There is growing evidence that heart valves are not passive structures, but can remodel with left ventricular dysfunction. To determine if these tissues remodel under non-pathological conditions, we examined the mirtal valve anterior leaflet during the volume loading and cardiac expansion of pregnancy using a bovine model. We measured leaflet dimensions, chordal attachments, and biaxial mechanical properties of leaflets collected from never-pregnant heifers and pregnant cows (pregnancy duration estimated from fetal length). Hydrothermal Isometric Tension (HIT) tests were performed to assess the denaturation temperature (Td) associated with collagen molecular stability, and the load-decay half-time (t1//2) associated with intermolecular crosslinking. Histological changes were examined using Verhoeff-Van Geison and Picrosirius Red-staining with polarized light. We observed striking changes to the structure and material properties of the mitral anterior leaflet during pregnancy. Leaflet area was increased 33 %, with a surprising increase (nearly 25 %) in chordae tendinae attachments. There was a biphasic change in leaflet extensibility: rapidly decreasing by 30 %, then reversing to pre-pregnant values by late pregnancy. A 2 °C decrease in Td in pregnancy was indicative of collagen remodeling, while a 70 % increase in HIT t1/2 indicated an increase in collagen crosslinking. Finally, histological results suggest a transient increases in leaflet thickness and transient decreases in collagen crimp. This remodeling may compensate for increased loading conditions associated with pregnancy by normalizing leaflet stress and maintaining coaptation. Understanding the mechanisms of mitral valve physiological remodeling in pregnancy could contribute to alternative treatments of pathological remodeling associated with LV dysfunction.
- heart valves
- mechanical properties
- Copyright © 2011, American Journal of Physiology - Heart and Circulatory Physiology