Partial Endocardial Cushion Defects

Seven partial endocardial cushion defects have been diagnosed and treated surgically without mortality—six of the ostium primum type and one with a defect from left ventricle to right atrium. The last patient likely has an associated cardiomyopathy. The most serious complication of repair is damage to the bundle of His.The electrocardiogram is helpful in diagnosis, showing left axis deviation in standard leads and right ventricular hypertrophy in chest leads (92%). The vector-cardiogram in the frontal plane shows counterclockwise rotation with the loop usually above the isoelectric line (97%). This is due to congenital aberration of the left bundle branch rather than to left ventricular hypertrophy from mitral incompetence. Radiography demonstrates moderate cardiac enlargement with right-sided hypertrophy, a prominent pulmonary artery, and pleonemic lung fields. Cardiac catheterization reveals a moderate rise in oxygen saturation at atrial level and a further minimal increase at ventricular level. The left atrial trace may show a minimal “c-v” configuration, with the “v” wave equal to the “a”.     

Personalized Computational Modeling of Mitral Valve Prolapse: Virtual Leaflet Resection

Posterior leaflet prolapse following chordal elongation or rupture is one of the primary valvular diseases in patients with degenerative mitral valves (MVs). Quadrangular resection followed by ring annuloplasty is a reliable and reproducible surgical repair technique for treatment of posterior leaflet prolapse. Virtual MV repair simulation of leaflet resection in association with patient-specific 3D echocardiographic data can provide quantitative biomechanical and physiologic characteristics of pre- and post-resection MV function. We have developed a solid personalized computational simulation protocol to perform virtual MV repair using standard clinical guidelines of posterior leaflet resection with annuloplasty ring implantation. A virtual MV model was created using 3D echocardiographic data of a patient with posterior chordal rupture and severe mitral regurgitation. A quadrangle-shaped leaflet portion in the prolapsed posterior leaflet was removed, and virtual plication and suturing were performed. An annuloplasty ring of proper size was reconstructed and virtual ring annuloplasty was performed by superimposing the ring and the mitral annulus. Following the quadrangular resection and ring annuloplasty simulations, patient-specific annular motion and physiologic transvalvular pressure gradient were implemented and dynamic finite element simulation of MV function was performed. The pre-resection MV demonstrated a substantial lack of leaflet coaptation which directly correlated with the severe mitral regurgitation. Excessive stress concentration was found along the free marginal edge of the posterior leaflet involving the chordal rupture. Following the virtual resection and ring annuloplasty, the severity of the posterior leaflet prolapse markedly decreased. Excessive stress concentration disappeared over both anterior and posterior leaflets, and complete leaflet coaptation was effectively restored. This novel personalized virtual MV repair strategy has great potential to help with preoperative selection of the patient-specific optimal MV repair techniques, allow innovative surgical planning to expect improved efficacy of MV repair with more predictable outcomes, and ultimately provide more effective medical care for the patient.     

Reduced Leaflet Stress in the Stentless Quadrileaflet Mitral Valve: A Finite Element Model

Background

Failure of bioprosthetics is usually caused by calcification of the leaflets as a consequence of high tensile stresses. The stentless valve resembles native mitral valve anatomy, has a flexible leaflet attachment and a suspension at the papillary muscles, and preserves annuloventricular continuity. In this study, the effects of the stentless valve design on leaflet stress were investigated with a finite element model.

Methods

Finite element models of the stentless quadrileaflet mitral valve were created in the close and open configurations. The geometry of the stented trileaflet mitral valve was also analyzed for comparative purposes. Under the designated pressures, the regional stresses were evaluated, and the distributions of stresses were assessed.

Results

Regardless of whether the valve is in the open or close configuration, the maximum first principal stress was significantly lower in the stentless valve than in the stented valve. For the stentless valves, limited stress concentration was discretely distributed in the papillary flaps under both close and open conditions. In contrast, in the stented valve, increased stress concentration was evident at the central belly under the open condition and at the commissural attachment under close condition. In either configuration, the maximum second principal stress was markedly lower in the stentless valve than in the stented valve.

Conclusions

The stentless valve was associated with a significant reduction in leaflet stress and a more homogeneous stress distribution compared to the stented valve. These findings are consistent with recent reports of the clinical effectiveness of the stentless quadrileaflet mitral valve.     

On the Presence of Affine Fibril and Fiber Kinematics in the Mitral Valve Anterior Leaflet

In this study, we evaluated the hypothesis that the constituent fibers follow an affine deformation kinematic model for planar collagenous tissues. Results from two experimental datasets were utilized, taken at two scales (nanometer and micrometer), using mitral valve anterior leaflet (MVAL) tissues as the representative tissue. We simulated MVAL collagen fiber network as an ensemble of undulated fibers under a generalized two-dimensional deformation state, by representing the collagen fibrils based on a planar sinusoidally shaped geometric model. The proposed approach accounted for collagen fibril amplitude, crimp period, and rotation with applied macroscopic tissue-level deformation. When compared to the small angle x-ray scattering measurements, the model fit the data well, with an r² = 0.976. This important finding suggests that, at the homogenized tissue-level scale of ∼1 mm, the collagen fiber network in the MVAL deforms according to an affine kinematics model. Moreover, with respect to understanding its function, affine kinematics suggests that the constituent fibers are largely noninteracting and deform in accordance with the bulk tissue. It also suggests that the collagen fibrils are tightly bounded and deform as a single fiber-level unit. This greatly simplifies the modeling efforts at the tissue and organ levels, because affine kinematics allows a straightforward connection between the macroscopic and local fiber strains. It also suggests that the collagen and elastin fiber networks act independently of each other, with the collagen and elastin forming long fiber networks that allow for free rotations. Such freedom of rotation can greatly facilitate the observed high degree of mechanical anisotropy in the MVAL and other heart valves, which is essential to heart valve function. These apparently novel findings support modeling efforts directed toward improving our fundamental understanding of tissue biomechanics in healthy and diseased conditions.     

Zebrafish Crip2 Plays a Critical Role in Atrioventricular Valve Development by Downregulating the Expression of ECM Genes in the Endocardial Cushion

The initial step of atrioventricular (AV) valve development involves the deposition of extracellular matrix (ECM) components of the endocardial cushion and the endocardialmesenchymal transition. While the appropriately regulated expression of the major ECM components, Versican and Hyaluronan, that form the endocardial cushion is important for heart valve development, the underlying mechanism that regulates ECM gene expression remains unclear. We found that zebrafish crip2 expression is restricted to a subset of cells in the AV canal (AVC) endocardium at 55 hours post-fertilization (hpf). Knockdown of crip2 induced a heart-looping defect in zebrafish embryos, although the development of cardiac chambers appeared to be normal. In the AVC of Crip2-deficient embryos, the expression of both versican a and hyaluronan synthase 2 (has2) was highly upregulated, but the expression of bone morphogenetic protein 4 (bmp4) and T-box 2b (tbx2b) in the myocardium and of notch1b in the endocardium in the AVC did not change. Taken together, these results indicate that crip2 plays an important role in AV valve development by downregulating the expression of ECM components in the endocardial cushion.     

二尖瓣成形术与二尖瓣生物瓣置换术治疗风湿性二尖瓣重度关闭不全的效果比较

目的:探讨二尖瓣成形术(Mitral valve plasty,MVP)与二尖瓣生物瓣置换术(Mitral valve replacement,MVR)治疗风湿性二尖瓣重度关闭的临床疗效和安全性。方法:选择我院2014年1月至2019年1月收治的因风湿性二尖瓣重度关闭而行二尖瓣成形术或二尖瓣生物瓣置换术的患者60例,其中二尖瓣成形术组(MVP组)27例,二尖瓣生物瓣置换术组(MVR组)33例。比较两组患者的围手术期各项指标,治疗前后的心功能指标(左心室射血分数,左心房内径、左心室收缩末期内径、左心室舒张末期内径)及二尖瓣反流情况以及术后并发症的发生情况。结果:(1)MVP组患者的手术时间、体外循环时间均明显长于MVR组(P0.05);而术中出血量、呼吸机使用时间、住院时间MVP组均显著低于MVR组(P0.05);(2)术后,MVP组的LVEF和LVEDD水平高于MVR组,而LAD和LVESD水平则低于MVR组(P 0.05);(3)出院前及末次随访时,MVP组二尖瓣反流发生率与MVR组相比差异均无统计学意义(P0.05)。(4)MVP组患者的术后并发症发生率低于MVR组(P 0.05)。结论:二尖瓣成形术治疗风湿性二尖瓣重度关闭的临床疗效和安全性优于二尖瓣生物瓣置换术,但术者需严格掌控MVP的手术适应症。     

Disturbances of Pulmonary Function in Mitral Valve Disease

To study the sequence of changes in respiratory function that occur in the natural history of mitral stenosis, and the physiological basis of “cardiac dyspnea”, 30 patients with chronic mitral valve disease were subjected to detailed pulmonary function tests. There was no significant change in vital capacity and functional residual capacity. The reduction in maximal mid-expiratory flow rate showed excellent correlation with the respiratory symptoms. The pulmonary capillary blood volume was increased in moderately advanced cases but was consistently reduced in the severest cases. Hyperventilation was due to an increased respiratory rate. Dyspnea was associated with increased respiratory work owing to the interrelation between the reduction in diffusion capacity, compliance, cardiac output, the increase in airway resistance, and the uneven ventilation and perfusion of the lungs. The amount of “effort” required to breathe is incommensurate with the external load in these patients.     

基于超声心动图的二尖瓣轮廓提取

针对超声心动图噪音大,灰阶少等弱点,采用多阈值的门限法对图象进行正确分割,在通过跟踪特征点进行匹配的基础上,采用匹配后插值的方法,提高了匹配的精度。并利用前一帧的速度解决了粘连在一起的二尖瓣轮廓线的分割问题。实验取得了较满意的结果。     

Mitral Valve Replacement in a 14-Month-Old Child

In a 14-month-old child with severe congenital mitral insufficiency, the mitral valve was replaced with a Starr-Edwards valve. This resulted in dramatic improvement and the child continues to thrive one year after surgery. The authors conclude that valve replacement should be considered in a child of any age if other methods of valve repair cannot be relied upon to produce a good result.     

Percutaneous Mitral Valve Repair in Mitral Regurgitation Reduces Cell-Free Hemoglobin and Improves Endothelial Function

Background and Objective

Endothelial dysfunction is predictive for cardiovascular events and may be caused by decreased bioavailability of nitric oxide (NO). NO is scavenged by cell-free hemoglobin with reduction of bioavailable NO up to 70% subsequently deteriorating vascular function. While patients with mitral regurgitation (MR) suffer from an impaired prognosis, mechanisms relating to coexistent vascular dysfunctions have not been described yet. Therapy of MR using a percutaneous mitral valve repair (PMVR) approach has been shown to lead to significant clinical benefits. We here sought to investigate the role of endothelial function in MR and the potential impact of PMVR.

Methods and Results

Twenty-seven patients with moderate-to-severe MR treated with the MitraClip® device were enrolled in an open-label single-center observational study. Patients underwent clinical assessment, conventional echocardiography, and determination of endothelial function by measuring flow-mediated dilation (FMD) of the brachial artery using high-resolution ultrasound at baseline and at 3-month follow-up. Patients with MR demonstrated decompartmentalized hemoglobin and reduced endothelial function (cell-free plasma hemoglobin in heme 28.9±3.8 μM, FMD 3.9±0.9%). Three months post-procedure, PMVR improved ejection fraction (from 41±3% to 46±3%, p = 0.03) and NYHA functional class (from 3.0±0.1 to 1.9±1.7, p<0.001). PMVR was associated with a decrease in cell free plasma hemoglobin (22.3±2.4 μM, p = 0.02) and improved endothelial functions (FMD 4.8±1.0%, p<0.0001).

Conclusion

We demonstrate here that plasma from patients with MR contains significant amounts of cell-free hemoglobin, which is accompanied by endothelial dysfunction. PMVR therapy is associated with an improved hemoglobin decompartmentalization and vascular function.     

Age-Related Peculiarities of Physiology of Human Mitral Valve

Hemodynamic characteristics of mitral valve of the human heart were studied in newborns and adults. The formulas for measuring transmitral flow velocity and for calculating the valve orifice area were proposed.     

Mitral Tissue Inhibitor of Metalloproteinase 2 Is Associated with Mitral Valve Surgery Outcome

Background

Matrix metalloproteinases play a role in regulating cardiac remodeling. We previously reported an association between tissue inhibitor of metalloproteinase 2 (TIMP-2) expression and mitral valve (MV) disease. However, the determinants and prognostic value of mitral TIMP2 after MV surgery are unknown.

Methods

This retrospective study of 164 patients after MV surgery in a tertiary medical center in Taiwan assessed mitral TIMP2 on a semiquantitative scale (0–2) by immunohistochemical staining. The primary endpoints were the composite of cardiovascular death and heart failure admission.

Results

Mean age was 50.4±13.7 years. After a mean follow-up period of 101±59 months, primary endpoints had occurred in 25 (15.2%) subjects. Patients with and without primary endpoint events significantly differed in terms of age (56.6±14.4 vs. 49.2±13.4 years, respectively; p = 0.013) and left ventricular end-systolic diameter (LVESD) (39.7±8.2 vs. 35.5±7.5 mm, p = 0.010) at surgery. The TIMP2 had a significant dose-dependent association with development of a primary endpoint (p = 0.002). Kaplan–Meier analysis showed that TIMP2 expression has a significant positive association with primary endpoint-free survival (log-rank test; p = 0.004). Cox regression analysis showed that independent predictors of primary endpoints were TIMP2 (hazard ratio [HR] 0.28; 95% confidence interval [CI] 0.12–0.65; p = 0.003), age (HR 1.05; 95% CI 1.02–1.09; p = 0.003) and LVESD (HR 1.05; 95% CI 1.01–1.10; p = 0.020).

Conclusions

The lack of mitral TIMP2 expression is associated with increases in cardiovascular death and heart failure following MV surgery.     

Clinical Use of a New Mitral Disc Valve

A disc valve of new design was used successfully for the replacement of the mitral valve in patients with rheumatic mitral valve disease. This valve would appear to have the following advantages over the mitral ball valve prosthesis:• Lower left atrial pressure after replacement.• Elimination of the hazard of left ventricular outflow tract obstruction with mitral valve replacement.• Decreased incidence of thromboembolization.• Abolition of possibility of ventricular septal irritation.Despite the better outlook for this valve compared with the ball valve for mitral valve substitution, the mitral valve should always be repaired whenever feasible. Repair is possible in the majority of patients.