The Dynamic Anterior Mitral Annulus

Simulated Effects of Acute Left Ventricular Myocardial Infarction on Mitral Regurgitation in an Ovine Model

Ischemic mitral regurgitation (IMR) occurs from incomplete coaptation of the mitral valve (MV) after myocardial infarction (MI), typically worsened by continued remodeling of the left ventricular (LV). The importance of LV remodeling is clear as IMR is induced by the post-MI dual mechanisms of mitral annular dilation and leaflet tethering from papillary muscle (PM) distension via the MV chordae tendineae (MVCT). However, the detailed etiology of IMR remains poorly understood, in large part due to the complex interactions of the MV and the post-MI LV remodeling processes. Given the patient-specific anatomical complexities of the IMR disease processes, simulation-based approaches represent an ideal approach to improve our understanding of this deadly disease. However, development of patient-specific models of left ventricle-mitral valve (LV-MV) interactions in IMR are complicated by the substantial variability and complexity of the MR etiology itself, making it difficult to extract underlying mechanisms from clinical data alone. To address these shortcomings, we developed a detailed ovine LV-MV finite element (FE) model based on extant comprehensive ovine experimental data. First, an extant ovine LV FE model (Sci. Rep. 2021 Jun 29;11(1):13466) was extended to incorporate the MV using a high fidelity ovine in vivo derived MV leaflet geometry. As it is not currently possible to image the MVCT in vivo, a functionally equivalent MVCT network was developed to create the final LV-MV model. Interestingly, in pilot studies, the MV leaflet strains did not agree well with known in vivo MV leaflet strain fields. We then incorporated previously reported MV leaflet prestrains (J. Biomech. Eng. 2023 Nov 1;145(11):111002) in the simulations. The resulting LV-MV model produced excellent agreement with the known in vivo ovine MV leaflet strains and deformed shapes in the normal state. We then simulated the effects of regional acute infarctions of varying sizes and anatomical locations by shutting down the local myocardial contractility. The remaining healthy (noninfarcted) myocardium mechanical behaviors were maintained, but allowed to adjust their active contractile patterns to maintain the prescribed pressure-volume loop behaviors in the acute post-MI state. For all cases studied, the LV-MV simulation demonstrated excellent agreement with known LV and MV in vivo strains and MV regurgitation orifice areas. Infarct location was shown to play a critical role in resultant MV leaflet strain fields. Specifically, extensional deformations of the posterior leaflets occurred in the posterobasal and laterobasal infarcts, while compressive deformations of the anterior leaflet were observed in the anterobasal infarct. Moreover, the simulated posterobasal infarct induced the largest MV regurgitation orifice area, consistent with experimental observations. The present study is the first detailed LV-MV simulation that reveals the important role of MV leaflet prestrain and functionally equivalent MVCT for accurate predictions of LV-MV interactions. Importantly, the current study further underscored simulation-based methods in understanding MV function as an integral part of the LV.

Characterisation of global and regional mitral annular strains in an acute porcine model

OBJECTIVES

This study aimed to explore regional mitral annular strain using a novel computational method.

METHODS

Eight pigs underwent implantation with piezoelectric transducers around the mitral annulus. Interventions of pre- and afterload were performed by inferior vena cava constriction and endovascular balloon occlusion of the descending aorta. The mitral annulus was reconstructed in a mathematical model and divided into 6 segments. Global and segmental annular strain were calculated from a discrete mathematical representation.

RESULTS

Global annular strain gradually decreased after isovolumetric contraction until late systole. Mitral annular end-systolic strain demonstrated shortening in all segments except the anterior segment, which showed the least deformation. The P2 annular segment demonstrated the most end-systolic shortening (-7.6 ± 1.1% at baseline, P < 0.001 compared to anterior segment). Systolic global annular strain showed no significant change in response to load interventions but correlated positively with left ventricular contractility at baseline and after preload reduction.

CONCLUSIONS

Mitral annular systolic strain demonstrates cyclical variations with considerable regional heterogeneity, with the most pronounced deformation in posterior annular segments. Measurements appear independent of changes to pre- and afterload.

Distribution of Aortic Root Calcium in Relation to Frame Expansion and Paravalvular Leakage After Transcatheter Aortic Valve Implantation (TAVI): An Observational Study Using a Patient-specific Contrast Attenuation Coefficient for Calcium Definition and Independent Core Lab Analysis of Paravalvular Leakage

BACKGROUND

Calcium is a determinant of paravalvular leakage (PVL) after transcatheter aortic valve implantation (TAVI). This is based on a fixed contrast attenuation value while X-ray attenuation is patient-dependent and without considering frame expansion and PVL location. We examined the role of calcium in (site-specific) PVL after TAVI using a patient-specific contrast attenuation coefficient combined with frame expansion.

METHODS

57 patients were included with baseline CT, post-TAVI transthoracic echocardiography and rotational angiography (R-angio). Calcium load was assessed using a patient-specific contrast attenuation coefficient. Baseline CT and post-TAVI R-angio were fused to assess frame expansion. PVL was assessed by a core lab.

RESULTS

Overall, the highest calcium load was at the non-coronary-cusp-region (NCR, 436 mm³) vs. the right-coronary-cusp-region (RCR, 233 mm³) and the left-coronary-cusp-region (LCR, 244 mm³), p < 0.001. Calcium load was higher in patients with vs. without PVL (1,137 vs. 742 mm³, p = 0.012) and was an independent predictor of PVL (odds ratio, 4.83, p = 0.004). PVL was seen most often in the LCR (39% vs. 21% [RCR] and 19% [NCR]). The degree of frame expansion was 71% at the NCR, 70% at the RCR and 74% at the LCR without difference between patients with or without PVL.

CONCLUSIONS

Calcium load was higher in patients with PVL and was an independent predictor of PVL. While calcium was predominantly seen at the NCR, PVL was most often at the LCR. These findings indicate that in addition to calcium, specific anatomic features play a role in PVL after TAVI.

Cellular and Extracellular Matrix Basis for Heterogeneity in Mitral Annular Contraction

PURPOSE

Regional heterogeneity in mitral annular contraction, which is generally ascribed to the fibrous vs. muscular annular composition, ensures proper leaflet motion and timing of coaptation. It is unknown whether the fibroblast-like cells in the annulus modulate this heterogeneity, even though valvular interstitial cells (VICs) can be mechanically "activated."

METHODS

Fourteen sheep underwent implantation of radiopaque markers around the mitral annulus defining four segments: septal (SEPT), lateral (LAT), and anterior (ANT-C) and posterior (POST-C) commissures. Segmental annular contraction was calculated using biplane videofluoroscopy. Immunohistochemistry of annular cross sections assessed regional matrix content, matrix turnover, and cell phenotype. Micropipette aspiration measured the Young's modulus of the leaflets adjacent to the myocardial border.

RESULTS

Whereas SEPT contained more collagen I and III, LAT demonstrated more collagen and elastin turnover as shown by greater decorin, lysyl oxidase, and matrix metalloprotease (MMP)-13 and smooth muscle alpha-actin (SMaA). This greater matrix turnover paralleled greater annular contraction in LAT vs. SEPT (22.5% vs. 4.1%). Similarly, POST-C had more SMaA and MMP13 than ANT-C, consistent with greater annular contraction in POST-C (18.8% vs. 11.1%). Interestingly, POST-C had the greatest effective modulus, significantly higher than LAT.

CONCLUSIONS

These data suggest that matrix turnover by activated VICs relates to annular motion heterogeneity, maintains steady-state mechanical properties in the annulus, and could be a therapeutic target when annular motion is impaired. Conversely, alterations in this heterogeneous annular contraction, whether through disease or secondary to ring annuloplasty, could disrupt this normal pattern of cell-mediated matrix remodeling and further adversely impact mitral valve function.

Movement of mitral fibrous components in an isolated porcine working heart model

BACKGROUND

There is little research regarding the movement of mitral fibrous components. We analyzed changes in mitral fibrous components in normal and deteriorated isolated working swine hearts.

METHODS

In 5 swine hearts, 6 sonomicrometry transducers were placed around the mitral annulus and 2 in the papillary muscle tip. During the working cycle, we evaluated the annular dimension and calculated the contraction range and contraction ratio during the cardiac cycle in normal and deteriorated modes.

RESULTS

The transverse (24.5 ± 2.3 vs. 27.4 ± 2.4 mm) and posterior longitudinal diameter (18.3 ± 7.0 vs. 22.5 ± 5.5 mm) increased significantly in deteriorated mode. The contraction range in transverse (1.8 ± 0.6 vs. 0.8 ± 0.7 mm) and posterior longitudinal (1.6 ± 0.6 vs. 0.8 ± 0.3 mm) diameters decreased significantly in deteriorated mode. The contraction range of the strut chordae was less than 1.0 mm in both modes, with no significant differences. The contraction ratio of the anterior strut chordae was significantly reduced in deteriorated mode (3.2 ± 1.1% vs. 2.2 ± 1.1%). The contraction ratio of the annulus was significantly lower in deteriorated mode with respect to transverse (6.9 ± 2.1% vs. 2.9 ± 2.9%) and longitudinal (13.3 ± 4.5% vs. 8.6 ± 5.1%) diameters.

CONCLUSIONS

In the deteriorated hearts, the mitral annulus was dilated and contractility decreased. The length of the strut chordae differed 1 mm between the deteriorated and normal modes; however, the contraction ratio of the anterior chordae during the cardiac cycle was reduced, indicating increased stretching.

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.

Dynamism of the mitral annulus: a spatial and temporal analysis

OBJECTIVE

In this study, the authors sought to investigate the extent and timing of changes in mitral annular area during the cardiac cycle. Particularly, the authors assessed whether these changes were limited to the posterior part of the annulus or were more global in nature.

DESIGN

Prospective, observational study

SETTING

Tertiary care university hospital

PARTICIPANTS

Twenty three patients undergoing non-valvular cardiac surgery and 3 patients undergoing vascular procedures.

INTERVENTIONS

Intraoperative 3-dimensional transesophageal echocardiographic data obtained from patients with normal mitral valves undergoing non-valvular cardiac surgery were analyzed geometrically. Annular areas and diameters were measured during various stages of the cardiac cycle. Intertrigonal distance also was measured using 3D data.

MEASUREMENTS AND MAIN RESULTS

Both anterior and posterior portions of the mitral annulus demonstrated dynamism throughout the cardiac cycle. The expansion phase ranged from mid-systole to early-diastole, whereas mid-diastole to early-systole was characterized by an annular contraction phase. Area changes were contributed equally by anterior and posterior parts of the annulus. Annular dimensions increased in accordance with mitral annular area (p<0.05). Echocardiographically-identified intertrigonal distance showed the least delta change.

CONCLUSIONS

Both the anterior and posterior parts of the annulus contribute to changes in mitral annular area, which undergoes discrete expansion and contraction phases that extend into both systole and diastole. Compared to other annular dimensions, the echocardiographically-identified intertrigonal distance does not change significantly during the cardiac cycle.

Dynamic 3-dimensional echocardiographic assessment of mitral annular geometry in patients with functional mitral regurgitation

BACKGROUND

Mitral valve (MV) annular dynamics have been well described in animal models of functional mitral regurgitation (FMR). Despite this, little if any data exist regarding the dynamic MV annular geometry in humans with FMR. In the current study we hypothesized that 3-dimensional (3D) echocardiography, in conjunction with commercially available software, could be used to quantify the dynamic changes in MV annular geometry associated with FMR.

METHODS

Intraoperative 3D transesophageal echocardiographic data obtained from 34 patients with FMR and 15 controls undergoing cardiac operations were dynamically analyzed for differences in mitral annular geometry with TomTec 4D MV Assessment 2.0 software (TomTec Imaging Systems GmbH, Munich, Germany).

RESULTS

In patients with FMR, the mean mitral annular area (14.6 cm(2) versus 9.6 cm(2)), circumference (14.1 cm versus 11.4 cm), anteroposterior (4.0 cm versus 3.0 cm) and anterolateral-posteromedial (4.3 cm versus 3.6 cm) diameters, tenting volume (6.2 mm(3) versus 3.5 mm(3)) and nonplanarity angle (NPA) (154 degrees ± 15 versus 136 degrees ± 11) were greater at all points during systole compared with controls (p < 0.01). Vertical mitral annular displacement (5.8 mm versus 8.3 mm) was reduced in FMR compared with controls (p < 0.01).

CONCLUSIONS

There are significant differences in dynamic mitral annular geometry between patients with FMR and those without. We were able to analyze these changes in a clinically feasible fashion. Ready availability of this information has the potential to aid comprehensive quantification of mitral annular function and possibly assist in both clinical decision making and annuloplasty ring selection.

Mitral valve surgery for dilated cardiomyopathy: current status and future roles

There are a large number of patients with functional mitral regurgitation resulting from dilated cardiomyopathy. The decision between surgical correction and medical management of severe mitral regurgitation in heart failure can be difficult. The data regarding long-term benefits and mortality after surgical intervention are contradictory. Recent data suggest that mitral regurgitation can be surgically corrected in heart failure with symptomatic improvements and beneficial reverse remodeling. Contrary to prior beliefs, mitral valve repair can be performed safely with minimal postoperative mortality. Data from multi-institutional, randomized prospective trials will help to elucidate many of the questions and concerns regarding repair of severe functional mitral regurgitation.

Mitral annular hinge motion contribution to changes in mitral septal-lateral dimension and annular area

OBJECTIVE

The mitral annulus is a dynamic, saddle-shaped structure consisting of fibrous and muscular regions. Normal physiologic mechanisms of annular motion are incompletely understood, and more complete characterization is needed to provide rational basis for annuloplasty ring design and to enhance clinical outcomes.

METHODS

Seventeen sheep had radiopaque markers implanted; 16 around the annulus and 2 on middle anterior and posterior leaflet edges. Four-dimensional marker coordinates were acquired with biplanar videofluoroscopy at 60 Hz. Hinge angle was quantified between fibrous and muscular annular planes, with 0 degrees defined at end diastole, to characterize its contribution to alterations in mitral septal-lateral dimension and 2-dimensional total annular area throughout the cardiac cycle.

RESULTS

During isovolumic contraction (pre-ejection), hinge angle abruptly increased, reaching maximum (steepest saddle shape, change 18 degrees +/- 13 degrees ) at peak left ventricular pressure. During ejection, hinge angle did not change; it then decreased during early filling (change 2 degrees +/- 2 degrees ). Septal-lateral dimension and total area paralleled hinge angle dynamics and leaflet distance (anterior to posterior marker). Pre-ejection septal-lateral reduction was 13% +/- 7% (3.3 +/- 1.5 mm) from 9% muscular dimension fall and 18 degrees +/- 13 degrees hinge angle increase.

CONCLUSIONS

Pre-ejection increase in hinge angle contributes substantially to septal-lateral and total area reduction, facilitating leaflet coaptation. Semirigid annuloplasty rings or partial bands may preserve hinge motion, but possible recurrent annular dilatation could result in recurrent mitral regurgitation. Long-term clinical studies are required to determine who might benefit most from preserving intrinsic hinge motion without compromising repair durability.

Toward the development of a fully elastic mitral ring: preliminary, acute, in vivo evaluation of physiomechanical behavior

OBJECTIVES

The optimal repair of functional mitral regurgitation is still debated. No device is able to simultaneously abolish mitral regurgitation and replicate natural mitral annular dynamics. We have tested a fully elastic mitral ring in an acute animal study with the purpose of evaluating (1) ring design and implantation technique, (2) elastic performance, and (3) acute effects on the native mitral annulus.

METHODS

Ten healthy sheep underwent surgical implantation of mitral devices, the elastic component of which is represented by a helicoid metallic spring. Preimplantation and postimplantation echocardiographic parameter measurements to evaluate annular dynamics and ventricular function comprise mitral annular motion, systolic tissue Doppler imaging peak wave, transmitral pressure gradient, peak transmitral flow velocity, and ejection fraction. Postimplantation angiographic analysis allowed measurement of the mitral annular area and perimeter variations by means of segmentation of the radiopaque mitral device contour.

RESULTS

No significant difference in terms of ejection fraction (P = .13) and systolic tissue Doppler imaging peak wave (P = .87) was found before and after implantation. Mitral annular motion (1.16 cm) was preserved. The percentage of systolic annular reduction derived from angiographic analysis was 14.1% (range, 7.7%-19.7%) in terms of area and 7.2% (range, 4.9%-10.0%) in terms of perimeter.

CONCLUSIONS

A mitral elastic ring, implantable by using a standard technique, acutely preserves mitral annular dynamics, allowing area and perimeter changes. Further chronic study is needed to verify the biocompatibility and durability of the device.

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.

Current surgical management of mitral regurgitation

From Walton Lillehei, who performed the first successful open mitral valve surgery in 1956, until the advent of robotic surgery in the 21st Century, only 50 years have passed. The introduction of the first heart valve prosthesis, in 1960, was the next major step forward. However, correction of mitral disease by valvuloplasty results in better survival and ventricular performance than mitral valve replacement. However, the European Heart Survey demonstrated that only 40% of the valves are repaired. The standard procedures (Carpentier's techniques and Alfieri's edge-to-edge suture) are the surgical basis for the new technical approaches. Minimally invasive surgery led to the development of video-assisted and robotic surgery and interventional cardiology is already making the first steps on endovascular procedures, using the classical concepts in highly differentiated approaches. Correction of mitral regurgitation is a complex field that is still growing, whereas classic surgery is still under debate as the new era arises.

Quantification of Mitral Apparatus Dynamics in Functional and Ischemic Mitral Regurgitation Using Real-time 3-Dimensional Echocardiography

Mitral regurgitation (MR) in dilated cardiomyopathy (DCM-MR) and MR in ischemic cardiomyopathy (ISC-MR) usually occurs as a result of mitral annulus (MA) dilatation and papillary muscle displacement secondary to global left ventricle remodelling. We propose a method to determine MA area and motion throughout the cardiac cycle and to define papillary muscle position in 3-dimensional space using real-time 3-dimensional echocardiography. Real-time 3-dimensional echocardiography was performed in 24 healthy individuals, and in 30 patients with DCM-MR (n = 15) or ISC-MR (n = 15). Significant intergroup differences were noted in MA surface area (control: 6.4 +/- 1.7 cm(2); DCM-MR: 11.1 +/- 2.6 cm(2); ISC-MR: 9.0 +/- 2.0 cm(2)) and in peak MA motion (control: 8.7 +/- 3.0 mm; DCM-MR: 3.4 +/- 1.7 mm; ISC-MR: 4.9 +/- 1.5 mm). In patients with DCM-MR, papillary muscle symmetry was preserved, whereas in patients with ISC-MR, papillary tethering lengths were unequal as a result of wall-motion abnormalities. Our methodology for dynamic volumetric measurements of the mitral apparatus allows better understanding of MR mechanisms.

Mitral Valve Tenting Index for Assessment of Subvalvular Remodeling

BACKGROUND

Ischemic mitral regurgitation results from a variable combination of annular dilatation and remodeling of the subvalvular apparatus. Current surgical techniques effectively treat annular dilatation, but methods for addressing subvalvular remodeling have not been standardized. An effective technique for determining the extent of subvalvular remodeling could improve surgical results by identifying patients who are unlikely to benefit from annuloplasty alone.

METHODS

A well-characterized ovine model of ischemic mitral regurgitation was used. Real-time three-dimensional echocardiography was performed on each animal at baseline and at 1 hour and 8 weeks after infarction. Multiple valvular geometric measurements were calculated at each time point.

RESULTS

Immediate and long-term changes in mitral valvular geometry were observed. Annular height-to-commissural width ratio decreased from 20.0% +/- 1.6% to 11.2% +/- 0.9% 1 hour after infarction (p < 0.001) and to 9.4% +/- 0.4% 8 weeks after infarction (p < 0.001), whereas mitral annular area increased from 8.1 +/- 0.3 cm2 to 9.2 +/- 0.4 cm2 (p < 0.05) and then to 10.5 +/- 0.6 cm2 (p < 0.05). Maximum mitral valve tenting area increased from 49.7 +/- 5.1 mm2 to 58.6 +/- 4.2 mm2 (p < 0.05) and then to 106.4 +/- 3.9 mm2 (p < 0.001), whereas mitral valve tenting volume increased from 679.0 +/- 75.5 mm3 to 828.6 +/- 102.4 mm3 (p = 0.050) and then to 1530.5 +/- 97.8 mm3 (p < 0.001). The mitral valve tenting index increased from 0.83 +/- 0.08 mm to 0.88 +/- 0.08 mm (p > 0.05) and then to 1.46 +/- 0.08 mm (p < 0.001).

CONCLUSIONS

We have described a technique that uses real-time three-dimensional echocardiography to perform a comprehensive assessment of leaflet tethering on the entire mitral valve. Our methodology is not influenced by viewing plane selection, regional tenting asymmetry, or annular dilatation and therefore represents a potentially useful, clinically relevant, and consistent measure of subvalvular remodeling.

Regional and global patterns of annular remodeling in ischemic mitral regurgitation

BACKGROUND

The mammalian mitral annulus is saddle shaped. Experimental studies have shown that loss of saddle shape occurs in ischemic mitral regurgitation. However, neither the temporal pattern of global annular remodeling nor the geometric pattern of regional annular remodeling has been described. We sought to characterize these changes using real-time three-dimensional echocardiography in an ovine model.

METHODS

Ten sheep underwent real-time three-dimensional echocardiography at baseline and 1 hour and 8 weeks after posterobasal myocardial infarction. Multiple mitral annular geometric indexes were measured at each time point to assess regional and global annular remodeling.

RESULTS

One hour after infarction, global annular height decreased from 5.8 +/- 0.5 mm to 4.0 +/- 0.4 mm (p < 0.001) while intercommissural width increased from 29.0 +/- 1.3 mm to 35.7 +/- 1.7 mm (p = 0.023), resulting in a decrease in the global annular height to commissural width ratio from 20.0% +/- 1.6% to 11.2% +/- 0.9% (p < 0.001). Eight weeks after infarction, global annular height decreased to 3.9 +/- 0.2 mm (p < 0.05) while intercommissural width increased to 40.7 +/- 1.5 mm (p < 0.001), resulting in an additional decrease in the global annular height to commissural width ratio to 9.4% +/- 0.4% (p < 0.001). Although annular remodeling involved the entire mitral annulus, there was regional heterogeneity in its extent.

CONCLUSIONS

Significant global annular flattening and dilatation occur during the development of ischemic mitral regurgitation in an ovine model. Regional annular remodeling is heterogeneous and is not limited the posterior commissure or the posterior annulus.

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.

Flexible Versus Nonflexible Mitral Valve Rings for Congestive Heart Failure: Differential Durability of Repair

BACKGROUND

Surgical intervention is playing an increasingly important therapeutic role in congestive heart failure (CHF) patients with ischemia and dilated cardiomyopathy. Their mitral regurgitation (MR) is a result of left ventricular (LV) geometrical distortion. The optimal type of ring for CHF patients with geometric ventricular-based MR is unknown. This study reviewed the results of flexible versus nonflexible complete mitral valve rings in CHF patients with geometric mitral regurgitation.

METHODS AND RESULTS

Using a prospectively maintained database, patients undergoing mitral valve reconstruction (MVR) with either a flexible or nonflexible complete ring were identified on the basis of preoperative ejection fraction (EF) < or = 30% and no primary mitral pathology. These 2 groups of CHF patients with severe geometric MR were then compared in terms of recurrent MR requiring reoperation. Between 1992 and 2004, 289 patients with EF < or = 30%, received an undersized complete mitral annuloplasty ring as their MVR procedure. Of these, 170 patients had a flexible complete ring. In follow-up, 16 "flexible" patients (9.4%) required a repeat procedure for significant recurrent geometric MR and CHF (10 replacements, 3 re-repairs, 3 transplants). The average time to reoperation was 2.4 years. In contrast, 119 patients with an EF < or = 30% received a MVR using an undersized nonflexible complete ring. Only 3 "non-flexible" patients required a repeat operation, MVR (1), and 2 patients required a transplant. The time to reoperation was 4.0 years. A significant difference in reoperation rates, for recurrent MR, between the 2 groups (P=0.012). There were no differences between groups, in terms of age, ring size used, preoperative EF, LV size, MR grade, or New York Heart Association class.

CONCLUSIONS

Patients with CHF having a flexible ring have a higher likelihood of developing recurrent MR requiring reoperation. The use of a nonflexible ring appears to significantly reduce the need for repeat surgical procedures. Further refinement and development of nonflexible ring systems, aimed at LV restoration, deserve ongoing investigation.