Influence of anterior mitral leaflet second-order chordae on leaflet dynamics and valve competence

Functional anatomy and echocardiographic assessment in secondary mitral regurgitation

BACKGROUND

Mitral valve apparatus is complex and involves the mitral annulus, the leaflets, the chordae tendinae, the papillary muscles as well as the left atrial and ventricular myocardium. Secondary mitral regurgitation is a consequence of regional or global left ventricle remodeling due to an acute myocardial infarction (75% of cases) or idiopathic dilated cardiomyopathy (25% of cases). It is associated with an increase in mortality and poor outcome. There is a potential survival benefit deriving from the reduction in the degree of severity of mitral regurgitation. So the correction of the valve defect can change the clinical course and prognosis of the patient. The rationale for mitral valve treatment depends on the mitral regurgitation mechanism. Therefore, it is essential to identify and understand the pathophysiology of mitral valve regurgitation.

AIM OF THE STUDY

The aim of this review is to describe the crucial role of transthoracic and trans-esophageal echocardiography, in particular with three-dimensional echocardiography, for the assessment of the severity of secondary mitral regurgitation, anatomy, and hemodynamic changes in the left ventricle. Moreover, the concept that the mitral valve has no organic lesions has been abandoned. The echocardiography must allow a complete anatomical and functional evaluation of each component of the mitral valve complex, also useful to the surgeon in choosing the best surgical approach to repair the valve.

CONCLUSIONS

Echocardiography is the first-line imaging modality for a better selection of patients, according to geometrical modifications of mitral apparatus and left ventricle viability, especially in preoperative phase.

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.

Mechanical testing of glutaraldehyde cross-linked mitral valves. Part two: Elastic and viscoelastic properties of chordae tendineae

The aim of this study was to assess whether the mechanical properties of mitral valve chordae tendineae are sensitive to being cross-linked under load. A total 64 chordae were extracted from eight porcine hearts. Two chordae (posterior basal) from each heart were subjected to uniaxial ramp testing and six chordae (two strut, two anterior basal and two posterior basal) were subjected to dynamic mechanical analysis over frequencies between 0.5 and 10 Hz. Chordae were either cross-linked in tension or cross-linked in the absence of loading. Chordae cross-linked under load transitioned from high to low extension at a lower strain than cross-linked unloaded chordae (0.07 cf. 0.22), with greater pre-transitional (30.8 MPa cf. 5.78 MPa) and post-transitional (139 MPa cf. 74.1 MPa) moduli. The mean storage modulus of anterior strut chordae ranged from 48 to 54 MPa for cross-linked unloaded chordae, as compared to 53-61 MPa cross-linked loaded chordae. The mean loss modulus of anterior strut chordae ranged from 2.3 to 2.9 MPa for cross-linked unloaded chordae, as compared to 3.8-4.8 MPa cross-linked loaded chordae. The elastic and viscoelastic properties of chordae following glutaraldehyde cross-linking are dependent on the inclusion/exclusion of loading during the cross-linking process; with loading increasing the magnitude of the material properties measured.

The role of strut chordae in mitral valve competence during annular dilation

Strut chordae, on their own, are not typically thought to aid mitral valve competence. The aim of this study is to assess whether strut chordae aid mitral valve competence during acute annular dilation. Twelve porcine hearts were dissected and tested using an in vitro simulator, with the mitral annulus tested in either a 'normal' or a dilated configuration. The normal configuration included a diameter of 30 mm, a posterior leaflet 'radius' of 15 mm and a commissural corner 'radius' of 7.5 mm; the dilated annular template instead used dimensions of 50 mm, 25 mm and 12.5 mm, respectively. Each mitral valve underwent ten repeat tests with a target systolic pressure of 100 mmHg. No significant difference in the pressure was detected between the dilated and regular annuli for the mitral valves tested (95 ± 3 mmHg cf. 95 ± 2 mmHg). However, the volume of regurgitation for a dilated annulus was 28 ml greater than for a valve with a normal annulus. Following severing of strut chordae, there was a significant reduction in the systolic pressure withstood before regurgitation by mitral valves with dilated annuli (60 ± 29 mmHg cf. 95 ± 2 mmHg for normal annular dimensions; p < 0.05). In conclusion, strut chordae tendineae may play a role in aiding mitral valve competence during pathophysiology.

The role of strut chordae in mitral valve competence during annular dilation

Strut chordae, on their own, are not typically thought to aid mitral valve competence. The aim of this study is to assess whether strut chordae aid mitral valve competence during acute annular dilation. Twelve porcine hearts were dissected and tested using an in vitro simulator, with the mitral annulus tested in either a 'normal' or a dilated configuration. The normal configuration included a diameter of 30 mm, a posterior leaflet 'radius' of 15 mm and a commissural corner 'radius' of 7.5 mm; the dilated annular template instead used dimensions of 50 mm, 25 mm and 12.5 mm, respectively. Each mitral valve underwent ten repeat tests with a target systolic pressure of 100 mmHg. No significant difference in the pressure was detected between the dilated and regular annuli for the mitral valves tested (95 ± 3 mmHg cf. 95 ± 2 mmHg). However, the volume of regurgitation for a dilated annulus was 28 ml greater than for a valve with a normal annulus. Following severing of strut chordae, there was a significant reduction in the systolic pressure withstood before regurgitation by mitral valves with dilated annuli (60 ± 29 mmHg cf. 95 ± 2 mmHg for normal annular dimensions; p < 0.05). In conclusion, strut chordae tendineae may play a role in aiding mitral valve competence during pathophysiology.

Geometric description for the anatomy of the mitral valve: A review

The mitral valve is a complex anatomical structure whose physiological functioning relies on the biomechanical properties and structural integrity of its components. Their compromise can lead to mitral valve dysfunction, associated with morbidity and mortality. Therefore, a review on the morphometry of the mitral valve is crucial, more specifically on the importance of valve dimensions and shape for its function. This review initially provides a brief background on the anatomy and physiology of the mitral valve, followed by an analysis of the morphological information available. A characterisation of mathematical descriptions of several parts of the valve is performed and the impact of different dimensions and shape changes in disease is then outlined. Finally, a section regarding future directions and recommendations for the use of morphometric information in clinical analysis of the mitral valve is presented.

Length of second-order chordae as a predictor of systolic anterior motion of the mitral valve

OBJECTIVES

The aim of the present study was to ascertain whether the length of anterior mitral leaflet second-order chordae (SOC) could be considered as a predictor of the incidence of post-repair systolic anterior motion (SAM) and left ventricular outflow tract obstruction (LVOTO) in patients with myxomatous mitral valve disease.

METHODS

With the implementation of preoperative transoesophageal echocardiography (TEE), the length of anterior mitral leaflet SOC, anterior leaflet (AL) and posterior leaflet (PL) as well as the distance from the coaptation point to the septum (C-S distance) before and after mitral valve repair (MVR) surgery were measured in 190 patients, comprising 12 who developed SAM and 178 who did not.

RESULTS

The results revealed that, in patients who developed SAM, SOC were significantly higher (2.76 ± 0.15 vs 1.83 ± 0.32 mm, P < 0.001) and the C-S distance was significantly lower (2.18 ± 0.36 vs 2.91 ± 0.36 mm, P < 0.001) in comparison to the obtained results for those who did not develop SAM. SOC and the C-S distance were independent risk factors of developing SAM and had the largest area under the receiver operating characteristic (ROC) curve (P < 0.001). With application of a cut-off ROC curve analysis, the cut-offs selected for the two variables of C-S distance and SOC were 2.5 and 2.6, respectively. Sensitivity and specificity of SAM development were 100% [95% confidence interval (CI): 73.5-100] and 87.1% (95% CI: 81.0-91.4) for SOC ≥2.6 and 83.3% (95% CI: 51.6-97.9) and 73.6% (95% CI: 66.4-79.9) for the C-S distance ≤2.5.

CONCLUSIONS

The two variables of the second-order chordae and the distance from the coaptation point to the septum were associated with an increased risk of the post-repair systolic anterior motion after mitral valve repair.

Morphological study of chordae tendinae in human cadaveric hearts

Objectives:

The chordae tendinae (CT) are strong, fibrous connections between the valve leaflets and the papillary muscles. Dysfunction of the papillary muscles and chordae is frequent. Mitral valve replacement with preservation of CT and papillary muscles may preserve postoperative left ventricular function better than conventional mitral valve replacement in patients with chronic mitral regurgitation.

Methods:

The study was carried out on 116 human cadaveric hearts. The heart was opened through the atrioventricular valve to view the constituents of the complex. Origin, attachments, insertions, distribution, branching pattern and gross structure of CT were observed and studied in detail.

Results:

In the present study more than 21 terminologies of CT were defined by classifying it into six different types. Classification is done according to the origin, attachments, insertion, distribution, branching pattern and gross structure. Terminologies defined are as follows. Apical pillar chordae, Basal pillar chordae, True chordae, False chordae, Interpillar chordae, Pillar wall chordae, Cusp chordae, Cleft chordae, Commissural chordae, First order chordae, Second order chordae, Free zone chordae, Marginal chordae, Rough zone chordae, Straight chordae, Branched-fan shaped chordae, Spiral chordae, Irregular-web chordae, Tendinous chordae, Muscular chordae, Membranous chordae. Basal pillar chordae are found in 9.48%. Mean number of chordae taking origin from apical half of a single papillary muscle or single head of papillary muscle was 9.09 with the range of 3-18. Mean number of the marginal chordae attached to a single cusp was 22.63 ranging from 11 to 35. Strut chordae showed interesting insertion with broad aponeurosis in 38.79% and large muscular flaps in 13.79%. Chordae muscularis were found in 14% and membranous chordae were found in 6%.

Conclusions:

This knowledge may prove useful for cardiologists and cardiac surgeons.

Comparison of artificial neochordae and native chordal transfer in the repair of a flail posterior mitral leaflet: an experimental study

BACKGROUND

Surgical reconstruction of a flail posterior leaflet is a routine mitral valve repair, the techniques for which have evolved from leaflet resection to leaflet preservation. Artificial expanded polytetrafluoroethylene neochordae are frequently used to stabilize the flail leaflet and seldom, translocation of the native secondary chordae of the valve to the leaflet free edge is used. In this study, we sought to investigate the efficacy of the 2 techniques to correct posterior leaflet prolapse and reduce mitral regurgitation, and quantify the acute post repair leaflet kinematics.

METHODS

Adult porcine mitral valves (n =7) were studied in a pulsatile left heart experimental model in which isolated P2 flail was mimicked by marginal chordal transection. Baseline conditions were established in each valve under normal conditions (control) and were followed by induction of isolated P2 flail by transecting the 2 marginal chordae on the posterior leaflet free edge (disease). The flail posterior leaflet was reconstructed using artificial neochordae (repair 1) and then native chordal translocation (repair 2). Reduction in leaflet flail, changes in mitral regurgitation fraction, leaflet coaptation length, and posterior leaflet mobility were measured using B-mode echocardiography or color Doppler.

RESULTS

At baseline, all the valves were competent with no mitral regurgitation. After transection of the marginal chordae on the posterior leaflet, isolated P2 flail was evident with 13.7% ± 13% regurgitation. Reconstruction with artificial neochordae eliminated leaflet flail and reduced mitral regurgitation to 3.2% ± 2.8%, and with chordal translocation leaflet flail was corrected and mitral regurgitation was measured at 2.3% ± 2.6%. Using either repair techniques, leaflet coaptation and mobility of the repaired leaflets were adequate and comparable with the baseline measurements.

CONCLUSIONS

Comparable reduction leaflet flail and regurgitation, and restoration of physiologic leaflet coaptation with the 2 techniques indicate that under acute conditions, use of artificial neochordae or native chordal translocations have similar benefits.

Comprehensive annular and subvalvular repair of chronic ischemic mitral regurgitation improves long-term results with the least ventricular remodeling

BACKGROUND

Undersized ring annuloplasty for ischemic mitral regurgitation (MR) is associated with variable results and >30% MR recurrence. We tested whether subvalvular repair by severing second-order mitral chordae can improve annuloplasty by reducing papillary muscle tethering.

METHODS AND RESULTS

Posterolateral myocardial infarction known to produce chronic remodeling and MR was created in 28 sheep. At 3 months, sheep were randomized to sham surgery versus isolated undersized annuloplasty versus isolated bileaflet chordal cutting versus the combined therapy (n=7 each). At baseline, chronic myocardial infarction (3 months), and euthanasia (6.6 months), we measured left ventricular (LV) volumes and ejection fraction, wall motion score index, MR regurgitation fraction and vena contracta, mitral annulus area, and posterior leaflet restriction angle (posterior leaflet to mitral annulus area) by 2-dimensional and 3-dimensional echocardiography. All groups were comparable at baseline and chronic myocardial infarction, with mild to moderate MR (MR vena contracta, 4.6±0.1 mm; MR regurgitation fraction, 24.2±2.9%) and mitral annulus dilatation (P<0.01). At euthanasia, MR progressed to moderate to severe in controls but decreased to trace with ring plus chordal cutting versus trace to mild with chordal cutting alone versus mild to moderate with ring alone (MR vena contracta, 5.9±1.1 mm in controls, 0.5±0.08 with both, 1.0±0.3 with chordal cutting alone, 2.0±0.4 with ring alone; P<0.01). In addition, LV end-systolic volume increased by 108% in controls versus 28% with ring plus chordal cutting, less than with each intervention alone (P<0.01). In multivariate analysis, LV end-systolic volume and mitral annulus area most strongly predicted MR (r(2)=0.82, P<0.01).

CONCLUSIONS

Comprehensive annular and subvalvular repair improves long-term reduction of both chronic ischemic MR and LV remodeling without decreasing global or segmental LV function at follow-up.

Biomechanical assessment of surgical repair of the mitral valve

Repair of the mitral valve is defined (loosely) as a procedure that alters the valve structure, without replacement, enabling the natural valve itself to continue to perform under the physical conditions to which it is exposed. As the mitral valve is driven by flow and pressure, it should be feasible to analyse and assess its function, failure and repair as a mechanical system. This article reviews the current state of mechanical evaluation of surgical repairs of the failed mitral valve of the heart. This review describes the anatomy and physiology of the mitral valve, followed by the failure of the mitral valve from a mechanical point of view. The surgical methods used to repair failed valves are introduced, while the use of engineering analysis to aid understanding of mitral valve repair is also reviewed. Finally, a section on recommendations for development and future uses of engineering techniques to surgical repair are presented.

MECHANICAL PROPERTIES OF CHORDAE TENDINEAE OF THE MITRAL HEART VALVE: YOUNG'S MODULUS, STRUCTURAL STIFFNESS, AND EFFECTS OF AGING

Young's modulus and structural stiffness were determined for chordae tendineae of the mitral valve from young (18–26 weeks) and old (over 2 years) porcine hearts. For chordae from the posterior leaflet of the valve, the Young's modulus values were significantly higher (p < 0.05) for the thinner marginal chordae (59 ± 31 MPa young; 88 ± 21 MPa old) than for the thicker basal chordae (31 ± 4 MPa young; 28 ± 9 MPa old). Marginal chordae (both anterior and posterior) had significantly higher (p < 0.05) value for their Young's modulus in old (88 ± 21 MPa anterior and posterior) than in young (62 ± 17 MPa anterior, 59 ± 18 MPa posterior) pig hearts. There was no significant difference in structural stiffness between marginal and basal (anterior and posterior leaflets) or between strut chordae (that are associated with anterior the leaflet only) and marginal and basal chordae. However, the value of structural stiffness of chordae was significantly higher (p < 0.05) for old (2.2 ± 0.2 kN/m) than for young (2.0 ± 0.4 kN/m) chordae. These results show that aging affects the properties of chordae and that all chordae need to be included in finite element models of valve function.

Mitral valve finite-element modelling from ultrasound data: a pilot study for a new approach to understand mitral function and clinical scenarios

In the current scientific literature, particular attention is dedicated to the study of the mitral valve and to comprehension of the mechanisms that lead to its normal function, as well as those that trigger possible pathological conditions. One of the adopted approaches consists of computational modelling, which allows quantitative analysis of the mechanical behaviour of the valve by means of continuum mechanics theory and numerical techniques. However, none of the currently available models realistically accounts for all of the aspects that characterize the function of the mitral valve. Here, a new computational model of the mitral valve has been developed from in vivo data, as a first step towards the development of patient-specific models for the evaluation of annuloplasty procedures. A structural finite-element model of the mitral valve has been developed to account for all of the main valvular substructures. In particular, it includes the real geometry and the movement of the annulus and papillary muscles, reconstructed from four-dimensional ultrasound data from a healthy human subject, and a realistic description of the complex mechanical properties of mitral tissues. Preliminary simulations allowed mitral valve closure to be realistically mimicked and the role of annulus and papillary muscle dynamics to be quantified.

Chordal "translocation" for functional mitral regurgitation with severe valve tenting: an effort to preserve left ventricular structure and function

OBJECTIVE

The chordal cutting method is performed for mitral valve tenting in functional mitral regurgitation, such as ischemic mitral regurgitation. However, the method may interfere with the mitral valvular-ventricular continuity. To maintain the continuity and the natural force direction between the papillary muscles and the mitral annulus after chordal cutting, we developed "translocation" of the secondary chordae tendineae.

METHODS

Six mongrel dogs had sonomicrometry crystal markers implanted in the left ventricle, mitral annulus, and papillary muscle tips. After the secondary chordae tendineae of the anterior mitral leaflet from each papillary muscle were resected, each papillary muscle tip was connected to the mid-anterior mitral annulus with 4-0 polypropylene sutures, and then the sutures were taken out of the left atrium to control the chordal tension. The condition under which the artificial chordae were released was defined as "redundant." The chordal tension of 15 g of weight was defined as "taut," whereas the tension for 2-mm chordal shortening after "taut" was defined as "tight." After the dogs were weaned from cardiopulmonary bypass, hemodynamic and 3-dimensional data were acquired under the condition of "redundant," and then "taut," "tight," and "redundant."

RESULTS

End-systolic elastance increased from 1.81 +/- 0.24 mm Hg/mL to 2.69 +/- 0.89 mm Hg/mL (P = .015) between "redundant" and "taut," and this was maintained between "taut" and "tight." However, preload recruitable stroke work increased from 41.3 +/- 12.0 mm Hg to 58.1 +/- 19.7 mm Hg (P = .005) between "redundant" and "taut," and was reduced to 51.7 +/- 22.9 mm Hg (P = .037) between "taut" and "tight."

CONCLUSION

"Translocation" of the secondary chordae tendineae after chordal cutting improved left ventricular systolic function compared with simple chordal cutting.

Mitral valve repair: critical analysis of the anatomy discussed

In this brief review, we discuss the anatomy of the mitral valve pertinent to surgical repair. First, we emphasise the need for diagnosticians to describe the valve in the context of the position of the heart within the body, following the standard rules of anatomy, and using attitudinally appropriate descriptions. It has become customary to describe cardiac structures as if the heart is positioned on its apex. This cannot be good in the current era, when the tomographic techniques increasingly used for diagnosis demonstrate the heart as seen in the body. We then discuss the overall valvar structure in terms of a complex made up of the annulus, the leaflets, their tendinous cords, and the supporting papillary muscles. After providing accounts of the salient structure of each part of the complex, we discuss potentially divisive issues, such as the number of leaflets, and the categorisation of the tendinous cords. We explain how most of the disagreements stem not from differences in observation, but rather from differences in definitions. We suggest that these can largely be dissipated if the valve is analysed in its closed, rather than its open, position. When seen in the closed position, it becomes obvious that the key feature is the solitary zone of apposition between the major components of the skirt of leaflet tissue, this being the major functional part of the valvar complex. Finally, we discuss the relationships of the valvar complex to the other cardiac structures, concentrating on the other cardiac valves, the conduction tissues, and the coronary arteries and veins.

Late incompetence of the left atrioventricular valve after repair of atrioventricular septal defects: The morphologic perspective

OBJECTIVE

The mortality following repair of atrioventricular septal defects has fallen dramatically in the last 4 decades, but reoperation for late regurgitation across the left atrioventricular valve has remained disconcertingly stagnant. Seeking potential structural causes, we compared the morphology of the surgically created septal leaflet of the left valve following repair of atrioventricular septal defects to the aortic leaflet of the normal mitral valve.

METHODS

We compared the mitral valves of 92 normal hearts to the left ventricular components of the bridging leaflets of hearts with atrioventricular septal defect with common atrioventricular junction, determining the shape of the leaflets and the arrangement of the subvalvar apparatus.

RESULTS

The aortic leaflet of the mitral valve is triangular compared with its rectangular septal counterpart after repair of atrioventricular septal defect. The cordal arrangement in the mitral valve is well organized, compared with the deficient cordal arrangement of the abnormal valve. A greater proportion of cords in the mitral valve divide to 3 generations (55.5% compared with 8.7%; P < .001), and a higher percentage of cords remain undivided in atrioventricular septal defects (60.8% compared with 25%; P < .001).

CONCLUSIONS

Not only is the annular component in the left atrioventricular valve abnormal, but the subvalvar apparatus is characterized by deficiency and disarray. Furthermore, the axis of cordal insertion may potentiate to separation over the long term of the leaflets joined surgically. Valvar repair in this setting will never restore the arrangement of the normal mitral valve.

Chordal Cutting Does Not Adversely Affect Left Ventricle Contractile Function

Background— Severing a limited number of second-order chordae to the anterior leaflet can improve ischemic mitral regurgitation (MR). Some concerns have been raised regarding possible influence on regional and global left ventricle (LV) function. We evaluated changes in cardiac function in 5 normal sheep with cutting of pre-instrumented chords in the beating heart to maintain constant load.

Methods and Results— Under cardiopulmonary bypass, wires were placed around the 2 central basal chordae and brought outside the heart, which was restarted. Hemodynamic and imaging data were collected before and after chordal cutting by radiofrequency ablation using those wires. Segmental contractility was assessed invasively using sonomicrometers and noninvasively using Doppler tissue velocity and strain rate (with strain rate viewed as less load-dependent than ejection fraction) at 6 sites: base, mid-ventricle, and apex along the anteroseptal and posterolateral walls. We found no changes from before to after chordal cutting in LV end-diastolic volume (47.2±3.3 after cutting versus 48.4±4.6 mL before cutting, P =0.66), end-systolic volume (21.5±1.2 versus 22.3±2.8 mL, P =0.68), ejection fraction (54.2±1.8 versus 54.2±2.7%, P =0.96), systolic ventricular elastance (7.28±1.68 versus 7.66±2.11 mm Hg/mL, P =0.64), preload-recruitable stroke work (46.6±7.7 versus 50.2±10.7 mm Hg, P =0.76), and LVdP/dt (1480±238 versus 1392±250 mm Hg/s, P =0.45). Doppler tissue velocities and longitudinal strain rates surrounding the papillary muscles were unchanged, as were sonomicrometer longitudinal and mediolateral absolute strains. No wall motion abnormalities were visible around the papillary muscles, and no MR developed.

Conclusion— We find no evidence for acutely decreased global or segmental LV contractility with chordal cutting. This absence of adverse effects is consistent with long-term clinical experience with cutting these chords in valve repair.

Midterm Results of the Edge-to-Edge Technique for Complex Mitral Valve Repair

BACKGROUND

The edge-to-edge technique (E2E) has been advocated for the complex repair of myxomatous mitral valves. We compared outcomes of E2E performed in patients at risk for systolic anterior motion (SAM) versus outcomes in patients with residual mitral regurgitation (MR) after repair completion.

METHODS

A total of 1,612 patients had repair of myxomatous mitral valves between June 1997 and December 2003 at Brigham and Women's Hospital. The E2E was used in 72 (4.5%) patients. Fifty-two patients (52/72; group I) had E2E for persistent MR after complex repair. Twenty patients (20/72; group II) had E2E for high risk of post-repair SAM and left ventricular outflow tract obstruction. Mean age of the patients was 61 +/- 14 years; 47 were male, average New York Heart Association class at admission was 2.4 +/- 0.6, and mean left ventricular ejection fraction was 56 +/- 12%.

RESULTS

The operative mortality was zero. Immediate postoperative MR was significantly improved in all patients compared with the preoperative grade (p value < 0.0005). Mean follow-up was 388 days. In those in whom E2E was used for residual MR without SAM risk (group I), postoperative MR (> or = 2+) was detected in 15 of 52 patients at 6 months. In group II, SAM was completely eliminated and the mean MR grade in the immediate postoperative period was 0.5 +/- 0.7. There was no long-term recurrence of MR in group II.

CONCLUSIONS

This study suggests that E2E eliminates SAM and long-term MR in patients with pre-repair echocardiographic predictors of SAM. The E2E is not efficacious in preventing long-term recurrent MR if performed for residual MR after complex mitral repair.

Determination of the pressure required to cause mitral valve failure

A method has been developed for applying water pressure to a closed mitral valve on the side corresponding to the heart's left ventricle. The pressure is increased until fluid flows through the valve, i.e. until it fails. A specific dissection technique has been developed to produce a specimen with two annular rings, mitral annulus and papillary muscle annulus. Since the valve is maintained intact, with its leaflets attached to papillary muscles by the chordae tendineae, this method allows the effects of ruptured chordae and their surgical repair or replacement to be assessed in vitro. The chamber that holds the valve supports both the mitral annulus and papillary muscle annulus of the specimen. The mitral annulus is sutured onto rubber sheeting held in the chamber. The papillary muscle annulus is held in place by a Perspex support. The main part of the apparatus consists of a water pump connected through flexible tubing to the chamber that holds the valve in place. The pressure at failure is measured using a pressure transducer. Preliminary experiments demonstrate that anterior leaflet marginal chordae, but not strut chordae, are vital to valve function. Posterior leaflet chordae have been found to be important for valve competence.

Development of a new animal model of chronic mitral regurgitation in rats under transesophageal echocardiographic guidance

Large animal models (dog and sheep) are often used for the investigation of the pathophysiology of chronic mitral regurgitation (MR). A major limitation of large animal models is cost. The aim of this study was to develop a new animal model of chronic MR. Left thoracotomy was performed in 34 rats. Under the guidance of transesophageal echocardiography, a fine needle was inserted into the left ventricle (LV) to damage the mitral leaflets and produce MR. Serial transthoracic echocardiography was performed to assess LV remodeling and function. Left atrial and LV diameters were significantly larger, and LV fractional shortening was lower in the MR group than in the sham group. The 150-day survival was 59% in the MR group and 100% in the sham group (P < .01). This new animal model of chronic MR may be used in the study of the pathophysiology of chronic MR and pharmacologic therapies.

An Annular Prosthesis for the Treatment of Functional Mitral Regurgitation: Finite Element Model Analysis of a Dog Bone–Shaped Ring Prosthesis

BACKGROUND

Undersized annuloplasty is commonly used in the treatment of functional mitral regurgitation. However, in the case of severely dilated ventricles, annuloplasty may be inadequate to counteract leaflet tethering. My colleagues and I hypothesized that modifying the shape of the annular prosthesis to account for the specific anatomy of functional mitral regurgitation could challenge extreme leaflet tethering.

METHODS

Using finite element model simulations, we tested valve competence after the implantation of conventional D-shaped versus dog bone-shaped annuloplasty rings, the latter of which was designed to selectively reduce the septolateral dimension of the annulus. Three models were compared: model A, simulating the native mitral valve; model B, simulating the same valve after annuloplasty with a conventional D-shaped annuloplasty; and model C, simulating a dog-bone annuloplasty ring implantation. Each model was then challenged by progressively pulling the tip of the papillary muscles away from the annulus plane to simulate ventricular remodeling and leaflet tethering. Valve competence was compared in each model for each degree of leaflet tethering.

RESULTS

After maximal leaflet tethering simulation (4-mm apical displacement of the papillary tips), the regurgitant area increase was 70.4 mm2 for model A and 52.9 mm2 for model B. In model C, the regurgitant area was only negligibly affected by papillary displacement, increasing to 3.9 mm2.

CONCLUSIONS

An annular prosthesis with selective reduction in the septolateral dimension is more effective than a conventional prosthesis for treating leaflet tethering in functional mitral regurgitation. Use of disease-specific annular prostheses is needed to improve the results of valve reconstruction.

Importance of Mitral Valve Second-Order Chordae for Left Ventricular Geometry, Wall Thickening Mechanics, and Global Systolic Function

Background— Mitral valvular–ventricular continuity is important for left ventricular (LV) systolic function, but the specific contributions of the anterior leaflet second-order “strut” chordae are unknown.

Methods and Results— Eight sheep had radiopaque markers implanted to silhouette the LV, annulus, and papillary muscles (PMs); 3 transmural bead columns were inserted into the mid-lateral wall between the PMs. The strut chordae were encircled with exteriorized wire snares. Three-dimensional marker images and hemodynamic data were acquired before and after chordal cutting. Preload recruitable stroke work (PRSW) and end-systolic elastance (E es ) were calculated to assess global LV systolic function (n=7). Transmural strains were measured from bead displacements (n=4). Chordal cutting caused global LV dysfunction: E es (1.48±1.12 versus 0.98±1.30 mm Hg/mL, P =0.04) and PRSW (69±16 versus 60±15 mm Hg, P =0.03) decreased. Although heart rate and time from ED to ES were unchanged, time of mid-ejection was delayed (125±18 versus 136±19 ms, P =0.01). Globally, the LV apex and posterior PM tip were displaced away from the fibrous annulus and LV base-apex length increased at end-diastole and end-systole (all +1 mm, P <0.05). Locally, subendocardial end-diastolic strains occurred: Longitudinal strain ( E 22 ) 0.030±0.013 and radial thickening ( E 33 ) 0.081±0.041 (both P <0.05 versus zero). Subendocardial systolic shear strains were also perturbed: Circumferential-longitudinal “micro-torsion” ( E 12 ) (0.099±0.035 versus 0.075±0.025) and circumferential radial shear ( E 13 ) (0.084±0.023 versus 0.039±0.008, both P <0.05).

Conclusion— Cutting second-order chords altered LV geometry, remodeled the myocardium between the PMs, perturbed local systolic strain patterns affecting micro-torsion and wall-thickening, and caused global systolic dysfunction, demonstrating the importance of these chordae for LV structure and function.

Efficacy of chordal cutting to relieve chronic persistent ischemic mitral regurgitation

BACKGROUND

Mitral regurgitation (MR) conveys adverse prognosis in ischemic heart disease. Leaflet closure is restricted by tethering to displaced papillary muscles, and is, therefore, incompletely treated by annular reduction. In an acute ischemic model, we reduced such MR by cutting a limited number of critically positioned chordae to the leaflet base that most restrict closure but are not required to prevent prolapse. Whether this is effective without prolapse, recurrent MR, or left ventricular (LV) failure in chronic persistent ischemic MR, despite greater LV remodeling, remains to be established. Therefore, we studied 7 sheep with chronic inferobasal infarcts known to produce progressive MR over 2 months. In all of those sheep, after a mean of 4.1 months, the 2 central basal (intermediate) chordae were cut at the chronic ischemic MR stage. 3-Dimensional echo quantified MR, LV function, and valve geometry. Five other sheep were followed for a mean of 7.8+/-1.2 months after inferobasal infarction with chordal cutting.

RESULTS

All 7 of the sheep with chronic ischemic MR (increased from 1.4+/-0.4 to 11.1+/-0.5 mL/beat, regurgitant fraction=39.0+/-4.2%, P<0.0001) showed anterior leaflet angulation at the basal chord insertion. Although end-systolic volume had doubled, cutting the 2 central basal chordae significantly decreased the MR to baseline (P<0.0001) without prolapse or decline in EF (41.1+/-1.5% to 42.6+/-1.6%, P=not significant [NS]). The five sheep with long-term follow-up showed no prolapse or MR, and no significant post-infarct decrease in LV ejection fraction (EF; 38.9+/-2.4% to 41.4+/-1.2%, P=NS).

CONCLUSIONS

Cutting a minimum number of basal (intermediate) chordae can improve coaptation and reduce chronic persistent ischemic MR without impairing LVEF. No adverse effects were noted long-term after chordal cutting at the time of infarction.

Influence of anterior mitral leaflet second-order chordae tendineae on left ventricular systolic function

BACKGROUND

The contribution of anterior mitral leaflet second-order ("strut") chordae tendineae to left ventricular (LV) systolic mechanics is debated; we measured the in vivo contribution of anterior chordae tendineae (ACT) and posterior chordae tendineae (PCT) to regional and global LV contractile function.

METHODS AND RESULTS

Eight sheep had radiopaque markers implanted in the LV epicardium, partitioning the ventricle into 12 regions. Microminiature force transducers and snares were sutured to anterior leaflet "strut" chordae originating from ACT and PCT papillary muscles. Chordal tension, marker images, and hemodynamic data were acquired before and after (CUT) severing ACT and PCT. Fractional area shrinkage and slope of the regional end-diastolic area-regional stroke work relation (r-PRSW) were computed for each LV region. CUT did not affect global LV systolic function but reduced FAS in LV segments near the PCT insertion site: equatorial posterior lateral (19+/-2% versus 16+/-2%, P<0.05), apical posterior lateral (23+/-4% versus 19+/-4%, P<0.05), and posterior medial LV segments (16+/-2% versus 13+/-2%, P<0.05). r-PRSW fell near both the ACT (equatorial anterior medial [84+/-8 versus 62+/-11 mm Hg, P<0.05] and lateral [73+/-7 versus 53+/-9 mm Hg, P<0.05]) and PCT (apical posterior medial [91+/-12 versus 67+/-17 mm Hg, P<0.05] and lateral [72+/-8 versus 59+/-9 mm Hg, P<0.05]) LV insertion sites. Maximum tension in PCT was higher than in ACT (0.81+/-0.1 versus 0.52+/-0.08N, P<0.01).

CONCLUSIONS

Dividing anterior leaflet strut chordae in sheep was associated acutely with regional LV systolic dysfunction near the chordal insertion sites. Caution is necessary when embarking on procedures that cut second-order chordae to treat ischemic mitral regurgitation, since this may compromise LV systolic function in ventricles that are already impaired.

Anterior mitral leaflet mobility is limited by the basal stay chords

BACKGROUND

We hypothesize that 2 tendon-like anterior basal stay chords, which remain taut during the entire cardiac cycle, limit the motion of the anterior mitral leaflet.

METHODS AND RESULTS

Sonomicrometric crystals were implanted in 6 sheep at the insertion of stay chords at anterior mitral leaflet (S1 and S2), papillary muscle tips, fibrous trigones, mitral annulus, and the tip of the anterior leaflet (AL). Distances between crystals were recorded before and after section of stay chords. During the cardiac cycle, the angle alpha between mitral annulus and AL changed by +54.2+/-12.4 degrees; the angles between mitral annulus and S1 (beta1) changed by +25.7+/-14.6 degrees, and between mitral annulus and S2 (beta2) by +20.4+/-7.8 degrees. During diastole, AL twice crossed the virtual plane formed by the stay chords: during E-wave by a maximum of 6.5 mm (mean, 2.5+/-2.2 mm) and during A-wave by a maximum of 3.2 mm (mean, 1.7+/-0.9 mm). After section of both stay chords, total anterior mitral leaflet motion increased as follows: AL, +6.9+/-3.4 degrees; S1, +13.1+/-4.4 degrees; and S2, +30.9+/-11.7 degrees (P<0.05).

CONCLUSIONS

Although the lateral movement of anterior mitral leaflet is limited by stay chords, the midportion moves unimpaired toward the septum, like a sail, between the 2 stay chords during diastole. A diastolic left ventricular-inflow and systolic left ventricular-outflow funnel mechanism is created. Stay chord section increased lateral anterior mitral leaflet movement.