Functional Collagen Fiber Architecture of the Pulmonary Heart Valve Cusp

Background. Defects in the pulmonary valve (PV) occur in a variety of forms of congenital heart diseases. Quantitative information on PV collagen fiber architecture, and particularly its response to diastolic forces, is necessary for the design and functional assessment of approaches for PV repair and replacement. This necessity is especially the case for novel tissue-engineered PV, which rely on extensive in-vivo remodeling for long-term function. Methods. Porcine PV and aortic valves (AV) were fixed under a 0 to 90 mm Hg transvalvular pressure. After dissection from the root, small-angle light-scattering measurements were conducted to quantify the collagen fiber architecture and changes with increasing applied transvalvular pressure over the entire cusp. Histomorphologic measurements were also performed to assess changes in cuspal layer thickness with pressure. Results. While the PV and AV displayed anticipated structural similarities, they also presented important functionally related differences. In the unloaded state, the AV cusp demonstrated substantial regional variations in fiber alignment, whereas the PV was surprisingly uniform. Further, the AV demonstrated substantially larger changes in collagen fiber alignment with applied transvalvular pressure compared with the PV. Overall, the AV collagen fiber network demonstrated greater ability to respond to applied transvalvular pressure. A decrease in crimp amplitude was the predominant mechanism for improvement in the degree of orientation of the collagen fibers in both valves. Conclusions. This study clarified the major similarities and differences between the PV and the AV. While underscoring how the PV can serve as an appropriate replacement of the diseased AV, the observed structural differences may also indicate limits to the ability of the PV to fully duplicate the AV. Moreover, quantitative data from this study on PV functional architecture will benefit development of tissue-engineered PV by defining the critical fiber architectural characteristics.