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Background: Cardiac surgery patients are commonly treated with diuretics, which can result in hypokalemia requiring potassium supplementation.Objective: Our objective was to determine whether cardiac surgery patients receiving therapy with potassium-wasting diuretics can safely and beneficially maintain serum potassium levels by eating potassium-rich foods.Design: A prospectively randomized trial of diet vs medication supplementation of potassium was undertaken. Patients who were to undergo cardiac surgery and who would be receiving therapy with oral furosemide postoperatively were eligible for the study. Forty-eight patients were enrolled in the trial, and 38 patients completed the study. Patients received either potassium-rich foods (diet) or potassium chloride pills (medication).Results: There was no significant difference in mean (+/- SD) serum potassium concentrations between groups preoperatively (4.25 +/- 0.30 vs 4.29 +/- 0.33 mEq/L, respectively), on postoperative day 3 (4.23 +/- 0.40 vs 4.27 +/- 0.40 mEq/L, respectively), or postoperative day 4 (4.23 +/- 0.48 vs 4.24 +/- 0.33 mEq/L, respectively) for the diet and medication groups. Length of stay was significantly lower in the diet group (5.0 +/- 0.9 vs 6.3 +/- 2.2 days, respectively). When asked their preferences for method of supplementation, 79% of patients preferred the diet method.Conclusions: Cardiac surgery patients receiving therapy with diuretics can maintain serum potassium levels at clinically adequate concentrations by eating potassium-rich foods. Length of stay was significantly reduced. This method of potassium supplementation demonstrates the potential for reduced costs and increased patient satisfaction. [ABSTRACT FROM AUTHOR]

Edge-to-edge repair for mitral valve regurgitation is being increasingly performed in high-surgical risk patients using minimally invasive mitral clipping devices. Known procedural complications include chordal rupture and mitral leaflet perforation. Hence, it is important to quantitatively evaluate the effect of edge-to-edge repair on chordal integrity. in this study, we employ a computational mitral valve model to simulate functional mitral regurgitation (FMR) by creating papillary muscle displacement. Edge-to-edge repair is then modeled by simulated coaptation of the mid portion of the mitral leaflets. in the setting of simulated FMR, edge-to-edge repair was shown to sustain low regurgitant orifice area, until a two fold increase in the inter-papillary muscle distance as compared to the normal mitral valve. Strain in the chordae was evaluated near the papillary muscles and the leaflets. Following edge-to-edge repair, strain near the papillary muscles did not significantly change relative to the unrepaired valve, while strain near the leaflets increased significantly relative to the unrepaired valve. These data demonstrate the potential for computational simulations to aid in the pre-procedural evaluation of possible complications such as chordal rupture and leaflet perforation following percutaneous edge-to-edge repair.

Over the years, three-dimensional models of the mitral valve have generally been organized around a simplified anatomy. Leaflets have been typically modeled as membranes, tethered to discrete chordae typically modeled as one-dimensional, non-linear cables. Yet, recent, high-resolution medical images have revealed that there is no clear boundary between the chordae and the leaflets. In fact, the mitral valve has been revealed to be more of a webbed structure whose architecture is continuous with the chordae and their extensions into the leaflets. Such detailed images can serve as the basis of anatomically accurate, subject-specific models, wherein the entire valve is modeled with solid elements that more faithfully represent the chordae, the leaflets, and the transition between the two. These models have the potential to enhance our understanding of mitral valve mechanics and to re-examine the role of the mitral valve chordae, which heretofore have been considered to be 'invisible' to the fluid and to be of secondary importance to the leaflets. However, these new models also require a rethinking of modeling assumptions. In this study, we examine the conventional practice of loading the leaflets only and not the chordae in order to study the structural response of the mitral valve apparatus. Specifically, we demonstrate that fully resolved 3D models of the mitral valve require a fluid-structure interaction analysis to correctly load the valve even in the case of quasi-static mechanics. While a fluid-structure interaction mode is still more computationally expensive than a structural-only model, we also show that advances in GPU computing have made such models tractable. Copyright © 2016 John Wiley & Sons, Ltd., (Copyright © 2016 John Wiley & Sons, Ltd.)

The chordal structure is a part of mitral valve geometry that has been commonly neglected or simplified in computational modeling due to its complexity. However, these simplifications cannot be used when investigating the roles of individual chordae tendineae in mitral valve closure. For the first time, advancements in imaging, computational techniques, and hardware technology make it possible to create models of the mitral valve without simplifications to its complex geometry, and to quickly run validated computer simulations that more realistically capture its function. Such simulations can then be used for a detailed analysis of chordae-related diseases. In this work, a comprehensive model of a subject-specific mitral valve with detailed chordal structure is used to analyze the distinct role played by individual chordae in closure of the mitral valve leaflets. Mitral closure was simulated for 51 possible chordal rupture points. Resultant regurgitant orifice area and strain change in the chordae at the papillary muscle tips were then calculated to examine the role of each ruptured chorda in the mitral valve closure. For certain subclassifications of chordae, regurgitant orifice area was found to trend positively with ruptured chordal diameter, and strain changes correlated negatively with regurgitant orifice area. Further advancements in clinical imaging modalities, coupled with the next generation of computational techniques will enable more physiologically realistic simulations.

The diversity of mitral valve (MV) geometries and multitude of surgical options for correction of MV diseases necessitates the use of computational modeling. Numerical simulations of the MV would allow surgeons and engineers to evaluate repairs, devices, procedures, and concepts before performing them and before moving on to more costly testing modalities. Constructing, tuning, and validating these models rely upon extensive in vitro characterization of valve structure, function, and response to change due to diseases. Micro-computed tomography ([Formula: see text]CT) allows for unmatched spatial resolution for soft tissue imaging. However, it is still technically challenging to obtain an accurate geometry of the diastolic MV. We discuss here the development of a novel technique for treating MV specimens with glutaraldehyde fixative in order to minimize geometric distortions in preparation for [Formula: see text]CT scanning. The technique provides a resulting MV geometry which is significantly more detailed in chordal structure, accurate in leaflet shape, and closer to its physiological diastolic geometry. In this paper, computational fluid-structure interaction (FSI) simulations are used to show the importance of more detailed subject-specific MV geometry with 3D chordal structure to simulate a proper closure validated against [Formula: see text]CT images of the closed valve. Two computational models, before and after use of the aforementioned technique, are used to simulate closure of the MV.

Numerical models of native heart valves are being used to study valve biomechanics to aid design and development of repair procedures and replacement devices. These models have evolved from simple two-dimensional approximations to complex three-dimensional, fully coupled fluid-structure interaction (FSI) systems. Such simulations are useful for predicting the mechanical and hemodynamic loading on implanted valve devices. A current challenge for improving the accuracy of these predictions is choosing and implementing modeling boundary conditions. In order to address this challenge, we are utilizing an advanced in vitro system to validate FSI conditions for the mitral valve system. Explanted ovine mitral valves were mounted in an in vitro setup, and structural data for the mitral valve was acquired with [Formula: see text]CT. Experimental data from the in vitro ovine mitral valve system were used to validate the computational model. As the valve closes, the hemodynamic data, high speed leaflet dynamics, and force vectors from the in vitro system were compared to the results of the FSI simulation computational model. The total force of 2.6 N per papillary muscle is matched by the computational model. In vitro and in vivo force measurements enable validating and adjusting material parameters to improve the accuracy of computational models. The simulations can then be used to answer questions that are otherwise not possible to investigate experimentally. This work is important to maximize the validity of computational models of not just the mitral valve, but any biomechanical aspect using computational simulation in designing medical devices.

Computational models for the heart's mitral valve (MV) exhibit several uncertainties that may be reduced by further developing these models using ground-truth data-sets. This study generated a ground-truth data-set by quantifying the effects of isolated mitral annular flattening, symmetric annular dilatation, symmetric papillary muscle (PM) displacement and asymmetric PM displacement on leaflet coaptation, mitral regurgitation (MR) and anterior leaflet strain. MVs were mounted in an in vitro left heart simulator and tested under pulsatile haemodynamics. Mitral leaflet coaptation length, coaptation depth, tenting area, MR volume, MR jet direction and anterior leaflet strain in the radial and circumferential directions were successfully quantified at increasing levels of geometric distortion. From these data, increase in the levels of isolated PM displacement resulted in the greatest mean change in coaptation depth (70% increase), tenting area (150% increase) and radial leaflet strain (37% increase) while annular dilatation resulted in the largest mean change in coaptation length (50% decrease) and regurgitation volume (134% increase). Regurgitant jets were centrally located for symmetric annular dilatation and symmetric PM displacement. Asymmetric PM displacement resulted in asymmetrically directed jets. Peak changes in anterior leaflet strain in the circumferential direction were smaller and exhibited non-significant differences across the tested conditions. When used together, this ground-truth data-set may be used to parametrically evaluate and develop modelling assumptions for both the MV leaflets and subvalvular apparatus. This novel data may improve MV computational models and provide a platform for the development of future surgical planning tools.

Purpose: Computational models of the heart's mitral valve (MV) exhibit potential for preoperative surgical planning in ischemic mitral regurgitation (IMR). However challenges exist in defining boundary conditions to accurately model the function and response of the chordae tendineae to both IMR and surgical annuloplasty repair. Towards this goal, a ground-truth data set was generated by quantifying the isolated effects of IMR and mitral annuloplasty on leaflet coaptation, regurgitation, and tethering forces of the anterior strut and posterior intermediary chordae tendineae., Methods: MVs were excised from ovine hearts (N=15) and mounted in a pulsatile heart simulator which has been demonstrated to mimic the systolic MV geometry and coaptation of healthy and chronic IMR sheep. Strut and intermediary chordae from both MV leaflets (N=4) were instrumented with force transducers. Tested conditions included a healthy control, IMR, oversized annuloplasty, true-sized annuloplasty, and undersized mitral annuloplasty. A2-P2 leaflet coaptation length, regurgitation, and chordal tethering were quantified and statistically compared across experimental conditions., Results: IMR was successfully simulated with significant increases in MR, tethering forces for each of the chordae, and decrease in leaflet coaptation (p<.05). Compared to the IMR condition, increasing levels of downsized annuloplasty significantly reduced regurgitation, increased coaptation, reduced posteromedial papillary muscle strut chordal forces, and reduced intermediary chordal forces from the anterolateral papillary muscle (p<.05)., Conclusions: These results provide for the first time a novel comprehensive data set for refining the ability of computational MV models to simulate IMR and varying sizes of complete rigid ring annuloplasty.

The remodeling that occurs after a posterolateral myocardial infarction can alter mitral valve function by creating conformational abnormalities in the mitral annulus and in the posteromedial papillary muscle, leading to mitral regurgitation (MR). It is generally assumed that this remodeling is caused by a volume load and is mediated by an increase in diastolic wall stress. Thus, mitral regurgitation can be both the cause and effect of an abnormal cardiac stress environment. Computational modeling of ischemic MR and its surgical correction is attractive because it enables an examination of whether a given intervention addresses the correction of regurgitation (fluid-flow) at the cost of abnormal tissue stress. This is significant because the negative effects of an increased wall stress due to the intervention will only be evident over time. However, a meaningful fluid-structure interaction model of the left heart is not trivial; it requires a careful characterization of the in-vivo cardiac geometry, tissue parameterization though inverse analysis, a robust coupled solver that handles collapsing Lagrangian interfaces, automatic grid-generation algorithms that are capable of accurately discretizing the cardiac geometry, innovations in image analysis, competent and efficient constitutive models and an understanding of the spatial organization of tissue microstructure. In this manuscript, we profile our work toward a comprehensive fluid-structure interaction model of the left heart by reviewing our early work, presenting our current work and laying out our future work in four broad categories: data collection, geometry, fluid-structure interaction and validation.

Background: Estimated glomerular filtration rate (eGFR) before coronary artery bypass graft (CABG) surgery is a key risk factor of in-hospital mortality. However, in patients with normal renal function before CABG, acute kidney injury develops after the procedure, making postoperative renal function assessment necessary for evaluation. Postoperative eGFR and its association with long-term survival have not been well studied., Methods: We studied 13,593 consecutive CABG patients in northern New England from 2001 to 2006. Patients with preoperative dialysis were excluded. Data were linked to the Social Security Association Death Master File to assess long-term survival. Kaplan-Meier and log-rank techniques were used. Patients were stratified by established categories of postoperative eGFR (90 or greater, 60 to 89, 30 to 59, 15 to 29, and less than 15 mL x min(-1) x 1.73 m(-2))., Results: Median follow-up was 2.8 years (mean, 2.7; range, 0 to 5.5). Patients with moderate to severe acute kidney injury (less than 60) after CABG had significantly worse survival than patients with little or no acute kidney injury (90 or greater)., Conclusions: Patients having moderate to severe acute kidney injury after CABG surgery had worse 5-year survival compared with patients who had normal or near-normal renal function.

Successful mitral valve repair is dependent upon a full understanding of normal and abnormal mitral valve anatomy and function. Computational analysis is one such method that can be applied to simulate mitral valve function in order to analyse the roles of individual components and evaluate proposed surgical repair. We developed the first three-dimensional finite element computer model of the mitral valve including leaflets and chordae tendineae; however, one critical aspect that has been missing until the last few years was the evaluation of fluid flow, as coupled to the function of the mitral valve structure. We present here our latest results for normal function and specific pathological changes using a fluid-structure interaction model. Normal valve function was first assessed, followed by pathological material changes in collagen fibre volume fraction, fibre stiffness, fibre splay and isotropic stiffness. Leaflet and chordal stress and strain and papillary muscle force were determined. In addition, transmitral flow, time to leaflet closure and heart valve sound were assessed. Model predictions in the normal state agreed well with a wide range of available in vivo and in vitro data. Further, pathological material changes that preserved the anisotropy of the valve leaflets were found to preserve valve function. By contrast, material changes that altered the anisotropy of the valve were found to profoundly alter valve function. The addition of blood flow and an experimentally driven microstructural description of mitral tissue represent significant advances in computational studies of the mitral valve, which allow further insight to be gained. This work is another building block in the foundation of a computational framework to aid in the refinement and development of a truly non-invasive diagnostic evaluation of the mitral valve. Ultimately, it represents the basis for simulation of surgical repair of pathological valves in a clinical and educational setting.

Background and Aim of the Study: The dynamics of the mitral valve result from the synergy of left heart geometry, local blood flow and tissue integrity. Herein is presented the first coupled fluid-structure computational model of the mitral valve in which valvular kinematics result from the interaction of local blood flow and a continuum representation of valvular microstructure., Methods: The diastolic geometry of the mitral valve was assembled from previously published experimental data. Anterior and posterior leaflets were modeled as networks of entangled collagen fibers, embedded in an isotropic matrix. The resulting non-linear continuum description of mitral tissue was implemented in a three-dimensional membrane formulation. Chordal tension-only behavior was defined from experimental tensile tests. The computational model considered the valve immersed in a domain of Newtonian blood, with an experimentally determined viscosity corresponding to a shear rate of 180 s(-1) at 37 degrees C. Ventricular and atrial pressure curves were applied to ventricular and atrial surfaces of the blood domain., Results: Peak closing flow and volume were 51 ml/s and 1.17 ml, respectively. Papillary muscle force ranged dynamically between 0.0 and 2.6 N. Acoustic pressure (RMS) was found to be 3.3 Pa, with a peak frequency of 72 Hz at 0.064 s from the onset of systole. Model predictions showed excellent agreement with available transmitral flow, papillary force and first heart sound (S1) acoustic data., Conclusion: The addition of blood flow and an experimentally driven microstructural description of mitral tissue represent a significant advance in computational studies of the mitral valve. This model will be the foundation for future computational studies on the effect of pathophysiological tissue alterations on mitral valve competence.

Background: Many diseases that affect the mitral valve are accompanied by the proliferation or degradation of tissue microstructure. The early acoustic detection of these changes may lead to the better management of mitral valve disease. In this study, we examine the nonstationary acoustic effects of perturbing material parameters that characterize mitral valve tissue in terms of its microstructural components. Specifically, we examine the influence of the volume fraction, stiffness and splay of collagen fibers as well as the stiffness of the nonlinear matrix in which they are embedded., Methods and Results: To model the transient vibrations of the mitral valve apparatus bathed in a blood medium, we have constructed a dynamic nonlinear fluid-coupled finite element model of the valve leaflets and chordae tendinae. The material behavior for the leaflets is based on an experimentally derived structural constitutive equation. The gross movement and small-scale acoustic vibrations of the valvular structures result from the application of physiologic pressure loads. Material changes that preserved the anisotropy of the valve leaflets were found to preserve valvular function. By contrast, material changes that altered the anisotropy of the valve were found to profoundly alter valvular function. These changes were manifest in the acoustic signatures of the valve closure sounds. Abnormally, stiffened valves closed more slowly and were accompanied by lower peak frequencies., Conclusion: The relationship between stiffness and frequency, though never documented in a native mitral valve, has been an axiom of heart sounds research. We find that the relationship is more subtle and that increases in stiffness may lead to either increases or decreases in peak frequency depending on their relationship to valvular function.

Automatic acoustic classification and diagnosis of mitral valve disease remain outstanding biomedical problems. Although considerable attention has been given to the evolution of signal processing techniques, the mechanics of the first heart sound generation has been largely overlooked. In this study, the haemodynamic determinants of the first heart sound were examined in a computational model. Specifically, the relationship of the transvalvular pressure and its maximum derivative to the time-frequency content of the acoustic pressure was examined. To model the transient vibrations of the mitral valve apparatus bathed in a blood medium, a dynamic, non-linear, fluid-coupled finite element model of the mitral valve leaflets and chordae tendinae was constructed. It was found that the root mean squared (RMS) acoustic pressure varied linearly (r2= 0.99) from 0.010 to 0.259 mmHg, following an increase in maximum dP/dt from 415 to 12470 mm Hg s(-1). Over that same range, peak frequency varied non-linearly from 59.6 to 88.1 Hz. An increase in left-ventricular pressure at coaptation from 22.5 to 58.5mm Hg resulted in a linear (r2= 0.91) rise in RMS acoustic pressure from 0.017 to 1.41mm Hg. This rise in transmitral pressure was accompanied by a non-linear rise in peak frequency from 63.5 to 74.1 Hz. The relationship between the transvalvular pressure and its derivative and the time-frequency content of the first heart sound has been examined comprehensively in a computational model for the first time. Results suggest that classification schemes should embed both of these variables for more accurate classification.

Background and Aim of the Study: The study aim was to develop a three-dimensional coupled fluid-structure finite element model of the aortic valve and root. This model extends previous purely structural finite element models, and represents a significant step toward realistic simulation of the complex interactions among tissue material properties and valvular function., Methods: The aortic root and valve geometry were extracted from magnetic resonance images and imported into the LS-Dyna explicit finite element package. Leaflet and root tissue were modeled with elastic material properties, and blood was modeled as a Newtonian liquid. A dynamic, fully unsteady analysis was performed in which blood flow through the valve was computed along with the motion of the leaflets and root in response to standard physiologic pressure wave profiles., Results: The opening and closing of the aortic valve under physiological loading conditions was successfully simulated, and feasibility of the model illustrated. The motion of the simulated leaflets was consistent with that seen in intact hearts. Analysis of fluid flow patterns revealed eddy structures in the sinus regions and flow into the coronary circulation., Conclusion: The addition of blood flow to structural models of the aortic valve and root is a significant advance in modeling, and allows a closer simulation of valvular function. The model will be used to further assess normal and abnormal physiology as well as the effects of surgical intervention.

Background and Aim of the Study: Biaxial mechanical properties have been reported for porcine aortic valve leaflets, but not for the aortic root wall. These data are important for understanding the relationship between tissue material properties and function, providing a baseline for diseased tissue, and for providing a basis for numerical models of aortic mechanics. The study aim was to determine the biaxial material properties of porcine aortic root wall tissue., Methods: Tissue samples (20 mm x 20 mm) were obtained from the aortic root walls of 18 pigs (anterior and posterior samples from each pig) and tested with a custom-built biaxial tensile testing apparatus. The data were fitted to the strain energy formulation: W = ?[a(long)E11(2) + a(circ)Ecc(2) + 2a(int)E11Ecc], where W is the strain energy, E11 = longitudinal strain, Ecc = circumferential strain, along, a(circ), and aint are the constants that were determined, and represent the longitudinal and circumferential elastic moduli, and interaction between the two axes, respectively., Results: The root wall tissue was less stiff in the longitudinal direction (along = 115.8 +/- 8.4 kPa) than the circumferential direction (a(circ) = 169.9.3 +/- 7.4 kPa). As expected, there was mechanical interaction between the two axes (a(int) = 45.7 +/- 3.4 kPa). Additionally, anterior tissue samples were less stiff than posterior samples. All tissue samples exhibited a linear stress-strain relationship up to 40% strain, in contrast to aortic leaflet tissue, which was highly non-linear., Conclusion: These results demonstrated that the porcine aortic root wall tissue is an anisotropic material with linear elastic properties, in contrast to leaflet tissue. Additionally, the data suggest that a finite element model using an isotropic material as a basis for the aorta is insufficient for a physiologically accurate representation.

Background: This study evaluates a modification of an ambulatory intraaortic balloon pump (IABP) technique used in patients with heart failure of ischemic origin for bridge to transplant., Methods: In this retrospective review we evaluated the ability to place the ambulatory IABP, any complications, time on device, and success in bridging to transplant on the ambulatory IABP device. In addition, the cost as compared to current ventricular assist devices was determined., Results: Between July 2000 and November 2001, 4 patients have been managed with ambulatory IABP in our combined University of Wisconsin and William S. Middleton Veterans Administration programs. All 4 patients had ischemia as their mode of heart failure, and each had a relative contraindication to standard ventricular assist device use. All 4 patients had ambulatory IABPs successfully placed through the left axillary artery without complication, and were able to ambulate early after ambulatory IABP placement, and increased their rehabilitation status before transplantation. Ambulatory IABP support ranged from 12 to 70 days. All 4 patients have been successfully transplanted and discharged from the hospital. Use of the ambulatory IABP support, even with multiple replacements, translated to 10- to 50-fold savings for each of the reported patients versus standard ventricular assist device use., Conclusions: As a result of our initial experience, we believe that ambulatory IABP is an excellent mode of support in selected patients, and is cost-effective, as compared to conventional ventricular assist device therapy.

Objectives: Progressive aortic root dilatation and an increased aortic root elastic modulus have been documented in persons with Marfan syndrome. To examine the effect of aortic root dilatation and increased elastic modulus on leaflet stress, strain, and coaptation, we used a finite-element model., Methods: The normal model incorporated the geometry, tissue thickness, and anisotropic elastic moduli of normal human roots and valves. Four Marfan models were evaluated, in which the diameter of the aortic root was dilated by 5%, 15%, 30%, and 50%. Aortic root elastic modulus in the 4 Marfan models was doubled. Under diastolic pressure, regional stresses and strains were evaluated, and the percentage of leaflet coaptation was calculated., Results: Root dilatation and stiffening significantly increased regional leaflet stress and strain compared with normal levels. Stress increases ranged from 80% to 360% and strain increases ranged from 60% to 200% in the 50% dilated Marfan model. Leaflet stresses and strains were disproportionately high at the attachment edge and coaptation area. Leaflet coaptation was decreased by approximately 20% in the 50% root dilatation model., Conclusions: Increasing root dilatation and root elastic modulus to simulate Marfan syndrome significantly increases leaflet stress and strain and reduces coaptation in an otherwise normal aortic valve. These alterations may influence the decision to use valve-sparing aortic root replacement procedures in patients with Marfan syndrome.

Aortic valve incompetence due to aortic root dilation may be surgically corrected by resuspension of the native valve within a vascular graft. This study was designed to examine the effect of graft shape and material properties on aortic valve function, using a three-dimensional finite-element model of the human aortic valve and root. First, the normal root elements in the model were replaced with graft elements, in either a cylindrical or a "pseudosinus" shape. Next, the elements were assigned the material properties of either polyethylene terephthalate, expanded polytetrafluoroethylene, or polyurethane. Diastolic pressures were applied, and stresses, strains, and coaptation were recorded for the valve, root, and graft. Regarding shape, the cylindrical graft models increased the valve stresses by up to 173%, whereas the root-shaped graft model increased valve stresses by up to 40% as compared to normal. Regarding material properties, the polyurethane models demonstrated valve stress, strain, and coaptation values closest to normal, for either root shape. Graft shape had a greater effect on the simulated valve function than did the material property of the graft. Optimizing the shape and material design of the graft may result in improved longevity of the spared valve if a normal environment is restored.

Background: Idiopathic root dilatation often results in dysfunction of an otherwise normal aortic valve. To examine the effect of root dilatation on leaflet stress, strain, and coaptation, we utilized a finite element model., Methods: The normal model incorporated the geometry, tissue thickness, stiffness, and collagen fiber alignment of normal human roots and valves. We evaluated four dilatation models in which diameters of the aortic root were dilated by 5%, 15%, 30%, and 50%. Regional stress and strain were evaluated and leaflet coaptation percent was calculated under diastolic pressure., Results: Root dilatation significantly increased regional leaflet stress and strain beyond that found in the normal model. Stress increases ranged from 57% to 399% and strain increases ranged from 39% to 189% in the 50% dilatation model. Leaflet stress and strain were disproportionately high at the attachment edge and coaptation area. Leaflet coaptation was decreased by 18% in the 50% root dilatation model., Conclusions: Idiopathic root dilatation significantly increases leaflet stress and strain and reduces coaptation in an otherwise normal aortic valve. These alterations may affect valve-sparing aortic root replacement procedures.

Objective: The treatment of choice for aortic valve insufficiency due to root dilatation has become root replacement with aortic valve sparing. However, root replacement with a synthetic graft may result in altered valve stresses. The purpose of this study was to compare the stress/strain patterns in the spared aortic valve in different root replacement procedures by means of finite element modeling., Methods: Our finite element model of the normal human root and valve was modified to simulate and evaluate three surgical techniques: (1) "cylindrical" graft sutured below the valve at the anulus, (2) "tailored" graft sutured just above the valve, and (3) "pseudosinus" graft, tailored and sutured below the valve at the anulus. Simulated diastolic pressures were applied, and stresses and strains were calculated for the valve, root, and graft. Leaflet coaptation was also quantified., Results: All three root replacement models demonstrated significantly altered leaflet stress patterns as compared with normal patterns. The cylindrical model showed the greatest increases in stress (16%-173%) and strain (10%-98%), followed by the tailored model (stress +10%-157%, strain +9%-36%). The pseudosinus model showed the smallest increase in stress (9%-28%) and strain (2%-31%), and leaflet coaptation was closest to normal., Conclusion: Valve-sparing techniques that allow the potential for sinus space formation (tailored, pseudosinus) result in simulated leaflet stresses that are closer to normal than the cylindrical technique. Normalized leaflet stresses in the clinical setting may result in improved longevity of the spared valve.

Background and Aim of Study: This study was designed to determine: (i) Whether acute mitral valve regurgitation (MVR) due to chordal rupture can be reproducibly created under echocardiographic guidance; (ii) what degree of MVR can be created; (iii) what degree of acute regurgitation is survivable; and (iv) whether acute MVR due to chordal rupture progresses over time., Methods: In a pilot group of six juvenile farm-bred sheep, selected chordae tendineae were ruptured using either a biopsy needle or endoscopic scissors under echocardiographic guidance, without need for cardiopulmonary bypass. Sheep were sacrificed acutely (n = 2), and at six weeks (n = 2) or eight weeks (n = 2). When the technique was optimized, five sheep entered a study group in which chords were ruptured using endoscopic scissors; the sheep were sacrificed 16 weeks after surgery., Results: In the pilot study, acute MVR (grade 2-4+) was produced in all sheep, normal ventricular wall motion was maintained, with minimal progression of regurgitation over time. In one pilot sheep which did not survive, grade 4+ MVR was created acutely. Use of endoscopic scissors was preferable to the biopsy needle. In the study group, acute MVR (grade 2-4+) was produced in all five sheep, and was still present at 16 weeks, with progression in only one animal., Conclusions: This pilot study demonstrated that controlled degrees of survivable acute MVR due to chordal rupture can be created under echocardiographic guidance, with minimal progression of MVR over time. This animal model can be applied to investigate the pathogenesis of clinical MVR, and to suggest appropriate medical or surgical intervention.

Background and Aim of the Study: The effect of aging on aortic valve and root function was examined using a three-dimensional finite element model of the aortic root and valve., Methods: Three models representing normal (< 35 years), middle (35-55 years) and older (> 55 years) age groups, were created by assigning tissue thickness and stiffness that increased with age (using ANSYS software). Diastolic pressure was applied; stresses and strains were then evaluated for the valve and root, and percent leaflet coaptation was calculated., Results: Leaflet stresses were increased with aging, whereas leaflet strain and coaptation were decreased with aging. Specifically, leaflet stresses were increased by 6-14% in the middle-age model, and by 2-11% in the older-age model, as compared with normal in specified leaflet regions. Conversely, leaflet strains were decreased by 27-41% and 42-50% in the middle-age and older-age models, respectively. This reduced strain resulted in markedly decreased coaptation (9% and 30% reduction for middle- and older-age models). In the root, stress remained fairly constant with age, but strain in the root was progressively reduced with age (11% and 35% reduction for the middle and older-age models, respectively)., Conclusions: In these models, increased stiffness and thickness due to aging reduces leaflet deformation and restricts coaptation. Clinically, valvular regurgitation may result due to leaflet thickening and stiffening with normal aging. Our model can now be utilized to evaluate the root-valve relationship in the presence of bioprosthetic valves or root replacements.

Background: Ischemic mitral regurgitation or ventricular wall motion abnormalities will alter the stress distribution in the mitral valve. We hypothesize that in response, the regional collagen concentration will be altered and will significantly impact the stress distribution in the mitral valve., Methods: Two sheep served as normal (sham) controls. Two other sheep had coronary ligation resulting in abnormal ventricular wall motion. Four sheep underwent ligation to infarct the posteromedial papillary muscle, resulting in ischemic regurgitation. After 4 or 8 weeks, the mitral valves were excised, and the anterior leaflet sections were subjected to an assay for collagen concentration. Next, in a finite element model, to simulate changes in collagen concentration, the tissue stiffness was increased by 20%, and then decreased by 20%. In another model, the thickness of the tissue was increased by 20%, and then combined with decreased tissue stiffness. Physiologic loading pressures were applied, and leaflet stress, chordal stress, and coaptation results were analyzed., Results: The average collagen concentration in the normal sheep leaflets was 59.2% (dry weight), 50.6% in the ischemic controls, and 45.8% in the papillary muscle infarct group. Collagen concentration was greatest at the midline and decreased toward the commissures. Increased tissue stiffness resulted in increased leaflet and chordal stresses, as well as reduced coaptation. Decreased stiffness resulted in the opposite. Increased tissue thickness reduced leaflet and chordal stresses, but also reduced coaptation. The combination of increased tissue thickness and decreased stiffness demonstrated the greatest reduction in leaflet and chordal stress, while maintaining normal leaflet coaptation., Conclusions: The observed changes may demonstrate an early effort to compensate for increased leaflet stress. Microstructural alterations may demonstrate an early effort to compensate for altered physiologic loading to reduce stress and maintain coaptation. It is crucial in repairing or partially replacing thickened tissue that normal geometry and physiology be restored.

Background: We used a finite element model to determine the effect of papillary muscle position on the stress distribution in the mitral valve., Methods: A normal model was modified to move the posteromedial papillary muscle outward by either 2.5 mm or 5.0 mm. Next, the thickness was increased by 20%, simulating diseased tissue. Physiologic loading pressures were applied, and leaflet stress, chordal stress, and coaptation results were analyzed., Results: Displacement of the posteromedial papillary muscle increased the leaflet stresses and altered the normal stress patterns. The displacement also restricted the leaflets from closing completely, allowing regurgitation. Combining increased thickness with papillary displacement decreased the stresses slightly. However, the amount of leaflet coaptation was further decreased, creating larger gaps for regurgitation. In all models, the stresses in the chordae were increased in the marginal chordae and decreased in the basal chordae, demonstrating a transfer of stress., Conclusions: Papillary muscle displacement creates abnormal valve stresses, and the potential for significant regurgitation. Papillary-chordal-leaflet geometry must be maintained in partial or complete mitral homograft replacement.

Background and Purpose: We have previously shown that perfluorocarbon emulsions (PFEs) reduce the severity of cerebral injury (indicated by infarct, reduced blood flow, and depressed EEG) induced by air embolism during cardiopulmonary bypass (CPB). This study used retinal fluorescein angiography to define the mechanisms of cerebral injury and to determine the efficacy of PFEs in cerebral protection. These angiographic findings were correlated to previously reported histologic findings., Methods: Twenty domestic pigs underwent CPB with a prime of standard crystalloid or PFE (5 mg/kg) and crystalloid. After 10 minutes on CPB, a single (5 mL/kg) or double (2x2.5 mL/kg) bolus of room air or saline (control) was delivered via the right carotid artery. Retinal fluorescein angiograms were captured at 4 time points: baseline, air insult, postbypass, and postreperfusion. Following euthanasia, both eyes were removed and the retinas isolated for histological analysis with horseradish peroxidase (HRP), as previously reported., Results: In control pigs, postreperfusion angiograms showed small nonperfused areas, and retinal whole mounts demonstrated vascular damage as previously reported. In 5 PFE-primed animals, postreperfusion angiograms showed hyperfluorescence, but angiograms and HRP mounts were otherwise not significantly different from baseline. Severely hyperfluorescent vessels observed angiographically also showed a correlation with HRP extravasation but were not consistently indicative of severe vascular damage., Conclusions: Retinal fluorescein angiography and retinal staining with HRP indicate that mechanisms of cerebral air embolism include nonperfusion, vascular leakage and spasm, red blood cell sludging, and hemorrhage. Priming with PFE prevented many of the sequelae associated with air embolism.

Objectives: To examine whether a second-generation perfluorocarbon (PFC) blood substitute added to the cardiopulmonary bypass (CPB) prime influences complement production., Design: A prospective, randomized, single-blinded, ex vivo model., Setting: A university hospital, laboratory, and clinics., Participants: Ten healthy adult consented volunteer blood donors (five men, five women)., Interventions: Ex vivo closed-loop extracorporeal circuit including membrane oxygenator, tubing, and filter primed with crystalloid or crystalloid plus PFC was circulated for 1 hour with the addition of 500 mL of heparinized fresh human whole blood., Measurements and Main Results: Laboratory specimens were drawn from the circuit at 10-minute intervals for 1 hour and measured for complement (C3a, Bb fragment) concentrations, blood gases, fibrinogen concentration, platelet count, and hematocrit. In the PFC group, C3a and Bb fragments were equal to or less than those in the group that received crystalloid alone., Conclusion: The second-generation PFC added to the prime of a CPB circuit does not independently increase complement production.

The asymmetry of the aortic valve and aortic root may influence their biomechanics, yet was not considered in previous valve models. This study developed an anatomically representative model to evaluate the regional stresses of the valve within the root environment. A finite-element model was created from magnetic-resonance images of nine human valve-root specimens, carefully preserving their asymmetry. Regional thicknesses and anisotropic material properties were assigned to higher-order elastic shell elements representing the valve and root. After diastolic pressurization, peak principal stresses were evaluated for the right, left, and noncoronary leaflets and root walls. Valve stresses were highest in the noncoronary leaflet (538 kPa vs right 473 kPa vs left 410 kPa); peak stresses were located at the free margin and belly near the coaptation surfaces (averages 537 and 482 kPa for all leaflets, respectively). Right and noncoronary sinus stresses were 21% and 10% greater than the left sinus. In all sinuses, stresses near the annulus were higher than near the sinotubular junction. Stresses vary across the valve and root, likely due to their inherent morphologic asymmetry and stress sharing. These factors may influence bioprosthetic valve durability and the incidence of isolated sinus dilatation.

Background: Sternal wound infection is a relatively rare but potentially devastating complication of open heart operations. The most common treatments after debridement are rewiring with antibiotic irrigation and muscle flaps. Here we present the results of a prospective trial to determine the appropriate roles of closed-chest catheter irrigation and muscle flap closure for sternotomy infection and to assess the effect of internal mammary artery bypass grafting on the outcome of each treatment modality., Methods: Between 1990 and 1994, 5,658 sternotomies were performed at the University of Washington Medical Center. Sternal dehiscence occurred in 43 patients, 25 of whom had infection (overall incidence, 0.44%). Because of the infrequency of this complication, a prospective, randomized trial was developed in which the initial approach to sternal dehiscence was rewiring and catheter irrigation. Muscle flaps were used as the primary treatment if the sternum could not be restabilized or as secondary treatment if catheter irrigation failed. Wound resolution, length of hospital stay, and complications were evaluated., Results: Sterile dehiscences were successfully closed with irrigation in 17 of 18 patients; the other patient required flap closure. Of the 25 patients with infection, 19 had irrigation and 6, closure with flaps primarily. In the group of infected patients, 17 of the 19 who received irrigation also had internal mammary artery bypass grafting. Irrigation failed in 15 (88.2%) of these 17 patients, and salvage was accomplished with muscle flap closure. All 6 patients with infection who were closed primarily with muscle flaps had a successful outcome. Hospitalization averaged 10.2 days when muscle flaps were used primarily and 14.3 additional days for unsuccessful irrigation. When irrigation was successful, the hospital stay averaged 11.2 days., Conclusions: Catheter irrigation should be reserved for patients without infection or patients with infection but without internal mammary artery bypass grafts in whom dehiscence occurs less than 1 month after sternotomy. All others should have closure with muscle flaps.

Background and Aims of the Study: The study objective was to compare coaptation, and leaflet and chordal stresses in normal and dilated mitral valves (18% annular dilatation) versus valves with flexible (Duran) and rigid (Carpentier-Edwards classic) ring annuloplasty, using a computer model. We have developed a 3D finite element model which allows us to evaluate valvular function in terms of coaptation and stresses in both leaflets and individual chordae., Methods: The mitral valve was simulated using ANSYS 4.4A software. Normal model geometry, collagen fiber orientation, tissue thickness and material properties were determined from fresh porcine valves. For annular dilatation, the annular circumference was increased by 18% versus normal. For annuloplasty, a simulated flexible ring was attached to the annulus, and a simulated rigid ring then attached. Valves were evaluated during systolic pressure loading, after which timing of coaptation and leaflet and chordal stresses were determined., Results: In the normal valve, the anterior leaflet was subject to higher tensile stresses than the posterior leaflet which was under compression. With annular dilatation, all stresses were increased, particularly in the posterior leaflet. The flexible ring returned leaflet and chordal stresses closer to normal than did the rigid ring. Leaflet coaptation began at 5 ms in the normal state, was delayed by dilatation, and returned towards normal with both rings. The flexible ring returned coaptation and stresses closer to normal than did the rigid ring., Conclusions: Ring annuloplasty reduces the stresses and improves coaptation relative to annular dilatation. The success of mitral annuloplasty is likely due to the re-establishment of posterior leaflet compressive stresses and near-normal coaptation.

Background and Purpose: This laboratory has previously shown that a second-generation perfluorocarbon emulsion (PFE) reduces the severity of cerebral injury induced by air embolism during cardiopulmonary bypass (CPB). Horseradish peroxidase examines vascular permeability and was used in this study of the mechanisms of cellular protection afforded by the PFE., Methods: Twenty domestic pigs underwent CPB with a prime of standard crystalloid or PFE (5 mg/kg) and crystalloid. After 10 minutes on CPB, a 5-mL/kg bolus of room air or saline (control) was delivered via the right carotid artery. The air insult was delivered as either a single bolus or double bolus. After 1 hour of CPB and 1 hour of spontaneous reperfusion, horseradish peroxidase was injected intravenously and circulated for 15 minutes. After euthanasia, both eyes were removed, and the retinas were isolated for histological analysis., Results: Total length of retinal vessels exhibiting horseradish peroxidase extravasation was significantly less in PFE pigs (P < .05). Vascular spasm and red blood cell hemorrhages were unaffected by PFE. PFE pigs exhibited mild to moderate vascular nonperfusion and red blood cell sludging; crystalloid groups demonstrated severe nonperfusion and sludging., Conclusions: Histological staining with horseradish peroxidase indicated that mechanisms of cerebral air embolism include vascular endothelial leakage, vascular nonperfusion, and red blood cell sludging and hemorrhage. Pretreatment with PFE prevented some sequelae associated with massive air embolism and CPB.

Background and Aims: Sizing the mitral annulus remains one of the more subjective areas of annuloplasty surgery. We compared the dimensions of annuloplasty rings to annuloplasty sizers and to human mitral valve annuli to determine whether any discrepancies exist that might impact repair results., Methods: The anterior and posterior length of rigid rings, flexible rings, and corresponding sizers were measured. The ratio of the anterior length to the total length was calculated (A/T ratio) and compared to normal human ratios., Results: Nearly all rings had A/T ratios between 30% and 35% (except for the 32-mm rigid ring at 37.5%). For both rigid and flexible rings, the ring A/T ratios and the sizer A/T ratios differed significantly (except for the 28-mm rigid ring and sizer). In comparison to the average human A/T ratio (36.6%), the ratio for most rings was significantly lower., Conclusions: The mismatch between rings and sizers results in three possible scenarios: the length of the anterior portion of the ring can be equal to, smaller than, or larger than the anterior portion of the sizer. The clinical implications are that the valve could become stenotic when the ring is implanted or that the anterior portion of the annulus could be altered (stretched or buckled). We feel that to assure improved long-term results, more accurate matching of sizers to rings is essential and that better matching to normal human anatomical ratios would be ideal.

The purpose of this study was to examine the effects of annular dilatation on coaptation, and leaflet and chordal stresses, using a three dimensional finite element computer model. To do this, the whole mitral valve was simulated using ANSYS 4.4A software. Normal model geometry, collagen fiber orientation, tissue thickness, and material properties were determined from fresh porcine valves. For annular dilatation, the annular circumference was increased by 18% versus normal. Isovolumic contraction and rapid ventricular ejection were simulated. Data showed that, in the annular dilatation model, the stress magnitudes increased more than two-fold compared with normal in both the anterior leaflet and posterior leaflet. Coaptation was greatly delayed in the dilatation model, and the leaflets never fully coapted. Chordal stresses were also greatly increased in the dilatation model. In conclusion, increased stress due to annular dilatation may lead to tissue disruption, further dilatation, delayed coaptation, and increased regurgitation, in a 'closed-loop' degenerative process.

Mitral regurgitation (MR) and abnormal ventricular wall motion (AVWM) are two cardiac conditions that may increase mitral valve (MV) stresses. Theoretically, increased stress could induce damaging MV tissue alterations. These alterations may impair the preferred option of repair, and mandate replacement. It is hypothesized that MV collagen synthesis is upregulated in response to MR and AVWM. To test this hypothesis in a pilot study, an ischemic sheep model (n = 8) was employed. Four sheep underwent selective coronary artery ligation to infarct a papillary muscle, which resulted in MR. Two other sheep underwent similar coronary ligation to create AVWM. As controls, two sheep underwent sham surgery (no ligation). Sheep were killed 4 and 8 weeks post operatively and their MVs were sectioned. Sections were stained with an antibody (SP1.D8, University of Iowa) to procollagen I (precursor to collagen I). The percent area of procollagen stain present present was measured by image analysis (Optimas Corporation) and used as an indicator of collagen synthesis. Procollagen results indicated that MV collagen synthesis was upregulated by factor of 1.8 in both the MR and AVWM groups versus controls. In addition, results showed greater upregulation in anterior leaflets compared with posterior leaflets in both infarct groups. These results indicate that MV collagen synthesis is upregulated in response to MR and AVWM.

Background: Perfluorocarbon emulsion has proved beneficial in the prevention and amelioration of experimental air embolism. We examined whether the addition of perfluorocarbon to the prime solution could lead to a reduction in the incidence and severity of neurologic injury after the formation of a massive air embolism during cardiopulmonary bypass., Methods: Fourteen pigs underwent bypass in which either a crystalloid prime solution or a perfluorocarbon prime solution (10 mL/kg) was used. Ten minutes into bypass a bolus (5 mL/kg) of air or saline (control) was delivered via the carotid artery. The resulting cerebral infarcts were graded on the basis of the findings in triphenyltetrazolium chloride-stained cerebral sections. Colored microspheres were used to measure cerebral blood flow. Bitemporal electroencephalography was used to evaluate cerebral function., Results: Cerebral infarction was not found in the perfluorocarbon-air group (0 to 5 animals), as compared with its occurrence in 3 of the 5 animals in the crystalloid-air group. Cerebral blood flow was also maintained or increased in the perfluorocarbon-air group (p < 0.05), and the electroencephalogram total power showed less of a decrease and recovered more completely (p < 0.05) than it did in the crystalloid-air group., Conclusions: The addition of perfluorocarbon emulsion to the cardiopulmonary bypass prime solution leads to a reduction in the incidence and severity of neurologic injury after the formation of a massive air embolism during bypass.

Background and Aims: The hemodynamic performance of a mechanical or stented bioprosthetic valve is primarily determined by the diameter of its orifice. Thus, in aortic or mitral valve replacement, assessment of the native annular size and selection of the correspondingly sized prosthetic valve is necessary to achieve maximum hemodynamic performance. The purpose of this study was to determine the actual dimensions of aortic and mitral valve sizers and their corresponding prostheses, and to determine whether they differed from their marked dimensions., Methods: Mechanical and stented bioprosthetic valves and sizers were obtained from the manufacturers (CarboMedics, St. Jude, Medtronic-Hall, Starr-Edwards, Carpentier-Edwards, and Medtronic-Hancock), and the diameters were measured., Results: For the mechanical models, both aortic and mitral sizers were larger than their marked size by 0.5 mm to 1.0 mm. The aortic valves were all smaller than their corresponding sizers, but the relationship of the mitral valves to corresponding sizers varied with the manufacturer. For the bioprosthetic models the aortic and mitral sizers were true to marked size, the aortic valves were close to marked size and the mitral valves were smaller than marked size., Conclusions: These differences make optimal sizing difficult at best, particularly if more than one manufacturers' product is used in an institution. These differences may or may not impact valve performance in an individual surgeon's hands. However, the wide range of variations across prosthetic type and manufacturer obligate the surgeon to be aware of these variances to achieve maximum hemodynamic performance for each patient.

Background and Aims of the Study: Replacement of ruptured mitral valve chordae using expanded polytetrafluoroethylene (ePTFE) sutures is becoming an increasingly utilized repair technique. However, setting the proper length of the replacement suture is technically challenging, and the effect of a non-optimal suture length is undefined. The purpose of this study was to assess how varying the length of replacement sutures affects mitral valve function and stresses., Materials and Methods: We employed a finite element model of the mitral valve used extensively in our laboratory. Seven different valve conditions were simulated using this model: (i)normal valve, (ii) chordal rupture without repair, and (iii-iv) chordal replacement using ePTFE sutures that were equal in length to the replaced chordae (equal length), 10% longer (Long10), 3% longer (Long3), 3% shorter (Short3), and 10% shorter (Short10) than the replaced chordae. Each model was loaded to physiologic pressures., Results: Both the Long10 and chordal rupture models achieved complete valve closure, but chordal stresses were nearly double normal values. The Long3 model also demonstrated complete valve closure, but chordal stresses were increased to only one-third more than normal. Using sutures equal to or shorter than the length of the replaced chordae prevented complete valve closure, and produced stress concentrations at the anterior leaflet free edge. The resulting gaps and stress concentrations were most significant in the Short10 model and least significant in the equal length model., Conclusions: These models demonstrate that replacement sutures equal to, or slightly longer than the replaced chordae optimize function and stresses in the repaired valve.

During the past 10 years chordal replacement with expanded polytetrafluoroethylene (ePTFE) suture has become an acceptable mitral valve repair technique. Unfortunately, its effect on the mechanical function of the valve is unclear. The purpose of this study was to test whether replacement of ruptured anterior leaflet chordae with ePTFE suture restores mitral valve function and stresses to normal ranges. To answer this question, the authors' existing finite element model of the mitral valve was modified to simulate six different valve conditions: 1) normal, 2) rupture of anterior chordae, 3) replacement using two 4-0 ePTFE sutures, 4) replacement using four 4-0 ePTFE sutures, 5) replacement using two 5-0 ePTFE sutures, and 6) replacement using four 5-0 ePTFE sutures. Physiologic pressures representing ventricular systole from the onset of isovolumic contraction to peak left ventricular pressure were applied to each model. It was found that after rupture, coaptation was impaired and stresses increased dramatically in chordae adjacent to the rupture site. Replacement with two ePTFE sutures restored proper coaptation and lowered stresses to near normal. Using four sutures also restored coaptation and lowered stresses even further. There was minimal difference between 4-0 and 5-0 suture. In conclusion, the replacement of ruptured anterior leaflet chordae with ePTFE suture restores both mitral valve function and stresses to normal ranges.

Mechanical valved conduit replacement of the aortic root is a durable and appropriate procedure for many diseases of the ascending aorta, but may sacrifice an anatomically salvageable aortic valve. For young active patients and for patients with "systemic" arterial disease (atherosclerosis, Marfan's syndrome) who may require future operations, life-long anticoagulation with its attendant thromboembolic versus hemorrhagic risks is not ideal. Several techniques have been suggested as aortic valve-sparing options. Recently, a procedure was described that combines the freehand homograft techniques with the standard Bentall techniques (David procedure). This innovative technique replaces the ascending aorta with a Dacron cylinder, spares the aortic valve, and restores competence and thus offers an excellent alternative. The durability of this procedure that places the aortic valve inside a cylindrical conduit without sinuses of Valsalva is unknown. In selected patients, we have used this technique to spare the aortic valve. On the basis of experimental data and preliminary computer modeling, with the hope of improving the durability, we have modified the conduit to create a "pseudosinus" in our most recent nine patients. We have done the David procedure in 10 patients. The pseudosinus modification was done in the most recent nine patients. Patients' ages ranged from 37 to 71 years (mean 49.9 years). There were five female and five male patients. Five patients had Marfan's syndrome and five patients had annuloaortic ectasia. There has been no mortality and all patients have had both early and late follow-up echocardiography. Five patients have zero to trace aortic insufficiency, four patients have trace to mild aortic insufficiency, and one patient has mild or "1+" aortic insufficiency. Aortic insufficiency has not progressed in any patient during the 18 months of follow-up. The patient with 1+ aortic insufficiency has no activity limits, good ventricular function, and no evidence of congestive symptoms. One patient who had extensive thoracoabdominal aneurysmal disease has undergone subsequent replacement of the descending aorta to the level of the renal arteries and has done well. Aortic valve-sparing replacement of the aortic root is an excellent procedure for any patient with an ascending aortic aneurysm and an anatomically salvageable valve. We believe that by modifying the proximal conduit and creating a "pseudosinus" into which the leaflets can retract without contact of the cylindrical conduit we may increase the longevity of the native aortic valve in this procedure.

The increasing popularity of mitral valve repair and current interest in replacement with a mitral homograft or heterograft warrant a new look at the normal functional anatomy of the system. We conducted a detailed review of the anatomic structure of both the intact and excised mitral apparatus of porcine and human species. The following intact structural dimensions were measured: total annular length, anterior and posterior annular length. Excised measurements included: total annular length, anterior and posterior annular lengths, leaflet edge lengths, leaflet heights, and anterolateral and posteromedial commissural heights. Leaflet area was calculated from planimetric measurements. Chordal lengths were measured and distribution recorded. The majority of leaflet measurements were not statistically different between groups. For both groups, the measured annular length increased significantly upon valve excision. In both groups, the posterior leaflet area was significantly larger than the anterior leaflet area, and the area of each leaflet alone was significantly greater than the calculated orifice area. Chordal length was not significantly different between groups, however, distribution varied slightly with the ratio of origins to insertions being 8:1 (porcine) and 5:1 (human). The results are consistent with previous studies of the human mitral valve. This study showed little difference between human and porcine data, and the porcine valve was identified as an appropriate model for further investigation of the mitral valve system.(ABSTRACT TRUNCATED AT 250 WORDS)

A surgical procedure has recently been described for patients with aortic incompetence caused by annular dilation, but with normal aortic leaflets. The dilated aortic root is replaced with a Dacron graft, and the native aortic valve is resuspended within the graft. Matching the size and shape of the graft to the size of the leaflets may have significant effects on valve closure and leaflet stress and thus on the longevity of the repair. To define the relationship of native aortic root structure to leaflet size, we morphologically examined normal human aortic roots (n = 10) and valve leaflets and applied mathematic analyses to the results. Our data show that the root has a consistent shape with varying size and that there is a definable mathematic relationship between root diameter and clinically measurable leaflet dimensions. We derived an equation that allows calculation of the appropriate diameter of the root at the sinus of Valsalva level from leaflet heights and perimeters. The diameter of the graft at the sinotubular junction and base should follow the relationship of the normalized root dimensions, either by tailoring of the graft or by new graft design. The current data imply that the graft should incorporate sinuses for proper valve closure and for sharing stress with the leaflets. Application of these results will allow prosthetic graft design to more closely resemble the native aorta. These new grafts should improve physiologic function of the valve, reduce leaflet stress, and increase the durability of the repair.

Clinical experience with the first generation porcine xenograft shows significant deterioration and mechanical failure after 7-8 years post-implantation. Although many mechanisms of valve failure have been identified, the inherent differences between porcine and human aortic valves have not been emphasized. To determine if these differences are significant, the authors studied the anatomy of the aortic valve in 10 post-mortem porcine hearts. The authors found that the non-coronary leaflet was the smallest and the right leaflet was the largest based on the dimensions of area, perimeter, weight, and attached edge length (p < 0.05). These results differ from reported analyses of human aortic valves, in which the smallest cusp is generally the right the largest is the non-coronary. The authors believe that these differences between the human and porcine aortic valves may result in atypical mechanical stresses and the disruption of blood flow patterns in the sinuses of Valsalva, and may decrease the long-term stability of the porcine bioprostheses. In other words, the failure found with porcine bioprostheses after 8 years of implantation might be expected from the inherent structure (and associated fluid dynamics) of the porcine aortic valve positioned in the human aortic root.

A finite element model was developed to examine deformation and stress patterns in the mitral valve under systolic loading conditions. This is the first three-dimensional finite element model of the mitral valve, incorporating all essential anatomic components, regional tissue thickness, collagen fiber orientation and related anisotropic material properties. A non-linear, transient, dynamic analysis was performed which included time-dependent loading, leaflet and chordal mass inertial effects and chordal element bi-linearity. The model was first analyzed without either annular or papillary muscle contraction and then with either or both. The hypothesis was that the combination of annular and papillary muscle contraction would have a beneficial effect on valve function. In all models, the computed anterior leaflet principal stresses were tensile and of greater magnitude than those in the posterior leaflet. The principal stress directions were observed to correlate well with collagen fiber orientation. Earlier leaflet coaptation was demonstrated with annular contraction, promoting valve closure, while papillary muscle contraction increased the stress on the chordae tendineae and both leaflets, tending to pull the latter apart. The combination of the two combined these effects, and showed the most even stress distribution. The effects of annular and papillary muscle contraction on valve function were shown to be beneficial by this model, and they can be further elucidated by varying the extent and timing of the individual contractions. This model can be used to examine the effects of pathologic changes, surgical manipulations and proposed material replacements. It can thus aid both the surgeon and the biomedical engineer in improving the materials and techniques available for the repair and/or replacement of mitral valve system components.

Surgical repair of the mitral valve primarily involves endogenous valve tissue, however, the intrinsic mechanical behaviour of the tissue is not well described. To address this issue, porcine mitral valve leaflets were examined histologically and engineering concepts were applied to understand the mechanical behaviour of the layered tissue. Rectangular portions were excised from the anterior and posterior leaflets, either parallel or perpendicular to the annulus, and sections were stained for collagen (Masson's trichrome). The cross sectional layers of the valve (atrialis/spongiosa, fibrosa, and ventricularis) were identified by differences in cellularity and collagen density. The fibrosa is composed of dense collagen, while the atrialis/spongiosa and ventricularis are composed of loose collagen. Layer thicknesses were recorded digitally across the section. These values were averaged within tissue groups to determine changes in layer thickness over the length of the sample and average thickness of each layer. In all tissue groups, the fibrosa was the thickest layer, and the atrialis/spongiosa layer was thicker than the ventricularis layer. The total and fibrosa layer thicknesses of the anterior leaflet were significantly thicker than in the posterior leaflet. Mechanical engineering analysis of the layered structures under tension indicated that the anterior leaflet would be able to support greater tensile loads than the posterior leaflet. The layered arrangement was then examined as a beam in bending, and was shown to decrease the resistance of leaflets to bending, and decrease the overall bending stresses on the leaflet. This type of analysis may be extrapolated to gain insight into changes in function in diseased valves as well.(ABSTRACT TRUNCATED AT 250 WORDS)

With the trend in open heart surgery toward normothermic bypass and warm blood cardioplegia, greater demand is being placed on the perfusionist to select an oxygenator that will perform safely and efficiently under a variety of conditions. While manufacturers report performance parameters for their products, the data is often not comparable due to widely differing conditions. Recent in vitro evaluation techniques employed to characterize membrane oxygenators do not simulate the actual oxygenator conditions observed during cardiopulmonary bypass. Biocompatibility and drug delivery are reported but comparisons of different oxygenator performance parameters are not completely addressed. We have designed a test circuit and an evaluation protocol to simultaneously characterize the performance of multiple oxygenators under identical conditions. The test circuit is designed to simulate clinical conditions and to evaluate gas exchange, blood path pressures, gas path pressures, and hemolysis. Previously reported studies have relied on a comparison of a single membrane oxygenator and a single bubble oxygenator. Our protocol will compare multiple membrane oxygenators, in vitro, under similar clinically relevant conditions. Such testing would be done prior to animal or clinical trials. Furthermore in vitro tests should be more reproducible and more discriminating than are ex vivo tests.