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J Thorac Cardiovasc Surg 2009;137:394-403
© 2009 The American Association for Thoracic Surgery

Congenital Heart Disease

Evaluation of a novel Y-shaped extracardiac Fontan baffle using computational fluid dynamics

^a Mechanical and Aerospace Engineering Department, University of California, San Diego, Calif
^b Electrical Engineering Department, Stanford University, Stanford, Calif
^c Department of Cardiothoracic Surgery, Stanford University, Stanford, Calif
^d Bioengineering Department, Stanford University, Stanford, Calif
^e Mechanical Engineering Department, Stanford University, Stanford, Calif
^f Department of Radiology, Stanford University, Stanford, Calif
^g Department of Pediatrics, Stanford University, Stanford, Calif

Received for publication November 9, 2007; revisions received April 1, 2008; accepted for publication June 15, 2008.

^_* Address for reprints: Alison L. Marsden, PhD, Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, CA. (Email: amarsden{at}stanford.edu).

Objectives: The objective of this work is to evaluate the hemodynamic performance of a new Y-graft modification of the extracardiac conduit Fontan operation. The performance of the Y-graft design is compared to two designs used in current practice: a t-junction connection of the venae cavae and an offset between the inferior and superior venae cavae.

Methods: The proposed design replaces the current tube grafts used to connect the inferior vena cava to the pulmonary arteries with a Y-shaped graft. Y-graft hemodynamics were evaluated at rest and during exercise with a patient-specific model from magnetic resonance imaging data together with computational fluid dynamics. Four clinically motivated performance measures were examined: Fontan pressures, energy efficiency, inferior vena cava flow distribution, and wall shear stress. Two variants of the Y-graft were evaluated: an "off-the-shelf" graft with 9-mm branches and an "area-preserving" graft with 12-mm branches.

Results: Energy efficiency of the 12-mm Y-graft was higher than all other models at rest and during exercise, and the reduction in efficiency from rest to exercise was improved by 38%. Both Y-graft designs reduced superior vena cava pressures during exercise by as much as 5 mm Hg. The Y-graft more equally distributed the inferior vena cava flow to both lungs, whereas the offset design skewed 70% of the flow to the left lung. The 12-mm graft resulted in slightly larger regions of low wall shear stress than other models; however, minimum shear stress values were similar.

Conclusions: The area-preserving 12-mm Y-graft is a promising modification of the Fontan procedure that should be clinically evaluated. Further work is needed to correlate our performance metrics with clinical outcomes, including exercise intolerance, incidence of protein-losing enteropathy, and thrombus formation.

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