MITRAL VALVE STRUCTURE FUNCTION DAVID J MCCORMACK BSCHONS

MITRAL VALVE STRUCTURE & FUNCTION DAVID J MCCORMACK BSC(HONS) MBBS MFSTED FRCSED(CTH) FRCS (CTH) CONSULTANT SURGEON WAIKATO CARDIOTHORACIC UNIT

TOPICS TO BE COVERED… • LOCATION OF THE MITRAL VALVE • RELATION TO THE OTHER VALVES AND IMPORTANT STRUCTURES • MITRAL VALVE COMPONENTS • ANNULUS • LEAFLETS • SUBVALVULAR APPARATUS • FUNCTIONAL ANATOMY OF THE MITRAL VALVE

ANNULUS • A ‘D’ SHAPED HINGE LINE OF THE VALVULAR LEAFLETS • CIRCUMFERENCE: ♂ 9 CM, ♀ 7. 2 CM • NOT A SOLID RING • FIBROCOLLAGENOUS ELEMENTS OF VARYING CONSISTENCY • ALLOWS MAJOR CHANGES IN SHAPE AND DIMENSIONS DURING THE CARDIAC CYCLE

LEAFLETS • ANTERIOR LEAFLET • SEMICIRCULAR • 1/3 OF ANNULAR CIRCUMFERENCE • FIBROUS CONTINUITY WITH NCC AND LCC • DEFINES BOUNDARY LVIT AND LVOT • POSTERIOR LEAFLET • QUADRANGULAR • 2/3 OF ANNULAR CIRCUMFERENCE • HEIGHT IS LESS THAN AMVL

LEAFLETS – HISTOLOGICAL STRUCTURE THREE LAYERS: 1. THE FIBROSA, THE SOLID COLLAGENOUS CORE THAT IS CONTINUOUS WITH THE CHORDAE TENDINEAE 2. THE SPONGIOSA, WHICH IS ON THEATRIAL SURFACE AND FORMS THE LEAFLET LEADING EDGE (IT CONSISTSOF FEW COLLAGEN FIBERS BUT HAS ABUNDANT PROTEOGLYCANS, ELASTIN, AND MIXED CONNECTIVE TISSUE CELLS) 3. A FIBROELASTIC COVERING OF MOST OF THE LEAFLETS • THE ATRIALIS IS THIN AND RICH IN ELASTIN • THE VENTRICULARIS IS MUCH THICKER, IS CONFINED MOSTLY TO THE ANTERIOR LEAFLET, AND IS DENSELY PACKED WITH ELASTIN

SUBVALVULAR APPARATUS • CHORDAE TENDINEAE • PAPILLARY MUSCLES • LEFT VENTRICLE

CHORDAE TENDINEAE • STRING LIKE STRUCTURES ATTACHING THE VENTRICULAR SURFACE OR THE FREE EDGE OF THE LEAFLETS TO THE PAPILLARY MUSCLES • CHORDAL FIBROBLAST ARE METABOLICALLY ACTIVE • CONVEY BLOOD TO THE LEAFLETS • WITHSTAND REPETITIVE CONTRACTILE STRESS GENERATED BY PAPILLARY MUSCLES

• PRIMARY CHORDS • FREE MARGIN • SECONDARY CORDS • VENTRICULAR SURFACE • TERTIARY CORDS • PMVL ONLY • FROM VENTRICLE TO BASAL ZONE (NEAR HINGE)

CHORDAE TENDINEAE COMMISSURAL CHORDS • ORIGINATING AS A SINGLE CHORD BUT FANNING OUT TO SPAN THE COMMISSURAL REGION CLEFT CHORDS STRUT CHORDS • ONE ORIGINATING FROM EACH PAPILLARY MUSCLE • INSERTING INTO THE AMVL • STRONGEST AND THICKEST

PAPILLARY MUSCLES • LOCATION IS VARIABLE • USUALLY ARISE FROM APICAL AND MIDDLE THIRDS OF LEFT VENTRICULAR WALL • COMMONLY DESCRIBED AS TWO MUSCLE GROUPS • ANTEROLATERAL (70% SINGLE MUSCLE) • POSTEROMEDIAL (60% TWO TO THREE MUSCLES)

PAPILLARY MUSCLES BLOOD SUPPLY • VESSELS ARE DEEP AND MID ASPECTS OF MUSCLES • ANTEROLATERAL – LAD AND CX • POSTERIORMEDIAL – RCA OR CX (MORE VULNERABLE TO ISCHAEMIA)

LEFT VENTRICLE • LATERAL WALL OF LEFT VENTRICLE PROVIDES ATTACHMENT FOR PAPILLARY MUSCLES • WITHIN THE LEFT VENTRICLE BRIDGES EXIST BETWEENPM AND AL PAPILLARY MUSCLES • DIRECT ORIGIN OF TERTIARY CHORDAE

MITRAL VALVE FUNCTION • REGULATED BLOOD FLOW FROM LA TOLV • NO SIGNIFICANT GRADIENT • PREVENTS SYSTOLIC REGURGITATION • INTEGRETY IS ESSENTIAL TO MAINTAIN NORMALLV SIZE, GEOMETRY AND FUNCTION

MITRAL ANNULUS • ANTERIOR ANNULUS MECHANICALLY COUPLED TO AORTIC ANNULUS (AORTOMITRAL CURTAIN)

MITRAL ANNULUS CONFORMATIONAL CHANGE DURING CARDIAC CYCLE 1. SPHINCTERIC CONTRACTURE • • REDUCTION IN ANNULAR AREA BY 25% MAXIMAL IN LATE DIASTOLE MINIMAL IN MID SYSTOLE SUBSTANTIAL PRESYSTOLIC CONTRACTION IS ATTRIBUTABLE TO ATRIAL CONTRACTION 2. TRANSLATION • • REDUCTION IN LV LONG AXIS DIMENSION INCREASES LA FILLING

CHORDAE TENDINAE • PRIMARY CHORDS • FACILITATE VALVE CLOSURE • MAINTAIN LEAFLET APPOSITION • SECTIONING GENERATES ACUTE MITRAL REGURGITATION • VARIABLE TENSION THROUGHOUT CARDIAC CYCLE • SECONDARY CHORDS • INVOLVED IN MARINATING NORMAL LV SIZE AND GEOMETRY • SECTIONING DOES NOT GENERATE MITRAL REGURGITATION • TAUGHT ‘LIKE A RUBBER BAND’ THROUGHOUT CARDIAC CYCLE

MITRAL LEAFLETS • LEAFLETS COAPT ALONG THEIR ROUGH ZONES • ZONE OF COAPTION ~ 1 CM • SCALLOPS ACT LIKE PLEATS SO AS TO ALLOW THE LEAFLETS TO ACCOMMODATE THE CURVED LINE OF VALVE CLOSURE. • SMOOTH SURFACE OF AMVL IS SUITED TO LAMINAR PROJECTION OF BLOOD THROUGH THE LVOT

THANK YOU