(1): ): 1–9 (2017) BJA Education, 17 (1 doi: 10.1093/bjaed/mkw032 Advance Access Publication Date: 20 May 2016 Matrix reference 1A01, 2A03, 3G00
Mitral valve and mitral valve disease K Holmes MBChB FANZCA1, B Gibbison MD FRCA FFICM2,* and H A Vohra Vohra MRCS MD FRCS(CTh)FET FRCS(CTh)FETCS CS PhD3 1
Fellow in Cardiac Anaesthesia and Intensive Care, Bristol Heart Institute, Bristol, UK, 2Consultant in Cardiac Anaesthesia and Intensive Care, Bristol Heart Institute, Bristol, UK, and 3 Consultant Cardiac Surgeon/Honorary Surgeon/Honorary Senior Lecturer, Bristol Heart Institute, Bristol, UK
*To whom correspo correspondenc ndence e should should be addressed. addressed. Departmen Departmentt of Anaesthesia,Bristol Anaesthesia,Bristol Royal In �rmary, rmary, Level Level 7, Queens Building, Building, UpperMaudlin Street, Street, Bristol Bristol BS2 8HW, UK. Tel: +44 117 342 2163; E-mail:
[email protected]
Annulus Key points •
Mitral valve and left ventricular (LV) function are interdependent interdependent on each other.
•
In mitral regurgitation (MR), measured LV ejection fractions are falsely high.
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Vas Vasopr opres essor sorss should should be used used with with cautio caution n in patients with severe MR.
•
New minimally invasive and percutaneous techniques are now available to repair the mitral valve.
•
Vasodilating drugs should be used with caution in mitral stenosis.
The mitral valve The mitral valve separates the left atrium from the left ventricle (LV) (LV) and, and, as such, such, is an integr integral al part part of thehigh-pre thehigh-pressu ssuresyst resystemi emicc circul circulati ation. on. Theref Therefore ore,, anypatholog anypathology y of the valve valve can have have criticcritical physiological effects that the anaesthetist must be aware of. Anaes Anaesthe thesia sia altersthe altersthe way way in which which theheart, theheart, valve valve,, andcirculaandcirculation interact and control of these changes needs to be both understood and anticipated.
Anatomy Themitral Themitral valveis valveis a comple complex x struct structurethatincorp urethatincorpora oratesnot tesnot only only the two main lea�ets, but an annulus, tendinous cords, and papillary muscles connecting the valve lea�ets to the LV (Fig. 1 (Fig. 1). ).
The mitral valve ’s annulus is a saddle-shaped saddle-shaped structure which is shapedmorelike shapedmorelike a ‘D’ than than an ‘O’. Theaorticvalveis wedge wedged d into into the straight side of the ‘ D’ and there is a � brous continuity between the two valves. This means that one can be easily affected by surgery on the other. The circum�ex artery follows follows the line of the annulus annulus as it passes anteriorly around the base of the heart, a position that places it at risk during any mitral valve surgery. Damage or ligation of the artery will result in lateral wall ischaemia, and this is an important area to assess on perioperative echocardiography.
Lea�ets The anterior lea�et hangs down from the straight side of the ‘ D’shaped annulus and is more superior and medial than truly anterior. terior. The posteriorlea posteriorlea�et is a C-shap C-shaped ed lea�et divide divided d into into three three sections by indentations that give it a scalloped appearance. These three segments segments are called P1, P2, and P3, with their opposing anterior lea�et segments termed A1, A2, and A3. The free edge edgess ofthe lea lea�etsdo notmeet exact exactly,but ly,but instea instead d have have aroun around d 5 mm of overlap. This overlap at the edges seals the valve as the body of the lea�ets push outwards like sails during systole (see Online video 1). 1 ). At the corners of the lea�ets, there are two commissures which ensure a seal in the corners of the valve.
Papillary muscles and chordae During systole, the lea�ets are prevented from billowing back into the left atrium by the chordae. These tether the free edges of the lea�ets to the two papillary muscles which grow out from thewall of the LV. LV. The papilla papillary ry muscle muscless are are anterol anterolate atera rall and posposteromedial and sit under the commissures of the valve, with each muscle passing chordae to both lea �ets. While the anterolateral muscle muscle receiv receives es a dual dual blood blood supply supply from the left left anteri anterior or
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Mitral valve and mitral valve disease
Fig1 Themitralvalve andsurroundingstructures. Thevalve is inthe ‘surgeon’s view’ orientationwiththehearttiltedto theleft. ( ) AC,anteriorcommissure;PC, posterior commissure. () The mitralvalvelea�ets, eachof whichusuallyconsistsof threediscretesegments orscallops.These aredesignatedA1,A2, andA3 fortheanteriorlea �et and P1, P2, and P3 for the posterior lea�et. () Primary chordae are attached to the free edge of the valve lea �et, and secondary chordae are attached to the ventricular surface of the lea�et. (From)1. Reprinted with permission from Massachusetts Medical Society.
descending and the circum�ex artery, the posteromedial is supplied solely by the right coronary artery in the more common right dominant circulation.As it is usually only supplied by a single artery, infarction and rupture of the posteromedial muscle is much more likely, as could be seen in the context of an inferior myocardial infarction.
Mitral stenosis A normal mitral valve will have an area of >4 cm2, but symptoms are usually only present once the stenosis is moderate–severe.
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Grading into mild, moderate, or severe disease is based on both the pressure needed to drive blood across the valve (mean pressure gradient) and the valve area.
Aetiology/epidemiology Rheumaticfeveris by farthe largest cause of mitral stenosis(MS), although it is relatively rare in developedcountries where degenerative calci�cation or endocarditis are more likely causes. Disease progression is usually around 0.1 –0.3 cm2 yr −1,2 but this is greatly increased in cases of repeated valve in �ammation such
Mitral valve and mitral valve disease
Table 1 Criteria for echocardiographic diagnosis of MS severity 3
Mitral stenosis Meanpressure decrease Pressure half-ti me Valve area
Mild
Moderate
Severe
10 mm Hg indicating severe stenosis. Valve area is usually derived using several techniques as simply tracing the area out using the echo software can be unreliable. While a normal mitral valve has an area of 4 –6 cm2, symptoms may only develop once the valve area is
