|Year : 2015 | Volume
| Issue : 2 | Page : 39-42
Variations in the Shape of Atrioventricular Cusps
Parmatma P Mishra1, Manvikar Purushottam Rao1, Vaishali Paranjape2, Jyoti P Kulkarni2
1 Department of Anatomy, Integral Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
2 Department of Anatomy, Dr. D.Y. Patil Medial College, Pimpri, Pune, Mahrashtra, India
|Date of Web Publication||16-Jun-2015|
Dr. Manvikar Purushottam Rao
Department of Anatomy, Padmashree Dr. D. Y. Patil Medical College, Pimpri, Pune - 411 018, Maharashtra
Source of Support: None, Conflict of Interest: None
Introduction: The right and the left atria of the human heart communicate with the right and left ventricle through the respective orifices. These orifices are guarded by atrioventricular valves. The right atrioventricular valve is called as tricuspid valve because it has three cusps. While the left atrioventricular valve referred to as mitral valve, or bicuspid valve because it has two cusps. Presence of one or multiple accessory leaflets in the valves and absence of one or multiple leaflets in the valves is known. Data regarding shape of cusps or leaflets on cadaveric study in literature is limited. Hence, an attempt is made to study variation in the shape of leaflets of valves and the shape of accessory leaflets when seen. Shape of leaflets play a key role in designing the prototype of valves for valve replacement. Materials and Methods: A total of 120 cadaveric human hearts were dissected in the Department of Anatomy at Padmashree Dr. D. Y. Patil Medical College, Pimpri, Pune. Data were also collected from Anatomy Departments of other Medical Colleges. Variations in the shape of leaflets of the mitral and tricuspid valves were noted. Presence of accessory leaflets and their shape was also recorded. Results: Leaflets of both the valves were predominantly triangular in shape. The shape of accessory leaflets was also triangular. However, the leaflets did show variations in shape such as rectangular, D shape, semicircular. The incidence and significance of the variations in the shapes are discussed in the study. Conclusion: Atrioventricular valve leaflets show numerous variations in the shapes. Such diversity in the shapes of valves is of immense value in designing prototype of mitral and tricuspid valve prosthesis. However, this is a study done by dissection on static hearts. In life, there may be subtle changes in the shape of valves. The study should be extended further by doing observations on two-dimensional echo and transesophageal echocardiography.
Keywords: Accessory valve, atrioventricular valve, cusp, leaflet, mitral valve, tricuspid valve
|How to cite this article:|
Mishra PP, Rao MP, Paranjape V, Kulkarni JP. Variations in the Shape of Atrioventricular Cusps. Heart India 2015;3:39-42
| Introduction|| |
Huang Ti in 2600 B.C.  wrote in his "Canon of Medicine" that "the heart is a king, who rules over all the organs of the body; the lungs are his executives, who carry out his orders." Heart is a compact, hollow, fibromuscular organ located in the middle mediastinum consisting of four chambers. Right atrium opens into right ventricle through the tricuspid valve, while left atrium into left ventricle through the mitral (bicuspid) valve. Both the above valves are formed of valvular complex which includes circumference of the opening, chordae tendinae, and papillary muscles. One end of chordae tendinae is attached to the cusps and the other end with papillary muscles. Morphologically cusps (leaflets) are of 'D' shape or rectangular shape. Bicuspid valve also named as mitral valve because of its resemblance to bishop's cap (mitre) has two cusps named as anterior and posterior.  Valve replacement is recommended in severe mitral insufficiency, atrial fibrillation, pulmonary hypertension, and other similar conditions. Two types of prosthetic valves are available namely mechanical valves and tissue valves (Xenograft). Mechanical prosthesis is highly durable but requires lifelong anticoagulant therapy whereas tissue valve are less durable more natural and less thrombogenic. Approximately, eighty varieties of model prosthesis are available in the market of which Ball - Valves, St. Jude's medical bi-leaflet, Star - Edward ball case, Bijor Shely titimg disk  are well known. 120 cadaveric hearts fixed in 10% formalin were included in the study. The aim was to study the variation in the shape of tricuspid and mitral valve, note the shape of accessory cusp if present, and note the absence of cusp.
| Materials and Methods|| |
Study was conducted in Department of Anatomy, Padmashree Dr. D.Y. Patil Medical College, Pimpri, Pune. A total of 120 formalin fixed hearts were dissected and data were collected. Normal adult human hearts without any malformations or pathology were included in the study. Heart specimens so obtained were preserved in 10% formalin. Specimens were numbered and valves were dissected out.
Dissection of valves
Tricuspid and mitral valves were dissected out by following method:
Removal of tricuspid valve
The incision to expose tricuspid valve was taken from the lower end of right border of heart, then along the upper margin of the coronary sulcus, curving upwards toward right auricle till root of superior vena cava. The flap so created was turned to left and right atrial chamber was opened. After cleaning the interior of the chamber thoroughly, right atrioventricular valve complex was observed. Tricuspid valve, A-V valve annulus, cusps, and chordae were examined. A second incision was taken around the outer margin of annulus. Thus, tricuspid valve with annulus was removed [Figure 1]a and b.
|Figure 1: (a) Incision for removal of tricuspid valve. (b) Normal tricuspid valve|
Click here to view
Removal of mitral valve
First, incision was taken from the middle left atrium, passing along the lower margin of left coronary sulcus till tip of auricle. Second, incision was taken along the outer margin of the annulus of mitral valve.
Third incision extended along the left border of the heart, till its apex, curved along the left of anterior interventricular groove till the left coronary sulcus. Flap so obtained was turned to right, and left ventricular chamber was entered. Finally, papillary muscles of both ventricles were divided near its wall attachments and the cusps were freed [Figure 2]a and b.
|Figure 2: (a) Incision to remove mitral valve. (b) Mitral valve with annulus|
Click here to view
| Results|| |
Shapes of cusps seen were triangular [Figure 3]a and [Figure 5]a, 'D' shape [Figure 3]b, and rectangular [Figure 3]c.
|Figure 3: (a) Triangular anterior and posterior cusp of mitral valve. (b) "D" shaped anterior cusp of mitral valve. (c) Rectangular posterior cusp of mitral valve|
Click here to view
Cusps of the mitral valve were identified as anterior and posterior according to their location. Various shapes have been tabulated as below [Table 1].
It was seen that in both anterior and posterior cusps the most frequent shape encountered was triangular [Figure 3]a. It was seen in 75-80% cases in both anterior and posterior cusps put together. 'D' shape was not seen in posterior cusps. However, 17.5% of anterior cusps were 'D' shape [Figure 3]b. Rectangular shape was seen in 1.67% of anterior cusps and 24.17% of posterior cusps [Figure 3]c. In 3 cases, the mitral valve showed accessory leaflet [Figure 4]. All of them were triangular in shape. No accessory cusps were seen in the mitral valve.
|Figure 5: (a) Triangular anterior, posterior and septal cusp of tricuspid valve. (b) Rectangular posterior cusp of tricuspid valve. (c) Missing cusp in tricuspid valve|
Click here to view
Cusps were identified according to the location as per standard text book description and shapes were observed and tabulated [Table 2].
Cumulatively, shape of all three cusps were predominantly triangular ranging from 95% to 97% of all hearts [Figure 5]a. However, there were missing posterior (5.83%) and septal (0.83%) cusps [Figure 5]c.Very few hearts showed D shaped cusps, that is, 5% of anterior cusps, 1.67% of posterior cusps, and 0.83% of septal cusps. None of the anterior and posterior cusps had rectangular shape but for a solitary septal cusp (0.83%) [Figure 5]b.
Accessory cusps were found in 51 cases of the tricuspid valve. All were of triangular in shape [Table 3] and [Figure 6]a-d.
|Figure 6: (a) Tricuspid valve with one accessory cusp. (b) Tricuspid valve with two accessory cusps (Xt1,Xt2). (c) Tricuspid valve with three accessory cusps (Xt.1,Xt.2,Xt.3). (d) Tricuspid valve with four accessory cusps ( Xt.1, Xt.2,Xt.3, Xt.4)|
Click here to view
Total number of hearts which showed accessory cusps was 51 (42.5%). Number of accessory cusps ranged from 1 to 4.
| Discussion|| |
During the development of mesenchymal cells of cardiac tube around the right and left atrioventricular canals proliferate to form collars of endocardial cushions. The ventricular surface of the proliferated mass is excavated to form the atrioventricular valves which are attached to the ventricular wall by the trabeculae. 
Leaflet's differ in their shape.  The shape of cusps of tricuspid valve are more variable than that of the mitral valve.  Various shape of cusps like rectangular,  semicircular (D shape)  or triangular have been reported in the literature.
In present study (2011), maximum number of cusps that is, 80.33% were found to be triangular in shape while D shape was seen in 17.5% of cases and rectangular cusps were seen in 1.67% of cases. These findings concurred with that of Walmsley. 
Posterior cusp of the mitral valve was found to be more rectangular in a study done by Morris,  Walmsley  and Bezerra et al.  However, in present study (2011), the shape of maximum number of posterior cusps of mitral valve that is, 75.83% was found to be triangular, rest that is, 24.17% was rectangular in shape. D shape cusp was not found in this study. All accessory cusps were triangular in shape.
Anterior cusp of the tricuspid valve was found to be triangular in shape in 100% of cases in a study done by Motabagani 2006-07.  In the present study (2011), maximum number that is, 95% of cusps were triangular in shape.
Posterior cusp of the tricuspid valve was found to be triangular in shape in a study done by Motabagani 2006-07.  In present study (2011) maximum number of cases that is, 92.5% of cusps were triangular in shape. Most common shape of cusps was triangular similar to other studies. However in 7 cases posterior cusp was missing.
The septal cusp of tricuspid valve was found to be semicircular in a study done by Motabagani 2006-07.  However, in the present study (2011), maximum number of cases that is, 97.5% of cusps were triangular in shape. One cusp was found to be rectangular in shape and one was D shaped. The findings in the present study differed from that of Motabagani. Triangular was more common than semicircular shape. All accessory cusps were triangular in shape.
Variation in the shape of the cusp may result in incomplete closure of the valve, leading to regurgitation. Knowledge of variation in the shape of cusps will serve as a guideline to the cardiac surgeons. It will also help in designing the valve prosthesis.
The presence of an accessory cusp may lead to the obstruction of atrioventricular outflow tract. The knowledge of accessory or missing cusp in atrioventricular valves is also necessary for cardiac surgeons. The results of the study are believed to help immensely the cardiothoracic surgeons. Such diversity in the shapes of valves is of immense value in designing prototype of mitral and tricuspid valve prosthesis.
| Conclusion|| |
In case of mitral valve, the most common shape of the cusp was triangular (80.33%). D shape cusp was seen in few valves (17.5%). Regarding shape of posterior cusp 75.83% were triangular and 24.17% it was rectangular. D shape was seen in the posterior cusp of tricuspid valve. All the accessory cusps of mitral valve were triangular in shape.
In case of tricuspid valve, almost all anterior cusps (95%) had triangular shape while rest (5%) had a rectangular shape. The shape of posterior cusp was triangular in 92.5% of hearts while in rest it was rectangular. Posterior cusp did not show 'D' shape in the present study. Posterior cusp was absent in 5.83% of cases. The most common shape of the septal cusp was triangular (97.5%) with occasional rectangular (0.83%) and 'D' shape (0.83%). In 1 case, septal cusp was missing. The number of accessory cusps differed and all the accessory cusps were found to be triangular in shape.
Study of variations of shapes of atrioventricular valves is important for cardio surgeons, interventional radiologists, and it will be of immense help in manufacturing of artificial valves as well.
The limitation of this study is that the observations are based on cadaveric dissection on static hearts unlike dynamic hearts as we see in two-dimensional or transesophageal echocardiography. In vivo there may be subtle difference in the shapes and measurements of valves.
| References|| |
Moore KL, Dalley AF. Clinically Oriented Anatomy. 5 th
ed. Baltimore: Lippincott Williams & Wilkins; 2006. p. 152.
Galloway AC. Acquired heart disease. In: Brunicardi FC, Andersen DK, Billiar TR, Dunn DL, Hunter JG, Mathews JB, et al
., editors. Schwartz′s Principles of Surgery/Specific Considerations. 8 th
ed. Mc-Graw Hill, New York; 2004. p. 661-2.
Dutta AK. Essentials of Human Embryology. 5 th
ed., Ch. 15. Current Publishers, Kolkata; 2005. p. 176.
Duplessis LA, Marchand P. The Anatomy of the mitral valve and its associated structures. Thorax 1964;19:221-7.
McMinn RM. Thorax. Last′s Anatomy. 9 th
ed. Reprinted in 1994. Churchil Livingstone: Edinburgh; 1995. p. 267-71.
Fullerton DA. Acquired heart diseases: Valvular. In: Townsend CM, editor. Sabiston Textbook of Surgery. 17 th
ed., Vol. 2. Elsevier Saunders: Philadelphia 2005. p. 1884-5.
Walmsley R. Anatomy of human mitral valve in adult cadaver and comparative anatomy of the valve. Br Heart J 1978;40:351-66.
Morris EW. Some features of the mitral valve. Thorax 1960;15:70-3.
Bezerra AJ, DiDio LJ, Prates JC. Variations of the area and shape of the left atrioventricular valve and its cusps and leaflets. Surg Radiol Anat 1994;16:277-80.
Motabagani MA. Comparative anatomical, morphometric and histological studies of the tricuspid valve complex in human and some mammalian hearts, Indmedica. J Anat Soc India 2006;55:1-23.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3]