Morphology and Morphometry of Aortic Valve in Humans and Porcines – A Comparative Study

Abstract

Background:

The aortic valve is a semilunar valve with three leaflets that are in the left ventricle's outflow tract and only permits unidirectional blood flow away from the ventricle. The valve leaflet can tolerate extremely high mechanical and hemodynamic forces resulting from the great complexity and complicated cellular and molecular functions.

Aims:

The aim of the study is to provide an add-on to the understanding of the morphological and morphometrical aspects of human and porcine aortic heart valves on comparative grounds so that they can be used as a guide in the construction of three-dimensional (3D)-printed mechanical valve.

Materials and Methods:

Twenty swine and twenty human hearts were compared and examined in this investigation. The porcine and human hearts weighing in between 300 g and 450 g were considered, and any variation from the normal and any mechanical damage rendered during procurement were all excluded from the study.

Results:

The length of the attached margin of the right coronary cusp, left coronary cusp, and noncoronary cusp of human and porcine were 45.15 mm, 36.47 mm, and 41.53 mm and 36.55 mm, 43.14 mm, and 36.10 mm, respectively. The length of the free margin and the height of the cusps from nadir to the sinotubular junction and the effective height of the cusp from nadir to the free margin of the cusps of human and porcine have been compared.

Conclusion:

The human and swine aortic valves share morphological and morphometrical characteristics, which can be used to create 3D valves and tissue engineering procedures with greater biocompatibility and biofunctionality.

Introduction

The aortic valve is a semilunar valve with three leaflets that are in the left ventricle's outflow tract and only permits unidirectional blood flow away from the ventricle. The valve leaflet can tolerate extremely high mechanical and hemodynamic forces resulting from the great complexity and complicated cellular and molecular functions.^[1],[2]

Mechanical heart valves are used in medical fields for approximately three decades. The ball and cage, bileaflet, and tilting disc are just a handful of the 70 distinct types of mechanical heart valves that have been used currently.^[3],[4] Allograft or xenograft bioprosthetic valves which made from bovine or porcine tissue are both options. The most often used xenograft tissues come from the pericardial valves of cows and pigs. Restoring and maintaining the function of living tissues is the focus of the field of tissue engineering in regenerative medicine. Heart valves which made through tissue engineering are designed to be nonthrombogenic and infection resistant. It is possible that the designed valve will be able to reconstruct and repair itself as the patient ages thanks to developments in material science and culture techniques.^[5],[6]

This study aims at providing an add-on to the understanding of the morphological and morphometrical aspects of human and porcine aortic heart valves on comparative grounds so that they can be used as a guide in the construction of three-dimensional (3D)-printed mechanical valve and in tissue engineering techniques.

Materials and Methods

For this investigation, 20 swine and 20 human hearts were compared and examined. The study was conducted in the Department of Anatomy of a Tertiary Care Teaching Institute, after receiving approval from the human and animal ethical committees with reference number CSP-MED/13/AUG/08/63. Vernier calliper, blotting paper, surgical silk thread, and scissors were the supplies utilized. Following sacrifice, porcine hearts were obtained from the slaughterhouse and preserved in 10% formal saline solution. The institution obtained the formalin-fixed human heart specimens from the embalmed cadavers utilized for undergraduate instruction.

The porcine and human hearts weighing in between 300 g and 450 g were considered, and any variation from the normal and any mechanical damage rendered during procurement were all excluded from the study. The circumference of the aortic valve was measured using silk thread at the sinotubular junction which is observed as a ridge above the aortic valve cusps. Then, the valve was opened between the left coronary cusp and the noncoronary cusp and extended further till the ventricular junction. The attached margin and the free margins were measured using silk thread along its margin. The height of the ostia was calculated using vernier calipers from the inner aspect of the attached margin to the opening of the coronary ostia. The parameters such as the circumference of the orifice at the sinotubular junction, length of the attached margin and free margin of the leaflet cusps, effective height of the cusp, height of the cusp from nadir to the point in the circumference, location of the coronary ostia from the bottom of the cusp, and diameter of the ostium were assessed in this study. Since the hearts were preserved in formalin, there were possibilities for shrinkage artifacts so the measurements were made to the nearest millimeter in metric scale.

Statistical analysis

Student's t-tests and independent sample tests were used to compare all of the dependent variables and statistically analyzed using “IBM Corp.'s IBM SPSS Statistics for Windows, Version 24.0, IBM Corp., Armonk, New York.

Results

In the present study, the mean aortic valve circumference measured at the sinotubular junction was 70.23 mm in human's cadaveric hearts and 61.69 mm in the porcine heart valves [Figure 1]. The basal attachments of the aortic leaflets are defined with three semilunar lines with crown-like formation and each aortic leaflet, due to its semilunar attachment; it is characterized by a nadir positioned in the most distal portion. The length of the attached margin of the right coronary cusp, left coronary cusp, and noncoronary cusp of human and porcine was 45.15 mm, 36.47 mm, and 41.53 mm and 36.55 mm, 43.14 mm, and 36.10 mm, respectively. The length of the free margin and the height of the cusps from nadir to the sinotubular junction and the effective height of the cusp from nadir to the free margin of the cusps of human and porcine have been compared and tabulated in [Table 1] and [Table 2]. The average height measured from the base of the center of the leaflet to its free edge of the right coronary cusp, left coronary cusp, and noncoronary cusp of human aortic valve and porcine aortic valves were 16.22 mm, 15.84 mm; 16.02 mm, 14.04 mm; and, 14.2 mm, 14.10 mm, respectively.

Figure 1

The opened ventricles with aortic valve (red arrow indicates the aortic valve)

Table 1

The mean value of the attached margin and free margin of the aortic valve (human and porcine)

Table 2

The mean height of the cusp and the height at which the aortic ostia is located (in human and porcine)

Discussion

More than 200,000 heart valve replacements are performed on average globally, which is presumed to increase to 850,000 in two decades. Implanting bioprosthetic heart valves are increasingly the preferred treatment for patients who require heart valve replacement.^[7] Porcine heart tissues have gained importance as an animal model in cardiovascular research through the similarity of their coronary circulation, hemodynamic values, size, and the relative convenience in implementing methods.^[8] The typical height calculated from the leaflet's base to the free edge of the right coronary cusp and left coronary cusp and noncoronary cusp of human aortic valve and porcine aortic valves were 16.22 mm, 15.84 mm; 16.02 mm, 14.04 mm; and 14.2 mm, 14.10 mm, respectively, and the results of the human aortic valve correlated with Piazza et al.,^[9] where the right coronary, noncoronary, and left coronary cusps were 14.1 mm, 14.1 mm, and 14.2 mm, respectively.

Under some circumstances, the acute initial angle, and the high position of the coronary ostium above the sinotubular junction were thought to be risk factors for an acute coronary attack.^[10] The average distance between the basal attachment of the respective leaflets and the ostium's of the right and left coronary arteries in human aortic valves and in porcine aortic valve were 11.5 mm, 5.16 mm and 10.6 mm, 6.13 mm, respectively, and this porcine aortic valve coronary ostia has high significance in coronary artery perfusion due to its low-lying nature and the human aortic ostia values correlated with Nasr and El Tahlawi.^[11] The mean diameter of the right coronary ostium and left coronary ostium in humans and porcines was 2.6 mm, 2.7 mm and 2.5 mm, 2.6 mm, respectively, and correlated with Jyoti and Vaishali.^[12] The limitation of the study is that histochemical analysis was not done which would have rendered a better understanding of the xenograft as bioprosthesis and this would be incorporated as the future scope of the study.

Conclusion

The human and swine aortic valves share morphological and morphometrical characteristics, which can be used to create 3D valves and tissue engineering procedures with greater biocompatibility and biofunctionality.