In vitro assessment of a combined radiofrequency ablation and cryo-anchoring catheter for treatment of mitral valve prolapse

Percutaneous approaches to mitral valve repair are an attractive alternative to surgical repair or replacement. Radiofrequency ablation has the potential to approximate surgical leaflet resection by using resistive heating to reduce leaflet size, and cryogenic temperatures on a percutaneous catheter can potentially be used to reversibly adhere to moving mitral valve leaflets for reliable application of radiofrequency energy. We tested a combined cryo-anchoring and radiofrequency ablation catheter using excised porcine mitral valves placed in a left heart flow loop capable of reproducing physiologic pressure and flow waveforms. Transmitral flow and pressure were monitored during the cryo-anchoring procedure and compared to baseline flow conditions, and the extent of radiofrequency energy delivery to the mitral valve was assessed post-treatment. Long term durability of radiofrequency ablation treatment was assessed using statically treated leaflets placed in a stretch bioreactor for four weeks. Transmitral flow and pressure waveforms were largely unaltered during cryo-anchoring. Parameter fitting to mechanical data from leaflets treated with radiofrequency ablation and cryo-anchoring revealed significant mechanical differences from untreated leaflets, demonstrating successful ablation of mitral valves in a hemodynamic environment. Picrosirius red staining showed clear differences in morphology and collagen birefringence between treated and untreated leaflets. The durability study indicated that statically treated leaflets did not significantly change size or mechanics over four weeks. A cryo-anchoring and radiofrequency ablation catheter can adhere to and ablate mitral valve leaflets in a physiologic hemodynamic environment, providing a possible percutaneous alternative to surgical leaflet resection of mitral valve tissue.     

Tension to passively cinch the mitral annulus through coronary sinus access: An ex vivo study in ovine model

Introduction

The transcatheter mitral valve repair (TMVR) technique utilizes a stent to cinch a segment of the mitral annulus (MA) and reduces mitral regurgitation. The cinching mechanism results in reduction of the septal–lateral distance. However, the mechanism has not been characterized completely. In this study, a method was developed to quantify the relation between cinching tension and MA area in an ex vivo ovine model.

Method

The cinching tension was measured from a suture inserted within the coronary sinus (CS) vessel with one end tied to the distal end of the vessel and the other end exited to the CS ostium where it was attached to a force transducer on a linear stage. The cinching tension, MA area, septal–lateral (S–L) and commissure–commissure (C–C) diameters and leakage was simultaneously measured in normal and dilated condition, under a hydrostatic left ventricular pressure of 90 mmHg.

Results

The MA area was increased up to 22.8% after MA dilation. A mean tension of 2.1±0.5 N reduced the MA area by 21.3±5.6% and S–L diameter by 24.2±5.3%. Thus, leakage was improved by 51.7±16.2% following restoration of normal MA geometry.

Conclusion

The cinching tension generated by the suture acts as a compensation force in MA reduction, implying the maximum tension needed to be generated by annuloplasty device to restore normal annular size. The relationship between cinching tension and the corresponding MA geometry will contribute to the development of future TMVR devices and understanding of myocardial contraction function.     

Finite element analysis of the mitral apparatus: annulus shape effect and chordal force distribution

This study presents a three-dimensional finite element model of the mitral apparatus using a hyperelastic transversely isotropic material model for the leaflets. The objectives of this study are to illustrate the effects of the annulus shape on the chordal force distribution and on the mitral valve response during systole, to investigate the role of the anterior secondary (strut) chordae and to study the influence of thickness of the leaflets on the leaflets stresses. Hence, analyses are conducted with a moving and fixed saddle shaped annulus and with and without anterior secondary chordae. We found that the tension in the secondary chordae represents 31% of the load carried by the papillary muscles. When removing the anterior secondary chordae, the tension in the primary anterior chordae is almost doubled, the displacement of the anterior leaflet toward the left atrium is also increased. The moving annulus configuration with an increasing annulus saddle height does not give significant changes in the chordal force distribution and in the leaflet stress compared to the fixed annulus. The results also show that the maximum principle stresses in the anterior leaflet are carried by the collagen fibers. The stresses calculated in the leaflets are very sensitive to the thickness employed.     

RecBCD is required to complete chromosomal replication: Implications for double-strand break frequencies and repair mechanisms

Several aspects of the mechanism of homologous double-strand break repair remain unclear. Although intensive efforts have focused on how recombination reactions initiate, far less is known about the molecular events that follow. Based upon biochemical studies, current models propose that RecBCD processes double-strand ends and loads RecA to initiate recombinational repair. However, recent studies have shown that RecBCD plays a critical role in completing replication events on the chromosome through a mechanism that does not involve RecA or recombination. Here, we examine several studies, both early and recent, that suggest RecBCD also operates late in the recombination process – after initiation, strand invasion, and crossover resolution have occurred. Similar to its role in completing replication, we propose a model in which RecBCD is required to resect and resolve the DNA synthesis associated with homologous recombination at the point where the missing sequences on the broken molecule have been restored. We explain how the impaired ability to complete chromosome replication in recBC and recD mutants is likely to account for the loss of viability and genome instability in these mutants, and conclude that spontaneous double-strand breaks and replication fork collapse occur far less frequently than previously speculated.     

Percutaneous implantation of the CoreValve aortic valve prosthesis in patients at high risk or rejected for surgical valve replacement: Clinical evaluation and feasibility of the procedure in the first 30 patients in the AMC-UvA

Objective. To report the feasibility, safety and efficacy of percutaneous aortic valve implantation (PAVI) with the CoreValve self-expanding aortic valve bioprosthesis in elderly patients with aortic valve stenosis who are rejected for surgery or have a high surgical risk.Methods. PAVI using the CoreValve ReValving System was performed under general anaesthesia in 30 high-risk (surgical) patients with a symptomatic severe aortic valve stenosis.Results. The patients had a mean age of 80.5±7.7 years, a mean aortic valve area of 0.71±0.19 cm², a peak transvalvular aortic gradient of 79±25 mmHg, as measured with echo Doppler, a logistic EuroSCORE of 15±10% and a Society of Thoracic Surgeons (STS) score of 5.2±2.9%. Device success was achieved in all patients and acute procedural success in 27 patients (90%). In the surviving patients, there was in a reduction of the peak aortic pressure gradient from 76±24 mmHg to 22±7 mmHg (n=24, p<0.00001) 30 days after successful device implantation. At 30 days, major adverse cardiovascular and cerebral events had occurred in seven patients (23%). This included mortality in six patients (20%), of which one death was cardiovascular. The other five non-cardiovascular deaths involved two patients who died of an exacerbation of severe pre-existent pulmonary disease and three of infectious complications.Conclusions. Percutaneous aortic valve implantation was successfully performed in our centre in highrisk patients, with a 30-day mortality of 20%. When successful, marked haemodynamic improvement and relief of symptoms was achieved. (Neth Heart J 2010;18:18-24.)     

Repair and Reconstruction of Telomeric and Subtelomeric Regions and Genesis of New Telomeres: Implications for Chromosome Evolution

DNA damage repair within telomeres are suppressed to maintain the integrity of linear chromosomes, but the accidental activation of repairs can lead to genome instability. This review develops the concept that mechanisms to repair DNA damage in telomeres contribute to genetic variability and karyotype evolution, rather than catastrophe. Spontaneous breaks in telomeres can be repaired by telomerase, but in some cases DNA repair pathways are activated, and can cause chromosomal rearrangements or fusions. The resultant changes can also affect subtelomeric regions that are adjacent to telomeres. Subtelomeres are actively involved in such chromosomal changes, and are therefore the most variable regions in the genome. The case of Caenorhabditis elegans in the context of changes of subtelomeric structures revealed by long-read sequencing is also discussed. Theoretical and methodological issues covered in this review will help to explore the mechanism of chromosome evolution by reconstruction of chromosomal ends in nature.     

RIP4 is a target of multiple signal transduction pathways in keratinocytes: Implications for epidermal differentiation and cutaneous wound repair

Receptor interacting protein 4 (RIP4) is an important regulator of epidermal morphogenesis during embryonic development. We could previously show that expression of the rip4 gene is strongly downregulated in cutaneous wound repair, which might be initiated by a broad variety of growth factors and cytokines. Here, we demonstrate that in keratinocytes, rip4 expression is controlled by a multitude of different signal transduction pathways, such as the p38 mitogen-activated protein kinase (MAPK) and the nuclear factor kappa B (NF-κB) cascade, in a unique and specific manner. Furthermore, we show that the steroid dexamethasone abolishes the physiological rip4 downregulation after injury and might thus contribute to the phenotype of reduced and delayed wound reepithelialization seen in glucocorticoid-treated patients. As a whole, our data indicate that rip4 expression is regulated in a complex manner, which might have therapeutic implications     

Transforming growth factor-β in the early mouse embryo: Implications for the regulation of muscle formation and implantation

In a search for functions of transforming growth factor-β during early embryonic development we used two different experimental approaches. In the first we made use of embryonic stem (ES) cells. ES cells in culture differentiate to derivatives of all three germ layers and mimic some aspects of organogenesis when grown as aggregates in suspension to form embryoid bodies. Differentiation procedes further when the embryold bodies attach to suitable substrates. Muscle and neuronal cells are among the most readily identified cell types then formed. We examined the effect of all-trans retinoic acid (RA) and members of the transforming growth factor-β family(TGF-βl, TGF-β2) under these conditions in an assay where single aggregates formed in hanging microdrops in medium supplemented with serum depleted of lipophilic substances which would include retinoids. Endoderm-like cells formed under all conditions tested. RA at concentrations of 10⁸ M and 10⁷ M induced the formation of neurons but in the absence of RA or at concentrations up to 10?⁹ M, neurons were not observed. Instead, beating muscle formed in about one-third of the plated aggregates; this was greatly reduced when RA concentrations increased above 10?⁹ M. Immunofluorescent staining for muscle specific myosin showed that two muscle cell types could be distinguished: elongated, non-contractile myoblasts and mononucleate flat cells. The mononucleate flat cells appeared to correspond with rhythmically contracting muscle. The number of non-contractile myoblasts increased 3-fold over controls in the presence of 10?⁹ M RA. TGF-βs increased the number of contractile and non-contractile muscle cells by a factor 3 to 7 over controls, depending on the TGF-β isoform added and the muscle cell type formed. TGF-β2 also invariably increased the rate at which contracting muscle cells were first observed in replated aggregates. The stimulatory effect of TGF-βs on the formation of mononucleate flat cells was completely abrogated by RA at 10?⁹ M while the number of myoblasts under similar conditions was unchanged. These data suggest that a complex interplay between retinoids and TGF-β isoforms may be involved in regulation of differentiation in early myogenesis. In the second approach, neutralizing polyclonal rabbit antibodies specific for TGF-β2 were injected into the cavity of mouse blastocysts 3.5 days post coitum (pc). After 1 day in culture, embryos were transferred to pseudopregnant females. The number of decidua, embryos and resorptions were counted at day 8.5–9.5 pc. Control antibody injected embryos implanted with high efficiency (87%) compared with anti-TGF-β2 injected embryos which implanted with an efficiency of only 43%. If empty decidua (resorptions) were included, the overall recovery was 71% and 32% for control and experimental embryos, respectively. Embryos that were recovered showed no overt macroscopic abnormalities. These results together impiy functions for TGF-βs in implantation as well as in later development of the embryo. © 1993Wiley-Liss, Inc.     

Assemblage diversity,cell density and within-slide variability: Implications for quality assurance/quality control and uncertainty assessment in diatom-based monitoring

This study was undertaken to evaluate the variability associated with the microscope analysis step in the application of the Eastern Canadian Diatom Index (IDEC: Indice Diatomées de l’Est du Canada), with the general objective of developing a suitable quality assurance/quality control (QA/QC) program for this biological index. For this purpose, we estimated within-slide variability (replicability) and inter-analysts variability (reproducibility), as a function of diatom assemblage diversity and slide cell density. Overall, our results show that variability associated with diatom assemblage characterization is low, which ensures that IDEC scores reflect environmental changes rather than variability at the microscope analysis step. The main recommendations ensuing from this study are (for the IDEC in particular but also for diatom-based monitoring in general):

• (1)An error term of ±2 IDEC units corresponding to the within-slide variability (replicability) should accompany all reported IDEC scores.
• (2)A deviation of ±3 points from the audit's IDEC scores should be considered as an acceptable difference. Considering the above-mentioned estimated error term of ±2 associated with all IDEC scores, an overall deviation of 7 would still be satisfactory.
• (3)Samples showing low diversity (Hill's N2 ≤5) should automatically be submitted for QA/QC.
• (4)A Bray–Curtis (analyst vs audit) similarity of ≥60% should also be included as a QA/QC criterion, and should increase to ≥70% for poorly diversified assemblages (Hill's N2 ≤5).
• (5)A diatom valve density of ≤15 per field of view should be targeted in order to reduce variability at the enumeration step.

The results of this study illustrate how a relatively simple and straightforward approach to QA/QC can greatly strengthen the reliability of ecological inferences from an index based on a group of organisms with a high taxonomical diversity. It also highlights the importance of regular communication between analysts in order to maintain a high degree of concordance within taxonomical identification.