Midterm outcomes using the physio ring in mitral valve reconstruction: experience in 492 patients

Physio and Physio II rings: beyond the annular physiology

BACKGROUND

Engineering of the Carpentier-Edwards Physio (PR-I) and Physio II (PR-II) rings (Edwards Lifesciences Corp., Irvine, CA, USA) combines flexibility with remodeling. PR-II is considered an improvement of PR-I, as it boasts of an improved shape, a double saddle, and a sewing cuff that reduces tension on sutures. Beyond the superior effect of the PR-II on the annular physiology, it has not been proven to be clinically better than the PR-I. This study compares the long-term clinical outcomes of MV repair for degenerative disease with these rings.

METHODS

From 2004 to 2020, MV repair with Physio ring annuloplasty (group PR-I) was performed in 231 patients, and with Physio-II ring annuloplasty (group PR-II) in 255 patients. A propensity score-matching analysis was used to pair 104 in each group. Primary outcome was recurrent MR≥3 and secondary outcomes were long-term survival, cardiac death, and MV-related events (MVREs). The 15-year follow-up data were complete in 97.3% of patients.

RESULTS

There were no differences in 15-year freedom from recurrent MR (P=0.721), survival and cardiac death between the matched groups (P=0.693 and P=0.135, respectively). MVREs, including cardiac death, pacemaker implantation, thromboembolism, bleeding, and reoperation were also similar between the matched groups (P=0.603). However, 5-year recurrent MR was significantly higher in PR-I than in PR-II (P=0.010). Multivariate analysis showed Barlow's disease and preoperative MR≥3 as risk factors for late MR recurrence.

CONCLUSIONS

Type of annuloplasty rings did not influence long-term clinical outcomes. Better annular dynamics seen in PR-II annuloplasty does not translate into superior freedom from recurrent MR.

Clinical Impact of Computational Heart Valve Models

This paper provides a review of engineering applications and computational methods used to analyze the dynamics of heart valve closures in healthy and diseased states. Computational methods are a cost-effective tool that can be used to evaluate the flow parameters of heart valves. Valve repair and replacement have long-term stability and biocompatibility issues, highlighting the need for a more robust method for resolving valvular disease. For example, while fluid-structure interaction analyses are still scarcely utilized to study aortic valves, computational fluid dynamics is used to assess the effect of different aortic valve morphologies on velocity profiles, flow patterns, helicity, wall shear stress, and oscillatory shear index in the thoracic aorta. It has been analyzed that computational flow dynamic analyses can be integrated with other methods to create a superior, more compatible method of understanding risk and compatibility.

The Carpentier-Edwards Classic and Physio Annuloplasty Rings in Repair of Degenerative Mitral Valve Disease: A Retrospective Study

Background

Physio ring (SR) is considered an improved version of the Classic rigid ring (RR). Today, SR is more widely used in mitral valve (MV) repair. We sought to compare the long-term outcomes of repair with RR and SR in degenerative mitral valve disease.

Methods

In a computerized registry of our institution, 306 patients had MV repair with either RR (139 patients) or SR (167 patients) ring between 2005 and 2015. Fifteen of them had concomitant tricuspid valve repair. Ninety-two (30.1%) had Barlow's disease and 214 (69.9%) had fibroelastic deficiency. The patients had similar demographic and echocardiographic characteristics.

Results

There were 4 (1.3%) operative mortalities. Mean follow-up time was 107.4 ± 13.2 months. Left ventricular end diastolic and end systolic diameters significantly improved in both groups but not between groups. Survival at 10 years was 84.6% (93.1% in RR and 91.5% in SR; p = 0.177) and 10-year freedom from recurrent MR ≥ 2+ was 74.5% (88.2% in RR and 86.3% in SR; p = 0.110). Reoperations for repair failure were 8 in RR and 6 in SR. By Cox regression analysis, Barlow's disease and preoperative MR = 4+ were predictors of repair failure. Old age (≥70 years), NYHA functional class IV and pulmonary artery systolic pressure (≥40 mmHg) were predictors of poor survival by univariate analysis.

Conclusion

Long-term outcomes of repair for degenerative MV disease with the Classic and Physio rings are comparable. We also reiterate the importance of large size annuloplasty rings for Barlow's disease to avoid the incidence left ventricular outflow obstruction.

Mid-term results of mitral valve repair using flexible bands versus complete rings in patients with degenerative mitral valve disease: a prospective, randomized study

Background

We aimed to compare the outcomes of mitral valve repair with flexible band (FB) versus complete semirigid ring (SR) in degenerative mitral valve disease patients.

Methods

From September 2011 to 2014, 171 patients were randomized and underwent successful mitral valve repair using a SR (n = 85) or FB (n = 86). There were no significant between-group differences at baseline.

Results

There were no early mortalities. The mean follow up was 24.7 months. The 2-year survival was 96.0 ± 2.3% (95% confidence interval [CI], 88.6–98.7%) and 94.3 ± 2.8% (95% CI, 85.5–97.9%) in the SR and FB groups, respectively (p = 0.899). The left ventricle remodeling was similar between the groups. Higher transmitral peak (8.5 [3.9–17] vs. 6 [2.1–18] mmHg, p < 0.001), mean pressure gradients (3.7 [1.3–8] vs. 2.8 [0.6–6.8] mmHg, p = 0.001), and systolic pulmonary artery pressure (34.5 [20–68] vs. 29.5 [8–48] mmHg, p < 0.001) was observed in the SR group. The 2-year freedom from recurrence of significant mitral regurgitation was significantly higher in the FB group than the SR group (p = 0.002). Residual mitral regurgitation was an independent prognostic factor of recurrence of mitral regurgitation. The 3-year freedom from reoperation was significantly higher in the FB group than the SR group (p = 0.044).

Conclusion

Patients with degenerative mitral valve disease may benefit from valve repair with FBs. Residual mitral regurgitation before discharge is an independent risk factor of late insufficiency recurrence.

Trial registration

ClinicalTrials.gov NCT03278574, retrospectively registered on 06.09.2017.

Electronic supplementary material

The online version of this article (10.1186/s13019-017-0679-0) contains supplementary material, which is available to authorized users.

Heart Valve Biomechanics and Underlying Mechanobiology

Heart valves control unidirectional blood flow within the heart during the cardiac cycle. They have a remarkable ability to withstand the demanding mechanical environment of the heart, achieving lifetime durability by processes involving the ongoing remodeling of the extracellular matrix. The focus of this review is on heart valve functional physiology, with insights into the link between disease-induced alterations in valve geometry, tissue stress, and the subsequent cell mechanobiological responses and tissue remodeling. We begin with an overview of the fundamentals of heart valve physiology and the characteristics and functions of valve interstitial cells (VICs). We then provide an overview of current experimental and computational approaches that connect VIC mechanobiological response to organ- and tissue-level deformations and improve our understanding of the underlying functional physiology of heart valves. We conclude with a summary of future trends and offer an outlook for the future of heart valve mechanobiology, specifically, multiscale modeling approaches, and the potential directions and possible challenges of research development. © 2016 American Physiological Society. Compr Physiol 6:1743-1780, 2016.

Annular dynamics after mitral valve repair with different prosthetic rings: A real-time three-dimensional transesophageal echocardiography study

PURPOSE

We assessed the effects of different types of prosthetic rings on mitral annular dynamics using real-time three-dimensional echocardiography (RT3DE).

METHODS

RT3DE was performed in 44 patients, including patients undergoing mitral annuloplasty using the Cosgrove-Edwards flexible band (Group A, n = 10), the semi-rigid Sorin Memo 3D ring (Group B, n = 17), the semi-rigid Edwards Physio II ring (Group C, n = 7) and ten control subjects. Various annular diameters were measured throughout the cardiac cycle.

RESULTS

We observed flexible anterior annulus motion in all of the groups except Group C. A flexible posterior annulus was only observed in Group B and the Control group. The mitral annular area changed during the cardiac cycle by 8.4 ± 3.2, 6.3 ± 2.0, 3.2 ± 1.3, and 11.6 ± 5.0 % in Group A, Group B, Group C, and the Control group, respectively. The dynamic diastolic to systolic change in mitral annular diameters was lost in Group C, while it was maintained in Group A, and to a good degree in Group B. In comparison to the Control group, the mitral annulus shape was more ellipsoid in Group B and Group C, and more circular in Group A.

CONCLUSION

Although mitral regurgitation was well controlled by all of the types of rings that were utilized in the present study, we demonstrated that the annulus motion and annulus shape differed according to the type of prosthetic ring that was used, which might provide important information for the selection of an appropriate prosthetic ring.

Mitral Valve Annuloplasty Rings: Review of Literature and Comparison of Functional Outcome and Ventricular Dimensions

In the past decades, more than 40 mitral valve annuloplasty rings of various shapes and consistency were marketed for mitral regurgitation (MR), although the effect of ring type on clinical outcome remains unclear. Our objective was to review the literature and apply a simplification method to make rings of different shapes and rigidity more comparable. We studied relevant literature from MEDLINE and EMBASE databases related to clinical studies as well as animal and finite element models. Annuloplasty rings were clustered into 3 groups as follows: rigid (R), flexible (F), and semirigid (S). Only clinical articles regarding degenerative (DEG) or ischemic/dilated cardiomyopathy (ICM) MR were included and stratified into these groups. A total of 37 rings were clustered into R, F, and S subgroups. Clinical studies with a mean follow-up of less than 1 year and a reported mean etiology of valve incompetence of less than 60% were excluded from the analysis. Forty-one publications were included. Preimplant and postimplant end points were New York Heart Association class, left ventricular ejection fraction (LVEF), left ventricular end-systolic dimension (LVESD), and left ventricular end-diastolic dimension (LVEDD). Statistical analysis included paired-samples t test and analysis of variance with post hoc Bonferroni correction. P < 0.05 indicated statistical difference. Mean ± SD follow-up was 38.6 ± 27 and 29.7 ± 13.2 months for DEG and ICM, respectively. In DEG, LVEF remained unchanged, and LVESD decreased in all subgroups. In our analysis, LVEDD decreased only in F and R, and S did not change; however, the 4 individual studies showed a significant decline. In ICM, New York Heart Association class improved in all subgroups, and LVEF increased. Moreover, LVESD and LVEDD decreased only in F and S; R was underpowered (1 study). No statistical difference among R, F, and S in either ICM or DEG could be detected for all end points. Overall, owing to underpowered data sets derived from limited available publications, major statistical differences in clinical outcome between ring types could not be substantiated. Essential end points such as recurrent MR and survival were incomparable. In conclusion, ring morphology and consistency do not seem to play a major clinical role in mitral valve repair based on the present literature. Hence, until demonstrated otherwise, surgeons may choose their ring upon their judgment, tailored to specific patient needs.

An inverse modeling approach for stress estimation in mitral valve anterior leaflet valvuloplasty for in-vivo valvular biomaterial assessment

Estimation of regional tissue stresses in the functioning heart valve remains an important goal in our understanding of normal valve function and in developing novel engineered tissue strategies for valvular repair and replacement. Methods to accurately estimate regional tissue stresses are thus needed for this purpose, and in particular to develop accurate, statistically informed means to validate computational models of valve function. Moreover, there exists no currently accepted method to evaluate engineered heart valve tissues and replacement heart valve biomaterials undergoing valvular stresses in blood contact. While we have utilized mitral valve anterior leaflet valvuloplasty as an experimental approach to address this limitation, robust computational techniques to estimate implant stresses are required. In the present study, we developed a novel numerical analysis approach for estimation of the in-vivo stresses of the central region of the mitral valve anterior leaflet (MVAL) delimited by a sonocrystal transducer array. The in-vivo material properties of the MVAL were simulated using an inverse FE modeling approach based on three pseudo-hyperelastic constitutive models: the neo-Hookean, exponential-type isotropic, and full collagen-fiber mapped transversely isotropic models. A series of numerical replications with varying structural configurations were developed by incorporating measured statistical variations in MVAL local preferred fiber directions and fiber splay. These model replications were then used to investigate how known variations in the valve tissue microstructure influence the estimated ROI stresses and its variation at each time point during a cardiac cycle. Simulations were also able to include estimates of the variation in tissue stresses for an individual specimen dataset over the cardiac cycle. Of the three material models, the transversely anisotropic model produced the most accurate results, with ROI averaged stresses at the fully-loaded state of 432.6±46.5 kPa and 241.4±40.5 kPa in the radial and circumferential directions, respectively. We conclude that the present approach can provide robust instantaneous mean and variation estimates of tissue stresses of the central regions of the MVAL.

[Mitral valve surgery in patients with extensively calcified mitral annulus: long-term echocardiographic and clinical follow-up]

OBJECTIVE

The aim of this study was the analysis of long-term results in patients with hemodynamically significant mitral valve disease due to extensively calcified mitral annulus who underwent decalcification and patch reconstruction.

PATIENTS AND METHODS

Between 1996 and 2008 a total of 109 patients underwent surgery for extensive calcification and severe mitral insufficiency and mitral stenosis. The mean age of the patients (65 women and 44 men) was 66.4 ± 13.8 years. In 53 patients (49%) mitral valve repair was performed and the remaining 56 patients (51%) received a mitral valve replacement. Of the patients 64 (59%) required concomitant surgery. The mean follow up time was 96 ± 48 months.

RESULTS

The in-hospital and late mortality was 8.3% (9 patients) and 25.6% (28 patients), respectively. The actuarial survival rates at 5, 8 and 12 years were 88.1%, 76.2% and 66.1%, respectively. Echocardiographic follow-up presented a mitral insufficiency grade III in 4 patients (6%). None of the patients had a mitral insufficiency grade IV. A significant reduction of left atrium diameter, of the LVEDD as well as the mean transvalvular gradient was observed. Freedom from reoperation at 5 and 8 years was 96.4% and 91.8%, respectively. Systemic hypertension, diabetes mellitus, age older than 65 years, concomitant aortic valve replacement, concomitant procedures, chronic renal insufficiency and cardiac decompensation in the medical history were found to be predictors for significantly increased early or late mortality.

CONCLUSION

The long-term results strongly suggest that en bloc decalcification and patch reconstruction of the mitral annulus can be safely undertaken in high risk patients.

[Long-term echocardiographic and clinical follow-up after mitral valve surgery in patients with extensive calcified mitral annulus]

OBJECTIVE

The aim of this study is the analysis of long-term results in patients with hemodynamically significant mitral valve disease due to extensive calcified mitral annulus who underwent decalcification and patch reconstruction.

PATIENTS AND METHODS

Between 1996 and 2008 a total of 109 patients underwent surgery in the presence of extensive calcification, severe mitral insufficiency and mitral stenosis. The mean age of patients (65 women, 44 men) was 66.4±13.8 years. Mitral valve repair was performed in 53 patients (49%), while the remaining 56 patients (51%) received a mitral valve replacement. In all, 64 patients (59%) required concomitant surgery. The mean follow-up time was 96±48 months.

RESULTS

Inpatient and late mortality rates were 8.3% (nine patients) and 25.6% (28 patients), respectively. The actuarial survival rates at 5, 8 and 12 years were 88.1%, 76.2% and 66.1%. Echocardiographic follow-up demonstrated mitral insufficiency III in four patients (6%). No patients had mitral insufficiency IV. We observed a significant reduction in left atrium diameter, LVEDD as well as mean transvalvular gradient. Freedom from reoperation at 5 and 8 years was 96.4% and 91.8%, respectively. We found systemic hypertension, diabetes mellitus, age above 65 years, concomitant aortic valve replacement, concomitant procedures, chronic renal insufficiency and cardiac decompensation in the medical history as predictors for significantly increased early or late mortality.

CONCLUSION

The long-term results strongly suggest that en bloc decalcification and patch reconstruction of the mitral annulus can be safely undertaken in high-risk patients.

Rigid, complete annuloplasty rings increase anterior mitral leaflet strains in the normal beating ovine heart

BACKGROUND

Annuloplasty ring or band implantation during surgical mitral valve repair perturbs mitral annular dimensions, dynamics, and shape, which have been associated with changes in anterior mitral leaflet (AML) strain patterns and suboptimal long-term repair durability. We hypothesized that rigid rings with nonphysiological three-dimensional shapes, but not saddle-shaped rigid rings or flexible bands, increase AML strains.

METHODS AND RESULTS

Sheep had 23 radiopaque markers inserted: 7 along the anterior mitral annulus and 16 equally spaced on the AML. True-sized Cosgrove-Edwards flexible, partial band (n=12), rigid, complete St Jude Medical rigid saddle-shaped (n=12), Carpentier-Edwards Physio (n=12), Edwards IMR ETlogix (n=11), and Edwards GeoForm (n=12) annuloplasty rings were implanted in a releasable fashion. Under acute open-chest conditions, 4-dimensional marker coordinates were obtained using biplane videofluoroscopy along with hemodynamic parameters with the ring inserted and after release. Marker coordinates were triangulated, and the largest maximum principal AML strains were determined during isovolumetric relaxation. No relevant changes in hemodynamics occurred. Compared with the respective control state, strains increased significantly with rigid saddle-shaped annuloplasty ring, Carpentier-Edwards Physio, Edwards IMR ETlogix, and Edwards GeoForm (0.14 ± 0.05 versus 0.16 ± 0.05, P=0.024, 0.15 ± 0.03 versus 0.18 ± 0.04, P=0.020, 0.11 ± 0.05 versus 0.14 ± 0.05, P=0.042, and 0.13 ± 0.05 versus 0.16 ± 0.05, P=0.009), but not with Cosgrove-Edwards band (0.15 ± 0.05 versus 0.15 ± 0.04, P=0.973).

CONCLUSIONS

Regardless of three-dimensional shape, rigid, complete annuloplasty rings, but not a flexible, partial band, increased AML strains in the normal beating ovine heart. Clinical studies are needed to determine whether annuloplasty rings affect AML strains in patients, and, if so, whether ring-induced perturbations in leaflet strain states are linked to repair failure.

Autologous ring vs. flexible prosthetic ring for ischemic mitral regurgitation

Ring annuloplasty is the most common strategy for correction of ischemic mitral regurgitation. When a commercial prosthesis is unavailable or too expensive, an autogenous annuloplasty ring can be handmade by the surgeon. The aim of this study was to compare short-term results of mitral valve repair with autologous annuloplasty rings and the SJM Tailor flexible prosthesis. Between March 2004 and April 2006, 100 patients undergoing coronary artery bypass grafting and mitral ring annuloplasty for ischemic regurgitation were randomly assigned to either type of prosthesis. Transesophageal and transthoracic echocardiography showed no significant differences between these techniques in terms of immediate success of the repair and its durability at 3, 6, and 9 months postoperatively. Autogenous rings are easy to make, cost-effective, and always available. Our short-term results suggest that they may be an acceptable alternative to a commercially produced prosthesis for patients with ischemic mitral regurgitation.

Mitral valve regurgitation and 3D echocardiography

The mitral valve is a complex, dynamic and functional apparatus that can be altered by a wide range of disorders leading to stenosis or regurgitation. Surgical management of mitral valve disease may be difficult. Planned intervention may not always be feasible when the surgeon is faced with complex pathology that cannot be assessed fully by conventional 2D echocardiography. Transthoracic and transesophageal 3D echocardiography can provide a more reliable functional and anatomical assessment of the different valve components and evaluation of its geometry, which can aid the surgeon in planning a more suitable surgical intervention and improve outcomes. Although 3D echocardiography is a new technology, it has proven to be an important modality for the accurate assessment of valvular heart disease and in the future, it promises to be an essential part in the routine assessment of cardiovascular patients.

In vivo dynamic deformation of the mitral valve annulus

Though mitral valve (MV) repair surgical procedures have increased in the United States [Gammie, J. S., et al. Ann. Thorac. Surg. 87(5):1431-1437, 2009; Nowicki, E. R., et al. Am. Heart J. 145(6):1058-1062, 2003], studies suggest that altering MV stress states may have an effect on tissue homeostasis, which could impact the long-term outcome [Accola, K. D., et al. Ann. Thorac. Surg. 79(4):1276-1283, 2005; Fasol, R., et al. Ann. Thorac. Surg. 77(6):1985-1988, 2004; Flameng, W., P. Herijgers, and K. Bogaerts. Circulation 107(12):1609-1613, 2003; Gillinov, A. M., et al. Ann. Thorac. Surg. 69(3):717-721, 2000]. Improved computational modeling that incorporates structural and geometrical data as well as cellular components has the potential to predict such changes; however, the absence of important boundary condition information limits current efforts. In this study, novel high definition in vivo annular kinematic data collected from surgically implanted sonocrystals in sheep was fit to a contiguous 3D spline based on quintic-order hermite shape functions with C(2) continuity. From the interpolated displacements, the annular axial strain and strain rate, bending, and twist along the entire annulus were calculated over the cardiac cycle. Axial strain was shown to be regionally and temporally variant with minimum and maximum values of -10 and 4%, respectively, observed. Similarly, regionally and temporally variant strain rate values, up to 100%/s contraction and 120%/s elongation, were observed. Both annular bend and twist data showed little deviation from unity with limited regional variations, indicating that most of the energy for deformation was associated with annular axial strain. The regionally and temporally variant strain/strain rate behavior of the annulus are related to the varied fibrous-muscle structure and contractile behavior of the annulus and surrounding ventricular structures, although specific details are still unavailable. With the high resolution shape and displacement information described in this work, high fidelity boundary conditions can be prescribed in future MV finite element models, leading to new insights into MV function and strategies for repair.

A methodology for assessing human mitral leaflet curvature using real-time 3-dimensional echocardiography

OBJECTIVES

Using 3-dimensional echocardiography in conjunction with novel geometric modeling and rendering techniques, we have developed a high-resolution, quantitative, 3-dimensional methodology for imaging the human mitral valve. Leaflet and annular geometry are important determinants of mitral valve stress. Repair techniques that optimize valvular geometry will reduce stress and potentially increase repair durability. The development of such procedures will require image-processing methodologies that provide a quantitative description of 3-dimensional valvular geometry.

METHODS

Ten healthy adult subjects underwent mitral valve imaging with real-time 3-dimensional echocardiography. By using specially designed image analysis software, multiple valvular geometric parameters, including 2- and 3-dimensional leaflet curvature, leaflet surface area, annular height, intercommissural width, septolateral annular diameter, and annular area were determined for each subject. Image-rendering techniques that allow for the clear and concise presentation of this detailed information are also presented.

RESULTS

Although 3-dimensional annular and leaflet geometry were found to be highly conserved between healthy human subjects in general, substantial intrasubject and intersubject regional geometric heterogeneity was observed in the midposterior leaflet, the region most commonly involved in leaflet flail in subjects with myxomatous disease.

CONCLUSIONS

The image-processing and graphic-rendering techniques that we have developed can be used to provide a complete description of 3-dimensional mitral valve geometry in human subjects. Widespread application of these techniques to healthy subjects and patients with mitral valve disease will provide insight into the geometric basis of both valvular pathology and repair durability.

The influence of annuloplasty ring geometry on mitral leaflet curvature

BACKGROUND

The effect of mitral leaflet curvature on stress reduction is an important mechanism in optimizing valve function. We hypothesize that annuloplasty ring shape could directly influence leaflet curvature and, potentially, repair durability. We describe an echocardiographically based methodology for quantifying mitral valve geometry and its application to the characterization of ovine mitral valve geometry before and after implantation of an annuloplasty ring.

METHODS

Multiple mitral annular and leaflet geometric variables were calculated for 8 naïve adult male sheep using real-time three-dimensional echocardiographic images. These indexes were recalculated after annuloplasty using a 30-mm Carpentier-Edward Physio ring (n = 4; Edwards Lifesciences, Irvine, CA) or a 30-mm saddle ring (n = 4).

RESULTS

After implantation of the Physio ring, the annular height to commissural width ratio (AHCWR) decreased from 19.4% +/- 2.3% to 11.1% +/- 2.5% (p = 0.06). After implantation of the saddle ring, AHCWR increased from 19.6% +/- 1.3% to 24.3% +/- 1.3% (p < 0.05). Statistically significant increases in three-dimensional Gaussian curvature occurred after implantation within six defined leaflet regions (A1 to A3, P1 to P3) of the saddle ring but only within the P1 and P3 leaflet regions with the Physio ring.

CONCLUSIONS

Annuloplasty ring shape affects leaflet curvature. Implantation of a saddle ring reflecting normal human annular geometry augmented ovine annular nonplanarity and increased three-dimensional leaflet curvature across the entire mitral valve surface. The Physio ring decreased annular nonplanarity and increased leaflet curvature only across limited regions of the posterior leaflet. These findings confirm the hypothesis that ring design influences leaflet curvature.

Description of regional mitral annular nonplanarity in healthy human subjects: a novel methodology

OBJECTIVE

Finite-element analysis demonstrates that the nonplanar shape of the mitral annulus diminishes mitral leaflet stress. It has therefore been postulated that repair with annuloplasty rings that maintain the nonplanar shape of the annulus could increase repair durability. Although the global nonplanarity of the mitral annulus has been adequately characterized, design of such a ring requires a quantitative description of regional annular geometry. By using real-time 3-dimensional echocardiography in conjunction with available image processing software, we developed a methodology for describing regional annular geometry and applied it to the characterization of the normal human mitral annulus.

METHODS

Five healthy volunteers underwent mitral valve imaging with real-time 3-dimensional echocardiography. Regional annular height was calculated at 36 evenly spaced intervals.

RESULTS

Maximal annular height/commissural width ratio was found to occur at the midpoint of the anterior annulus in all cases. These values averaged 26% +/- 3.1%, whereas those for the midposterior annulus averaged 18% +/- 3.0%. The average commissural width was 35.2 +/- 6.0 mm. Although substantial spatial heterogeneity was observed, regional annular height at a given rotational position was highly conserved among subjects when normalized to commissural width.

CONCLUSIONS

These quantitative imaging and analytic techniques demonstrate that the normal human mitral annulus is regionally heterogeneous in its nonplanarity, and they establish a means of describing annular geometry at a regional level. With wider application, these techniques may be used both to characterize pathologic annular geometry and to optimize the design of mitral valve annuloplasty devices.

Effects of hemodynamic alterations on anterior mitral leaflet curvature during systole

OBJECTIVES

The application of repair techniques to treat mitral valve incompetence has increased progressively during the past 20 years. Unfortunately, recent reports have demonstrated the longevity of these repairs to be less than previously believed. Most repair failures are stress related. Computational models to optimize valve repair are in development, but to be brought to fruition, a better understanding of dynamic leaflet geometry is necessary. In this study, sonomicrometry was used in an ovine model to compute systolic leaflet curvature at varying afterloads and states of contractility.

METHODS

The anterior leaflet of 12 sheep was instrumented with 5 piezoelectric transducers in a cruciate array. Systolic blood pressure ranged from 90 to 200 mm Hg with increasing phenylephrine hydrochloride infusion. Epinephrine was used to vary contractile state. Leaflet curvature was calculated continuously (200 Hz) during systole.

RESULTS

Anterior leaflet curvature in the septolateral direction was double that in the intercommisural direction. There were also significant changes in leaflet curvature during systole. Curvature in neither direction was affected by afterload. Epinephrine augmented intercommisural curvature in a dose-independent fashion, whereas it had no effect on curvature in the septolateral direction.

CONCLUSIONS

Dynamic mitral anterior leaflet geometry was found to be amazingly constant over a wide range of hemodynamic conditions. These data provide information about leaflet geometry that will aid in the construction of realistic computational models. Such models may facilitate the design of annuloplasty rings and surgical techniques that minimize leaflet stress and increase mitral valve repair longevity.

Planar biaxial creep and stress relaxation of the mitral valve anterior leaflet

A fundamental assumption in mitral valve (MV) therapies is that a repaired or replaced valve should mimic the functionality of the native valve as closely as possible. Thus, improvements in valvular treatments are dependent on the establishment of a complete understanding of the function and mechanical properties of the native normal MV. In a recent study [Grashow et al. ABME 34(2), 2006] we demonstrated that the planar biaxial stress-strain relationship of the MV anterior leaflet (MVAL) exhibited minimal hysteresis and a stress-strain response independent of strain rate, suggesting that MVAL could be modeled as a "quasi-elastic" material. The objective of our current study was to expand these results to provide a more complete picture of the time-dependent mechanical properties of the MVAL. To accomplish this, biaxial stress-relaxation and creep studies were performed on porcine MVAL specimens. Our primary finding was that while the MVAL leaflet exhibited significant stress relaxation, it exhibited negligible creep over the 3-h test. These results furthered our assertion that the MVAL functionally behaves not as a linear or non-linear viscoelastic material, but as an anisotropic quasi-elastic material. These results appear to be unique in the soft tissue literature; suggesting that valvular tissues are unequalled in their ability to withstand significant loading without time-dependent material effects. Moreover, insight into these specialized characteristics can help guide and inform efforts directed toward surgical repair and engineered valvular tissue replacements.

In-Vivo Dynamic Deformation of the Mitral Valve Anterior Leaflet

BACKGROUND

Surgical techniques have been developed for mitral valve repair for a wide range of pathologies. However, excessive tissue stress and damage have been identified as etiologic factors limiting long-term durability. Before computational models to optimize valve repair can be realistically developed, in-vivo dynamic mitral valve leaflet strain data are required. However, these data do not presently exist. In the present study, a sheep model and sonomicrometry were used to compute the in-surface Eulerian strain tensor of the anterior leaflet over the cardiac cycle at varying afterloads.

METHODS

The anterior leaflet of nine Dorsett sheep (35 kg to 45 kg) was instrumented with nine 1-mm hemispherical piezoelectric transducers in a 15-mm square array. Three-dimensional crystal spatial positions were recorded at 250 Hz over several cardiac cycles, with peak left ventricular pressures varying from 90 mm Hg to 200 mm Hg. The in-surface Eulerian strain tensor was computed from the crystal displacements.

RESULTS

The mitral valve anterior leaflet experiences large anisotropic strains and peak strain rates of 400%/s, followed by an absolute cessation of any deformation during systole. Increasing left ventricular pressure also increased the effective leaflet stiffness but not the peak strains.

CONCLUSIONS

We report the first data on the dynamic in-vivo strain tensor of a functioning mitral valve anterior leaflet, which indicated large anisotropic strains and very high strain rates. Our observations also suggest that changes in left ventricular pressure and annular geometry result in altered effective leaflet stiffness, and may be an important factor in reducing leaflet stress and as such potentially affect mitral valve repair longevity.

The Emerging Role of Three-Dimensional Echocardiography in Mitral Valve Repair

Although three-dimensional (3D) echocardiography is still in its evolution, cutting edge advances that allow quantifiable images of cardiac structures to be created in real-time will begin to increase its use drastically. One of the most promising uses of the technology is in the planning, optimization, and postoperative surveillance of mitral valve repair techniques and devices. This article reviews the development of 3D echocardiography and presents illustrations of how it may be applied to improving mitral valve repair techniques. It is conceivable in the near future that mitral repair procedures will be designed and customized for each patient preoperatively using data obtained from 3D echo images and computerized virtual surgery techniques. Such tools will allow the surgeon to design operations that thoroughly analyze valve geometry and stress distribution before ever entering the operating room.