Aortic valve opening and closure: the clover dynamics.

BACKGROUND: Systolic aortic root expansion is reported to facilitate valve opening, but the precise dynamics remain unknown. A sonometric study with a high data sampling rate (200 to 800 Hz) was conducted in an acute ovine model to better understand the timing, mechanisms, and shape of aortic valve opening and closure. METHODS: Eighteen piezoelectric crystals were implanted in 8 sheep at each annular base, commissures, sinus of Valsalva, sinotubular junction, nodulus of Arantius, and ascending aorta (AA). Geometric changes were time related to pressures and flows. RESULTS: The aortic root was hemodynamically divided into left ventricular (LV) and aortic compartments situated, respectively, below and above the leaflets. During isovolumetric contraction (IVC), aortic root expansion started in the LV compartment, most likely due to volume redistribution in the LV outflow tract below the leaflets. This expansion initiated leaflet separation prior to ejection (2.1%±0.5% of total opening area). Aortic compartment expansion was delayed toward the end of IVC, likely related to volume redistribution above the leaflets due to accelerating aortic backflow toward the aortic valve and coronary flow reduction due to myocardial contraction. Maximum valve opening during the first third of ejection acquired a truncated cone shape [leaflet free edge area smaller than annular base area (-41.5%±5.5%)]. The distal orifice became clover shaped because the leaflet free edge area is larger than the commissural area by 16.3%±2.0%. CONCLUSIONS: Aortic valve opening is initiated prior to ejection related to delicate balance between LV, aortic root, and coronary dynamics. It is clover shaped at maximum opening in systole. A better understanding of these mechanisms should stimulate more physiological surgical approaches of valve repair and replacement.

Transection of anterior mitral basal stay chords alters left ventricular outflow dynamics and wall shear stress.

BACKGROUND AND AIM OF THE STUDY: Anterior mitral basal stay chords are relocated to correct prolapse of the anterior mitral leaflet (AML); it has also been suggested that their transection might be used to treat functional ischemic mitral regurgitation. The study aim was to clarify the effect of stay chord transection (SCT) on the hemodynamic aspects of left ventricular outflow. METHODS: Two three-dimensional left ventricular models including the left ventricular outflow tract and saddle-shaped mitral valve before and after SCT were constructed. After SCT, the AML was specified to be more concave and the aortomitral angle to be narrower than before SCT. Time-dependent turbulent flow in a flow range of 10 to 28 l/min during rapid ejection was simulated using the commercial software, FLUENT. RESULTS: Left ventricular outflow before SCT was streamlined along the AML throughout rapid ejection. After SCT, this flow was redirected in the vicinity of the AML, thereby creating a zone of persistent low-momentum recirculation associated with additional energy loss. Consequently, the axial forward flow delivered into the aorta after SCT was diminished. The high wall shear stress, which was concentrated at the fibrous trigones before SCT, was redistributed along the intertrigonal distance after SCT. CONCLUSION: The stay chords, which maintain the natural profile of the AML, are essential to streamline left ventricular outflow, facilitate flow delivery into the aorta, minimize dissipation of potential energy, and to create an optimum wall shear stress pattern that conforms to the fibrous trigones. Transection of the stay chords compromises local hemodynamics, resulting in greater energy loss and unfavorable wall shear stress distribution. The study results emphasize the importance of preserving stay chord function in mitral valve surgeries.

Truly stentless molded autologous pericardial aortic valve prosthesis with single point attached commissures in a sheep model.

OBJECTIVE: Aortic valve cusp extension and free-hand aortic valve replacement with autologous pericardium has been described. The long-term results were shown to be comparable with commercially available aortic bioprostheses. Nevertheless the relatively demanding surgical technique could not find wide acceptance. We developed a new design of a molded aortic valve, fashioned from autologous pericardium, treated briefly with glutaraldehyde, and simplified the implantation technique using single point attached commissures (SPAC). METHODS: Molded autologous valve prostheses were implanted in the subcoronary aortic position in 10 sheep with the commissures connected to the aortic wall at three single commissural points (SPAC). The prosthesis mean size was 21.6+/-1.3 mm and the construction time (excluding 10 min glutaraldehyde treatment) was 6.2+/-1.2 min. Cardiopulmonary bypass and cross-clamp time was 111.1+/-12.4 min and 75.0+/-16.3 min, respectively. Six sheep were euthanized after 201.2+/-10.3 days (6 months) and four sheep were euthanized after 330.8+/-6.5 days (11 months) postoperatively. RESULTS: In all sheep, the valve was immediately competent. At sacrifice, SPAC has proven to be well anchored to the aortic wall and the pericardial valve to be pliable in all cases. The maximum transvalvular gradient after cardiopulmonary bypass and at sacrifice was 3.7+/-2.2 mmHg and 10.6+/-5.2 mmHg, respectively. CONCLUSIONS: This new truly stentless molded autologous aortic valve with simplified implantation technique (SPAC) makes a reliable implantation in a standard timeframe possible. The simplicity of construction, low cost and absent need for anticoagulation of this molded autologous aortic bioprosthesis offers an attractive alternative and not only for patients in the developing world.

Autologous pericardial pulmonary conduit with single point attached commissures in a sheep model.

OBJECTIVE: For the surgical treatment of congenital heart disease and in Ross procedure a valved conduit is frequently required. Since homografts are not readily available in every country, a reliable alternative is needed. We developed a novel technique to construct a valved pulmonary conduit with single point attached commissures (SPAC) in a simple and fast way from a small strip of autologous pericardium, molded and briefly treated with glutaraldehyde. METHODS: Autologous pericardial pulmonary conduit was constructed intraoperatively and implanted in pulmonary position in a beating heart in six sheep. The prosthesis size was 31 mm for all sheep and the construction time (including 10 min glutaraldehyde treatment) was 19.0+/-3.3 min. Implantation time and cardiopulmonary by-pass was 27.3+/-5.4 min and 40.5+/-7.7 min, respectively. The sheep were euthanized after 6 months (222.7+/-5.8 days) postoperatively. RESULTS: In all sheep, the autologous pericardial valve was immediately competent. At sacrifice, the pericardial valve was pliable and competent in all cases with SPAC well anchored to the pericardial conduit wall. The maximum transvalvular gradient at implant and at sacrifice was 3.3+/-2.8 mmHg and 3.3+/-2.0 mmHg, respectively. CONCLUSIONS: This novel autologous pericardial pulmonary conduit with SPAC can be reliably produced in a very short time intraoperatively before cardiopulmonary by-pass. The simplicity of construction, biocompatibility and freedom of stenosis or thrombosis makes this autologous pulmonary conduit especially useful for patients at locations where homografts are not readily available.

Further information from a sonometric study of the normal tricuspid valve annulus in sheep: geometric changes during the cardiac cycle.

BACKGROUND AND AIM OF THE STUDY: In a previous sono-metric study, changes were described that occurred in the normal tricuspid valve during the cardiac cycle. However, the wealth of data available suggested the need for reporting further findings that should contribute to a better understanding of the dynamics of the tricuspid valve. METHODS: Thirteen sonomicrometry transducers were placed in the hearts of each of seven sheep. Six transducers were placed in the tricuspid annulus (TA), at the base of each leaflet, and at each commissure; three at the tips of the papillary muscles (PMs); three in the free edges of the leaflets; and one transducer was placed at the apex. Distances between transducers, pulmonary and right ventricular pressures, and pulmonary flow were recorded simultaneously. RESULTS: The TA area underwent two major contractions and expansions during the cardiac cycle, reaching its maximum during isovolumic relaxation and its minimum in diastole. The TA height-to-width ratio changed from 8.4 +/- 1.9% to 15.3 +/- 4.2%. The leaflets began to open before end-systole. By the end of isovolumic relaxation, the leaflets had completed 54.1 +/- 13.4% of their opening. The PM and TA planes were not parallel, but were offset by 11.5 +/- 1.9 degrees to 17.8 +/- 2.1 degrees. The PM rotated 6.9 +/- 0.9 degrees with respect to the TA, with 3.1 +/- 1.1 degrees of the rotation occurring during ejection. CONCLUSION: The tricuspid valve is not a passive structure but rather forms a dynamic part of the right ventricle. Its orifice area changes not only due to the contraction and expansion of its perimeter but also to changes in its saddle shape. Leaflet opening and closure is not simply a response to pressure. The PMs rotate in relation to the TA. These data should impact upon the diagnosis and surgery of functional tricuspid regurgitation.

Dimensional ratios of normal mitral valve structures: a tool for determining the degree of geometric distortion in individual patients.

BACKGROUND AND AIM OF THE STUDY: One objective of mitral valve repair is to restore the distorted mitral apparatus geometry to its normal dimensions specific for each patient. Because all dimensions of the normal aortic and mitral valves should be related, it was hypothesized that, in the presence of a normal aortic annulus, it would be possible to determine the dimensions of the structures needed for mitral valve repair. METHODS: In seven sheep, sonometric ultrasound crystals were implanted at the left and right trigones (T1, T2), lateral annulus (P1, P2), and the tips of the anterior and posterior papillary muscles (Ml, M2). The distances T1-T2, M1-M2, T1-M1, T2-M2, P1-P2, P1-M1, and P2-M2 were measured at end-systole (ES), end-diastole (ED), and maximum and minimum lengths. Using these measured distances, fractional relationships were computed, and the average fractional relationship was used to determine a 'calculated' distance. The 'measured' and 'calculated' distances were then compared using a paired t-test. RESULTS: All fractional relationships were close to 1, with ED 1.00 +/- 0.21, ES 0.99 +/- 0.19, maximum length 0.99 +/- 0.19, and minimum length 0.94 +/- 0.21. The intertrigonal distance (T1-T2) expanded by 4.19 +/- 3.81%, and the transverse diameter (P1-P2) contracted by -6.15 +/- 3.69% from ED to ES. The interpapillary muscle distance (M1-M2) contracted -22.3 +/- 6.5%. The two distances with the least amount of contraction were those of T1-M1 and T2-M2, with contractions of -3.06 +/- 2.39% and -3.27 +/- 1.37%, respectively. P1-M1 and P2-M2 expanded 5.60 +/- 2.89% and 6.84 +/- 3.60% from ED to ES. CONCLUSION: The mitral valve dimensions and calculated fractional relationships were similar in all sheep. As shown previously, the ratio of aortic annulus diameter (easily measured echocardiographically) to the intertrigonal distance (T1-T2) is 0.79 and 0.80 in humans and sheep, respectively. This distance can be used to determine normal mitral valve geometry and, therefore, preoperatively to calculate the degree of geometric distortion present in individual patients.

Ventriculo-aortic junction in human root. A geometric approach.

With advances in tissue engineering and improvement of surgical techniques, stentless biological valves and valve-sparing procedures have become alternatives to traditional aortic valve replacement with stented bioprostheses or mechanical valves. New surgical techniques preserve the advantages of native valves but require better understanding of the anatomical structure of the aortic root. Silicone rubber was injected in fresh aortic roots of nine human cadavers under the physiological closing pressure of 80 mmHg. The casts reproduced every detail of the aortic root anatomy and were used to digitize 27 leaflet attachment lines (LALs) of the aortic valves. LALs were normalized and described with a mathematical model. LALs were found to follow a pattern with the right coronary being the largest followed by the non-coronary and then the left coronary. During diastole, the aortic valve LAL can be described by an intersection between a created tube and an extruded parabolic surface. This geometrical definition of the LAL during end diastole gives a better understanding of the aortic root anatomy and could be useful for heart valve design and improvement of aortic valve reconstruction technique.

Forces at single point attached commissures (SPAC) in pericardial aortic valve prosthesis.

OBJECTIVE: New pericardial aortic bioprostheses (3F Therapeutics and temporarily stented autologous pericardial valve prosthesis) were developed recently. These valves are designed with commissures connected to the aortic wall at only three single points (single point attached commissures (SPAC)). The aim of this study was to investigate the forces acting on SPAC during varying pressure load. METHODS: Aortic roots with diameters 19, 25, and 29 mm were made using silicone polymer. A bovine pericardial SPAC aortic valve prosthesis was constructed using a 3D-mold and was implanted in the silicone aortic root. The base of the valve was sutured onto the aortic annulus with 4-0 polypropylene running suture and each commissure was sutured to a miniaturized force transducer with only one 3-0 polypropylene U-stitch. Three silicon aortic roots of each size were pressurized up to 200 mmHg and forces on SPAC were measured. RESULTS: All valves remained competent at a pressure of 200 mmHg. Recordings showed a linear correlation between applied pressure and forces measured at SPAC. At a pressure of 80 mmHg (equivalent to diastolic pressure), the forces were 0.44+/-0.22N, 1.15+/-0.18N, and 2.00+/-0.35N in annular diameters 19 mm, 25 mm, and 29 mm, respectively. It was observed, that the main forces were acting along the axial direction and not along the radial direction. CONCLUSIONS: Forces on "single point attached commissures" in pericardial aortic valves were measured. These forces were acting mainly in axial direction and not in radial direction. This knowledge is important for the implantation technique of SPAC pericardial aortic valves.

Three-dimensional asymmetrical modeling of the mitral valve: a finite element study with dynamic boundaries.

BACKGROUND AND AIM OF THE STUDY: Previous computational studies of the normal mitral valve have been limited because they assumed symmetrical modeling and artificial boundary conditions. The study aim was to model the mitral valve complex asymmetrically with three-dimensional (3-D) dynamic boundaries obtained from in-vivo experimental data. METHODS: Distance tracings between ultrasound crystals placed in the sheep mitral valve were converted into 3-D coordinates to reconstruct an initial asymmetric mitral model and subsequent dynamic boundary conditions. The non-linear, real-time left ventricular and aortic pressure loads were acquired synchronously. A quasi-static solution was applied over one cardiac cycle. RESULTS: The mitral valve leaflet stress was heterogeneous. The trigones experienced highest stresses, while the mid-anterior annulus between trigones experienced low stress. High leaflet stress was observed during peak pressure loading. During isovolumic relaxation, the leaflets were highly stretched between the anterolateral trigone and the posteromedial commissure, resulting in a prominent secondary leaflet stress re-increment. This has not been observed previously, as symmetric models with artificial boundary conditions were studied only in the ejection phase. CONCLUSION: Here, the first asymmetrical mitral valve model synchronized with 3-D dynamic boundaries and non-linear pressure loadings over the whole cardiac cycle based on in vivo experimental data is described. Despite its limitations, this model provides new insights into the distribution of leaflet stress in the mitral valve.

Aortic root dynamics are asymmetric.

BACKGROUND AND AIM OF THE STUDY: The presence of conformational changes in the aortic root during the cardiac cycle is well known, but precise information on time-related changes at each level of the root is lacking. METHODS: High-resolution, 3D sonomicrometry (200 Hz) was applied in an acute sheep model. Twelve crystals were implanted in eight sheep at each base (n = 3), commissure (n = 3), sinotubular junction (n = 3) and ascending aorta (n = 3). Under stable hemodynamic conditions, geometric changes of the perimeter of each sinus of Valsalva, sinus height, and twist and root tilt angles were time-related to left ventricluar (LV) and aortic pressures. RESULTS: Expansion of the perimeter of the three sinuses of Valsalva was homogeneous, but in significantly different proportions (p < 0.001): the right sinus expanded (+32.4 +/- 2.4%) more than the left (+29.3 +/- 3.2%), and more than the non-coronary (NC) sinus (+25.8 +/- 1.7%). A similar pattern was found for aortic root height: right greater than left, and left greater than NC sinus (p < 0.001). This asymmetry resulted in changes of the root's twist and tilt angles. Although the twist deformation was consistent for each sheep, no general pattern was found. The aortic root tilt angle (between the basal plane and the commissural plane) was 16.3 +/- 1.5 degrees at end-diastole (angle oriented posteriorly and to the left). During systole, it was reduced by 6.6 +/- 0.5 degrees, aligning the LV outflow tract with the ascending aorta. This tilt angle returned to its original value after valve closure. CONCLUSION: Aortic root expansion is asymmetric, generating precise changes in its tilt angle. During systole, tilt angle reduction resulted in a straight cylinder that probably facilitates ejection; during diastole, the tilt angle increased, probably reducing leaflet stress. These findings should impact upon surgical procedures and the design of new prostheses.

Flat or curved pericardial aortic valve cusps: a finite element study.

BACKGROUND AND AIM OF THE STUDY: The finite element method (FEM) has frequently been used to investigate the behavior of the aortic valve, but studies on the performance and behavior of free-hand autologous pericardial aortic valves reconstructed using specially designed valve molds have not been performed. The study aim was to demonstrate the effectiveness of a three-dimensional (3-D) cusp of the authors' design (H-Mold) versus a two-dimensional (2-D) (flat) cusp using a FEM to compare stress distribution and leaflet contact properties. METHODS: Solid models of the aortic root and valve cusps were constructed using a computer-aided design package. All models had different free edge lengths and surface areas, but a constant leaflet attachment length corresponding to a 19 mm annulus diameter. A static pressure of 80 mmHg was applied to all models. RESULTS: The maximum von Mises stress value in the H-Mold at the cusp commissure was 34.5% lower than the stress value in the flat leaflet, while the contact area in the H-Mold leaflet was 85.7% greater than that of the flat leaflet. The length of leaflet free edge greatly influenced maximum von Mises stress intensity at the commissures, and the contact area between leaflets was mainly affected by the geometric shape of the leaflet and its surface area. CONCLUSION: 3-D leaflet geometry was found positively to influence leaflet stress distribution and coaptation. This geometry should have a significant impact on the reliability and long-term durability of pericardial aortic valve reconstruction.

Sonometric study of the normal tricuspid valve annulus in sheep.

BACKGROUND AND AIM OF THE STUDY: Mitral valve dynamic changes during the cardiac cycle have been previously studied in sheep using sonomicrometry. The study aim was to analyze geometric changes of the normal tricuspid annulus in sheep using a similar methodology. This is most likely the first tricuspid valve study using high temporal resolution (200 Hz = 200 data points per second). METHODS: Thirteen crystals were implanted in seven sheep along the annulus (n = 6), at the tips of papillary muscles (n = 3), at the free edge of the leaflets (n = 3), and at the apex of the left ventricle (n = 1). Recordings (10 s) of crystal distances were used to create a three-dimensional (3D) coordinate system based on the least-squares plane of the annulus, and maximum and minimum values were calculated for length, area, and position in xyz coordinates. RESULTS: During the cardiac cycle, the tricuspid annulus area expanded 28.6 +/- 3.6% with similar maximum expansions of each segment along the annulus: septal (10.4 +/- 1.2%), anterior (13.0 +/- 1.5%), and posterior (14.0 +/- 1.6%). The annulus was saddle-shaped, with a circumferential expansion from elliptical at minimum area to more circular at maximum area. The time delay to maximum leaflet area and maximum papillary area occurred 83 +/- 13 ms and 279 +/- 30 ms respectively after maximum annulus area. CONCLUSION: The tricuspid valve undergoes continual and complex geometric changes during the cardiac cycle. In addition, the annulus expands significantly due to similar increases in length of the septal and free wall segments. The annulus is not in a single plane, but is saddle-shaped. The expansion and contraction of the tricuspid valve complex is stepwise, and sequential from base to apex.

Comparison of human and porcine aortic valves.

We compared the anatomy of human and porcine aortic valves. Porcine hearts were collected from the abattoir. Human hearts from patients who had died of non-cardiac causes were examined in the mortuary; only undamaged and anatomically normal hearts were used. Silicon casts were prepared by injecting engineering silicon at 80 mm Hg into the aortic arch. Various features of the aortic valve were measured: circumference, length between the commissural end point and central point of coaptation, surface diameter, and surface area. In total, 12 porcine and 12 human aortic valves were studied. The average circumferences of the human and porcine aortic valves were 8.00 +/- 0.2 (SD) cm and 7.90 +/- 1.0 cm, respectively. The central point of coaptation in human valves was skewed toward the left coronary cusp, whereas in porcine valves it was skewed toward the non-coronary cusp. In human aortic valves, the non-coronary cusp had the largest surface diameter and surface area with mean measurements of 3.6 +/- 0.2 cm and 1.230 +/- 0.228 cm(2), respectively; the left coronary cusp was smallest for the same variables with measurements of 3.1 +/- 0.3 cm and 0.898 +/- 0.357 cm(2). In porcine valves, the right coronary cusp had the largest surface diameter and surface area with mean measurements of 3.9 +/- 0.7 cm and 1.716 +/- 0.81 cm(2), respectively; the non-coronary cusp was the smallest for the same variables with measurements of 2.9 +/- 0.5 cm and 1.023 +/- 0.659 cm(2). These differences suggest that when using porcine valves as transplant material (e.g., stentless valves), geometric considerations, such as commissural length, may be important.

Dynamic balance of the aortomitral junction.

OBJECTIVE: The aortic and mitral valves have been studied in isolation, as if their functions were independent. We hypothesized that both valves work in synchrony on the basis of the shared myocardial pump and orifice. METHODS: Six sonometric crystals (7 sheep) were placed in both trigones, the midpoint of the anterior and posterior anulus, and the lateral extremities of the posterior anulus. In a separate series of animals, 3 crystals (8 sheep) were implanted in the aortic annular base of the right, left, and noncoronary sinuses of Valsalva. In an acute, open-chest model, under stable hemodynamic conditions, geometric changes were time related to simultaneous left ventricular and aortic pressures. RESULTS: From mid-diastole to end-systole, the mitral anulus area contracted by -16.1% +/- 1.9% (mean +/- SEM), whereas the aortic base area expanded by +29.8% +/- 3.3% during systole. The mitral anulus deformation was heterogeneous. In systole, the anterior mitral anulus expanded (intertrigonal distance, +11.5% +/- 2.3%) and the posterior mitral anulus contracted (distance between lateral extremities of the posterior anulus, -12.1% +/- 1.5%). The intertrigonal distance corresponded to the base of the left and noncoronary sinus of Valsalva, which expanded similarly during systole (+12.9% +/- 2.0%). The anteroposterior diameter of the mitral anulus was reduced twice that of the transverse diameter. This disparity of reduction can be explained by the posterior displacement of the intertrigonal area corresponding to the systolic aortic root expansion. CONCLUSIONS: Mitral anulus deformation is closely related to aortic root dynamics. During systole, the posterior movement of the aortic curtain allows for aortic root expansion, probably to maximize ejection, whereas during diastole, aortic root reduction participates in mitral anulus dilatation. These findings should affect mitral and aortic surgical approaches.