Overexpression of Cx43 in cells of the myocardial scar: Correction of post-infarct arrhythmias through heterotypic cell-cell coupling.

Ventricular tachycardia (VT) is the most common and potentially lethal complication following myocardial infarction (MI). Biological correction of the conduction inhomogeneity that underlies re-entry could be a major advance in infarction therapy. As minimal increases in conduction of infarcted tissue markedly influence VT susceptibility, we reasoned that enhanced propagation of the electrical signal between non-excitable cells within a resolving infarct might comprise a simple means to decrease post-infarction arrhythmia risk. We therefore tested lentivirus-mediated delivery of the gap-junction protein Connexin 43 (Cx43) into acute myocardial lesions. Cx43 was expressed in (myo)fibroblasts and CD45+ cells within the scar and provided prominent and long lasting arrhythmia protection in vivo. Optical mapping of Cx43 injected hearts revealed enhanced conduction velocity within the scar, indicating Cx43-mediated electrical coupling between myocytes and (myo)fibroblasts. Thus, Cx43 gene therapy, by direct in vivo transduction of non-cardiomyocytes, comprises a simple and clinically applicable biological therapy that markedly reduces post-infarction VT.

Impact of moderate exercise workload on predicted optimal AV and VV delays determined by an intracardiac electrogram-based method for optimizing cardiac resynchronization therapy.

AIMS: Aim of this study is to evaluate reproducibility, consistency and the impact of moderate exercise workload on optimized PV and VV delays as determined by the IEGM-based QuickOpt™ method (St. Jude Medical), that was shown to produce hemodynamic performance similar to that obtained by echo-guided aortic VTI maximization. METHODS: Sixty patients with CRT-ICD (65 ± 9 years, 12% female, LVEF 28 ± 9%, 48% CAD and 52% DCM) were enrolled. IEGM-based PV/VV optimization was conducted six times: twice at rest, twice immediately after a 6-min walk test and twice following a 3-min recovery period. Timing cycle delays were programmed in accordance with the optimization results. Follow-up was performed after 1 year. RESULTS: Although significant difference in heart rate was reached [68 ± 9 bpm (REST) vs. 79 ± 12 (6MWT), p < 0.001], differences were not observed between IEGM-based optimized PV/VV delays: PV(opt) = 128 ± 14 ms (REST) versus 130 ± 17 ms (6MWT) versus 129 ± 16 ms (RECOV); VV(opt) = 15 ± 24 ms (REST) versus 15 ± 22 ms (6MWT) versus 16 ± 24 ms (RECOV). During 1-year follow-up PV(opt) and VV(opt) remained stable (ΔPV(opt) = 10 ± 10 ms, ΔVV(opt) = 9 ± 11 ms). CONCLUSION: Optimized IEGM-based timing cycle delays are independent of moderate exercise status within a particular patient but varied between patients. This supports the use of PV/VV optimization in each CRT patient.

Impact of left ventricular lead position on the incidence of ventricular arrhythmia and clinical outcome in patients with cardiac resynchronization therapy.

PURPOSE: The aim of the study was to evaluate the incidence of ventricular arrhythmia and clinical outcome in patients receiving a cardiac resynchronization therapy (CRT) depending on the left ventricular (LV) lead position. METHODS: A total of 187 consecutive patients with advanced heart failure who received a CRT-implantable cardioverter defibrillator were analyzed. Forty patients (21%) had a LV lead in the anterior/apical (anterior) and 147 patients (79%) in the posterior/posterolateral (posterior) region. The total median follow-up time was 644 days. RESULTS: The incidence of ventricular arrhythmia was 35% in patients with an anterior LV lead versus 30% in patients with a posterior LV lead (p = 0.53). The 1- and 2-year mortality in the anterior LV lead group was 19% and 22%, as compared with 0.7% and 3.2%, respectively, in the posterior LV lead group (p < 0.001). In a multivariable analysis, an anterior LV lead was independently associated with an increased mortality (hazard ratio 5.88, 95% confidence interval 2.22-16.67). The major cause of death was end-stage heart failure whereas the incidence of sudden cardiac death was not different between both groups. CONCLUSIONS: Thus, biventricular pacing with an anterior LV lead seems to have no impact on the incidence of ventricular arrhythmia but may be associated with an increased mortality rate due to worsening heart failure.

Prevalence of bacterial colonization of generator pockets in implantable cardioverter defibrillator patients without signs of infection undergoing generator replacement or lead revision.

AIMS: This study was designed to evaluate the prevalence of bacterial colonization of generator pockets in implantable cardioverter defibrillator (ICD) patients without signs of infection and to analyse the impact of bacterial colonization on the incidence of device infection during follow-up. METHODS AND RESULTS: In 122 ICD patients undergoing generator replacement or surgical lead revision between January 2006 and July 2008, microbiological cultures of generator pockets and extracted leads were consecutively obtained. Patients with clinical evidence of a device infection were excluded. Positive cultures from the generator pocket and leads were found in 40 (33%) patients. The most common bacteria isolated were coagulase negative staphylococci (68%). During a median follow-up time of 203 days after the revision device infection occurred in three [7.5%, confidence interval (CI) 1.6-20.4%] patients with a positive culture vs. two (2.4%, CI 0.3-8.5%) patients with a negative culture (P = 0.33). Time from revision to infection was 108 +/- 73 days in patients with positive culture vs. 60 +/- 39 days in patients with negative culture (P = 0.50). CONCLUSION: A third of ICD patients undergoing generator replacement or lead revision have an asymptomatic bacterial colonization of generator pockets. After revision 7.5% of these patients develop a device infection with the same species of microorganism.

Prevalence of left atrial thrombus and dense spontaneous echo contrast in patients with short-term atrial fibrillation < 48 hours undergoing cardioversion: value of transesophageal echocardiography to guide cardioversion.

BACKGROUND: The aim of this study was to investigate the value of transesophageal echocardiography (TEE)-guided cardioversion (CV) to prevent thromboembolic complications in patients with short-term atrial fibrillation (AF) < 48 hours in duration. METHODS: This single-center, observational study comprised 366 consecutive, unselected patients with short-term AF < 48 hours in duration. During the first 2 years, CV was performed using the conventional approach without TEE. Thereafter, CV guided by TEE was performed in consecutive patients. RESULTS: TEE revealed left atrial thrombi in 1.4% and left atrial dense spontaneous echo contrast in 10% of patients with short-term AF (n = 207), of whom 63% were receiving anticoagulation therapy. Patients without prior anticoagulation had a 4% prevalence of left atrial thrombi. A low ejection fraction and an enlarged left atrium tended to be associated with an increased prevalence of thrombus or dense spontaneous echo contrast. During the first month after CV, there were no significant differences in the rate of embolic events between the two treatment groups. CONCLUSIONS: These results underline the need for further studies on the usefulness of TEE-guided CV in patients with short-term AF who are not therapeutically anticoagulated at presentation.

Simulation of ammonium and chromium transport in porous media using coupling scheme of a numerical algorithm and a stochastic algorithm.

The migration of the species of chromium and ammonium in groundwater and their effective remediation depend on the various hydro-geological characteristics of the system. The computational modeling of the reactive transport problems is one of the most preferred tools for field engineers in groundwater studies to make decision in pollution abatement. The analytical models are less modular in nature with low computational demand where the modification is difficult during the formulation of different reactive systems. Numerical models provide more detailed information with high computational demand. Coupling of linear partial differential Equations (PDE) for the transport step with a non-linear system of ordinary differential equations (ODE) for the reactive step is the usual mode of solving a kinetically controlled reactive transport equation. This assumption is not appropriate for a system with low concentration of species such as chromium. Such reaction systems can be simulated using a stochastic algorithm. In this paper, a finite difference scheme coupled with a stochastic algorithm for the simulation of the transport of ammonium and chromium in subsurface media has been detailed.

Prevalence and clinical impact of left atrial thrombus and dense spontaneous echo contrast in patients with atrial fibrillation and low CHADS2 score.

AIMS: To evaluate the prevalence and clinical impact of left atrial (LA) thrombus and dense spontaneous echo contrast (SEC) in patients with atrial fibrillation (AF) and low CHADS(2) score undergoing cardioversion. METHODS AND RESULTS: A total of 295 consecutive patients with non-valvular AF and a CHADS(2) score of 0 or 1 from the prospective single-centre registry ANTIK, who underwent transoesophageal echocardiography before cardioversion, were included in the study. Median follow-up was 5 years. LA thrombus was present in 3% and dense SEC in 8% of patients. Independent predictors for the presence of thrombus or dense SEC were ejection fraction (EF) <40% and LA diameter > or =50 mm. In anticoagulated patients, thrombus and dense SEC were not independently associated with an increased risk for stroke or death during the 5 year follow-up (OR 1.55, 95% CI 0.50-4.83). CONCLUSIONS: Despite a low CHADS(2) score of 0/1, 3% of patients have LA thrombus and 8% of patients have dense SEC. Independent predictors for the presence of thrombus and dense SEC were EF <40% and LA dimension > or =50 mm. Thus, echocardiography might be a useful tool for further risk stratification in patients with low CHADS(2) score.

Simulating the proton transfer in gramicidin A by a sequential dynamical Monte Carlo method.

The large interest in long-range proton transfer in biomolecules is triggered by its importance for many biochemical processes such as biological energy transduction and drug detoxification. Since long-range proton transfer occurs on a microsecond time scale, simulating this process on a molecular level is still a challenging task and not possible with standard simulation methods. In general, the dynamics of a reactive system can be described by a master equation. A natural way to describe long-range charge transfer in biomolecules is to decompose the process into elementary steps which are transitions between microstates. Each microstate has a defined protonation pattern. Although such a master equation can in principle be solved analytically, it is often too demanding to solve this equation because of the large number of microstates. In this paper, we describe a new method which solves the master equation by a sequential dynamical Monte Carlo algorithm. Starting from one microstate, the evolution of the system is simulated as a stochastic process. The energetic parameters required for these simulations are determined by continuum electrostatic calculations. We apply this method to simulate the proton transfer through gramicidin A, a transmembrane proton channel, in dependence on the applied membrane potential and the pH value of the solution. As elementary steps in our reaction, we consider proton uptake and release, proton transfer along a hydrogen bond, and rotations of water molecules that constitute a proton wire through the channel. A simulation of 8 mus length took about 5 min on an Intel Pentium 4 CPU with 3.2 GHz. We obtained good agreement with experimental data for the proton flux through gramicidin A over a wide range of pH values and membrane potentials. We find that proton desolvation as well as water rotations are equally important for the proton transfer through gramicidin A at physiological membrane potentials. Our method allows to simulate long-range charge transfer in biological systems at time scales, which are not accessible by other methods.

Prehospital cardiac arrest: a marker for higher mortality in patients with acute myocardial infarction and moderately reduced left ventricular function: results from the MITRA plus registry.

BACKGROUND: According to the current guidelines for acute myocardial infarction, ventricular fibrillation during the acute phase of myocardial infarction is no indication for specific treatment like ICD implantation. Primary objective of our study was to evaluate the prognostic significance of cardiac arrest within the acute phase of myocardial infarction in patients with moderately reduced left ventricular function. METHODS AND RESULTS: From 1994 until 2004, we included 7111 patients with acute STEMI and an LVEF >30% from the MITRA plus registry who were discharged alive from hospital and had a complete follow up. We compared long term prognosis on total mortality in patients with and without prehospital cardiac arrest. 286 out of 7111 patients (4%) with moderately reduced LVEF >30% after STEMI had prehospital cardiac arrest and were discharged alive from hospital. In these patients, total mortality during a mean follow up of 13 months was 13.6% compared to 8.7% in patients without cardiac arrest, although patients with cardiac arrest were younger and had less risk factors. Higher mortality after cardiac arrest was independent from gender, risk factors and medical treatment. Only in patients with preserved LVEF >55% after STEMI, mortality was equal in patients with and without cardiac arrest. CONCLUSION: Prehospital cardiac arrest in the acute phase of STEMI is an independent risk indicator for higher mortality in patients with moderately reduced left ventricular function (LVEF 30-55%). To evaluate the prognostic impact of the implantation of an ICD in these patients, further investigation is needed.

Investigating the mechanisms of photosynthetic proteins using continuum electrostatics.

Computational methods based on continuum electrostatics are widely used in theoretical biochemistry to analyze the function of proteins. Continuum electrostatic methods in combination with quantum chemical and molecular mechanical methods can help to analyze even very complex biochemical systems. In this article, applications of these methods to proteins involved in photosynthesis are reviewed. After giving a short introduction to the basic concepts of the continuum electrostatic model based on the Poisson-Boltzmann equation, we describe the application of this approach to the docking of electron transfer proteins, to the comparison of isofunctional proteins, to the tuning of absorption spectra, to the analysis of the coupling of electron and proton transfer, to the analysis of the effect of membrane potentials on the energetics of membrane proteins, and to the kinetics of charge transfer reactions. Simulations as those reviewed in this article help to analyze molecular mechanisms on the basis of the structure of the protein, guide new experiments, and provide a better and deeper understanding of protein functions.

Long-term prognosis after cardioversion of the first episode of symptomatic atrial fibrillation: a condition believed to be benign revised.

AIMS: We evaluated the prognostic impact of a first episode of symptomatic atrial fibrillation under real life conditions. BACKGROUND: Most studies regarding the treatment and long-term outcome of patients with atrial fibrillation mainly refer to patients with recurrent episodes. In contrast, data on the prognostic implications of a first episode of atrial fibrillation are scarce. METHODS: Over a follow-up period of 5 years, we analyzed 1053 patients, initially scheduled for cardioversion of symptomatic atrial fibrillation, who were included into the prospective registry ANTIK (Ludwigshafener ANTIKoagulationsstudie). RESULTS: Of those, 618 patients (59%) were included with a first episode of symptomatic atrial fibrillation whereas 435 patients (41%) presented with recurrent episodes. As a consequence of referral for cardioversion of symptomatic atrial fibrillation, structural heart disease was newly diagnosed in a significantly higher proportion of patients with a first episode (27 vs 13%, OR 2.4, 95% CI 1.7-3.3) and patients with a first episode were more likely to have an EF

Annual rate of transvenous defibrillation lead defects in implantable cardioverter-defibrillators over a period of >10 years.

BACKGROUND: The number of patients with longer follow-up after implantation of an implantable cardioverter-defibrillator is increasing continuously. Defibrillation lead failure is a typical long-term complication. Therefore, the long-term reliability of implantable cardioverter-defibrillator leads has become an increasing concern. The aim of the present study was to assess the annual rate of transvenous defibrillation lead defects related to follow-up time after lead implantation. METHODS AND RESULTS: A total of 990 consecutive patients who underwent first implantation of an implantable cardioverter-defibrillator between 1992 and May 2005 were analyzed. Median follow-up time was 934 days (interquartile range, 368 to 1870). Overall, 148 defibrillation leads (15%) failed during the follow-up. The estimated lead survival rates at 5 and 8 years after implantation were 85% and 60%, respectively. The annual failure rate increased progressively with time after implantation and reached 20% in 10-year-old leads (P<0.001). Lead defects affected newer as well as older models. Patients with lead defects were 3 years younger at implantation and more often female. Multiple lead implantation was associated with a trend to a higher rate of defibrillation lead defects (P=0.06). The major lead complications were insulation defects (56%), lead fractures (12%), loss of ventricular capture (11%), abnormal lead impedance (10%), and sensing failure (10%). CONCLUSIONS: An increasing annual lead failure rate is noted primarily during long-term follow-up and reached 20% in 10-year-old leads. Patients with lead defects are younger and more often female.

An extended dead-end elimination algorithm to determine gap-free lists of low energy states.

Proteins are flexible systems and commonly populate several functionally important states. To understand protein function, these states and their energies have to be identified. We introduce an algorithm that allows the determination of a gap-free list of the low energy states. This algorithm is based on the dead-end elimination (DEE) theorem and is termed X-DEE (extended DEE). X-DEE is applicable to discrete systems whose state energy can be formulated as pairwise interaction between sites and their intrinsic energies. In this article, the computational performance of X-DEE is analyzed and discussed. X-DEE is implemented to determine the lowest energy protonation states of proteins, a problem to which DEE has not been applied so far. We use X-DEE to calculate a list of low energy protonation states for two bacteriorhodopsin structures that represent the first proton transfer step of the bacteriorhodopsin photocycle.

Simulation of the electron transfer between the tetraheme subunit and the special pair of the photosynthetic reaction center using a microstate description.

Charge transfer through biological macromolecules is essential for many biological processes such as, for instance, photosynthesis and respiration. Protons or electrons are transferred between titratable residues or redox-active cofactors, respectively. Transfer rates between these sites depend on the current charge configuration of neighboring sites. Here, we formulate the kinetics of charge-transfer systems in a microstate formalism. A unique transfer rate constant can be assigned to the interconversion of microstates. Mutual interactions between sites participating in the transfer reactions are naturally taken into account. The formalism is applied to the kinetics of electron transfer in the tetraheme subunit and the special pair of the reaction center of Blastochloris viridis. It is shown that continuum electrostatic calculations can be used in combination with an existing empirical rate law to obtain electron-transfer rate constants. The re-reduction kinetics of the photo-oxidized special pair simulated in a microstate formalism is shown to be in good agreement with experimental data. A flux analysis is used to follow the individual electron-transfer steps.

Stepped defibrillation waveform is substantially more efficient than the 50/50% tilt biphasic.

BACKGROUND: Even with biphasic waveforms, patients with high defibrillation thresholds (DFTs) still are seen; thus, improved defibrillation waveforms may be of clinical utility. The stepped waveform has three parts: the first portion is positive with two capacitors in parallel, the second is positive with the capacitors in series, and the last portion is negative, also with the capacitors in series. OBJECTIVES: The purpose of this study was to assess the clinical utility of improved defibrillation waveforms. METHODS: We measured the delivered energy DFT in 20 patients in a dual-site study using the stepped waveform and a 50/50% tilt biphasic truncated exponential as the control. All shocks were delivered using an arbitrary waveform defibrillator, which was programmed to mimic two 220-microF capacitors (110 microF in series and 440 microF in parallel). RESULTS: The peak voltage at DFT was reduced in 19 of the 20 patients. The median peak voltage was reduced by 32.0%, from 472 V to 321 V (P <.001). The median energy DFT was reduced by 33%, from 11.7 J to 7.8 J (P = .008). The mean voltage and energy were reduced by 25.3% and 20.2%, respectively. On average, the stepped waveform was able to defibrillate as well as the 50/50% tilt biphasic, with 33% more energy. The benefit was more pronounced in patients with either a lower ejection fraction or a superior vena cava coil. The benefit of the stepped waveform had an inverse quadratic correlation with the resistance (r(2) = 0.47), suggesting that the capacitance values chosen for the stepped waveform were close to optimal for a 35-Omega resistance. CONCLUSION: The stepped waveform reduced the DFT compared to the 50/50% tilt waveform in this preliminary study.

Synthetic glycopeptides from the mucin family as potential tools in cancer immunotherapy.

Compared to glycoproteins of healthy cells, glycoproteins of tumor cells are often aberrantly glycosylated. Thus, glycopeptide fragments of surface glycoproteins of tumor cells are of interest as tumor-associated antigens for the distinction between normal and tumor cells. Cancer immunotherapy directed at selectively targeting these tumor-associated glycoprotein structure alterations--deficient glycosylation and, thus, exposure of peptide epitopes which are masked in normal cells--is considered a promising approach for the treatment of cancer. For this purpose, glycoproteins from the mucin family are of particular interest. Mucins belong to a class of heavily O-glycosylated, high-molecular weight glycoproteins present on the surface of many epithelial cells. The mucin core protein consists of numerous tandem repeats rich in serine, threonine and proline. In their tumor-associated forms, epithelial mucins carry cryptic saccharide structures such as T(N)-, T-, sialyl-T(N)- and sialyl-T antigens and more complex oligosaccharides (e.g. Lewis(y)). In contrast to glycoproteins isolated from natural sources, synthetic glycopeptides can be obtained in high purity and with exactly defined structure. In this review, methodologies for the synthesis of mucin-type glycopeptides containing complex tumor-associated antigen structures are described. Due to the low immunogenicity often exhibited by synthetic tumor-associated glycopeptide antigens, their conjugation to carrier proteins or suitable T-cell epitopes is essential for the development of anti-tumor vaccines. The results of immunological evaluations of synthetic (glyco)peptides and oligosaccharides are described. Some of these synthetic vaccines show promising activities inducing proliferation of T-cells and cytotoxic T-cell responses.

Influence of the membrane potential on the protonation of bacteriorhodopsin: insights from electrostatic calculations into the regulation of proton pumping.

Proton binding and release are elementary steps for the transfer of protons within proteins, which is a process that is crucial in biochemical catalysis and biological energy transduction. Local electric fields in proteins affect the proton binding energy compared to aqueous solution. In membrane proteins, also the membrane potential affects the local electrostatics and can thus be crucial for protein function. In this paper, we introduce a procedure to calculate the protonation probability of titratable sites of a membrane protein in the presence of a membrane potential. In the framework of continuum electrostatics, we use a modified Poisson-Boltzmann equation to include the influence of the membrane potential. Our method considers that in a transmembrane protein each titratable site is accessible for protons from only one side of the membrane depending on the hydrogen bond pattern of the protein. We show that the protonation of sites receiving their protons from different sides of the membrane is differently influenced by the membrane potential. In addition, the effect of the membrane potential is combined with the effect of the pH gradient resulting from proton pumping. Our method is applied to bacteriorhodopsin, a light-activated proton pump. We find that the proton pumping of this protein might be regulated by Asp115, a conserved residue for which no function has been identified yet. According to our calculations, the interaction of Asp115 with Asp85 leads to the protonation of the latter if the pH gradient or the membrane potential becomes too large. Since Asp85 is the primary proton acceptor in the photocycle, bacteriorhodopsin molecules in which Asp85 is protonated cannot pump protons. Furthermore, we estimate how the membrane potential affects the energetics of the individual proton-transfer reactions of the photocycle. Most reactions, except the initial proton transfer from the Schiff base to Asp85, are influenced. Our calculations give new insights into the mechanism with which bacteriorhodopsin senses the membrane potential and the pH gradient and how the proton pumping is regulated by these parameters.

Electrostatic potential at the retinal of three archaeal rhodopsins: implications for their different absorption spectra.

The color tuning mechanism of the rhodopsin protein family has been in the focus of research for decades. However, the structural basis of the tuning mechanism in general and of the absorption shift between rhodopsins in particular remains under discussion. It is clear that a major determinant for spectral shifts between different rhodopsins are electrostatic interactions between the chromophore retinal and the protein. Based on the Poisson-Boltzmann equation, we computed and compared the electrostatic potential at the retinal of three archaeal rhodopsins: bacteriorhodopsin (BR), halorhodopsin (HR), and sensory rhodopsin II (SRII) for which high-resolution structures are available. These proteins are an excellent test case for understanding the spectral tuning of retinal. The absorption maxima of BR and HR are very similar, whereas the spectrum of SRII is considerably blue shifted--despite the structural similarity between these three proteins. In agreement with their absorption maxima, we find that the electrostatic potential is similar in BR and HR, whereas significant differences are seen for SRII. The decomposition of the electrostatic potential into contributions of individual residues, allowed us to identify seven residues that are responsible for the differences in electrostatic potential between the proteins. Three of these residues are located in the retinal binding pocket and have in fact been shown to account for part of the absorption shift between BR and SRII by mutational studies. One residue is located close to the beta-ionone ring of retinal and the remaining three residues are more than 8 A away from the retinal. These residues have not been discussed before, because they are, partly because of their location, no obvious candidates for the spectral shift among BR, HR, and SRII. However, their contribution to the differences in electrostatic potential is evident. The counterion of the Schiff base, which is frequently discussed to be involved in the spectral tuning, does not contribute to the dissimilarities between the electrostatic potentials.