Comparative anatomy of the mitral valve in four species (human, ovine, porcine and canine): A pre-clinical perspective.

This study aimed to provide comparative anatomical data on the mitral valve and to substantiate the choice between large species for pre-clinical testing of cardiac devices. Different anatomical parameters of the anterior and posterior leaflets, chordae and papillary muscles were measured to characterize the anatomy of the mitral valve in 10 individuals for each four species. Ratios were calculated and used to circumvent the interspecies variations of body and heart size and weight. The results underline many relevant anatomical similarities and differences between man and the three animal species. We confirm that the porcine species is a better model based on anatomical measurements. But many parameters should be considered depending on the shape, size and purpose of the device. The mitral and aortic valve are closer than in man leading to potential damage of the aortic valve by a mitral device. The ovine mitral annulus is more flattened and would sustain more mechanical forces on a round-shaped stent. The anterior and posterior leaflets have comparable height in the animal species leading to more space for implantation. The porcine valve has more chordae allowing less space around the valve for a transcatheter stent. Our observations introduce new comparative data in the perspective of the choice of a large animal model for pre-clinical testing of mitral devices. They are very helpful for all cardiologists, surgeons or engineers who need to understand the reasons for success or failure of a device and to have key elements of discussion.

Ex Vivo Biomechanical Study of Apical Versus Papillary Neochord Anchoring for Mitral Regurgitation.

BACKGROUND: Neochordoplasty is an important repair technique, but optimal anchoring position is unknown. Although typically anchored at papillary muscles, new percutaneous devices anchor the neochordae at or near the ventricular apex, which may have an effect on chordal forces and the long-term durability of the repair. METHODS: Porcine mitral valves (n = 6) were mounted in a left heart simulator that generates physiologic pressure and flow through the valves, and chordal forces were measured with Fiber Bragg Grating strain gauge sensors. Isolated mitral regurgitation was induced by cutting P2 primary chordae, and the regurgitant valve was repaired with polytetrafluoroethylene neochord with apical anchoring, followed by papillary muscle fixation for comparison. In both situations, the neochord was anchored to a customized force-sensing post positioned to mimic the relevant in vivo placement. RESULTS: Echocardiographic and hemodynamic data confirmed that the repairs restored physiologic hemodynamics. Forces on the chordae and neochord were lower for papillary fixation than for the apical fixation (p = 0.003). In addition, the maximum rate of change of force on the chordae and neochordae was higher for apical fixation than for papillary fixation (p = 0.028). CONCLUSIONS: Apical neochord anchoring results in effective repair of mitral regurgitation, albeit with somewhat higher forces on the chordae and neochord suture, as well as an increased rate of loading on the neochord compared with the papillary muscle fixation. These results may guide strategies to reduce stresses on neochordae as well as aid optimal patient selection.

Determination of the mechanical properties of normal and calcified human mitral chordae tendineae.

The aim of the present research is to determine the influence of the calcification of human mitral valves on the mechanical properties of their marginal chordae tendineae. The study was performed on marginal chords obtained from thirteen human mitral valves, explanted at surgery, including six non-calcified, four moderately calcified and three strongly calcified valves. The mechanical response of the chords from the non-calcified and moderately calcified valves was determined by means of quasi-static tensile tests (the poor condition of the strongly calcified valves prevented them from being mechanically characterised). The material parameters that were obtained and analysed (the Young's modulus, the secant modulus, the proportional limit stress, the ultimate strength, the strain at fracture and the density of energy stored up to maximum load) revealed noticeable differences in mechanical behaviour between the two groups of mitral chordae tendineae. Large scatter was obtained in all cases, nevertheless, considering the mean values, it was observed that the normal chords are between three and seven times stiffer or more resistant than the moderately calcified ones. On the contrary, the results obtained for the strain at fracture showed a rather different picture as, in this case, no significant differences were observed between the two families of chords. A scanning electron microscopy study was conducted in order to find out the relevant features of the calcium deposits present in the calcified chordae tendineae. In addition, the general aspects appreciated in the stress vs. strain curves were correlated with the collagen morphological evidences determined microscopically. Finally, the calcium content present in the three groups of chords was quantitatively determined through atomic absorption spectroscopy; then, the relation between the mechanical properties of normal and moderately calcified chords as a function of its calcium content was obtained. This analysis confirmed the existence of a strong correlation between calcium content and stiffness or resistance whereas the influence on the ductility seems to be negligible.

Mitral leaflet anatomy revisited.

OBJECTIVE: The aims of this work were to employ functional imaging capabilities of the Visible Heart laboratory and endoscopic visualization of mitral valves in perfusion-fixed specimens to better characterize variability in mitral valve leaflet anatomy and to provide a method to classify mitral leaflets that varies from the current nomenclature. METHODS: We gathered functional endoscopic video footage (11 isolated reanimated human hearts) and static endoscopic anatomical images (38 perfusion-fixed specimens) of mitral leaflets. Commissure and cleft locations were charted using Carpentier's accepted description. RESULTS: All hearts had 2 commissures separating anterior and posterior leaflets. "Standard" clefts separating P1/P2 were found in 66% of hearts (n = 25), and standard clefts separating P2/P3 were present in 71% of hearts (n = 27). "Deviant" clefts occurred in each region of the anterior leaflet (A1, A2, A3), and their relative occurrences were 5%, 8%, and 13% (n = 2, 3, 5), respectively. Deviant clefts were found in posterior leaflets: 13.2% in P1 (n = 5), 32% in P2 (n = 12), and 21% in P3 (n = 8). CONCLUSIONS: Humans elicit complex and highly variable mitral valve anatomy. We suggest a complementary, yet simple nomenclature to address variation in mitral valve anatomy by describing clefts as either standard or deviant and locating regions in which they occur (A1 to A3 or P1 to P3).

Study of the traction resistance of mitral valve chordae tendineae

OBJECTIVE: To determinate the extension and the resistance of the primary mitral valve chordae tendineae when submitted to traction. The importance of keeping the integrity of papillary muscle, chordae tendineae, and mitral valve cuspid when the replacement of this valve occurs is clear, but the knowledge of the maximum resistance that a primary tendinea chorda can withstand is not known. METHODS: Eight hearts were dissected, and one hundred and thirty two primary human chordae tendineae were measured (length and thickness) and submitted to traction under controlled conditions so that the absolute resistance, resistance relative to thickness (relative resistance), and elongation could be measured. RESULTS: The correlation between the elongation at the moment of rupture and the thickness was equal to 1.54 + 17.02 x thickness (P = 0.026); and to absolute resistance was equal to 0.95 + 1.42 x resistance (P < 0.001); and to the resistance relative to thickness (relative resistance) was equal to 1.95 + 0.08 x relative resistance (P = 0.009). The correlation between the absolute resistance and the thickness was equal to 0.26 + 14.53 x thickness (P < 0.001). CONCLUSION: The resistance of primary mitral valve chordae tendineae is associated with its thickness and elongation at the moment of rupture, but is not associated with the length. The elongation at the moment of rupture shows a relationship with the resistance relative to thickness (relative resistance) and with the thickness of the primary chordae tendineae, but not with the length of the chordae tendineae.

OBJETIVO: Determinar o alongamento e a resistência à tração das cordas tendíneas primárias humanas da valva mitral cardíaca. Sabe-se da importância de se manter a integridade do músculo papilar, corda tendínea e cúspide da valva mitral, quando da substituição desta valva, mas não se tem conhecimento da resistência máxima que uma corda tendínea primaria pode sofrer resistência máxima que uma corda tendínea apresenta. MÉTODO: Foram dissecados 8 corações que permitiram a tração de cento e trinta e duas cordas tendíneas primárias humanas. Foram dissecados 8 corações que permitiram a tração de cento e trinta e duas cordas tendíneas primárias humanas, as quais foram medidas (comprimento e espessura) e submetidas a trações em condições controladas, e assim a resistência absoluta, a resistência relativa a espessura (resistência relativa) e o alongamento puderam ser medidos. RESULTADOS: A correlação entre alongamento no momento da ruptura e espessura foi igual a 1,54 + 17,02*espessura (p=0,026); e à resistência absoluta foi igual a 0,95 + 1,42*resistência (p<0,001); e à resistência relativa à espessura foi igual a 1,95 + 0,08*resistência relativa (p=0,009). A correlação entre resistência absoluta e espessura foi igual a 0,26 + 14,53*espessura (p<0,001). CONCLUSÃO: A resistência da corda tendínea primaria humana da valva mitral está relacionada com sua espessura e com o alongamento no momento da ruptura à tração, não estando relacionada ao seu comprimento; e que o alongamento no momento da ruptura apresenta correlação com a resistência relativa à espessura e com a espessura da corda tendínea primaria humana, não estando relacionada com o comprimento da mesma.

Fabrication of mitral valve chordae by directed collagen gel shrinkage.

The principles of tissue engineering are being used to explore numerous applications in reconstructive surgery. Mitral valve chordae are one such potential area, as mitral valve repair is increasing in popularity and synthetic materials have not been used widely. The use of cells, combined with reconstituted type I collagen, is an attractive option for fabricating materials for the replacement of thin tendonous structures such as mitral valve chordae. We have been using the principle of directed collagen gel shrinkage to fabricate tendinous structures with good mechanical properties. In this study, our objective was to maximize the strength of the collagen constructs by choosing cell type and optimizing cell-seeding density, culture time, and initial collagen concentration. A collagen-cell suspension was cast into silicone rubber wells with microporous anchors at the ends and cultured in an incubator. The anchors allowed shrinkage to occur only transverse to the long axis of the wells, thus creating highly aligned collagenous constructs. Collagen gel contraction increased with higher cell-seeding density. The optimal value was 10(6) cells/mL. The rate of gel contraction decreased with the initial collagen concentration. Fibril density increased with culture time, as the gel contracted. After the system was optimized, the mechanical strength of the constructs increased to 1.1 MPa, a value at least an order of magnitude greater than previously published results with similar systems. This study has demonstrated that collagen-cell constructs, with material properties similar to those of native mitral valve chordae, can be developed using the principle of directed collagen gel shrinkage. These structures may have application in other areas that require small-diameter tendons.

Patterns of systolic stress distribution on mitral valve anterior leaflet chordal apparatus. A structural mechanical theoretical analysis.

Increasing diffusion and complexity of mitral valve repair procedures may prompt an interest in the evaluation of the patterns of stress distribution on the chords, which are, from the structural mechanical point of view, the weakest element of valve apparatus. This theoretical analysis concentrates in particular on the mitral valve anterior leaflet. As is known, the vast majority of the chordae are attached to the anterior leaflet within the coaptation area; during systole they are then necessarily parallel, aligned along the same plane as that of the leaflets' coaptation surface, to which they are attached; moreover the thickness of the chordae increases significantly from the marginal chordae to the more central ones. In normal conditions during systole the progressively wider coaptation surface causes the increasing stress to be supported by an increasing number of progressively thicker chords, which are substantially parallel and aligned on the coaptation surface plane in such a way that they can share the stress between them, according to their thickness; in other words chords form a multifilament functional unit which enrolls elements of increasing thickness in response to the mounting stress. The geometrical modifications of the valve apparatus architecture (annulus dilatation, leaflet retraction, chordal elongation or retraction) often associated with valve insufficiency due to chordal rupture, have the common result of causing, during systole, a radial disarrangement of the direction of most of the secondary chordae which are no longer parallel, aligned on the coaptation surface plane. Due to the negligible elastic module of the valve leaflet, in this new arrangement the various chordae cannot share the stress between themselves as they do in a normal physiological situation; on the contrary the thinner chordae nearer to the free margin are also loaded with the peak systolic stress, thus generating conditions favoring their rupture. It can, therefore, be hypothesized that the anatomopathological picture of valve insufficiency due to chordal rupture may be the final event of a series of geometrical modifications of valve apparatus architecture, the common consequence of which is to load thinner marginal chords with peak systolic stress from which they are normally spared, thus favoring their rupture.

Effects of mitral valve replacement on regional left ventricular systolic strain.

BACKGROUND: Mitral valve replacement (MVR) with chordal excision impairs left ventricular (LV) systolic function, but the responsible mechanisms remain incompletely characterized. Loss of normal annular-papillary continuity also adversely affects LV torsional deformation, possibly due to changes in myocardial fiber contraction pattern. METHODS: Twenty-seven dogs underwent insertion of LV myocardial markers and a sham procedure (cardiopulmonary bypass, no MVR, n = 6), conventional MVR with chordae tendineae excision (n = 7), or chordal-sparing MVR with reattachment of the anterior leaflet chordae to the anterior annulus (n = 7) or to the posterior annulus (n = 7). In the anterior, lateral, posterior, and septal LV regions, linear chords were constructed from each region's central marker to its surrounding markers. Percent systolic shortening (regional LV strain) was calculated for each chord, and the chords were assigned to one of four angular groups: I, left-handed oblique (subepicardial fiber direction); II, circumferential (midwall); III, right-handed oblique (subendocardial); or IV, longitudinal. Regional LV strain data were compared before and after MVR. RESULTS: Sham and anterior chordal-sparing MVR had minimal effects on regional LV strain. With posterior chordal-sparing MVR: anteriorly, left-oblique (I) strain fell (31%, p<0.05), as did circumferential (II) and right-oblique (III) strains (by 49% and 51%, respectively; p<0.01). Laterally, left-oblique (I) strain fell by 36% (p<0.05), as did longitudinal (IV) strain (54% decline, p<0.01). Conventional MVR with chordal excision disrupted regional fiber shortening diffusely, affecting oblique fibers (I and III) in the anterior and septal regions and impairing longitudinal (IV) strain in all regions (45% to 68% fall, p<0.05). CONCLUSIONS: Sham and anterior chordal-sparing MVR did not substantially alter regional LV strain; however, loss of normal anatomic valvular-ventricular integrity (conventional MVR) or posterior chordal-sparing MVR resulted in pronounced alterations in LV strain, most notably in the longitudinal and oblique fiber directions. These findings demonstrate that the deleterious effects of chordal excision are associated with perturbed internal myocardial systolic deformation, which suggests that chordal disruption distorts myofiber architecture or regional systolic loading.

Preoperative left ventricular systolic dysfunction correlates with the adverse postoperative consequences of annular-papillary disconnection in the course of mitral valve replacement for stenosis.

BACKGROUND AND AIMS OF THE STUDY: Preservation of chordae tendineae helps maintain ventricular performance in patients having surgery for mitral regurgitation. The importance of chordal integrity in patients with rheumatic mitral stenosis is unknown. The purpose of this study was to determine the influence of chordal preservation on left ventricular function following relief of rheumatic mitral stenosis. METHODS: A total of 142 patients with mitral stenosis had balloon valvulotomy (group 1, n = 63), surgical commissurotomy (group 2, n = 33) or mitral valve replacement (group 3, n = 46). Chordae were resected in all group 3 patients. Left ventricular dimension in end-diastole (LVEDD), end-systole (LVESD) and fractional shortening (FS) were measured at baseline and at a mean interval of 11 +/- months post intervention. RESULTS: At one year, FS increased in groups 1 and 2, but decreased in group 3 (+11.5%, +9%, -6.1%, p < 0.005 for group 3 versus groups 1 and 2). a borderline significant increase LVEDD was seen in group 1 compared with groups 2 and 3 (11%, 5%, 4% respectively, p = 0.05). Differences in FS at follow up were due mainly to diametrically opposite changes in LVESD in the subgroup of patients with baseline left ventricular dysfunction (-1.9%, 0%, +9.8%, p < 0.005 for group 3 versus groups 1 and 2). CONCLUSIONS: Deterioration of left ventricular function only in patients having mitral valve replacement indicates chordal resection as a putative mechanism. The result of this study suggest that chordal preservation is particularly important in patients with mitral stenosis who have depressed preoperative left ventricular systolic function.

Repair of congenital tricuspid valve abnormalities with artificial chordae tendineae.

BACKGROUND: Congenital abnormalities of the tricuspid valve, including Ebstein's malformation, dysplasia, straddling, and those found in pulmonary atresia with intact septum and congenitally corrected transposition, are an uncommon cause of tricuspid regurgitation. Congenital tricuspid valve anomalies are found as a spectrum of disease in which both the leaflets and the subvalvar apparatus are often involved. Tricuspid valve repair is complicated in such patients because the chordae tendineae are often abnormally short and thick. Replacement or augmentation of chordae tendineae has proved to be a useful component of mitral valve repair. In the present report, we describe the techniques and results of chordal augmentation in the repair of congenital tricuspid valve abnormalities. METHODS: Since July 1992, tricuspid valve repair has been performed in 5 children with severe tricuspid regurgitation secondary to congenital abnormalities of the tricuspid valve with significant chordal pathology. As a component of the repair, chordal replacement or augmentation was performed using expanded polytetrafluoroethylene suture. RESULTS: Intraoperative and postoperative echocardiographic assessment showed good mobility of the tricuspid valve leaflets and trivial to mild tricuspid regurgitation. There were no complications and no early or late mortality. At follow-up of 34 to 60 months (median, 49 months), tricuspid valve function has remained excellent in 4 of the 5 patients. In the remaining patient, progressive regurgitation of the right ventricle to pulmonary artery allograft conduit has led to right ventricular dilatation, with a secondary increase in tricuspid regurgitation from trivial to moderate. CONCLUSIONS: Chordal replacement or augmentation with expanded polytetrafluoroethylene suture is a useful technique in the repair of congenitally dysplastic tricuspid valves with abnormal chordal structures.

Annular dilatation increases stress in the mitral valve and delays coaptation: a finite element computer model.

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

Dynamic three-dimensional imaging of the mitral valve and left ventricle by rapid sonomicrometry array localization.

OBJECTIVES: The first objective was to develop a quantitative method for tracking the three-dimensional geometry of the mitral valve. The second was to determine the complex interrelationships of various components of the mitral valve in vivo. METHODS AND RESULTS: Sixteen sonomicrometry transducers were placed around the mitral vale anulus, at the tips and bases of both papillary muscles, at the ventricular apex, across the ventricular epicardial short axis, and on the anterior chest wall before and during cardiopulmonary bypass in eight anesthetized sheep. Animals were studied later on 17 occasions. Reproducibility of derived chord lengths and three-dimensional coordinates from sonomicrometry array localization, longevity of transducer signals, and the dynamics of the mitral valve and left ventricle were studied. Reproducibility of distance measurements averages 1.6%; Procrustes analysis of three-dimensional arrays of coordinate locations predicts an average error of 2.2 mm. Duration of serial sonomicrometry array localization signals ranges between 60 and 151 days (mean 114 days). Sonomicrometry array localization demonstrates the saddle-shaped mitral anulus, its minimal orifice area immediately before end-diastole, and uneven, apical descent during systole. Papillary muscles shorten only 3.0 to 3.5 mm. Sonomicrometry array localization demonstrates nonuniform torsion of papillary muscle transducers around a longitudinal axis and shows rotation of papillary muscular bases toward each other during systole. CONCLUSION: Tagging of ventricular structures in experimental animals by sonomicrometry array localization images is highly reproducible and suitable for serial observations. In sheep the method provides unique, quantitative information regarding the interrelationship of mitral valvular and left ventricular structures throughout the cardiac cycle.

Importance of preserving the mitral subvalvular apparatus in mitral valve replacement.

BACKGROUND: This clinical study sought to determine whether mitral valve replacement (MVR) with the preservation of both anterior and posterior chordae tendineae (MVR group II) would be more effective on the improvement of left ventricular regional wall motion than MVR with the preservation of posterior chordae tendineae alone (MVR group I). METHODS: Postoperative left ventricular wall motion was analyzed by a centerline method in three groups of MVR--group I (n = 13), group II (n = 15), and repair group (n = 15)--for mitral regurgitation. Shortening fraction of chordal length was determined in 100 chords, and these chords were divided into five regions. RESULTS: The comparison of postoperative versus preoperative shortening fraction among the three groups revealed that postoperative wall motion improved more strikingly at apical and diaphragmatic regions in the MVR group II and repair group in comparison to the MVR group I. The postoperative shortening fraction at the apical region in the MVR group II was significantly increased in comparison to preoperative shortening fraction (preoperative, 3.68% +/- 1.87%; postoperative, 5.38% +/- 2.33%; p < 0.05). However, postoperative shortening fraction in cardiac base was decreased in the MVR group II as well as other two groups. CONCLUSIONS: The MVR with the preservation of both anterior and posterior chordae tendineae contributed to the improvement of left ventricular regional wall motion in the apical and diaphragmatic regions.

[Left ventricular systolic and diastolic function after mitral valve replacement with preservation of posterior chordae tendineae].

Left ventricular function was compared in 14 patients who underwent mitral valve replacement with preservation of the posterior leaflet, chordae tendineae and papillary muscle (preserved group) and 14 patients who underwent conventional mitral valve replacement (non-preserved group). 99mTc radionuclide ventriculography was performed before surgery and one month after surgery. The early diastolic filling rate, an indicator of the efficiency of diastolic function, was measured. The patients in the non-preserved group showed an anteroseptal ejection fraction of 28 +/- 10% before surgery and 32 +/- 10% after surgery, an apical ejection fraction (71 +/- 10% vs 73 +/- 16%), and an inferolateral ejection fraction (56 +/- 16% vs 53 +/- 16%). The global ejection fraction tended to decrease from 56 +/- 9% to 52 +/- 10%. The patients in the preserved group showed an anteroseptal ejection fraction of 37 +/- 13% before surgery and 43 +/- 19% after surgery, an apical ejection fraction (74 +/- 20% vs 77 +/- 17%) and an inferolateral ejection fraction (53 +/- 11% vs 68 +/- 16%). The global ejection fraction, reflecting improvement in the inferolateral ejection fraction, tended to increase from 53 +/- 11% to 58 +/- 11%. The early diastolic filling rate for the preserved group was 1.73 +/- 0.43 before surgery and 1.05 +/- 0.61 after surgery, while that for the nonpreserved group was 1.59 +/- 0.24 vs 0.97 +/- 0.48. Although the early diastolic filling rate normalized in both groups, there was no significant difference between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Late hemodynamic effects of the preserved papillary muscles during mitral valve replacement.

BACKGROUND: The late hemodynamic effects of preserving the papillary muscles during mitral valve replacement have not been evaluated. METHODS AND RESULTS: Sixteen patients who had chronic mitral regurgitation due to myxomatous degeneration were randomized to preservation (Pres group, n = 8) or no preservation (No Pres group, n = 8) of the chordae tendineae and papillary muscles during mitral valve replacement. Rest and exercise nuclear ventriculograms were performed early (3 months) and late (5 years) after surgery. Early after surgery, the No Pres group had lower ejection fractions and stroke work indexes (P < .05 by repeated-measures [rm] ANOVA) than the Pres group did at similar end-diastolic volume indexes. The No Pres group had similar cardiac indexes after exercise because heart rate increased (P < .005 by rm ANOVA). Late after surgery, ejection fraction was greater at similar end-diastolic volume indexes (P < .005 by rm ANCOVA), and preload recruitable stroke work indexes (P < .001 by rm ANCOVA) were better in the Pres group. CONCLUSIONS: Preserving chordal attachments enhanced the late hemodynamic recovery after mitral valve replacement for mitral regurgitation.

Mitral valve anatomy and morphology: relevance to mitral valve replacement and valve reconstruction.

An endoscope was used to study the anatomy and morphology of the native mitral valve inside an isolated pig heart working under physiological conditions. Annulus motion, valve leaflet function, and the anatomy of the chords and branching pattern are described. Anatomical and functional details relevant to mitral valve reconstruction and valve replacement are outlined. Because of the similarity with the human heart, we have assumed that the observations made in the pig heart also apply to humans.

Estudo morfológico e histoquímico em nível ultra-estrutural da corda tendínea de coraçöes de rato albino / Morphological and histochemical study in structural pattern of chordae tendinae of hearts from albino rat

Fragmentos de cordas tendíneas dos complexos valores mitral e tricúspide de ratos albinos foram observados ao microscópio eletrônico de transmissäo com o objetivo de estudar os componentes da matriz extracelulair. Foram utilizados dois tipos de fixador, um contendo ácido tânico para demonstrar a presença de fibras dos sistemas colágeno e elástico, e outro contendo vermelho de rutênio para a visualizaçäo de proteuglicans. Alguns fragmentos foram tratados previamente pela colagenase ou pela tripisina antes de serem fixados pelo glutaraldeído com vermelho de rutênio. Foi observado que as cordas tendíneas de rato säo revestidas por um endotélio contínuo que repousa sobre uma camada de conjuntivo contendo fibroblastos e esparsas fibras de colágeno, compondo a zona esponjosa. Tal camada circunda uma zona central (zaza fibrosa) constituída de grossos feixes de colágeno onde se encontram vários fibroblastos. Tanto na zona esponjosa como na fibrosa foram detectadas inúmeras fibras com padräo ultra-estrutural de fibras elaunínicas, os quais, juntamente com o colágeno, desempenham funçöes de resistência mecânica ao transmitirem as forças de traçäo exercidas pelo músculo papilar às bordas das válvulas. Adicionalmente, foram observadas as relaçöes morfológicas entre proteoglicans, fibrilas de colágeno e microfibrilas elaunínicas, tendo sido enfatizada a importância do equilíbrio de funçöes entre os diversos componentes da matriz extracelular concorrendo para o perfeito funcionamento deste complexo morfofuncional na fisiologia da corda tendínea.

Effects of preserving mitral apparatus on ventricular systolic function in mitral valve operations in dogs.

The mitral apparatus can affect left ventricular function through various mechanisms, such as the direct mechanical coupling between the mitral anulus and papillary muscle and the mitral annular contraction. To evaluate the relative contribution of these mechanisms, we investigated in five groups of 35 dogs that underwent open chest operations how preservation of the mitral apparatus affects left ventricular systolic function. We performed atriotomy in the first group. We sutured a prosthetic rigid ring around the mitral anulus in the second group. We replaced the mitral valve and preserved the anterior chordae in the third group, the posterior chordae in the fourth group, and no chordae in the fifth group. The postoperative percentage of recovery of ventricular function (as assessed by the slope of the end-systolic pressure-volume relation) from preoperative control values were 92.2% +/- 4.8%, 89.5% +/- 12.8%, 85.7% +/- 9.5%, 75.1% +/- 12.9%, and 61.3% +/- 8.0%, respectively. Preservation of the mitral apparatus significantly improved left ventricular function compared with that of conventional mitral valve replacement. The average relative contribution of the ventricular muscle to left ventricular function, the mitral anulus-papillary muscle continuity, and the mitral annular contraction were 66.5%, 30.6%, and 2.9%, respectively. We conclude that it is more beneficial to preserve the mitral apparatus in mitral valve replacement. The prosthetic ring does not detract from the functional benefit of the preservation of the mitral apparatus.