Active stiffening of mitral valve leaflets in the beating heart.
The anterior leaflet of the mitral valve (MV), viewed traditionally as a passive membrane, is shown to be a highly active structure in the beating heart. Two types of leaflet contractile activity are demonstrated: 1) a brief twitch at the beginning of each beat (reflecting contraction of myocytes in the leaflet in communication with and excited by left atrial muscle) that is relaxed by midsystole and whose contractile activity is eliminated with beta-receptor blockade and 2) sustained tone during isovolumic relaxation, insensitive to beta-blockade, but doubled by stimulation of the neurally rich region of aortic-mitral continuity. These findings raise the possibility that these leaflets are neurally controlled tissues, with potentially adaptive capabilities to meet the changing physiological demands on the heart. They also provide a basis for a permanent paradigm shift from one viewing the leaflets as passive flaps to one viewing them as active tissues whose complex function and dysfunction must be taken into account when considering not only therapeutic approaches to MV disease, but even the definitions of MV disease itself.
Department of Cardiothoracic Surgery, School of Medicine, Stanford University, Stanford, California, USA.
Akinobu
A
Itoh
Gaurav
G
Krishnamurthy
Julia C
JC
Swanson
Daniel B
DB
Ennis
Wolfgang
W
Bothe
Ellen
E
Kuhl
Matts
M
Karlsson
Lauren R
LR
Davis
D Craig
DC
Miller
Neil B
NB
Ingels
D000222:Adaptation, Physiological / Q000502:physiology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D003094:Collagen / Q000502:physiology; D004548:Elasticity; D004558:Electric Stimulation; D020342:Finite Element Analysis; D008943:Mitral Valve / Q000502:physiology*; D008955:Models, Cardiovascular; D009130:Muscle, Smooth / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D010210:Papillary Muscles / Q000502:physiology; D011412:Propanolamines / Q000494:pharmacology; D012756:Sheep
D000319:Adrenergic beta-Antagonists; D011412:Propanolamines; D003094:Collagen; C036604:esmolol