due to FL outflow obstruction [20]. Interestingly,
while FL peak velocity, net flow and flow eccentricity have been
previously reported to be associated with aortic growth by Clough
et al. [12], we did not observe such associations in analyses.
Current treatment algorithms are largely based baseline diam-
eter, given that diameter has a clear relationship with wall stress,
risk of aneurysm formation and other complications. However,
FL pressurization also plays a role in promoting growth and other
outcomes in TBAD. A recent study of 83 patients with acute, un-
complicated TBAD found that decreased FL outflow (as predicted
from CT branch vessel anatomy) was a significant predictor of
adverse events, an effect that is likely attributable to insufficient
outflow leading to FL pressurization [4,7]. However, FL pressur-
ization is a difficult phenomenon to assess in clinical practice
using available non-invasive imaging techniques, and while
branch vessel anatomy based on CT can be used to estimate the
relative amount of FL outflow, without a method to assess FL in-
flow, the degree of inflow–outflow imbalance that leads to FL
pressurization cannot be reliably determined. Computational
modelling techniques have been applied to study FL haemo-
dynamics, and while such highly controlled experimental studies
are critical for isolating the haemodynamics effects of tear size,
tear location and other anatomic features, they are currently lim-
ited for the routine assessment of clinical patients due to their
time-consuming nature, the difficulty of accurately accounting
for the effects of small tears and a variety of assumptions about
the wall thickness/elasticity and flap motion [7,21]. However, re-
cent developments in 4D flow MRI-based techniques that utilize
work-energy methods virtual work-energy relative pressure
(vWERP) allow for relative pressure mapping across any vascular
segment in clinically applicable timeframes, and has been used
to assess bicuspid aortic valve and aortic haemodynamics, and
may be useful for the non-invasive assessment of FL relative pres-
sure gradients [2224].
Measurement of FL EF by 4D flow MRI may avoid many of the
limitations of CT and computational modelling, and while 4D
flow does not directly yield FL pressure measurements, the quan-
tification of retrograde diastolic flow at the entry tear may be a
method to estimate FL pressurization non-invasively.
Furthermore, considering that TBAD anatomy can be complex,
and that distal re-entry pathways are more frequently small and
difficult to define by non-invasive imaging, the fact that FL EF
measured is based on the dominant entry tear—which is almost
always clearly identifiable—avoids the challenges of directly
measuring FL outflow. Furthermore, as FL EF reflects a ratio of
flow rates, its measurement is less susceptible to errors related to
image artefacts and other technical factors than more advanced
4D flow parameters, and 4D flow assessment of flow rate in
Figure 3: Scatter plots demonstrating the correlations between aortic growth rate baseline maximal aortic diameter (A), false lumen ejection fraction (B), dominant
entry tear size (C) and distance from the LSC to the entry tear (D). LSC: left subclavian artery.
Table 3: Multivariate regression—predictors of aortic growth
rate
Characteristics bCoefficient 95% CI P-value
False lumen ejection fraction 0.15 0.07–0.23 0.001
Baseline maximal aortic diameter 0.37 0.18–0.56 0.001
Interval
2
-0.11 -0.28 to 0.07 0.205
Dominant entry tear size 0.21 -0.12 to 0.53 0.184
False lumen net flow -1.50 -3.45 to 0.44 0.116
False lumen peak velocity 0.04 -0.03 to 0.11 0.262
Entry tear distance from left
subclavian
0.07 0.02–0.12 0.016
Adjusted R
2
= 0.87.
CI: confidence interval.
6N.S. Burris et al. / European Journal of Cardio-Thoracic Surgery
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TBAD has shown excellent reproducibility [25]. In practice, 4D
flow imaging can be acquired immediately following a standard
MRA, and in addition assessing FL pressurization can help iden-
tify secondary entry/re-entry tears that may guide endovascular
repair planning [26].
Limitations
Our study has 3 main limitations. First, the study cohort is relatively
small and recruited from a high-volume aortic referral centre, so
there is potential for bias. However, given that 4D flow in aortic
dissection is a relatively understudied topic, to our knowledge, this
18-patient cohort represents the largest 4D flow evaluation of
TBAD patients to date. Second, our cohort is composed of chronic
dissections. Given the timing of 4D flow imaging, it is possible that
elevated FL EF is a result of aortic growth rather than a cause.
However, we think this is unlikely, given that the mechanism of in-
flow–outflow imbalance leading to FL pressurization has been sup-
ported by Sailer et al. using CT images from acute dissection
patients, as well as in computational and flow phantom studies [4,
7,9]. Continued research by our group will focus on enrolment of
acute TBAD patients. Lastly, while the popularity of 4D flow MRI
continues to rise, given significant decreases in scan time and the
availability of commercial postprocessing software, it remains a
technique that is used for clinical assessment in only a small num-
ber of specialized centres, thus limiting the generalizability of our
findings. However, despite this limitation, we believe that our find-
ings provide further support for the importance of FL haemo-
dynamics in the risk assessment of TBAD patients.
In an era of increasing rates of TEVAR for treatment of TBAD,
there is a significant need for methods to identify high-risk patients
to allow for early targeted repair. In addition to standard anatomic
assessments, a more comprehensive risk-stratification strategy
would ideally include an assessment of FL pressurization such as
that afforded by measurement of FL EF. With continued research
and validation of FL EF as a predictor of aortic growth and other
outcomes, we envision a future MRI-based approach to assess
TBAD patients that will allow for a combined assessment of stand-
ard anatomic parameters in addition to haemodynamic markers of
FL pressurization to help better predict patient risk.
SUPPLEMENTARY MATERIAL
Supplementary material is available at EJCTS online.
ACKNOWLEDGEMENTS
The authors would like to acknowledge Bo Yang, Karen Kim,
Shinichi Fukuhara and G. Michael Deeb, UM Cardiovascular Health
Improvement Project (CHIP) team members, and clinical coordina-
tors Mary Passow, Lynn Hendee, Susan Hooker and Maureen Daly
for their assistance with patient enrolment, as well as our research
MRI staff including James Pool, Ladonna Austin, Suzan Lowe and
James O’Conner for their assistance with enrolment and research
MRI examinations.
Funding
This work was supported by the Radiologic Society of North
America Research Scholar Grant [RSCH1801] to N.S.B; Millennium
Science Initiative of the Ministry of Economy, Development and
Tourism, grant Nucleus for Cardiovascular Magnetic Resonance,
and CONICYT—FONDECYT [#1181057] and FONDECYT [#1180832]
and CONICYT—FONDECYT Postdoctorado 2017 [#3170737] to J.A.S.
and S.U; Engineering and Physical Sciences Research Council [EP/
N011554/1 and EP/R003866/1] to D.A.N; and Joe D. Morris
Collegiate Professorship, Phil Jenkins Breakthrough Fund and David
Hamilton Fund in Cardiac Surgery to H.J.P.
Conflict of interest: none declared.
Author contributions
Nicholas S. Burris: Conceptualization; Data curation; Formal analysis;
Funding acquisition; Investigation; Methodology; Project administration;
Resources; Software; Supervision; Validation; Visualization; Writing—original
draft; Writing—review & editing. David A. Nordsletten: Data curation;
Formal analysis; Investigation; Methodology; Project administration;
Resources; Supervision; Validation; Visualization; Writing—review & editing.
Julio A. Sotelo: Data curation; Formal analysis; Investigation; Methodology;
Resources; Software; Supervision; Validation; Visualization; Writing—original
draft; Writing—review & editing. Ross Grogan-Kaylor: Data curation; Formal
analysis; Investigation; Methodology; Software; Validation; Visualization;
Writing—review & editing. Ignas B. Houben: Conceptualization; Formal ana-
lysis; Investigation; Methodology; Resources; Software; Writing—review & edit-
ing. C. Alberto Figueroa: Conceptualization; Formal analysis; Investigation;
Methodology; Project administration; Resources; Software; Supervision;
Validation; Writing—review & editing. Sergio Uribe: Data curation; Formal
analysis; Investigation; Project administration; Resources; Software;
Supervision; Visualization; Writing—review & editing. Himanshu J. Patel:
Conceptualization; Data curation; Formal analysis; Funding acquisition;
Investigation; Methodology; Project administration; Resources; Supervision;
Validation; Visualization; Writing—review & editing.
REFERENCES
[1] Fattori R, Montgomery D, Lovato L, Kische S, Di Eusanio M, Ince H et al.
Survival after endovascular therapy in patients with
type B aortic dissection: a report from the International Registry
of Acute Aortic Dissection (IRAD). JACC Cardiovasc Interv 2013;6:
876–82.
[2] Nienaber CA, Kische S, Rousseau H, Eggebrecht H, Rehders TC, Kundt G
et al. Endovascular repair of type B aortic dissection: long-term results of
the randomized investigation of stent grafts in aortic dissection trial. Circ
Cardiovasc Interv 2013;6:407–16.
[3] Iannuzzi JC, Stapleton SM, Bababekov YJ, Chang D, Lancaster RT, Conrad
MF et al. Favorable impact of thoracic endovascular aortic repair on sur-
vival of patients with acute uncomplicated type B aortic dissection.
J Vasc Surg 2018;68:1649–55.
[4] Sailer AM, van Kuijk SM, Nelemans PJ, Chin AS, Kino A, Huininga M
et al. Computed tomography imaging features in acute uncomplicated
Stanford type-B aortic dissection predict late adverse events. Circ
Cardiovasc Imaging 2017;10:e005709.
[5] Schwartz SI, Durham C, Clouse WD, Patel VI, Lancaster RT, Cambria RP
et al. Predictors of late aortic intervention in patients with medically
treated type B aortic dissection. J Vasc Surg 2018;67:78–84.
[6] Spinelli D, Benedetto F, Donato R, Piffaretti G, Marrocco-Trischitta MM,
Patel HJ et al. Current evidence in predictors of aortic growth
and events in acute type B aortic dissection. J Vasc Surg 2018;68:
1925–35.e8.
[7] Rudenick PA, Segers P, Pineda V, Cuellar H, Garcia-Dorado D,
Evangelista A et al. False lumen flow patterns and their relation with
morphological and biomechanical characteristics of chronic aortic dis-
sections. Computational model compared with magnetic resonance
imaging measurements. PLoS One 2017;12:e0170888.
[8] Tsai TT, Schlicht MS, Khanafer K, Bull JL, Valassis DT, Williams DM et al.
Tear size and location impacts false lumen pressure in an ex vivo model
of chronic type B aortic dissection. J Vasc Surg 2008;47:844–51.
CONVENTIONAL
AORTIC SURGERY
7N.S. Burris et al. / European Journal of Cardio-Thoracic Surgery
Downloaded from https://academic.oup.com/ejcts/advance-article-abstract/doi/10.1093/ejcts/ezz343/5671737 by University of Michigan, nburris@med.umich.edu on 16 December 2019
[9] Canchi S, Guo X, Phillips M, Berwick Z, Kratzberg J, Krieger J et al. Role of
re-entry tears on the dynamics of type B dissection flap. Ann Biomed
Eng 2018;46:186–96.
[10] Birjiniuk J, Timmins LH, Young M, Leshnower BG, Oshinski JN, Ku DN
et al. Pulsatile flow leads to intimal flap motion and flow reversal in an
in vitro model of type B aortic dissection. Cardiovasc Eng Tech 2017;8:
378–89.
[11] Burris NS, Hope MD. 4D flow MRI applications for aortic disease. Magn
Reson Imaging Clin N Am 2015;23:15–23.
[12] Clough RE, Waltham M, Giese D, Taylor PR, Schaeffter T. A new imaging
method for assessment of aortic dissection using four-dimensional
phase contrast magnetic resonance imaging. J Vasc Surg 2012;55:
914–23.
[13] Burris NS, Patel HJ, Hope MD. Retrograde flow in the false lumen: mark-
er of a false lumen under stress? J Thorac Cardiovasc Surg 2019;157:
488–91.
[14] Francois CJ, Markl M, Schiebler ML, Niespodzany E, Landgraf BR,
Schlensak C et al. Four-dimensional, flow-sensitive magnetic resonance
imaging of blood flow patterns in thoracic aortic dissections. J Thorac
Cardiovasc Surg 2013;145:1359–66.
[15] Sotelo J, Dux-Santoy L, Guala A, Rodriguez-Palomares J, Evangelista A,
Sing-Long C et al. 3D axial and circumferential wall shear stress from 4D
flow MRI data using a finite element method and a Laplacian approach.
Magn Reson Med 2018;79:2816–23.
[16] Sotelo J, Urbina J, Valverde I, Mura J, Tejos C, Irarrazaval P et al. Three-
dimensional quantification of vorticity and helicity from 3D cine PC-
MRI using finite-element interpolations. Magn Reson Med 2018;79:
541–53.
[17] Sueyoshi E, Sakamoto I, Hayashi K, Yamaguchi T, Imada T. Growth rate
of aortic diameter in patients with type B aortic dissection during the
chronic phase. Circulation 2004;110:II-256–61.
[18] Karmonik C, Muller-Eschner M, Partovi S, Geisbusch P, Ganten MK,
Bismuth J et al. Computational fluid dynamics investigation of chronic
aortic dissection hemodynamics versus normal aorta. Vasc Endovascular
Surg 2013;47:625–31.
[19] Cheng Z, Juli C, Wood NB, Gibbs RG, Xu XY. Predicting flow in aortic dis-
section: comparison of computational model with PC-MRI velocity
measurements. Med Eng Phys 2014;36:1176–84.
[20] Tsai TT, Evangelista A, Nienaber CA, Myrmel T, Meinhardt G, Cooper JV
et al. Partial thrombosis of the false lumen in patients with acute type B
aortic dissection. N Engl J Med 2007;357:349–59.
[21] Dillon-Murphy D, Noorani A, Nordsletten D, Figueroa CA. Multi-modal-
ity image-based computational analysis of haemodynamics in aortic dis-
section. Biomech Model Mechanobiol 2016;15:857–76.
[22] Donati F, Myerson S, Bissell MM, Smith NP, Neubauer S, Monaghan MJ
et al. Beyond Bernoulli: improving the accuracy and precision of
noninvasive estimation of peak pressure drops. Circ Cardiovasc Imaging
2017;10:e005207.
[23] Lamata P, Pitcher A, Krittian S, Nordsletten D, Bissell MM, Cassar T et al.
Aortic relative pressure components derived from four-dimensional flow
cardiovascular magnetic resonance. Magn Reson Med 2013;72:1162–9.
[24] Marlevi D, Ruijsink B, Balmus M, Dillon-Murphy D, Fovargue D,
Pushparajah K et al. Estimation of cardiovascular relative pressure using
virtual work-energy. Sci Rep 2019;9:1375.
[25] de Beaufort HW, Shah DJ, Patel AP, Jackson MS, Spinelli D, Yang EY et al.
Four-dimensional flow cardiovascular magnetic resonance in aortic dis-
section: assessment in an ex vivo model and preliminary clinical experi-
ence. J Thorac Cardiovasc Surg 2019;157:467–76.e1.
[26] Allen BD, Aouad PJ, Burris NS, Rahsepar AA, Jarvis KB, Francois CJ et al .
Detection and hemodynamic evaluation of flap fenestrations in type B aor-
tic dissection with 4D flow MRI: comparison with conventional MRI and
CT angiography. Radiol Cardiothorac Imaging 2019;1:[Epub ahead of print].
8N.S. Burris et al. / European Journal of Cardio-Thoracic Surgery
Downloaded from https://academic.oup.com/ejcts/advance-article-abstract/doi/10.1093/ejcts/ezz343/5671737 by University of Michigan, nburris@med.umich.edu on 16 December 2019
... Although a patent false lumen in the descending aorta has been associated with aortic enlargement [13], need of aortic intervention/repair or late mortality [14], studies quantifying flow in the false lumen and its relationship with aortic growth rate are still limited. Studies based on 4-dimensional (4D) phase-contrast cardiovascular magnetic resonance (4D flow CMR) analysing flow dynamics in the true and false lumen have been published [15][16][17][18][19]. However, these studies reported qualitative or semi-quantitative analysis of flow data [16,17], included a limited number of patients (≤ 20), and mixed individuals with and without genetic connective tissue disorders [15][16][17][18][19]. Additionally, the potential role of wall shear stress (WSS) and the biomechanical properties of the aortic wall (aortic stiffness) in patients with a chronic, patent false lumen in the descending aorta after an AD still remain unexplored. ...
... Studies based on 4-dimensional (4D) phase-contrast cardiovascular magnetic resonance (4D flow CMR) analysing flow dynamics in the true and false lumen have been published [15][16][17][18][19]. However, these studies reported qualitative or semi-quantitative analysis of flow data [16,17], included a limited number of patients (≤ 20), and mixed individuals with and without genetic connective tissue disorders [15][16][17][18][19]. Additionally, the potential role of wall shear stress (WSS) and the biomechanical properties of the aortic wall (aortic stiffness) in patients with a chronic, patent false lumen in the descending aorta after an AD still remain unexplored. ...
... Retrograde systolic and diastolic flow were calculated as the time-integral of backward through-plane flow rate curve over systolic or diastolic phases, respectively. False lumen retrograde flow fraction was calculated as the ratio of retrograde diastolic flow rate over the anterograde systolic flow rate, as proposed [18]. IRF, a parameter used to quantify flow rotation within a plane, was calculated as the integral of vorticity with respect to cross-sectional area at the systolic peak [24,25] (Fig. 2D). ...
Article
Full-text available
Background Patency of the false lumen in chronic aortic dissection (AD) is associated with aortic dilation and long-term aortic events. However, predictors of adverse outcomes in this population are limited. The aim of this study was to evaluate the relationship between aortic growth rate and false lumen flow dynamics and biomechanics in patients with chronic, patent AD. Methods Patients with a chronic AD with patent false lumen in the descending aorta and no genetic connective tissue disorder underwent an imaging follow-up including a contrast-enhanced 4D flow cardiovascular magnetic resonance (CMR) protocol and two consecutive computed tomography angiograms (CTA) acquired at least 1 year apart. A comprehensive analysis of anatomical features (including thrombus quantification), and false lumen flow dynamics and biomechanics (pulse wave velocity) was performed. Results Fifty-four consecutive patients with a chronic, patent false lumen in the descending aorta were included (35 surgically-treated type A AD with residual tear and 19 medically-treated type B AD). Median follow-up was 40 months. The in-plane rotational flow, pulse wave velocity and the percentage of thrombus in the false lumen were positively related to aortic growth rate (p = 0.006, 0.017, and 0.037, respectively), whereas wall shear stress showed a trend for a positive association (p = 0.060). These results were found irrespectively of the type of AD. Conclusions In patients with chronic AD and patent false lumen of the descending aorta, rotational flow, pulse wave velocity and wall shear stress are positively related to aortic growth rate, and should be implemented in the follow-up algorithm of these patients. Further prospective studies are needed to confirm if the assessment of these parameters helps to identify patients at higher risk of adverse clinical events.
... However, recent studies using 4D flow MRI have suggested that in vivo hemodynamic assessment of blood flow at entry tears and in the false lumen may help identify TBAD patients with Abbreviations: TBAD, type B aortic dissection; TAAD, type A aortic dissection; rTAAD, repaired TAAD with residual TBAD; TEVAR, thoracic endovascular aortic repair; CTA, computed tomography angiography; MRA, magnetic resonance angiography; PC-MRA, 3D phase-contrast angiogram; AARO, adverse aortarelated outcomes; FOV, field of view; TR, repetition time; TE, echo time; VENC, velocity encoding; TL, true lumen; FL, false lumen; KE, kinetic energy; PV, peak velocity; FF, forward flow; RF, reverse flow. growing aortas (17)(18)(19)(20). In the current study, we seek to further expand on these findings by using 4D flow MRI to perform voxel-wise hemodynamic quantification of the TL and FL. ...
... Again, retrograde flow in the FL (specifically at the dissection tear) was analyzed as FL ejection fraction (EF: diastolic retrograde flow divided by systolic antegrade flow through an entry tear) in 18 patients by Burris et al. and in 12 patients by Marlevi et al. Both studies reported a strong positive correlation between FL EF and aortic growth rate, contrary to the negative correlation that we found (17,18). This discrepancy may due to the fact that our analysis of reverse flow involves data collected from an entire luminal volume, and further studies focusing on a specific location of interest may reveal regional hemodynamic differences in this parameter. ...
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... A comprehensive methodology can help to identify those parameters related to aortic dilation in patients with BAV. Previously, we have developed a seamless computational framework to obtain several 3D quantitative parameters, which have been validated in phantoms and different cohorts of patients including aortic dissection (24,25) and transposition of the great arteries (26,27). This study aimed to compare quantitative 3D hemodynamic parameters between healthy volunteers (HVs) and patients with BAV and their relationships with aortic dilation in clinically relevant subgroups of patients with BAV. ...
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Background: In uncomplicated type B aortic dissection (UTBAD), the "gold standard" has been nonoperative treatment with medical therapy, although this has been questioned by studies demonstrating improved outcomes in those treated with thoracic endovascular aortic repair (TEVAR). This study assessed long-term survival after acute UTBAD comparing medical therapy, open repair, and TEVAR. Methods: The California Office of Statewide Hospital Planning Development database was analyzed from 2000 to 2010 for adult patients with acute UTBAD. Patients with nonemergent admission for aortic dissection, type A dissection, trauma, bowel ischemia, lower extremity ischemia, acidosis, or shock were excluded. The cohort was stratified by treatment type at index admission into medical therapy, open surgical repair, and TEVAR. Multivariable regression and survival analyses were used to evaluate the association of treatment type with long-term overall survival. Results: There were 9165 cases, 95% medical therapy, 2% open repair, and 2.9% TEVAR. The mean age was 66 ± 15 years, with 39% female, 2.4% cocaine users, 18% with congestive heart failure, and 17% with Charlson Comorbidity Index >3. Mean inpatient costs were $57,000 for medical therapy, $200,000 for open repair, and $130,000 for TEVAR (P < .01). Inpatient mortality was 6.5% overall, 6.3% for medical therapy, 14% for open repair, and 7.1% for TEVAR (P < .01). One-year and 5-year survivals were 84% and 60% in medical therapy, 76% and 67% in open repair, and 85% and 76% in TEVAR (log-rank, P < .01). On risk-adjusted multivariable analysis, TEVAR had improved survival compared with medical therapy (hazard ratio, 0.68; 95% confidence interval, 0.6-0.8; P < .01), with no difference between open repair and medical therapy (hazard ratio, 1.0; 95% confidence interval, 0.8-1.3; P < .01). Conclusions: This statewide study on survival after acute UTBADs shows an independent survival advantage for TEVAR over medical therapy. These data add further evidence for a paradigm shift in acute management of type B dissection in favor of early TEVAR.
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Background: Patients with medically managed type B aortic dissection (TBAD) have a high incidence of aorta-related complications over time. Whereas early thoracic endovascular aortic repair (TEVAR) to seal the entry tear can promote aortic remodeling and prevent late aneurysm formation, there are sparse data as to which patients will benefit from such therapy. The goal of this study was to identify clinical and anatomic factors that are associated with the need for subsequent aortic intervention in patients who present with uncomplicated TBAD. These factors could guide the selection of patients who will benefit from TEVAR in the subacute phase. Methods: Patients who presented with acute uncomplicated TBAD and were initially managed medically from January 2000 to December 2013 were included in the study. Timing of intervention was stratified into early (within 180 days of initial presentation) and late (181 days and later) cohorts. All patients had follow-up axial imaging studies. These imaging studies were reviewed for anatomic criteria in a retrospective fashion. Predictors of aortic intervention were determined using Cox regression analyses. Results: There were 254 patients (65% men) with medically managed acute TBAD. The average age at presentation was 66.3 years, and 82.5% had a history of hypertension. Mean follow-up was 6.8 years (range, 0.1-13.6 years). There were a total of 97 (38%) patients who required an aortic intervention during follow-up; 30 (12%) patients required an early intervention, and 67 (26%) were treated during late follow-up (100% for aneurysmal degeneration). Predictors of late aortic intervention included entry tear >10 mm (odds ratio [OR], 2.1; 95% confidence interval [CI], 1.5-3.8; P = .03), total aortic diameter >40 mm at time of presentation (OR, 2.2; 95% CI, 1.8-4.3; P = .02), false lumen diameter >20 mm (OR, 1.8; 95% CI, 1.3-4.7; P = .03), and increase in total aortic diameter >5 mm between serial imaging studies (OR, 2.3; 95% CI, 1.3-3.5; P = .02). Complete thrombosis of the false lumen was protective against late operative intervention (OR, 0.22; 95% CI, 0.11-0.48; P < .01). Conclusions: Nearly 40% of patients who present with an uncomplicated TBAD will ultimately require an aortic intervention. All of the late interventions were performed for aneurysmal degeneration. A variety of readily available anatomic features can predict the need for eventual operative intervention in TBAD; accordingly, these parameters can guide the desirability of early TEVAR.
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Purpose: To decompose the 3D wall shear stress (WSS) vector field into its axial (WSSA) and circumferential (WSSC) components using a Laplacian finite element approach. Methods: We validated our method with in silico experiments involving different geometries and a modified Poiseuille flow. We computed 3D maps of the WSS, WSSA, and WSSC using 4D flow MRI data obtained from 10 volunteers and 10 patients with bicuspid aortic valve (BAV). We compared our method with the centerline method. The mean value, standard deviation, root mean‐squared error, and Wilcoxon signed rank test are reported. Results: We obtained an error <0.05% processing analytical geometries. We found good agreement between our method and the modified Poiseuille flow for the WSS, WSSA, and WSSC. We found statistically significance differences between our method and a 3D centerline method. In BAV patients, we found a 220% significant increase in the WSSC in the ascending aorta with respect to volunteers. Conclusion: We developed a novel methodology to decompose the WSS vector in WSSA and WSSC in 3D domains, using 4D flow MRI data. Our method provides a more robust quantification of WSSA and WSSC in comparison with other reported methods.