Is the mitral valve passive flap theory overstated? An active valve is hypothesized

Active stiffening of mitral valve leaflets in the beating heart

“…Medical and surgical therapies for this disease have traditionally assumed that the valve leaflets, the key components of the valve, are passive flaps (46). However, muscle fibers (2, 6, 11, 12, 18, 25, 30 -32, 34, 39, 41, 47, 48), blood vessels (6,8,11,24,26,37,39), and nerves (1, 6 -13, 18 -20, 26, 29, 35, 36, 39, 43-45) have been recognized in the MV leaflets of animals and humans since the 19th century, and the physiological function of these entities, along with other contractile elements in the leaflets, such as smooth muscle (8,18,26,47) and valvular interstitial cells (VICs) (4,13,18,23,26,28,38,40), is not understood.…”

“…Our recent study (21), however, suggested that leaflet stiffness in the beating heart (slope of the leaflet stress-strain curve) was much greater than that of passive tissue, and studies of freshly isolated, oxygenated, stimulated leaflets in myographs (39) and in open hearts on cardiopulmonary bypass (CBP) (7,32) have suggested that the mechanical properties of MV leaflets may be altered actively. Two important hypotheses have been advanced regarding this activity (46). 1) Contractile element force development within the leaflets, in response to leaflet excitation (7,12,32,33,48), provides modulation of leaflet tone to adapt to changes in left ventricular (LV) pressure (LVP) load on the closed valve (33,49).…”

Regulação autonômica das propriedades mecânicas em bioprótese valvar porcina

“…There are more known adrenoceptor subtypes, a number of which have been found in human heart valve tissue: α1, α2, β1 and β2 adrenoceptors 10,11 . Williams TH et al 3 reported that rat mitral valves had been shown to display spontaneous contraction-like movements localized to the leaflet itself, immediately after being dissected from the heart, which was enhanced by addition of norepinephrine (NE) in a dose-dependent fashion. Otherwisely, in an effort to examine valve cusps' responses to neuromodulators ex vivo and determine the specific receptors involved in mediating these effects, porcine aortic valve cusps, mounted uniaxially in an organ chamber, contracted significantly in response to increasing concentrations of α adrenoreceptor agonists, including norepinephrine.…”

“…However, very little focus has been given to the regulation of heart valves by the autonomic nervous system. Recent studies have indicated that the addition of norepinephrine (NE) and acetylcholine (ACH) produced dose-dependent increases in mitral valve contractility and aortic valve tissue relaxation in an ex vivo model, respectively 3,4 . The functional role of neurotransmitters in the mechanical properties of cusp tissue remains undetermined.…”

The clinical anatomy of the mitral valve

“…Each of the aforementioned components is equally important, as alterations in the structure and function of any of these elements may cause hampered emptying of the left atrium, mitral valvular incompetence, and/or alterations of the left ventricular ejection. Accumulating data suggest the fact that mitral valve closure does not represent a passive process; instead, the model of an active valve emerges (Williams and Jew, 2004).…”