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Commentary: Yet another Fontan computational study—but this one has clay

  • Ronald K. Woods
    Correspondence
    Address for reprints: Ronald K. Woods, MD, PhD, Division of Pediatric Cardiothoracic Surgery, Department of Surgery Medical College of Wisconsin, Children's Wisconsin, 9000 W Wisconsin Ave, MS B 730, Milwaukee, WI 53226.
    Affiliations
    Division of Pediatric Cardiothoracic Surgery, Department of Surgery, Medical College of Wisconsin, and Herma Heart Institute, Children's Wisconsin, Milwaukee, Wis
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  • Salil Ginde
    Affiliations
    Division of Pediatric Cardiology, Department of Pediatrics, Medical College of Wisconsin, and Herma Heart Institute, Children's Wisconsin, Milwaukee, Wis
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Open ArchivePublished:January 11, 2020DOI:https://doi.org/10.1016/j.jtcvs.2019.12.080
      Figure thumbnail fx1
      Ronald K. Woods, MD, PhD, and Salil Ginde, MD, MPH
      Surgeon-fashioned clay models may improve the efficiency of computational flow dynamics and optimization of the personalized Fontan. Optimal models require verification in reality.
      See Article page 203.
      What does clay have to do with computational flow dynamics (CFD) and the personalized Fontan (herein referred to as the TCPC)? Loke and colleagues' response
      • Loke Y.H.
      • Kim B.
      • Mass P.
      • Opfermann J.D.
      • Hibino N.
      • Krieger A.
      • et al.
      Role of surgeon intuition and computer-aided design in Fontan optimization: a computational fluid dynamic simulation study.
      is that a surgeon-fashioned clay TCPC actually performed reasonably well and could reduce the computational time and money by serving as starting input for the CFD iterative process. With the availability of surgical modeling software, we don't fully understand the need for clay and haptic feedback but, must admit, find the use of clay kind of appealing—can't explain it, maybe it invokes pleasant childhood memories.
      In contrast, I (the surgeon author) am somewhat intimidated by the implications of a personalized TCPC—that I should be capable of creating an operative field with sufficient degrees of freedom that would permit creating any TCPC the model indicates. Typically, I am working on a flaccid pulmonary artery, usually with dense adhesions behind a larger than normal neoaorta. Quite frankly, I feel fortunate if I can place an 18-mm conduit with an offset, somewhat-angulated, smooth transition to the pulmonary artery and no compression of the underlying vein. While I might be able to get close to what is specified by the model (exact location on artery, exact offset, exact angle, etc), I doubt I could get it consistently right. The impact on model-defined performance might be minimal, but it could be substantial, depending on which combination of errors I make. Moreover, the model specifies what is best at present, even though superior and inferior caval flow and native vessel diameters change with time.
      I encourage anyone remotely interested in the issues of energy loss and the personalized TCPC to read the excellent review by Rijnberg and colleagues.
      • Rijnberg F.M.
      • Hazekamp M.G.
      • Wentzel J.J.
      • de Koning P.J.H.
      • Westenberg J.J.M.
      • Jongbloed M.R.M.
      • et al.
      Energetics of blood flow in cardiovascular disease concepts and clinical implications of adverse energetics in patients with a Fontan circulation.
      Most CFD models (3 general methods of computing energy loss) produce similar output trends but different absolute values of energy loss for a given geometry and flow condition. To date, most have made the assumption of steady flow, despite the increase of inferior caval flow with inspiration and/or exercise and with age (up to around 6 years). Models also consistently demonstrate that caval offset decreases energy loss at the expense of more uniform right/left hepatic flow distribution. Most have not accounted for the presence of systemic to pulmonary artery collateral flow, which could have a relevant contribution to resistance.
      • Ascuitto R.J.
      • Ross-Ascuitto N.T.
      Systemic to pulmonary collaterals: a source of flow energy loss in Fontan physiology.
      Although reports vary, for most patients, the cross-sectional area of the pulmonary arteries is a more important resistive element
      • Dasi L.P.
      • KrishnankuttyRema R.
      • Kitajima H.D.
      • Pekkan K.
      • Sundareswaran K.S.
      • Fogel M.
      • et al.
      Fontan hemodynamics: importance of pulmonary artery diameter.
      ; TCPC resistance may contribute to limited exercise performance and, thus far, there is no clear association between TCPC energy loss and protein-losing enteropathy or cirrhosis of the liver. Four-dimensional flow magnetic resonance imaging overcomes many CFD assumption-related limitations. If the technology is improved to address the inter-related and competing issues of scan time, signal to noise, and spatial resolution, then 4-dimensional flow magnetic resonance imaging and CFD models with state-dependent parameters and boundary conditions could improve our understanding of the relative importance of energy loss in the TCPC and any relationship to longer-term outcomes.

      References

        • Loke Y.H.
        • Kim B.
        • Mass P.
        • Opfermann J.D.
        • Hibino N.
        • Krieger A.
        • et al.
        Role of surgeon intuition and computer-aided design in Fontan optimization: a computational fluid dynamic simulation study.
        J Thorac Cardiovasc Surg. 2020; 160: 203-212.e2
        • Rijnberg F.M.
        • Hazekamp M.G.
        • Wentzel J.J.
        • de Koning P.J.H.
        • Westenberg J.J.M.
        • Jongbloed M.R.M.
        • et al.
        Energetics of blood flow in cardiovascular disease concepts and clinical implications of adverse energetics in patients with a Fontan circulation.
        Circulation. 2018; 137: 2393-2407
        • Ascuitto R.J.
        • Ross-Ascuitto N.T.
        Systemic to pulmonary collaterals: a source of flow energy loss in Fontan physiology.
        Pediatr Cardiol. 2004; 25: 472-481
        • Dasi L.P.
        • KrishnankuttyRema R.
        • Kitajima H.D.
        • Pekkan K.
        • Sundareswaran K.S.
        • Fogel M.
        • et al.
        Fontan hemodynamics: importance of pulmonary artery diameter.
        J Thorac Cardiovasc Surg. 2009; 137: 560-564

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