Rupture risk estimation in ATAAs using distensibility measurements
Dr Olfa TRABELSI, Dr Ambroise DUPREY, Prof Stéphane AVRIL ([email protected])
ESB-ITA Thematic symposium, Palermo
Where do I come from?
PARIS
RHONE-ALPS AREA
LYON-SAINT-ETIENNE
Historical site Founded in 1816
Demanget et al., Perrin et al.
What is an ATAA and why is serious?
dissection
Epidemiology statistics
Incidence : 10.4 per 100 000 persons
Elevated mortality without treatment for acute aortic dissection:
50% in 48 hours / 90% in 3 months
BAV patients: ½ develops an ATAA
Risk management
The International Registry of Acute Aortic Dissection (IRAD):
among 591 type A aortic dissection, 59% had a diameter <5.5 cm (Pape, 2007)
5.5 cm
Possible complication Possible
stability
Decision of surgical repair based on a measure if the Maximal Diameter
Recent developments in computational modeling and challenges
Index of Rupture?
Peak Wall Stress
Strength
Finite-element modeling
O. Trabelsi, et al, Patient specific stress and rupture analysis of ascending thoracic aneurysms, J. Biomech. (2015).
G. Martufi, et al, Is There a Role for Biomechanical Engineering in Helping to Elucidate the Risk Profile of the Thoracic Aorta?, Ann. Thorac. Surg. 101 (2016) 390–398.
S. Pasta et al., Constitutive modeling of ascending thoracic aortic aneurysms using microstructural parameters, Med. Eng. Phys. 38 (2016) 121–130.
SAINT-ETIENNE PROTOCOL
31 Patients with ATAA
Preoperative dynamic imaging
Dynamic CT Scanner
4D MRI
Collection of intraoperative aortic segment
Mechanical inflation tests
Histological Analysis
2014
2016
Inverse membrane analysis + digital image correlation stress
& strain reconstruction.
biaxial failure properties
Trabelsi, O., Davis, F.M., Rodriguez-Matas, J.F., Duprey, A., Avril, S. Patient specific stress and rupture analysis of ascending thoracic aneurysms.
Journal of Biomechanics, 2015.
Bulge inflation tests
Blood flow
Bulge inflation tests
Stress strain analysis in the bulge test
σ
rup: Rupture stress, λ
rup: Rupture stretch,
Physiological Stress
Stretch Stretch/Stress Curve
Rupture Stress
Physiological elastic modulus
Ca uchy Stre ss (MPa)
1 1.1 1.2 1.3
Physiological Stretch
1.4 1.5 1.6 1.7
Rupture Stretch
Results
Rupture properties in function of:
• Age
• Type of test: inflation, axial and circumferential tensile tests
• Physiological circumferential modulus E physio
• Aortic valve: 8 BAV / 23 TAV
31 patients :
• Mean age 65 (24-80)
• 84% male
• Mean in vivo diameter 54 mm (49-65)
Rupture mode:
• Only Intima/media in 55% of cases, similar to dissection
σ rup and λ rup not correlated with the diameter or the type of
aortic valve
Rupture profiles
50% of aortas r uptured wi th an angle θ equal to 90 ° Bl ood flow
(p<0,01)
(p<0,01)
σ rup
λ rup
Age dependence of rupture properties
Corr elation wi th age
Comparison of mechanical tests
Duprey A, et al. Biaxial rupture properties of ascending thoracic aortic aneurysms. Acta Biomaterialia 2016.
Comparison with other studies
0 1 2 3 4 5 6
0 10 20 30 40 50 60 70 80 90 100
σ rup
Age
R.J. Okamoto et al,, Ann. Biomed. Eng. 30 (2002) 624–635.
D.A. Vorp et al,, Ann. Thorac. Surg. 75 (2003) 1210–1214.
C.M. García-Herrera et al., Med. Biol. Eng. Comput. 50 (2012) 559–566.
D.P. Sokolis et al, Med. Biol. Eng. Comput. 50 (2012) 1227–1237 C. Forsell et al, Ann. Thorac. Surg. 98 (2014) 65–71
S. Sugita. Card Eng Tech. 3:1 (2011) 41-51.
J.E. Pichamuthu et al., Ann. Thorac. Surg. 96 (2013) 2147–2154 A. Duprey at al. Acta Biomater 2016)
Comparison with other studies
1 1.2 1.4 1.6 1.8 2 2.2
0 10 20 30 40 50 60 70 80 90 100
λ rup
Age
R.J. Okamoto et al,, Ann. Biomed. Eng. 30 (2002) 624–635.
D.A. Vorp et al,, Ann. Thorac. Surg. 75 (2003) 1210–1214.
C.M. García-Herrera et al., Med. Biol. Eng. Comput. 50 (2012) 559–566..
D.P. Sokolis et al, Med. Biol. Eng. Comput. 50 (2012) 1227–1237 C. Forsell et al, Ann. Thorac. Surg. 98 (2014) 65–71
S. Sugita. Card Eng Tech. 3:1 (2011) 41-51.
J.E. Pichamuthu et al., Ann. Thorac. Surg. 96 (2013) 2147–2154 A. Duprey at al. Acta Biomater 2016)
Rupture risk estimation
Physiological Stress
Stretch Stretch/Stress Curve
Rupture Stress
E
physio= Physiological elastic modulus
Cauch y Stress (MP a)
1 1.1 1.2 1.3
Physiological
1.4 1.5 1.6 1.7
Rupture Stretch
γ stress = Physiological stress Rupture stress γ stretch = Physiological stretch
Rupture stretch
Age dependence of rupture risks
γ stress γ stretch
Duprey A, et al. Biaxial rupture properties of ascending thoracic aortic aneurysms. Acta Biomaterialia 2016.
E physio is correlated to the risk of rupture
MPa MPa MPa MPa
Duprey A, et al. Biaxial rupture properties of ascending thoracic aortic aneurysms. Acta Biomaterialia 2016.
Correlation between γ stretch and E physio
Duprey A, et al. Biaxial rupture properties of ascending thoracic aortic aneurysms. Acta Biomaterialia 2016.
31 Patient with ATAA
Preoperative dynamic imaging
Dynamic CT Scanner
4D MRI
Collection of intraoperative aortic segment
Mechanical inflation tests
Histological Analysis
2014
2016
SAINT-ETIENNE PROTOCOL
Histological interpretation
ATAA enlargement is a consequence of elastin damage
More and more collagen tends to be recruited in the physiological range
Patient with
smallest γ stretch Patient with
largest γ stretch
elast col
M.R. Hill et al,, J. Biomech. 45 (2012) 762–771
31 Patient with ATAA
Preoperative dynamic imaging
Dynamic CT Scanner
4D MRI
Collection of intraoperative aortic segment
Mechanical inflation tests
Histological Analysis
2014
2016
SAINT-ETIENNE PROTOCOL
Distensibility measurements using the dynamic CT scan
D = (A max -A min )/A min /(P max -P min )
E physio = 2R/Dh
Correlation between γ stretch and E physio
R² = 0.7709 R² = 0.6959
0.8 0.82 0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 1
in vivo in vitro
Linéaire (in vivo) Linéaire (in vitro)
g stretch
E physio (MPa)
Summary
2 ways of defining rupture:
PWS – but unknown patient-specific strength
γ stretch correlated with in vivo distensibility
Higher distensibility less risk because the aneurysm can more easily withstand volume variation
C. Martin et al., Acta Biomater. 9 (2013) 9392–9400
