Introduction

During mitral valve surgery surgeons need detailed anatomy and many publications have appeared dealing with its detailed anatomy but with lack of numerical values and measurements. We present data of the dimensions of the mitral valve that will be helpful to anatomists and surgeons.

Familiarity with the normal measurements of the component parts of the valve will, at operation, help the surgeon to assess the Mitral valve Annular circumference was first described by Louis A. Du Plessis and Paul Marchand ² in 1964 that mitral valve inlet is larger than its outlet, but an oblique setting of the plane of the outlet orifice to some extent compensates for the discrepancy in size. The proximity of the bundle of His, the coronary sinus, the aortic cusps, and other coronary vessels to various parts of the mitral annulus are described. Careless suturing during total valve replacement may damage these structures. Certain dimensional data concerning the mitral valve are presented. The annular attachment of the anterior leaflet is half that of the posterior leaflet the anterior leaflet is twice as deep as the posterior one.

Leaflets differ in shape and in relation with width of mitral valve leaflets E. W. T. Morris ³ (1960) observed its attached border forms an arc and its free border is subdivided into three regions: a middle one free from chordae tendineae, and two lateral regions. The contour of the free border is responsible for the characteristic crescentic form of the closed aperture. The posterior cusp is narrower and more rectangular than anterior. The width of the anterior cusp was found to be greater than posterior cusp. Notches are commonly seen in the free border of the posterior cusp.

There is variation in measurement of annular length and width of leaflets in different studies and lack of such study in Indians. The present study has been undertaken for detailed anatomical study of mitral valve specially data analysis.

Tetsuro Sakai, Yutaka Okita ⁴ and others in 1999 describe an anatomic study of the distance between the mitral annulus and papillary muscles in normal hearts for a guide to the resuspension procedure in mitral valve replacement. Find out statistically significant correlations between the mean annulo–papillary muscle distances and the mitral annular diameters, the heart weights and the body surface areas.

JA Ormiston, PM Shah, C Tei and M Wong ⁵ in 1981 Using wide-angle, phased-array, two-dimensional echocardiography, mitral leaflets and their annular attachments were recorded during the cardiac cycle. They note in study, annuli were elliptical and changed shape during the cardiac cycle, being more circular in late diastole and flatter in systole. There was a coincident reduction in annular circumference. They note wide variation in annular size during the cardiac cycle.

Robert walmsley ⁶ in 1978 claimed that fibrous mitral ring in human heart is incomplete anteriorly along entire length of the basal attachment of the mitral aortic cusp. The posterior part of the ring is interposed between myocardium of left atrium and left ventricle and corresponds to region of attachment of mural (posterior) cusp of mitral valve. This posterior part plays an important role in change of circumference of ring during cardiac cycle. He also find out each major mitral cusp has two zones an appositional (comes into contact with a corresponding zone on the opposing cusp during valve closure) and a free basal non-appositional zone. There is no any data available in this study related with mitral valve but mainly he compares mitral valves of different animals.

S Y Ho ⁷ in 2002 stated that the annulus marking the hinge line of the valvar leaflets is more D shaped than the circular shape. The annulus opposite the area of valvar fibrous continuity tends to be weaker lacking a well-formed fibrous cord. The leaflets sometimes have a hooded appearance with slight pocket-like doming toward the atrium. The tendinous cords of the mitral valve are attached to two groups of papillary muscles or directly to the postero-inferior ventricular wall.

R. C. Brock ⁸ in 1952 point out values that the anterior cusp is long at its middle part than the posterior cusp, the area of the atrioventricular orifice and the surface area of the two cusps. He gives the proportion of valve area to orifice area. Then he describes diseased mitral valve gives size of diseased stenosed valve.

J. C. Van der Spuy ⁹ in 1958 claimed that the posterior half of the mitral ring is semi-ovoid; its anterior half is bi-concave. The papillary muscles and chorde tendineae prevent prolapse of both cusps into the cavity of the left atrium and of the antero-medial cusp towards the root of the aorta; they convert the cusp and ring unit into a cone, which they help to flatten during systole. The billowing “trigone” of the long antero-medial cusp fits snugly into the bulging concave base of the shorter postero-lateral cusp. During systole the mitral “ring” becomes flattened between the postero-lateral root of the aorta and the base of the left ventricle. During mitral valve closure the antero-medial cusp rolls on the postero-lateral cusp in a direction from its apex towards base. He also discussed the mechanism whereby mitral valve stenosis is produced.

Hugo spindola-franco ¹⁰ et al in 1980 in their radiological study of mitral valve percentage change in mitral ring diameter from diastole to systole showed no correlation with the patient's age.

Aims And Objectives

A mitral valve of heart shows leaflets with the annulus, chordae and papillary muscles. There have been variable reports of annular circumference and leaflet length of mitral valve of heart.

Materials And Methods

Total 50 hearts were included in present study. The mitral valve descriptions and measurements are based upon observations made during dissections of human cadavers (Dead bodies) hearts. These hearts are taken from human cadavers Anatomy Department, Government Medical College Surat preserved by Embalming procedure gravity method of injection and later on preserved in 10% formalin after removal from body. Specimens were in good condition after removal from body during dissection and retain their true features, relationships. The measurements of the valve were taken from 50 normal hearts. The mitral leaflets with the annulus, chordae and papillary muscles were removed, and the valve was flattened out in a single plane by dividing its ring at the lateral commissure and by half splitting the medial papillary muscle mass as described by Louis a. Du Plessis and Paul Marchand (1964) ² with slight modification. The opened-out valves were then pinned to white Thermacol sheet. Measurements were made with an ordinary metric ruler. This is simple method to use require no complicated instruments. But limitation of this method is that it may cause human error during measurements.

Figure 1

Figure 1: Opened out mitral valve with Aortic valve from ventricular aspect

AL- Anterior mitral leaflet, PL- Posterior mitral leaflet. (b) The angle formed by the planes of the aortic and mitral valves is approximately 45 ⁰

Figure 2

Fig.2: The atrial surface of the mitral valve (splayed open mitral and aortic valves seen)

Anatomy of Mitral valve: As per text (Gray’s ¹ Anatomy 39 ^th Edition) the mitral valve consists of orifice and its associated annulus, the cusp, the supporting chordae tendineae and papillary muscles. Mechanical support provided by fibro elastic cardiac skeleton. Mitral valve orifice mean circumference is 9.0cm in males and 7.2cm in females. The circular orifice is almost vertical in diastole and at 45 ⁰ to the sagittal plane. Connected centrally with central fibrous body. Annulus changes its shape and dimension during cardiac cycle. Mitral valve shows anterior and posterior cusps (Anteromedial and Posterolatral) with 2 commissures. Anterior cusp is 2/3 ^rd and posterior cusp 1/3 ^rd of circumference of orifice. Chordae supports entire free edge of valvular cusps with varying degrees of their ventricular aspect and bases. Two papillary muscles support mitral cusps (anterolatral and posteromedial).

Observations

In present study we measure and calculate average of each value as follows length of valve ring (circumference) 8.248cm, Length of free edge of valve ring 7.362cm, maximum length of leaflet anterior1.924cm and 1.104cm by dissection method. (Table 1)

Figure 3

Table 1 (Average of all values)

Out of 50 hearts annular circumference is maximum in range of 7-7.99cm (40%) followed by 8-8.99(30%), 9-9.99(18%) and lowest in range of 10-10.99cm (6%) and 6-6.99cm (6%). (Table 2)

Figure 4

Table 2 (Annular circumference)

In case of length of free edge of valve curtain the length was maximum in range 6-6.99 (36%) followed by 8-8.99(28%) 7-7.99(26%),5-5.99(6%) lowest in range 9-9.99(4%).(Table3)

Figure 5

Column chart 1

Figure 6

Table 3 (Length of free edge of valve curtain)

Length of leaflet (from free to attached margin) was maximum in range of 1-1.99 for both anterior (60%) and posterior (74%), minimum in range 2-2.99 for anterior (40%) and 0-0.99 for posterior (26%). (Table 4)

Figure 7

Column chart 2

Figure 8

Table 4 (Length of leaflet)

Therefore from above it is observed that average annular circumference was 8.248cm and maximum in range of 7-7.99cm, length of free edge of valve curtain the length was maximum in range 6-6.99cm, Length of leaflet was maximum in range of 1-1.99cm for both anterior and posterior leaflets.

Figure 9

Column chart 3

Figure 10

Figure 3: Ventricular aspect of the mitral valve.

Figure 11

Figure 4: Splayed open mitral valve (atrial aspect)

Discussion

Mitral valve Anatomy described by many textbooks previously but lack of any data in relation with valve measurements.

Walmsley T. ¹¹ in 1929 first mentioned mitral valve Measurements. Later on by Rusted, I. E et al ¹² in 1952.

Observations regarding mitral valve show variable findings depending upon method used. In 2D Echocardiography method mitral leaflets and their annular attachments were recorded during the cardiac cycle, the present study done by dissection method mitral leaflet and annular attachment demonstrated in cadaveric hearts.

Table 1 shows the measurements of mitral valve reported and the earlier studies compared with the present study Table no. 5

Figure 12

Table no. 5

The circumference of the mitral valve in this study (Table 5) corresponds with values reported by Tetsuro Sakai, MD ⁴ (1999) by dissection method and JA Ormiston ⁵ (1981) by 2D echocardiographic method if we consider range given by them but significantly lesser than findings of Louis A. Du Plessis ² (1964) (fresh hearts) and R. C. Brock ⁸ (1952); Bulkley & Roberts ¹⁴ (1975); Rusted, I. E ¹² (1952)(both male and female); Chiechi et al ¹³ (1956) (both male and female); Mcalpine ¹⁵ (1975) using dissection method.

However Length of free edge of valve curtain 7.362cm reported in present study is lower than Louis A. Du Plessis ² (1964); 9.1cm.

In present study Maximum length of leaflet (attached margin to free margin) of Anterior leaflet 1.924cm (Table 5) was observed it was less as compared to Louis A. DuPlessis ² (1964); E. W. T. Morris ³ (1960); Rusted, I. E ¹² (1952); by dissection method but it was slightly more than range given by Walmsley T. ¹¹ (1929); R. C. Brock ⁸ 1952.

Posterior leaflet 1.104cm (Table 5) was observed and it was less as compared to Louis A. Du Plessis ² (1964); E. W. T. Morris ³ (1960); Rusted, I. E ¹² (1952) but it falls in range given by Walmsley, T. ¹¹ (1929); R. C. Brock ⁸ (1952).

In resent study highest measurements falls in range of Annular circumference 7-7.99cm (Table 2) 40%; length of free edge of valve curtain the length was maximum in range 6-6.99 (Table3) 36%; length of leaflet (from free to attached margin) was maximum in range of 1-1.99 for both anterior 60% and posterior 74%(Table 4).

Thus in present study annular circumference was observed to be less than previous observations given by different authors. We observed additional separate measurement of individual leaflets. Length of free edge of valve curtain was also observed less. Maximum length of leaflet (attached margin to free margin) was observed to be in anterior leaflet in range given by others and posterior leaflet also without any difference.

Robert walmsley ⁶ in 1978 stated that fibrous mitral ring in human heart is incomplete anteriorly along attachment of the mitral aortic cusp. The posterior part of the ring is interposed between myocardium of left atrium and left ventricle and corresponds to region of attachment of mural (posterior) cusp of mitral valve. Posterior part help in change of circumference of ring during cardiac cycle. He differentiate two zones of mitral leaflets an appositional and a free basal non-appositional zone. There is no any data available in this study related with mitral valve but mainly he compares mitral valves of different animals. In our study cadavers are used so we get here idea about change in circumference during cardiac cycle.

Louis A. Du Plessis and Paul Marchand ² in 1964 stated that data of the dimensions of the valve, which may be of interest to anatomists and surgeons. Normal measurements of the component parts of the mitral valve will help the surgeon to assess the exact mechanical reason for valve insufficiency.

J. C. Vander spuy ¹⁶ in 1964 find out that the detailed anatomical and functional features are essential in the manufacture of an entirely anatomical whole mitral valve from autogenous tissues. We can use data assessed by us for manufacturing of these valves.

R. T. Brownlee and A. K. Yates ¹⁷ in 1971 their work design valve from Autologous fascia lata. Great horizontal mobility of the mitral annulus plays a considerable role in its function. The mitral annulus is not flat but oblique in the antero-posterior direction. It would, therefore, seem desirable to eliminate the wide, round, flat, and rigid sewing ring integral to all presently used mitral valve replacements. If the valve leaflets could be sewn directly to the mitral annulus, 1 cm or more effective flow orifice diameter would be gained over those valve replacement techniques employing a rigid sewing ring. Furthermore, a bicuspid valve whose cusp tip orifice diameter exceeds that of the inlet diameter would eliminate stenotic turbulent flow during diastole.

The variation in (racial) circumference of mitral valve, length of leaflet and length of free edge of valve curtain can be explained by study of J Mayet et al ¹⁸ in 1994 while study of hypertensive patients in black and white population he noted that there may be primary cardiovascular differences between the races and it may be an increase in peripheral resistance or left ventricular mass that makes black subjects more likely to develop hypertension. As our study mainly includes hearts of Indian origin therefore we can compare values by others, which are probably other races. So we can say difference in measurements may be due to this racial difference, which need detailed study.

Hinderliter AL et al ¹⁹ in 1992 in their study of Racial differences in cardiac structure and function were evaluated in black and white healthy young adults using M-mode echocardiography. Ventricular wall thickness was significantly greater in black than in white subjects. This difference was found in both men and women. Black subjects also had a higher resting systemic vascular resistance index and lower resting cardiac index. These results suggest that racial differences in LV structure and systemic hemodynamics exist even in patients without sustained hypertension. This will support our opinion of racial difference.

Paolo Pattoneris ²⁰ in 2007 study evaluates racial differences in left ventricular (LV) structure and performance by tissue Doppler echocardiography and myocardial performance index (MPI). In black to white young males no differences were found in LV diameters, volumes, mass, and hemodynamic measurements septal and posterior wall thicknesses were significantly increased in black. MPI was significantly higher in black findings suggest that racial differences in LV performance exist in the systolic function.

A. Wessels and et al ²¹ in 1996 his embryological study describes formation of mitral valve and leaflets during 42 to 51 days left lateral cushion contributes to the formation of the mural leaflet of the mitral valve the developing leaflets of the atrioventricular valves are partly mesenchymal due to the delamination of the valvar tissue from the ventricular muscle mass and partly muscular in composition. In 3 ^rd months of developing leaflets consist of ventricular myocytes and partly of cushion-derived mesenchymal cells. At the end of the 3 ^rd month few myocardial cells present within the leaflets of the atrioventricular valves. This needs further study to correlate difference in embryological development of mitral valve and circumference, length of leaflet, length of free edge of leaflet. So such mitral valve development may be a reason.

Summary

The mitral valve descriptions and measurements are based upon observations made during dissections of human cadavers in 50 hearts by dissection method.

In present study we get average measurements of length of valve ring (circumference) 8.248cm, Length of free edge of valve ring 7.362cm, maximum length of leaflet anterior1.924cm and 1.104cm by dissection method.

Annular circumference is maximum in range of 7-7.99cm (40%) followed by 8-8.99(30%), 9-9.99(18%) and lowest in range of 10-10.99cm (6%) and 6-6.99cm (6%).

Length of free edge of valve curtain the length was maximum in range 6-6.99 (36%) followed by 8-8.99(28%) 7-7.99(26%),5-5.99(6%) lowest in range 9-9.99(4%).

Length of leaflet was maximum in range of 1-1.99 for both anterior (60%) and posterior (74%), minimum in range 2-2.99 for anterior (40%) and 0-0.99 for posterior (26%).

A co-relation between measurements of mitral valve and racial difference has been attempted in present study.

We find less circumference of mitral valve in hearts as compared to other studies.

We present data of the dimensions of mitral valve, which may be of interest to anatomists and surgeons. Knowledge of normal measurements of the component parts of the valve will help the surgeon during operation to assess the exact mechanical reason for valve insufficiency. Thus measurements of mitral valve and its associate structures are essential.