Mesostructures
of the Aortic Valve
Todd C. Doehring, Michael Kahelin, Ivan Vesely
Department of Biomedical Engineering, Lerner Research
Institute, The Cleveland Clinic Foundation, Cleveland, Ohio, Saban Research
Institute, Children’s Hospital Los Angeles, Keck School of Medicine,
University of Southern California, Los Angeles, CA, USA |
Background and aim of the study: The aortic valve
cusp is commonly described as a three-layered structure containing circumferentially
aligned fiber bundles. Little is known, however, regarding fiber bundle
sizes, branching patterns, or how they are connected. This is because
previous morphological studies relied primarily on histological sectioning
and staining techniques, which tend to affect all of the collagen, regardless
of structure or orientation.
Methods: To address this problem, a novel system was developed
for the visualization and analysis of the intermediate-scale ‘mesostructures’
of aortic valve cusps. Mesostructures are defined as the branching fiber
bundle and membrane structures that make up the valve. This system uses
elliptically polarized light to provide contrast between collagen mesostructures
without the need for embedding, staining, or other contrast-enhancing techniques.
Using this system, high-resolution images of 42 whole porcine aortic valve
cusps were acquired in an unloaded (i.e. resting) condition and during
application of controlled |
manipulation. Image-processing algorithms were developed
to quantify fiber bundle morphological features and produce detailed
maps of the fiber bundle patterns.
Results: Fiber bundle sizes and patterns were found to
be significantly different for each of the three cusps. The non-coronary
cusp had a significantly smaller bundle diameter (0.9 ± 0.07
mm) than the left and right coronary cusps (1.1 ± 0.08 mm).
The left and non-coronary cusps appeared to be mirror images of
each other, whereas the right coronary cusp was self-symmetric.
When applying controlled loads to the cusp specimens, thin, overlapping,
collagenous membranes were often found which connected the fiber
bundles. Interesting pinnate fiber branching patterns were also
found.
Conclusion: These morphological results were strikingly
different than the currently accepted three-layer description,
and may provide valuable insight into aortic valve structure-function
relationships.
The Journal of Heart Valve Disease 2005;14:679-686 |