Impairment of pericardial leaflet structure from balloon-expanded valved stents.

OBJECTIVE: Malpositioning is one of the major problems in transcatheter aortic valve implantation. To evaluate the influence of mechanical balloon inflation on aortic valve stent positioning, the expansion process and the impact on the valve leaflet's structure were investigated. METHODS: Custom-made stents were laser cut from a 22-mm diameter stainless steel tube and mounted with a glutaraldehyde-treated bovine pericardial valve. The valved stents were crimped onto a standard balloon catheter and expanded by inflation of the balloon with 2 bar for 3 seconds. Expansion was studied using a high-speed camera, and the histology of the pericardial tissue was analyzed. RESULTS: The valved stents were fully expanded within 3 seconds. Balloon inflation was observed to be asymmetric starting proximally. At the beginning of expansion, the valved stents were pulled proximally. During further inflation, the stents slipped distally on the balloon and experienced a total displacement of 13.5 mm. Macroscopic examination showed severe imprinting of the stent struts into the pericardial tissue. Histology revealed disrupted tissue layers and collagen fibers. CONCLUSIONS: Analysis of valved stent expansion showed a displacement of the stent on the catheter during balloon inflation. Therefore, precise placement of the valved stent cannot be accomplished. Histologic analysis of the expanded pericardial tissue revealed disruption of collagen fibers. Disruption of pericardial tissue structures due to balloon expansion may result in early functional valve failure.

Finite element investigation of stentless pericardial aortic valves: relevance of leaflet geometry.

Recent developments in aortic valve replacement include the truly stentless pericardial bioprostheses with single point attached commissures (SPAC) implantation technique. The leaflet geometry available for the SPAC valves can either be a simple tubular or a complex three-dimensional structure molded using specially designed molds. Our main objective was to compare these two leaflet designs, the tubular vs. the molded, by dynamic finite element simulation. Time-varying physiological pressure loadings over a full cardiac cycle were simulated using ABAQUS. Dynamic leaflet behavior, leaflet coaptation parameters, and stress distribution were compared. The maximum effective valve orifice area during systole is 633.5 mm(2) in the molded valve vs. 400.6 mm(2) in the tubular valve, and the leaflet coaptation height during diastole is 4.5 mm in the former, in contrast to 1.6 mm in the latter. Computed compressive stress indicates high magnitudes at the commissures and inter-leaflet margins of the tubular valve, the highest being 3.83 MPa, more than twice greater than 1.80 MPa in the molded valve. The molded leaflet design which resembles the native valve exerts a positive influence on the mechanical performance of the SPAC pericardial valves compared with the simple tubular design. This may suggest enhanced valve efficacy and durability.

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.

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.

Kinking of the atrioventricular plane during the cardiac cycle.

Systolic descent of the atrioventricular plane toward the relatively stationary left ventricular apex is well described. As the atrioventricular plane includes two separate valvular units, systolic atrioventricular plane displacement should not be homogenous. In 6 sheep, sonomicrometric crystals were implanted at the base of the right coronary sinus, anterolateral and posteromedial fibrous trigones, posterior mitral annulus, left ventricular apex, and the tips of the anterior and posterior mitral leaflets. The aortomitral angle was calculated and related to simultaneous left ventricular and aortic pressures and mitral valve movement. The aortomitral angle was largest at end diastole (150.73 degrees +/- 15.48 degrees ). During isovolumic contraction, it narrowed rapidly to 144.90 degrees +/- 16.64 degrees , followed by a slower narrowing during ejection until it reached its smallest angle at end systole (139.66 degrees +/- 16.78 degrees ). During isovolumic relaxation, the aortomitral angle increased to 143.66 degrees +/- 16.02 degrees at the beginning of diastole. During the first third of diastole, it narrowed again to 141 degrees +/- 16.24 degrees before re-expanding to maximum at end diastole. During systole, the atrioventricular plane descended non-homogeneously toward the apex, with kinking at the hinge between the aortic and mitral annulus plane. This deformation of the atrioventricular plane has relevance in valve surgery.

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.

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.

Solid-organ transplantation in HBsAg-negative patients with antibodies to HBV core antigen: low risk of HBV reactivation.

Hepatitis B virus (HBV) reactivation is a well-described event in HBV surface antigen (HbsAg)-positive patients undergoing immunosuppression. There are only few data about the risk of HBV reactivation in HBsAg-negative solid-organ transplant recipients with resolved HBV infection. We conducted a systematic screening of serum and liver samples from 38 HBsAg-negative and anti-HBV core antigen (anti-HBc)-positive patients for the presence of HBV-DNA and for serologic HBV markers before and after solid-organ transplantation (kidney, n=23; liver, n=9; heart, n=6). Pretransplant prevalence of HBV-DNA was 24% (6/25) in serum and 33% (3/9) in liver samples. Forty-four percent (15/34) of the recipients were viremic after transplantation; this finding was more common in patients coinfected with hepatitis C (P=0.011) and in patients negative for anti-HBs (P=0.001). Two recipients became antigenemic (HBsAg-positive), but none developed clinical signs of hepatitis. In conclusion, subclinical reactivation of HBV infection was detected in a significant proportion of HBsAg-negative solid-organ-transplant recipients.

Anterior mitral basal 'stay' chords are essential for left ventricular geometry and function.

BACKGROUND AND AIM OF THE STUDY: Among the anterior mitral basal chords, two particularly strong and thick stay chords (SC) remain under tension during the entire cardiac cycle. Collagen fibers of the anterior mitral leaflet (AML) are oriented from insertion of the SC on the AML to the fibrous trigones (FT), suggesting that local stress is directed from the papillary muscles (PM) over the SC and AML to the FT, maintaining left ventricular (LV) geometry. METHODS: Sonomicrometry crystals were implanted in sheep at the LV apex (A), the anterior (AW) and septal (SW) LV wall, the PM tips (M1 and M2), the SC insertion into the AML (S1 and S2), the posterior (PMA) and lateral (P1 and P2) mitral annulus, the FT (T1 and T2), the tips of the anterior (AL) and posterior (PL) mitral leaflets, and the base of the aortic right coronary sinus (RCS). Changes in distances, areas, and volume were time-related to aortic flow and LV and ascending aorta pressures. Recordings were taken at baseline and after transection of the SC. RESULTS: After transection of the SC, the systolic distance from M1-T1 increased by +0.96 +/- 0.41 mm (p < 0.05) and from M2-T2 by +0.97 +/- 0.42 mm (p < 0.05). The LV length increased at T1-A by +1.14 +/- 0.60 mm (p < 0.05) and at T2-A by +0.97 +/- 0.37 mm (p < 0.05). The aortomitral angle narrowed at end-systole by -3.26 +/- 0.85 degrees (p < 0.05). Transection of the SC reduced dP/dt by -11.20 +/- 5.29% (p < 0.05), maximum aortic flow by -16.89 +/- 7.86% (p < 0.05), and maximum pressure-volume ratio by -10.83 +/- 3.36% (p < 0.05). CONCLUSION: Transection of the anterior mitral SC did not result in mitral regurgitation but induced significant changes in LV geometry, including narrowing of the aortomitral angle and subsequent deterioration of LV function. The SC are essential for maintaining normal LV geometry and function.

Left ventricular endocardial longitudinal and transverse changes during isovolumic contraction and relaxation: a challenge.

Left ventricular (LV) longitudinal and transverse geometric changes during isovolumic contraction and relaxation are still controversial. This confusion is compounded by traditional definitions of these phases of the cardiac cycle. High-resolution sonomicrometry studies might clarify these issues. Crystals were implanted in six sheep at the LV apex, fibrous trigones, lateral and posterior mitral annulus, base of the aortic right coronary sinus, anterior and septal endocardial wall, papillary muscle tips, and edge of the anterior and posterior mitral leaflets. Changes in distances were time related to LV and aortic pressures and to mitral valve opening. At the beginning of isovolumic contraction, while the mitral valve was still open, the LV endocardial transverse diameter started to shorten while the endocardial longitudinal diameter increased. During isovolumic relaxation, while the mitral valve was closed, LV transverse diameter started to increase while the longitudinal diameter continued to decrease. These findings are inconsistent with the classic definitions of the phases of the cardiac cycle.

Tricuspid valve repair in a case with congenital absence of left thoracic pericardium.

We present a case of severe tricuspid valve insufficiency because of disruption of the anterior tricuspid leaflet with congenital absence of left thoracic pericardium. Findings suggest that tricuspid valve disruption was a result of distorted right ventricular geometry because of luxation of the heart into left thoracic cavity. Tricuspid valve could be repaired by reinsertion of anterior tricuspid leaflet and De-Vega annuloplasty. Normal hemodynamic was obtained and weaning from cardio pulmonary bypass was possible by lifting the heart in orthotopic position using increased positive end expiratory pressure. Postoperative course was uneventful.

Anterior mitral leaflet mobility is limited by the basal stay chords.

BACKGROUND: We hypothesize that 2 tendon-like anterior basal stay chords, which remain taut during the entire cardiac cycle, limit the motion of the anterior mitral leaflet. METHODS AND RESULTS: Sonomicrometric crystals were implanted in 6 sheep at the insertion of stay chords at anterior mitral leaflet (S1 and S2), papillary muscle tips, fibrous trigones, mitral annulus, and the tip of the anterior leaflet (AL). Distances between crystals were recorded before and after section of stay chords. During the cardiac cycle, the angle alpha between mitral annulus and AL changed by +54.2+/-12.4 degrees; the angles between mitral annulus and S1 (beta1) changed by +25.7+/-14.6 degrees, and between mitral annulus and S2 (beta2) by +20.4+/-7.8 degrees. During diastole, AL twice crossed the virtual plane formed by the stay chords: during E-wave by a maximum of 6.5 mm (mean, 2.5+/-2.2 mm) and during A-wave by a maximum of 3.2 mm (mean, 1.7+/-0.9 mm). After section of both stay chords, total anterior mitral leaflet motion increased as follows: AL, +6.9+/-3.4 degrees; S1, +13.1+/-4.4 degrees; and S2, +30.9+/-11.7 degrees (P<0.05). CONCLUSIONS: Although the lateral movement of anterior mitral leaflet is limited by stay chords, the midportion moves unimpaired toward the septum, like a sail, between the 2 stay chords during diastole. A diastolic left ventricular-inflow and systolic left ventricular-outflow funnel mechanism is created. Stay chord section increased lateral anterior mitral leaflet movement.

A temporarily stented, autologous pericardial aortic valve prosthesis.

BACKGROUND AND AIM OF THE STUDY: A new bioprosthesis has been developed that is: (i) constructed from glutaraldehyde-treated autologous pericardium due to its lack of antigenicity and low cost; (ii) easily constructed in the operating room; (iii) stentless but easy to implant by using a temporary stent that is removed once its function is no longer necessary; and (iv) implanted with a single proximal suture and three commissural stitches. METHODS: This prosthesis was implanted in the subcoronary aortic position of six sheep. The mean prosthesis size was 19.7 +/- 3.5 mm, and manufacturing time 16 +/- 3 min. Cardiopulmonary bypass and cross-clamp times were 142.5 +/- 26.7 min and 100.2 +/- 28.8 min, respectively. Three sheep were euthanized at three, seven, or 27 days, and the remainder at five months postoperatively. RESULTS: In all cases the valve was competent and the single commissural stitches were well-anchored. The pericardium was pliable in all cases, but one animal had obvious endocarditis (at 27 days). Small calcific nodules were found at the commissures in valves explanted at five months. Histology showed an intact collagen and elastin structure, and neointimal growth was seen covering the basal quarter of the leaflets and commissures. CONCLUSION: This new bioprosthesis might offer a particularly attractive alternative for the young patient population of the developing world. The simplicity of construction, low cost, and absence of any need for anticoagulation makes this prosthesis close to the ideal aortic valve substitute.

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.