title: An experimental investigation of the impact of thoracic endovascular aortic repair on longitudinal strain.
abstract: OBJECTIVE
  To investigate the impact of thoracic endovascular aortic repair (TEVAR) on longitudinal strain and assess aortic tensile properties in order to better understand complications associated with TEVAR.
  
  
  METHODS
  Twenty fresh thoracic porcine aortas were harvested and connected to a mock circulatory loop driven by a centrifugal flow pump at body temperature. Length measurements were conducted before and after TEVAR through aortic marking, high-definition imaging and custom-developed software under physiological pressure conditions (i.e. between 100 and 180 mmHg with 20 mmHg increments). Longitudinal strain was derived from length amplitude divided by the baseline length at 100 mmHg. Three groups of stent-graft oversizing were created (0-9, 10-19 and 20-29%). Finally, elastic properties of the aortic samples were assessed in both longitudinal and circumferential directions through uniaxial tensile testing. Longitudinal strain was compared before and after TEVAR, and stress-to-rupture was compared among specimens and locations.
  
  
  RESULTS
  TEVAR induced a longitudinal strain decrease from 11.9 to 5.6% (P< 0.001) in the stented segments and a longitudinal strain mismatch between stented (5.6%) and non-stented segments (9.1%, P< 0.001). Stent-graft oversizing did not affect the magnitude of strain reduction (P= 0.77). Tensile testing showed that peak stress-to-rupture was lower for longitudinal (1.4 ± 0.4 MPa) than for circumferential fragments (2.3 ± 0.4 MPa, P< 0.001). In addition, longitudinal fragments were more prone to rupture proximally than distally (P= 0.01).
  
  
  CONCLUSIONS
  This experimental study showed that TEVAR acutely stiffens the aorta in the longitudinal direction and thereby induces a strain mismatch, while tensile testing confirmed that longitudinal aortic fragments are most prone to rupture, particularly close to the arch. Such an acute strain mismatch of potentially vulnerable tissue might play a role in TEVAR-related complications, including retrograde dissection and aneurysm formation. The finding that TEVAR stiffens the aorta longitudinally may also shed light on systemic complications following TEVAR, such as hypertension and cardiac remodelling. These observations may imply the need for further improvement of stent-graft designs.
authors.affiliation: Thoracic Aortic Research Center, Policlinico San Donato IRCCS, University of Milan, Italy foekenauta@gmail.com.|Department of Vascular Surgery, University Medical Center Utrecht, the Netherlands.
authors.forename: Foeke J H
authors.initials: FJ
authors.lastname: Nauta
authors.affiliation: Department of Civil Engineering and Architecture, Beta-lab, University of Pavia, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Conti
authors.affiliation: Department of Civil Engineering and Architecture, Beta-lab, University of Pavia, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Marconi
authors.affiliation: Thoracic Aortic Research Center, Policlinico San Donato IRCCS, University of Milan, Italy.|Department of Vascular Surgery, University Medical Center Utrecht, the Netherlands.
authors.forename: Arnoud V
authors.initials: AV
authors.lastname: Kamman
authors.affiliation: Department of Civil Engineering and Architecture, Beta-lab, University of Pavia, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Alaimo
authors.affiliation: Department of Industrial Engineering and Informatics, University of Pavia, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Morganti
authors.affiliation: Department of Civil Engineering and Architecture, Beta-lab, University of Pavia, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Ferrara
authors.affiliation: Department of Vascular Surgery, University Medical Center Utrecht, the Netherlands.
authors.forename: Joost A
authors.initials: JA
authors.lastname: van Herwaarden
authors.affiliation: Department of Vascular Surgery, University Medical Center Utrecht, the Netherlands.
authors.forename: Frans L
authors.initials: FL
authors.lastname: Moll
authors.affiliation: Department of Industrial Engineering and Informatics, University of Pavia, Italy.
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Auricchio
authors.affiliation: Thoracic Aortic Research Center, Policlinico San Donato IRCCS, University of Milan, Italy.
authors.forename: Santi
authors.initials: S
authors.lastname: Trimarchi
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000503:physiopathology / Q000601:surgery*; D001807:Blood Vessel Prosthesis; D019917:Blood Vessel Prosthesis Implantation / Q000379:methods; D004548:Elasticity; D057510:Endovascular Procedures / Q000379:methods; D008422:Materials Testing / Q000379:methods; D008955:Models, Cardiovascular; D015588:Observer Variation; D015203:Reproducibility of Results; D015607:Stents; D013314:Stress, Mechanical; D034421:Sus scrofa; D013718:Tensile Strength
keywords: Aortic strain; Stent-graft; TEVAR; Thoracic aorta; Uniaxial tensile testing