title: Transient stiffening of mitral valve leaflets in the beating heart.
abstract: Anterior mitral leaflet stiffness during isovolumic contraction (IVC) is much greater than that during isovolumic relaxation (IVR). We have hypothesized that this stiffening is due to transient early systolic force development in the slip of cardiac myocytes in the annular third of the anterior leaflet. Because the atrium is excited before IVC and leaflet myocytes contract for < or = 250 ms, this hypothesis predicts that IVC leaflet stiffness will drop to near-IVR values in the latter half of ventricular systole. We tested this prediction using radiopaque markers and inverse finite element analysis of 30 beats in 10 ovine hearts. For each beat, circumferential (E(c)) and radial (E(r)) stiffness was determined during IVC (Deltat(1)), end IVC to midsystole (Deltat(2)), midsystole to IVR onset (Deltat(3)), and IVR (Deltat(4)). Group mean stiffness (E(c) + or - SD; E(r) + or - SD; in N/mm(2)) during Deltat(1) (44 + or - 16; 15 + or - 4) was 1.6-1.7 times that during Deltat(4) (28 + or - 11; 9 + or - 3); Deltat(2) stiffness (39 + or - 15; 14 + or - 4) was 1.3-1.5 times that of Deltat(4), but Deltat(3) stiffness (32 + or - 12; 11 + or - 3) was only 1.1-1.2 times that of Deltat(4). The stiffness drop during Deltat(3) supports the hypothesis that anterior leaflet stiffening during IVC arises primarily from transient force development in leaflet cardiac myocytes, with stiffness reduced as this leaflet muscle relaxes in the latter half of ventricular systole.
authors.affiliation: Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Krishnamurthy
authors.forename: Akinobu
authors.initials: A
authors.lastname: Itoh
authors.forename: Julia C
authors.initials: JC
authors.lastname: Swanson
authors.forename: D Craig
authors.initials: DC
authors.lastname: Miller
authors.forename: Neil B
authors.initials: NB
authors.lastname: Ingels
mesh_terms: D000818:Animals; D016880:Anisotropy; D003287:Contrast Media; D004548:Elasticity / Q000502:physiology*; D020342:Finite Element Analysis; D006321:Heart / Q000502:physiology*; D008943:Mitral Valve / Q000502:physiology*; D023421:Models, Animal; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology; D012756:Sheep; D013599:Systole / Q000502:physiology
chemical_list: D003287:Contrast Media
references.citation: Am J Physiol Heart Circ Physiol. 2008 Sep;295(3):H1141-H1149
references.pmid: 18621858
references.citation: J Biomech. 2009 Dec 11;42(16):2697-701
references.pmid: 19766222
references.citation: Am J Physiol Heart Circ Physiol. 2003 Oct;285(4):H1668-74
references.pmid: 12969884
references.citation: J Heart Valve Dis. 2005 Sep;14(5):592-601; discussion 601-2
references.pmid: 16245497
references.citation: J Card Surg. 1992 Mar;7(1):71-8
references.pmid: 1554980
references.citation: Comput Biomed Res. 1991 Apr;24(2):129-42
references.pmid: 2036779
references.citation: J Biomech. 2009 Aug 25;42(12):1909-16
references.pmid: 19535081
references.citation: Circulation. 1989 Sep;80(3):589-98
references.pmid: 2766511
references.citation: Circ Res. 1972 Sep;31(3):417-30
references.pmid: 5057021
references.citation: Am J Physiol Heart Circ Physiol. 2009 Jun;296(6):H1766-73
references.pmid: 19363135