Mapping the spatial variation of mitral valve elastic properties using air-pulse optical coherence elastography

The mitral valve is a highly heterogeneous tissue composed of two leaflets, anterior and posterior, whose unique composition and regional differences in material properties are essential to overall valve function. While mitral valve mechanics have been studied for many decades, traditional testing methods limit the spatial resolution of measurements and can be destructive. Optical coherence elastography (OCE) is an emerging method for measuring viscoelastic properties of tissues in a noninvasive, nondestructive manner. In this study, we employed air-pulse OCE to measure the spatial variation in mitral valve elastic properties with micro-scale resolution at 1 mm increments along the radial length of the leaflets. We analyzed differences between the leaflets, as well as between regions of the valve. We found that the anterior leaflet has a higher elastic wave velocity, which is reported as a surrogate for stiffness, than the posterior leaflet, most notably at the annular edge of the sample. In addition, we found a spatial elastic gradient in the anterior leaflet, where the annular edge was found to have a greater elastic wave velocity than the free edge. This gradient was less pronounced in the posterior leaflet. These patterns were confirmed using established uniaxial tensile testing methods. Overall, the anterior leaflet was stiffer and had greater heterogeneity in its mechanical properties than the posterior leaflet. This study measures differences between the two mitral leaflets with greater resolution than previously feasible and demonstrates a method that may be suitable for assessing valve mechanics following repair or during the engineering of synthetic valve replacements.     

Shear stress-induced upregulation of connexin 43 expression in endothelial cells on upstream surfaces of rat cardiac valves

Endothelial expression of the gap junction proteins, connexin (Cx) 37, Cx40, and Cx43, varies within the vascular network. While previous studies suggest that shear stress may upregulate Cx43, it is not well understood if shear stress affects the expression of all endothelial connexins and to what extent. Endothelial cells on the upstream and downstream surfaces of cardiac valves are subjected to considerably different intensities of shear stress. We therefore reasoned that we could determine the extent hemodynamic forces affect the expression of Cx37, Cx40, and Cx43 by comparing their immunohistochemical distribution on the upstream and downstream surfaces of rat cardiac valves. We found 70- to 200-fold greater expression of Cx43 in the endothelial cells on the upstream than on the downstream surfaces. However, Cx37 was expressed almost equally in the endothelial cells on upstream and downstream surfaces, and Cx40, a major connexin in most vascular endothelial cells, was not detected on either surface. In addition to the heterogeneity in Cx43 expression, endothelial cells on the upstream surface were 35% to 65% smaller than those on the corresponding downstream surface. These results suggest that shear stress may affect endothelial cell size and Cx43 expression but not Cx37 expression.     

A fatal case of fungal endocarditis of the tricuspid valve associated with long-term venous catheterization and treatment with antibiotics in a patient with a history of alcohol abuse

We report a fatal case of fungal (candidal) endocarditis of the tricuspid valve with clinico-pathologically interesting findings following and associated with candidal pneumonia during long-term central venous catheterization (CVC) for intravenous therapy and long-term treatment with antibiotics for bacterial and fungal infection in a patient with a history of alcohol abuse. We review the literature on fungal cardiac infection related to long-term catheterization and alcohol abuse, and discuss the pathogenesis. This revised version was published online in June 2006 with corrections to the Cover Date.     

A calcified polymeric valve for valve-in-valve applications

The prevalence of aortic valve stenosis (AS) is increasing in the aging society. More recently, novel treatments and devices for AS, especially transcatheter aortic valve replacement (TAVR) have significantly changed the therapeutic approach to this disease. Research and development related to TAVR require testing these devices in the calcified heart valves that closely mimic a native calcific valve. However, no animal model of AS has yet been available. Alternatively, animals with normal aortic valve that are currently used for TAVR experiments do not closely replicate the aortic valve pathology required for proper testing of these devices. To solve this limitation, for the first time, we developed a novel polymeric valve whose leaflets possess calcium hydroxyapatite inclusions immersed in them. This study reports the characteristics and feasibility of these valves. Two types of the polymeric valve, i.e., moderate and severe calcified AS models were developed and tested by deploying a transcatheter valve in those and measuring the related hemodynamics. The valves were tested in a heart flow simulator, and were studied using echocardiography. Our results showed high echogenicity of the polymeric valve, that was correlated to the severity of the calcification. Aortic valve area of the polymeric valves was measured, and the severity of stenosis was defined according to the clinical guidelines. Accordingly, we showed that these novel polymeric valves closely mimic AS, and can be a desired cost-saving solution for testing the performance of the transcatheter aortic valve systems in vitro.     

Can isolated annular dilatation cause significant ischemic mitral regurgitation? Another look at the causative mechanisms

This study was to investigate the mechanisms of ischemic mitral regurgitation (IMR) by using a finite element (FE) approach. IMR is a common complication of coronary artery disease; and it usually occurs due to myocardial infarction. The pathophysiological mechanisms of IMR have not been fully understood, much debate remains about the exact contribution of each mechanism to IMR. Two patient-specific FE models of normal mitral valves (MV) were reconstructed from multi-slice computed tomography scans. Different grades of IMR during its pathogenesis were created by perturbation of the normal MV geometry. Effects of annular dilatation and papillary muscle (PM) displacement (both isolated and combined) on the severity of IMR were examined. We observed greater increase in IMR (in terms of regurgitant area and coaptation length) in response to isolated annular dilatation than that caused by isolated PM displacement, while a larger PM displacement resulted in higher PM forces. Annular dilation, combined with PM displacement, was able to significantly increase the severity of IMR and PM forces. Our simulations demonstrated that isolated annular dilatation might be a more important determinant of IMR than isolated PM displacement, which could help explain the clinical observation that annular size reduction by restrictive annuloplasty is generally effective in treating IMR.     

成人动脉导管未闭合并重度二尖瓣返流的外科治疗

目的:探讨外科手术治疗成人动脉导管未闭(PDA)合并重度二尖瓣返流(MR)的疗效.方法:回顾性分析2009年1月至2011年1月在本中心实施外科手术治疗6例PDA合并MR患者的临床资料.5例实施PDA缝扎术和二尖瓣置换术,1例实施PDA缝扎术和二尖瓣成形术.分别于术前、术后1周、1月、3月和1年行超声心动图检查,观察并测定左室舒张末期内径(LVEDD)和左室射血分数(LVEF)等指标的变化.结果:6例术后PDA均无残余分流.心脏彩超检查显示,术后1周与术前相比,LVEDD显著缩小(P＜0.01),术后1个月较术后1周进一步缩小(P＜0.01),术后3个月与术后1个月比较以及术后1年和术后3月比较LVEDD有所减少,但差异无统计学意义.LVEF术后比术前有所降低,但差异无统计学意义.所有病例在术后随访中未出现栓塞和出血等并发症.结论:外科手术治疗PDA合并MR疗效满意.术前单纯重度MR患者易漏诊PDA,应尽可能明确诊断.     

Competition between electron acceptors in photosynthesis: Regulation of the malate valve during CO2 fixation and nitrite reduction

For maximal rates of CO₂ assimilation in isolated intact spinach chloroplasts the generation of the adequate NADPH/ATP ratio is achieved either by cyclic electron flow around photosystem I or by linear electron transport to oxaloacetate, nitrite or oxygen (Mehler-reaction). The interrelationships between these poising mechanisms turn out to be strictly hierarchical. In the presence of antimycin A, an inhibitor of ferredoxin-dependent cyclic electron transport, the reduction of both, oxaloacetate and nitrite, but not that of oxygen restores CO₂ fixation. When oxaloacetate and nitrite are added at low concentrations simultaneously during steady-state CO₂ fixation, the reduction of nitrite is clearly preferred over the reduction of oxaloacetate, but CO₂ fixation is not influenced. Nitrite reduction is not decreased upon addition of oxaloacetate, but vice versa. This is due to the regulation of NADP-malate dehydrogenase activation by electron pressure via the ferredoxin/thioredoxin system on the one hand, and by the NADPH/(NADP+NADPH) ratio (anabolic reduction charge, ARC) on the other hand. Thus the closing of the malate valve prevents drainage of reducing equivalents from the chloroplast (1) when a low ARC indicates a high demand for NADPH in the stroma and (2) when nitrite reduction reduces the electron pressure at ferredoxin. The malate valve is opened when cyclic electron transport is inhibited by antimycin A. Under these conditions the rate of malate formation is higher than in the absence of the inhibitor even in the presence of oxaloacetate, thus indicating that the regulation of the malate valve functions at various redox states of the acceptor side of Photosystem I.Abbreviations ARC anabolic reduction charge (NADPH/(NADP+NADPH)) - Chl chlorophyll - DTT dithiothreitol; Fd-ferredoxin - NADP-MDH NADP-malate dehydrogenase - OAA oxaloacetate - PS photosystem - qN non-photochemical quenching - qP photochemical quenching - _E quantum efficiency of PS II Dedicated to Prof. Dr. Hans Walter Heldt on the occasion of his 60th birthday.     

Survey of transposable elements from rice genomic sequences

Oryza sativa L. (domesticated rice) is a monocotyledonous plant, and its 430 Mb genome has been targeted for complete sequencing. We performed a high-resolution computer-based survey for transposable elements on 910 Kb of rice genomic DNA sequences. Both class I and II transposable elements were present, contributing 19.9% of the sequences surveyed. Class II elements greatly outnumbered class I elements (166 versus 22), although class I elements made up a greater percentage (12.2% versus 6.6%) of nucleotides surveyed. Several Mutator-like elements (MULEs) were identified, including rice elements that harbor truncated host cellular genes. MITEs (miniature inverted-repeat transposable elements) account for 71.6% of the mined transposable elements and are clearly the predominant type of transposable element in the sequences examined. Moreover, a putative Stowaway transposase has been identified based on shared sequence similarity with the mined MITEs and previously identified plant mariner-like elements (MLEs). Members of a group of novel rice elements resembling the structurally unusual members of the Basho family in Arabidopsis suggest a wide distribution of these transposons among plants. Our survey provides a preview of transposable element diversity and abundance in rice, and allows for comparison with genomes of other plant species.     

Percutaneous mitral valve repair using the edge-to-edge technique in a high-risk population

Background. Percutaneous mitral valve (MV) repair using the edge-to-edge clip technique might be an alternative for patients with significant mitral regurgitation (MR) and an unacceptably high risk for operative repair or replacement. We report the short-term safety and efficacy of this new technique in a high-risk population. Methods. All consecutive high-risk patients who underwent percutaneous MV repair with the Mitraclip^® between January and August 2009 were included. All complications related to the procedure were reported. Transthoracic echocardiography for MR grading and right ventricular systolic pressure (RVSP) measurement were performed before, and at three and 30 days after the procedure. Differences in NYHA functional class and quality of life (QoL) index were reported. Results. Nine patients were enrolled (78% male, age 75.9±9.0 years, logistic EuroSCORE 33.8±9.0%). One patient developed inguinal bleeding. In one patient partial clip detachment occurred, a second clip was placed successfully. The MR grade before repair was ≥3 in 100%, one month after repair a reduction in MR grade to ≤2 was present in 78% (p=0.001). RVSP decreased from 43.9±12.1 to 31.6±11.7 mmHg (p=0.009), NYHA functional class improved from median 3 (range 3 to 4) to 2 (range 1 to 4) (p=0.04), and QoL index improved from 62.9±16.3 to 49.9±30.7 (p=0.12). Conclusion. In high-risk patients, transcatheter MV repair seems to be safe and a reduction in MR can be achieved in most patients, resulting in a short-term improvement of functional capacity and QoL. (Neth Heart J 2010;18:437-43.)