Surgical reconstruction of semilunar valves in the growing child: Should we mimic the venous valve? A simulation study

Abstract

Objectives: Neither heart valve repair methods nor current prostheses can accommodate patient growth. Normal aortic and pulmonary valves have 3 leaflets, and the goal of valve repair and replacement is typically to restore normal 3-leaflet morphology. However, mammalian venous valves have bileaflet morphology and open and close effectively over a wide range of vessel sizes. We propose that they might serve as a model for pediatric heart valve reconstruction and replacement valve design. We explore this concept using computer simulation.

Methods: We use a finite element method to simulate the ability of a reconstructed cardiac semilunar valve to close competently in a growing vessel, comparing a 3-leaflet design with a 2-leaflet design that mimics a venous valve. Three venous valve designs were simulated to begin to explore the parameter space.

Results: Simulations show that for an initial vessel diameter of 12 mm, the venous valve design remains competent as the vessel grows to 20 mm (67%), whereas the normal semilunar design remains competent only to 13 mm (8%). Simulations also suggested that systolic function, estimated as effective orifice area, was not detrimentally affected by the venous valve design, with all 3 venous valve designs exhibiting greater effective orifice area than the semilunar valve design at a given level of vessel growth.

Conclusions: Morphologic features of the venous valve design make it well suited for competent closure over a wide range of vessel sizes, suggesting its use as a model for semilunar valve reconstruction in the growing child.

Keywords: accommodate growth; reconstruction; repair; semilunar valve; simulation; venous valve.

Copyright © 2016 The American Association for Thoracic Surgery. Published by Elsevier Inc. All rights reserved.

Figures

Fig. 1

Top image shows the cross section of a reconstructed semilunar valve in the closed position, with preserved (growing) vessel shown in red and leaflet grafts (non-growing) shown in gray. Bottom image illustrates that as the vessel grows, the non-growing leaflet grafts are pulled apart as the vessel (to which the leaflets are attached) moves radially outward with growth.

Fig. 2

Segments of a human femoral vein (top) and porcine aortic valve (bottom) from which the valve leaflets have been excised. Dimension C indicates the circumference of the vessel at the top of the leaflet attachment, and dimension LA indicates the length of the leaflet attachment in the axial direction of the vessel. Scales in both photographs indicate mm. In the venous valve, the axial length of the valve is considerably greater than the vessel diameter (1.3 times) whereas in the aortic valve, the axial length of the valve is approximately equal to half the vessel diameter.

Fig. 3

(A) Planar outlines of the leaflets from a semilunar valve (SV) design was meshed with triangles and replicated. (B) Planar leaflet mesh was then wrapped into a cylinder with diameter of 12 mm. (C) Planar outlines of the leaflets from a venous valve (VV) design was meshed with triangles and replicated. (D) Planar leaflet mesh was then wrapped into a cylinder with diameter of 12 mm. (E) Three different VV leaflet designs were tested: VV1 with a midline height to overall height ratio of approximately 0.4 (based on our human femoral vein valve specimen), VV2 with height ratio of 0.5, and VV3 with height ratio of 0.6.

Fig. 4

Results of simulations showing the loaded state of the reconstructed valve following the maximum vessel growth under which the valve remained competent. (A) VV1 design at vessel diameter of 16 mm. (B) VV2 design at vessel diameter of 19 mm. (C) VV3 design at vessel diameter of 20 mm. (D) SV design at vessel diameter of 13 mm.

Fig. 5

Results of simulations showing central coaptation height (A) and coaptation area (B) versus vessel diameter for four different valve reconstruction designs: SV1 (light blue), VV1 (red), VV2 (green), and VV3 (dark blue).

Fig. 6

Results of simulations that estimate the ability of the reconstructed valve to open during systole as the patient/vessel grows. Normalized effective orifice area is computed by dividing the projected area of the open valve by the vessel cross-sectional area. The curves represent the semilunar valve (SV) design (light blue) and the three venous valve (VV) designs: VV1 (red), VV2, (green), and VV3 (dark blue).