Studies of Fractal Microstructure in Nanocarbon Polymer Composites.

The in situ study of fractal microstructure in nanocarbon polymers is an actual task for their application and for the improvement in their functional properties. This article presents a visualization of the bulk structural features of the composites using pulsed acoustic microscopy and synchrotron X-ray microtomography. This article presents details of fractal structure formation using carbon particles of different sizes and shapes-exfoliated graphite, carbon platelets and nanotubes. Individual structural elements of the composite, i.e., conglomerations of the particles in the air capsule as well as their distribution in the composite volume, were observed at the micro- and nanoscale. We have considered the influence of particle architecture on the fractal formation and elastic properties of the composite. Acoustic and X-ray imaging results were compared to validate the carbon agglomeration.

Three-Dimensional Study of Polymer Composite Destruction in the Early Stages.

The investigation of destruction processes in composite materials is a current problem for their structural application and the improvement of their functional properties. This work aimed to visualize structural changes induced in layered carbon fiber reinforced plastics (CFRP) with the help of synchrotron X-ray microtomography. This article presents the details of destructive processes in the early stages of the deformation of reinforced polymers under uniaxial stretching, investigated at the micro level. Individual structural elements of the composite-filaments, parallel fiber bundles, the nonuniformity of the polymer binder distribution, and continuity defects-were observed under an external load. We have considered the influence of the material architecture and technological defects on fracture evolution in cross-ply and quasi-isotropic fiber-reinforced plastics. The results indicate the sequence of irreversible structural changes before the destruction of the material.

Noninvasive high-frequency acoustic microscopy for 3D visualization of microstructure and estimation of elastic properties during hydrolytic degradation of lactide and ε-caprolactone polymers.

The monitoring of degradation processes' kinetics in polymers is one of the attractive possibilities of ultrasound technique applications that provide non-destructive imaging of polymers' internal microstructure and measurements of elastic properties. In this work, biodegradable polymers and copolymers based on L,L-lactide, D,L-lactide and ε-caprolactone have been studied at different stages of hydrolysis at 37 °C by high-frequency (100 and 200 MHz) ultrasound. The acoustic microscopy technique has been developed to reveal changes in the internal microstructure and bulk sound speed in polymer samples over a hydrolysis period of 25 weeks. Ultrasound imaging provides visualization of amorphous and crystalline phases, internal imperfections, variation in packing density, and other microstructural features. Acoustic images demonstrate nucleation, growth, and the changes in internal inhomogeneities in polymers during degradation accompanied by a decrease in the polymers' molecular weight. We associate the changes in the elastic properties (the speed of a longitudinal wave) with crystallinity variations in polymers during hydrothermal aging. The results of the ultrasound investigations are supplemented by gel permeation chromatography, differential scanning calorimetry, and wide-angle X-ray spectroscopy. STATEMENT OF SIGNIFICANCE: Monitoring the kinetics of degradation processes in polymers is one of the attractive possibilities of applying ultrasound techniques that provide non-destructive imaging of the polymers' internal microstructure and measurements of elastic properties. In this work, visualization of nucleation, growth, and evolution of internal inhomogeneities in the volume of polymers and variation of values of speed of longitudinal and transverse sound waves during hydrolysis are compared with measurements of molecular weight, density, data of DSC curves, and X-ray scattering analysis. We discuss several common phenomena that occur in the volume of poly(L-lactide) and poly(D,L-lactide) over the degradation process as well as improvement of elastic properties of the poly(ε -caprolactone) and poly(L-lactide-co-caprolactone) during hydrothermal aging.

Noninvasive ultrasound imaging for assessment of intact microstructure of extracellular matrix in tissue engineering.

Development of artificial tissues or organs is one of the actual tasks in regenerative medicine that requires observation and evaluation of intact volume microstructure of tissue engineering products at all stages of their formation, from native donor tissues and decellularized scaffolds to recipient cell migration in the matrix. Unfortunately in practice, methods of vital noninvasive imaging of volume microstructure in matrixes are absent. In this work, we propose a new approach based on high-frequency acoustic microscopy for noninvasive evaluation and visualization of volume microstructure in tissue engineering products. The results present the ultrasound characterization of native rat diaphragms and lungs and their decellularized scaffolds. Verification of the method for visualization of tissue formation in the matrix volume was described in the model samples of diaphragm scaffolds with stepwise collagenization. Results demonstrate acoustic microscopic sensitivity to cell content concentration, variation in local density, and orientation of protein fibers in the volume, micron air inclusions, and other inhomogeneities of matrixes.

Postapproval Community Hospital Experience in the United States with Left Atrial Appendage Closure Device (Watchman).

BACKGROUND: To review the procedural safety and postimplantation complications of Watchman device implanted at 2 community hospitals for primary prevention of systemic embolization in patients with nonvalvular atrial fibrillation (NVAF) who were not candidates for long-term oral anticoagulation (OAC). METHODS: This was a retrospective case series of 48 patients carried out in 2 community hospitals in the United States. Patients with NVAF who had a CHADS2 higher than 2 or CHADS2VASc2 (congestive heart failure, hypertension, age ≥75 years, diabetes mellitus, prior stroke or transient ischemic attack [TIA] or thromboembolism, vascular disease, age 65-74 years, and female gender) score of 3 or higher and were not candidates for long-term OAC. These patients were selected for implantation of Watchman device. They were followed up at 45 days, 6 months, 9 months, and 12 months after implantation of Watchman device to assess for complications involving the device and to determine if anticoagulation could be discontinued at the 45 days follow-up. They were monitored for any systemic thromboembolism while off anticoagulation. RESULTS: The success rate of device implantation was 98% (48 of 49). Only a single patient could not get Watchman implantation because of unfavorable left atrial appendage anatomy. Access-related and device implantation-related complications were zero (0%). At 45 days follow-up and end of follow-up duration, the rate of thrombus formation on the Watchman device was 4% (2 of 48). One patient had TIA after warfarin discontinuation. CONCLUSION: With improved procedural technique and well-trained operators, Watchman implantation is feasible in a community hospital also.

Drug Therapy in Adult Congenital Heart Disease.

Adults with congenital heart disease are at risk for atrial and ventricular arrhythmias that can lead to an increased morbidity as well as mortality. When catheter ablation is not an option or unsuccessful, antiarrhythmic drugs are the mainstay of treatment. There is limited data on the use of antiarrhythmics in this population. The purpose of this article is to discuss the practical aspects of the use of antiarrhythmics in adults with congenital heart disease. Several tables have been provided to provide clinicians a reference for daily use.

Optical Properties of Pyrolytic Carbon Films Versus Graphite and Graphene.

We report a comparative study of optical properties of 5-20 nm thick pyrolytic carbon (PyC) films, graphite, and graphene. The complex dielectric permittivity of PyC is obtained by measuring polarization-sensitive reflectance and transmittance spectra of the PyC films deposited on silica substrate. The Lorentz-Drude model describes well the general features of the optical properties of PyC from 360 to 1100 nm. By comparing the obtained results with literature data for graphene and highly ordered pyrolytic graphite, we found that in the visible spectral range, the effective dielectric permittivity of the ultrathin PyC films are comparable with those of graphite and graphene.

Addressing the controversy of rate-versus-rhythm control in atrial fibrillation.

Atrial fibrillation is the most common sustained cardiac arrhythmia and significantly increases patient risk of stroke, cardiomyopathy, and mortality. Rate versus rhythm control as the "best" treatment strategy remains an issue of considerable, ongoing debate. A multitude of clinical trials have compared the 2 strategies and have not shown any benefit of one approach over the other. However, the trials were conducted in specific subgroups of patients and demonstrated low success rates with antiarrhythmic drug (AAD) therapy and a high incidence of adverse AAD effects. Sub-analyses of the trials have confirmed that successful rhythm control with sinus rhythm restoration is associated with a significant reduction in patient mortality. More recently, radiofrequency ablation (RFA) has emerged as a relatively effective procedure for maintaining sinus rhythm compared with use of AADs. Prospective randomized studies have shown good treatment results after the use of RFA, with acceptable risk. Given the limitation of pharmacologic rate versus rhythm control studies, and the promise of RFA, rhythm control should again be reconsidered as the "best" approach for managing many subgroups of patients with atrial fibrillation.

Novel oral anticoagulants for stroke prevention in patients with atrial fibrillation: dawn of a new era.

Atrial fibrillation (AF) is an important cause of ischemic stroke and is the underlying cause of > 20% of all strokes, with increasing age being a risk factor. Until recently, warfarin was the only available oral anticoagulant used to decrease this risk in patients with AF. However, there are several disadvantages of warfarin use, such as the requirement for monitoring the international normalized ratio, its wide range of drug-food interactions, and its narrow therapeutic index. Thus, there has been a strong impetus for the development of newer oral anticoagulants with predictable pharmacokinetics that obviate the need for monitoring the international normalized ratio. The US Food and Drug Administration has approved a direct thrombin inhibitor (dabigatran) and 2 factor Xa inhibitors (rivaroxaban and apixaban) for stroke prevention in patients with nonvalvular AF. There are several other new oral anticoagulant agents on the horizon, including the factor Xa inhibitor edoxaban. This review article discusses the pharmacological properties, clinical trial data, and practical issues associated with the use of these novel oral anticoagulants.

Cerebral Embolization During AF Ablation -Pathophysiology, Prevention and Management.

Catheter based ablation therapy has evolved as an invaluable tool in the management of symptomatic patients with atrial fibrillation (AF). The procedure of AF ablation requires instrumentation in the systemic circulation predisposing to various concerns that can result in systemic embolization. We will describe the reported incidence of these events and refer to the various pathophysiologic explanations for their occurrence. Details on the risk factors and the relevant studies will also be reviewed. Preventive and treatment strategies in patients undergoing the ablation procedure will be discussed.

Dabigatran: a new chapter in anticoagulation.

For the last 60 years warfarin has been the cornerstone for chronic anticoagulation in prevention of ischemic strokes and systemic embolization. Warfarin therapy has several limitations including frequent monitoring and various food and significant drug interactions, which make it a less than ideal chronic oral anticoagulant. The continued search for safe, effective, medications with predictable pharmacokinetic profiles has led to newer alternatives. Dabigatran is a potent reversible, competitive direct thrombin inhibitor which is available as the prodrug, Dabigatran etexilate. It was first approved in Europe and recently in October 2010, the US food and drug administration (FDA) has approved the use of this novel oral anticoagulation for prevention of stroke in those with non valvular atrial fibrillation. This review will cover the chemical structure, mechanism of action, pharmacokinetic profile, clinical trials, dosage, clinical implication and adverse effects of dabigatran.

Venous thromboembolism in patients with heart failure: in-hospital and chronic use of anti-coagulants for prevention.

Heart failure (HF) is a common clinical syndrome characterized by high morbidity and frequent hospitalizations. HF is an independent and major risk factor for venous thromboembolism (VTE) and VTE occurring in patients with HF carries a worse prognosis. The present review will focus on short and long term role of anti-coagulants in prevention of venous thrombosis in HF patients. We will also be discussing the recently investigated and patented anti-coagulants which could have a role in this specific population.

Atrial fibrillation in patients with heart failure: Role of catheter ablation therapies.

Atrial fibrillation (AF) represents the most common sustained cardiac arrhythmia in patients with heart failure (HF). AF in HF patients is associated with worsening of symptoms and also results in a substantial increase in mortality. Although HF patients in sinus rhythm have a better outcome than patients with AF, several randomized studies investigating pharmacological rhythm control versus rate control have shown no advantage of one strategy over the other in terms of patient outcomes. Catheter-based ablation therapy is a newer therapeutic option with a rapidly evolving and changing role in the management of this arrhythmia. In the present review, the authors discuss the epidemiology, pathophysiology and prognostic significance of AF in patients with HF. Exclusively addressed are studies investigating catheter-based ablation for rhythm-control and rate-control therapies in the management of AF in HF patients.

Safety and efficacy of dronedarone in the treatment of atrial fibrillation/flutter.

Dronedarone is an amiodarone analog but differs structurally from amiodarone in that the iodine moiety was removed and a methane-sulfonyl group was added. These modifications reduced thyroid and other end-organ adverse effects and makes dronedarone less lipophilic, shortening its half-life. Dronedarone has been shown to prevent atrial fibrillation/flutter (AF/AFl) recurrences in several multi-center trials. In addition to its rhythm control properties, dronedarone has rate control properties and slows the ventricular response during AF. Dronedarone is approved in Europe for rhythm and rate control indications. In patients with decompensated heart failure, dronedarone treatment increased mortality and cardiovascular hospitalizations. However, when dronedarone was used in elderly high risk AF/AFl patients excluding such high risk heart failure, cardiovascular hospitalizations were significantly reduced and the drug was approved in the USA for this indication in 2009 by the Food and Drug Administration. Updated guidelines suggest dronedarone as a front-line antiarrhythmic in many patients with AF/Fl but caution that the drug should not be used in patients with advanced heart failure. In addition, the recent results of the PALLAS trial suggest that dronedarone should not be used in the long-term treatment of patients with permanent AF.

Interatrial conduction correlates with optimal atrioventricular timing in cardiac resynchronization therapy devices.

BACKGROUND: Echocardiographic optimization of the atrioventricular delay (AV) may result in improvement in cardiac resynchronization therapy (CRT) outcome. Optimal AV has been shown to correlate with interatrial conduction time (IACT) during right atrial pacing. This study aimed to prospectively validate the correlation at different paced heart rates and examine it during sinus rhythm (Sinus). METHODS: An electrophysiology catheter was placed in the coronary sinus (CS) during CRT implant (n = 33). IACT was measured during Sinus and atrial pacing at 5 beats per minute (bpm) and 20 bpm above the sinus rate as the interval from atrial sensing or pacing to the beginning of the left atrial activation in the CS electrogram. P-wave duration (PWd) was measured from 12-lead surface electrocardiogram, and the interval from the right atrial to intrinsic right ventricular activation (RA-RV) was measured from device electrograms. Within 3 weeks after the implant patients underwent echocardiographic optimization of the sensed and paced AVs by the mitral inflow method. RESULTS: Optimal sensed and paced AVs were 129 ± 19 ms and 175 ± 24 ms, respectively, and correlated with IACT during Sinus (R = 0.76, P < 0.0001) and atrial pacing (R = 0.75, P < 0.0001), respectively. They also moderately correlated with PWd (R = 0.60, P = 0.0003 during Sinus and R = 0.66, P < 0.0001 during atrial pacing) and RA-RV interval (R = 0.47, P = 0.009 during Sinus and R = 0.66, P < 0.0001 during atrial pacing). The electrical intervals were prolonged by the increased atrial pacing rate. CONCLUSION: IACT is a critical determinant of the optimal AV for CRT programming. Heart rate-dependent AV shortening may not be appropriate for CRT patients during atrial pacing.

Suppression of ventricular tachycardia with dronedarone: a case report.

UNLABELLED: INTRODUCTION: Dronedarone is a multichannel blocker with similar electrophysiological properties to amiodarone. Dronedarone has not been studied in humans as an agent to suppress ventricular arrhythmias. METHODS: This case report describes the dramatic antiarrhythmic effects of dronedarone in a patient with nonischemic cardiomyopathy and recurrent ventricular tachycardia, which was resistant to multiple antiarrhythmic agents and endocardial catheter ablation. RESULTS: Dronedarone was effective in completely suppressing ventricular tachycardia. CONCLUSION: Further research is needed to establish a potential larger role for dronedarone in controlling ventricular arrhythmias in humans.

Optimal atrioventricular delay in CRT patients can be approximated using surface electrocardiography and device electrograms.

UNLABELLED: Electrocardiographic AV Delay Adjustment. BACKGROUND: Optimization of the atrioventricular (AV) delay (AVD) may result in an improvement in cardiac resynchronization therapy (CRT) outcome. Previous studies have shown positive correlation between interatrial conduction time measured invasively during the implant procedure and optimal AVD determined postimplant using Doppler echocardiography. We hypothesized that the optimal AVD can be predicted noninvasively from surface electrocardiogram (ECG). METHODS: The optimal sensed (SAV) and paced (PAV) AVDs were determined for CRT patients (n = 63) by programming different AVDs (in 20 ms steps, in random sequence) and evaluating Doppler images of the mitral flow (iterative method). The time intervals between atrial sensing (As) and pacing (Ap) to the end of the P-wave (Pend) and to the right ventricular sensing (RVs) were measured from 5 ECG leads (limb, V1, and V3) and device telemetry during sinus rhythm and atrial pacing. RESULTS: Optimal SAV was 120 ± 30 ms and correlated with As-Pend (R = 0.69, P < 0.0001) and As-RVs (R = 0.45, P = 0.0003). Optimal PAV was 172 ± 38 ms and correlated with Ap-Pend (R = 0.65, P < 0.0001) and Ap-RVs (R = 0.60, P < 0.0001). Regression analysis suggested a simple method of AVD adjustment by pacing the ventricles 40 ms after the end of the sensed P-wave or 30 ms after the end of the paced P-wave but not at the expense of biventricular capture. Such a method would have resulted in significantly lower deviation from echo-optimal AVDs compared with programming fixed values. CONCLUSION: A simple method of providing 30-40 ms separation between the end of the P-wave and ventricular pacing pulse can be used to approximate echocardiographically optimal AV delays.

Ranolazine--treatment of ventricular tachycardia and symptomatic ventricular premature beats in ischemic cardiomyopathy.

Premature ventricular complexes (PVCs) are a frequent occurrence in the presence of ischemic heart disease. A very high PVC load can be symptomatic or occasionally result in a cardiomyopathy (CMP). Treatment options include pharmacologic agents and radiofrequency ablation (RFA). RFA has been successful in treating PVCs in symptomatic patients or in the presence of unexplained CMP. Ranolazine is a piperazine derivative used for treating chronic stable angina. It also has antiarrhythmic properties. We report a patient with ischemic CMP, symptomatic PVCs, and monomorphic ventricular tachycardia (VT) despite attempts to control symptoms with two antiarrhythmic drugs. Initiation of ranolazine led to marked reduction in PVCs along with control of VT and symptoms.

Interatrial conduction measured during biventricular pacemaker implantation accurately predicts optimal paced atrioventricular intervals.

BACKGROUND: Optimizing atrioventricular (AV) delay during biventricular (BiV) pacemaker implantation can require substantial resources. Hence, a simpler method is desirable. We hypothesized that interatrial conduction time (IACT), measured at the time of BiV device implant, could be a surrogate value for the optimal AV delay. OBJECTIVE: This study determined the relationship between paced IACT and the optimal paced AV delay (PAV), as determined by echocardiography. METHODS: Consecutive subjects (N = 25; age = 66 +/- 10 years; M/F: 17/8) undergoing BiV pacemaker implantation and in sinus rhythm were included. Cannulation of the coronary sinus (CS) was at the operator's discretion. A quadripolar electrophysiology catheter was inserted via the guiding sheath into the inferiolateral CS to measure left atrial depolarization. The IACT was calculated as the interval between right atrial stimulation artifact and earliest deflection on the coronary sinus catheter electrogram. Subsequently, during atrial pacing the PAV was determined using transmitral pulsed wave Doppler echocardiography (iterative method). The relationship between paced IACT and PAV was then determined. RESULTS: The mean +/- SD paced IACT and PAV were 126 +/- 25 msec and 157 +/- 23 msec, respectively. There was a strong positive correlation between the paced IACT and PAV (r = 0.73, P < 0.001). The equation describing the relationship was PAV = 0.68 * (IACT + 104) msec. CONCLUSIONS: The paced IACT has a strong correlation with the echo derived optimal PAV. This method may be used to program PAV intervals without need for echocardiography in patients undergoing BiV pacemaker implantation.