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Commentary: Biomechanical remodeling of the pulmonary autograft after the Ross procedure

Published:October 29, 2021DOI:https://doi.org/10.1016/j.jtcvs.2021.10.043
      Figure thumbnail fx1
      Gediminas Gaidulis, PhD, and Muralidhar Padala, PhD
      Can the pulmonary autograft thrive in the systemic environment?
      See Article page 1728.
      The Ross procedure is a safe and effective aortic valve replacement option for younger patients with aortic valve disease. Being a living valve substitute, with tissue architecture, hemocompatibility, and dynamics close to the native aortic valve, the theoretical benefits of such an option are several, especially in patients with a longer life expectancy. Although its use has been limited to few specialized centers across the world, the outcomes of Ross procedure have been superior to most other options. Age-corrected survival rates after Ross procedure have been equivalent to the general population, which demonstrates the superiority of this approach over other available techniques.
      • Romeo J.L.R.
      • Papageorgiou G.
      • da Costa F.F.D.
      • Sievers H.H.
      • Bogers A.J.J.C.
      • El-Hamamsy I.
      • et al.
      Long-term clinical and echocardiographic outcomes in young and middle-aged adults undergoing the Ross procedure.
      Despite the anatomical and structural similarities between the pulmonary autograft and the native aortic valve, the pulmonary autograft is in a lower-pressure environment until the time of surgery. Once transpositioned into the aortic position, it experiences a greater luminal pressure, which can elevate wall stresses in each cardiac cycle. Anatomically, the pulmonary autograft is part of the main pulmonary artery, which is a relatively long, straight conduit, whereas in the aortic position, it assumes the curvature of the ascending aorta. Furthermore, in the aortic position, the coronary ostia implanted into the autograft alter the fluid mechanics on the ventricular surface of the pulmonary valve leaflets. This non-native hemodynamics and mechanics can be transduced by the pulmonary autograft, leading to its potential remodeling and in some cases failure from exaggerated autograft dilatation.
      This research question has been studied by several, and it continues in this manuscript
      • Xuan Y.
      • Alonso E.
      • Emmott A.
      • Wang Z.
      • Kumar S.
      • Mongeon F.-P.
      • et al.
      Wall stresses of early remodeled pulmonary autografts.
      from Dr Elaine Tseng's group at University of California San Francisco, in collaboration with the clinical Ross program of Dr Ismail Elhahamsy at Montreal Heart Institute and Mt Sinai Hospital.
      • Matthews P.B.
      • Jhun C.S.
      • Yaung S.
      • Azadani A.N.
      • Guccione J.M.
      • Ge L.
      • et al.
      Finite element modeling of the pulmonary autograft at systemic pressure before remodeling.
      • Vanderveken E.
      • Vastmans J.
      • Claus P.
      • Verbeken E.
      • Fehervary H.
      • Van Hoof L.
      • et al.
      Mechano-biological adaptation of the pulmonary artery exposed to systemic conditions.
      • Nappi F.
      • Nenna A.
      • Lemmo F.
      • Chello M.
      • Chachques J.C.
      • Acar C.
      • et al.
      Finite element analysis investigate pulmonary autograft root and leaflet stresses to understand late durability of Ross operation.
      The authors sought to examine autograft wall stresses after the Ross procedure using patient-specific material properties of the tissue. Several novel aspects make it a commendable effort toward a better understanding of autograft remodeling and dilatation. First, the authors created and used realistic image-based computational models, and it is advantageous over the studies with idealized models that are not patient-specific. In addition, patient-specific material properties were determined for each case separately. Since determination of such material properties is time-consuming for every study, the authors also examined the influence of patient-specific versus averaged material properties and found no significant differences in the magnitude and location of wall stresses. Computational models were validated by overlaying the computed geometries and magnetic resonance imaging at diastole. A good agreement between simulation results and medical images was found.
      A thing worth mentioning is the large volume of this study, with data sets of 16 patients used to create computational models. Usually, similar studies use 1 or 2 models to test the hypothesis, since computational models are solving for mathematical equations and they do not have the same measurement errors as experimental models have. In contrast, a large-volume study allows a strong validation of the simulation workflow and enables a wider range stress analysis, a quantity that cannot be directly measured in vivo and can only be determined numerically.
      While the study is interesting and provides important results for further autograft remodeling research, there are some limitations that need to be highlighted. First, the pulmonary autograft geometries were obtained from magnetic resonance imaging in patients performed at 1 year after the Ross procedure. The autograft may have already remodeled by this time, and the wall stresses are indicative of remodeling and may not provide a causative link between the biomechanical state and graft remodeling. Second, the aortic valve was not included in the computational models, since the authors were focused mainly on wall stresses and had not investigated velocity distribution and flow characteristics. While reconstruction of the valve geometry and its coupling with the aorta is a complicated task, adding the aortic valve would have an impact on blood flow, likely to be significant. This in turn might also influence stress distribution along the aortic wall, thus leading to more realistic simulation results. In addition, patient-specific blood pressures were not accounted for. This is a little bit disappointing, especially since all the other aspects of the simulation protocol were patient-specific, including the material properties, rarely seen in computational studies of such a large volume.

      References

        • Romeo J.L.R.
        • Papageorgiou G.
        • da Costa F.F.D.
        • Sievers H.H.
        • Bogers A.J.J.C.
        • El-Hamamsy I.
        • et al.
        Long-term clinical and echocardiographic outcomes in young and middle-aged adults undergoing the Ross procedure.
        JAMA Cardiol. 2021; 6: 539-548
        • Xuan Y.
        • Alonso E.
        • Emmott A.
        • Wang Z.
        • Kumar S.
        • Mongeon F.-P.
        • et al.
        Wall stresses of early remodeled pulmonary autografts.
        J Thorac Cardiovasc Surg. 2022; 164: 1728-1738.e2
        • Matthews P.B.
        • Jhun C.S.
        • Yaung S.
        • Azadani A.N.
        • Guccione J.M.
        • Ge L.
        • et al.
        Finite element modeling of the pulmonary autograft at systemic pressure before remodeling.
        J Heart Valve Dis. 2011; 20: 45-52
        • Vanderveken E.
        • Vastmans J.
        • Claus P.
        • Verbeken E.
        • Fehervary H.
        • Van Hoof L.
        • et al.
        Mechano-biological adaptation of the pulmonary artery exposed to systemic conditions.
        Sci Rep. 2020; 10: 2724
        • Nappi F.
        • Nenna A.
        • Lemmo F.
        • Chello M.
        • Chachques J.C.
        • Acar C.
        • et al.
        Finite element analysis investigate pulmonary autograft root and leaflet stresses to understand late durability of Ross operation.
        Biomimetics (Basel). 2020; 5: 37

      Linked Article

      • Wall stresses of early remodeled pulmonary autografts
        The Journal of Thoracic and Cardiovascular SurgeryVol. 164Issue 6
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          The Ross procedure is an excellent option for children or young adults who need aortic valve replacement because it can restore survival to that of the normal aged-matched population. However, autograft remodeling can lead to aneurysmal formation and reoperation, and the biomechanics of this process is unknown. This study investigated postoperative autograft remodeling after the Ross procedure by examining patient-specific autograft wall stresses.
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