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Research Papers

Statistical Shape Modeling for Cavopulmonary Assist Device Development: Variability of Vascular Graft Geometry and Implications for Hemodynamics

[+] Author and Article Information
Jan L. Bruse

Centre for Cardiovascular Imaging,
Great Ormond Street Hospital for Children,
UCL Institute of Cardiovascular Science,
Level 6, Nurses Home, Great Ormond Street,
London WC1N 3JH, UK
e-mail: jan.bruse.12@ucl.ac.uk

Giuliano Giusti

Centre for Cardiovascular Imaging,
Great Ormond Street Hospital for Children,
UCL Institute of Cardiovascular Science,
Level 6, Nurses Home, Great Ormond Street,
London WC1N 3JH, UK
e-mail: giusti.giul@gmail.com

Catriona Baker

Centre for Cardiovascular Imaging,
Great Ormond Street Hospital for Children,
UCL Institute of Cardiovascular Science,
Level 6, Nurses Home, Great Ormond Street,
London WC1N 3JH, UK
e-mail: catriona.baker@ucl.ac.uk

Elena Cervi

Centre for Cardiovascular Imaging,
Great Ormond Street Hospital for Children,
UCL Institute of Cardiovascular Science,
Level 6, Nurses Home, Great Ormond Street,
London WC1N 3JH, UK
e-mail: Elena.Cervi@gosh.nhs.uk

Tain-Yen Hsia

Centre for Cardiovascular Imaging,
Great Ormond Street Hospital for Children,
UCL Institute of Cardiovascular Science,
Level 7, Nurses Home, Great Ormond Street,
London WC1N 3JH, UK
e-mail: tyhsia@virginmedia.com

Andrew M. Taylor

Centre for Cardiovascular Imaging,
Great Ormond Street Hospital for Children,
UCL Institute of Cardiovascular Science,
Level 7, Nurses Home, Great Ormond Street,
London WC1N 3JH, UK
e-mail: a.taylor76@ucl.ac.uk

Silvia Schievano

Centre for Cardiovascular Imaging,
Great Ormond Street Hospital for Children,
UCL Institute of Cardiovascular Science,
Level 6, Nurses Home, Great Ormond Street,
London WC1N 3JH, UK
e-mail: s.schievano@ucl.ac.uk

Manuscript received July 31, 2016; final manuscript received January 23, 2017; published online May 3, 2017. Assoc. Editor: Marc Horner.

J. Med. Devices 11(2), 021011 (May 03, 2017) (11 pages) Paper No: MED-16-1290; doi: 10.1115/1.4035865 History: Received July 31, 2016; Revised January 23, 2017

Patients born with a single functional ventricle typically undergo three-staged surgical palliation in the first years of life, with the last stage realizing a cross-like total cavopulmonary connection (TCPC) of superior and inferior vena cavas (SVC and IVC) with both left and right pulmonary arteries (LPA and RPA), allowing all deoxygenated blood to flow passively back to the lungs (Fontan circulation). Even though within the past decades more patients survive into adulthood, the connection comes at the prize of deficiencies such as chronic systemic venous hypertension and low cardiac output (CO), which ultimately may lead to Fontan failure. Many studies have suggested that the TCPC’s inherent insufficiencies might be addressed by adding a cavopulmonary assist device (CPAD) to provide the necessary pressure boost. While many device concepts are being explored, few take into account the complex cardiac anatomy typically associated with TCPCs. In this study, we focus on the extra cardiac conduit (ECC) vascular graft connecting IVC and pulmonary arteries (PAs) as one possible landing zone for a CPAD and describe its geometric variability in a cohort of 18 patients that had their TCPC realized with a 20 mm vascular graft. We report traditional morphometric parameters and apply statistical shape modeling (SSM) to determine the main contributors of graft shape variability. Such information may prove useful when designing CPADs that are adapted to the challenging anatomical boundaries in Fontan patients. We further compute the anatomical mean 3D graft shape (template graft) as a representative of key shape features of our cohort and prove this template graft to be a significantly better approximation of population and individual patient’s hemodynamics than a commonly used simplified tube geometry. We therefore conclude that statistical shape modeling results can provide better models of geometric and hemodynamic boundary conditions associated with complex cardiac anatomy, which in turn may impact on improved cardiac device development.

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References

Figures

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Fig. 1

Commonly found generic simplification of a TCPC approximated as an orthogonal cross. Deoxygenated blood enters from IVC and SVC and flows into LPA and RPA (a). Example TCPCs derived from CMR data of five patients who underwent Fontan palliation with ECC vascular graft. Connection configuration differs considerably from a simple cross and vessel anatomy (including the ECC graft) differs substantially from straight tubes (b).

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Fig. 2

Three-dimensional TCPC models were segmented and reconstructed from CMR data and cut consistently at the height of hepatic vein/IVC junction and PA anastomosis in order to obtain graft models represented by surface meshes

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Fig. 3

All 18 ECC patient graft models reconstructed from CMR data used for template computation and CFD analyses

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Fig. 4

Overview of CFD boundary conditions. Inflow and outlet pressure were set constant; blood was modeled as a Newtonian fluid.

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Fig. 5

Computed template graft (i.e., mean 3D graft shape) from different view angles and key geometric parameters. The template comprised graft shape features characteristic for our patient cohort such as an overall c-shaped graft with slimmer midsection and slight flaring toward the PA anastomosis site.

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Fig. 6

Surface distances between nine-fold cross validated template shapes and full template shape (overlaid in gray). Following cross validation, the full template shape was not overly affected by removing subjects from the analysis.

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Fig. 7

Scree plot describing how much of the total shape variability is explained by each PCA shape mode (individual explained shape variability in dashed line; cumulated explained shape variability in solid line). Ten shape modes described 90% of the total shape variability, with the first shape mode accounting for 29.5%.

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Fig. 8

First three PCA shape modes, visualized as deformation of the computed template graft along each mode direction from −3 to +3 standard deviations (SD). Mode 1 accounted for most of the shape variability and mainly described graft shape changes associated with difference in graft length (a). Shape mode 2 accounted for shape variability introduced by differences in curvature/bending of the graft (b) and mode 3 visualized small differences in graft diameter (c). Those three shape parameters need to be taken into account when designing a CPAD to fit into the ECC graft.

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Fig. 9

Individual, volume-rendered pressure maps for all 18 patients showing higher pressure in the area of hepatic vein/IVC junction and the outward bend toward the PA anastomosis (a). The computed template showed a better approximation of the patient pressure maps than the simple tube and had a pressure drop closer to the average pressure drop of the population (b).

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Fig. 10

Deviations between template pressure drop and individual patient’s pressure drops showed to be significantly lower (** denotes significance level p < 0.01) than those of the tube. The tube thereby strongly underestimated patient pressure drops (by 65–75%) and is thus not a suitable approximation of patient hemodynamics. Error bars denote ±1 SD.

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