Vagal nerve stimulation reduces anterior mitral valve leaflet stiffness in the beating ovine heart.
OBJECTIVE
The functional significance of the autonomic nerves in the anterior mitral valve leaflet (AML) is unknown. We tested the hypothesis that remote stimulation of the vagus nerve (VNS) reduces AML stiffness in the beating heart.


METHODS
Forty-eight radiopaque-markers were implanted into eleven ovine hearts to delineate left ventricular and mitral anatomy, including an AML array. The anesthetized animals were then taken to the catheterization laboratory and 4-D marker coordinates obtained from biplane videofluoroscopy before and after VNS. Circumferential (E(circ)) and radial (E(rad)) stiffness values for three separate AML regions, Annulus, Belly and Edge, were obtained from inverse finite element analysis of AML displacements in response to trans-leaflet pressure changes during isovolumic contraction (IVC) and isovolumic relaxation (IVR).


RESULTS
VNS reduced heart rate: 94±9 vs. 82±10min(-1), (mean±SD, p<0.001). Circumferential AML stiffness was significantly reduced in all three regions during IVC and IVR (all p<0.05). Radial AML stiffness was reduced from control in the annular and belly regions at both IVC and IVR (P<0.05), while the reduction did not reach significance at the AML edge.


CONCLUSIONS
These observations suggest that one potential functional role for the parasympathetic nerves in the AML is to alter leaflet stiffness. Neural control of the contractile tissue in the AML could be part of a central control system capable of altering valve stiffness to adapt to changing hemodynamic demands.
Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, CA, USA.
Julia C
JC
Swanson
Gaurav
G
Krishnamurthy
Akinobu
A
Itoh
John-Peder Escobar
JP
Kvitting
Wolfgang
W
Bothe
D Craig
DC
Miller
Neil B
NB
Ingels
D000818:Animals; D003198:Computer Simulation; D055119:Elastic Modulus / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods*; D008943:Mitral Valve / Q000294:innervation* / Q000502:physiology*; D008955:Models, Cardiovascular; D010275:Parasympathetic Nervous System / Q000502:physiology*; D012756:Sheep; D014630:Vagus Nerve / Q000502:physiology*