Porcine Myocardium Research Articles

A Thin Layer of Decellularized Porcine Myocardium for Cell Delivery

Decellularized porcine myocardium has shown many benefits as a cell delivery scaffold for cardiac therapy. However, using full thickness decellularized myocardium as cardiac patch may lead to poor viability and inhomogeneous distribution of delivered cells, due to perfusion limitations. In this study, we explored the feasibility of decellularized porcine myocardial slice (dPMS) to construct a vascularized cardiac patch for cell delivery. Decellularized porcine myocardium was sliced into thin layers (thickness~300 µm). Adipose-derived Stem cells (ASCs) obtained from rat and pig were seeded on dPMS. The viability, infiltration, and differentiation of seeded ASCs were examined. The mechanical properties of dPMSs of various thickness and native myocardium were tested. We noticed dPMS supported attachment and growth of rat and pig ASCs. Both rat and pig ASCs showed high viability, similar patterns of proliferation and infiltration within dPMS. Rat ASCs showed expression of early-endothelial markers followed by mature-endothelial marker without any additional inducers on dPMS. Using rat myocardial infarction model, we delivered ASCs using dPMS patched to the infarcted myocardium. After 1 week, a higher number of transplanted cells were present in the infarcted area when cells were delivered using dPMS versus direct injection. Compared with MI group, increased vascular formation was also observed.

Characterization and implications of the dynamics of eosinophils in blood and in the infarcted myocardium after coronary reperfusion.

ObjectiveWe characterized the dynamics of eosinophils in blood and in the infarcted myocardium in patients and in a swine model of reperfused myocardial infarction (MI). The association of eosinophil dynamics with various outcomes was assessed.MethodsSerial eosinophil count and pre-discharge cardiac magnetic resonance were carried out in a prospective series of 620 patients with a first ST-elevation MI. In a swine model of reperfused MI, the dynamics of circulating eosinophils and their presence in the infarcted myocardium were determined. In autopsies from chronic MI patients, eosinophils were quantified.ResultsPatient eosinophil count sharply decreased 12h post-reperfusion compared to arrival. A lower minimum eosinophil count was associated with more extensive edema, microvascular obstruction, and infarct size as measured by cardiac magnetic resonance, and also with a higher rate of cardiac events (death, re-infarction, or heart failure) during follow-up. In the experimental model, eosinophil count boosted during ischemia and dropped back immediately post-reperfusion. Myocardial samples revealed progressive eosinophil migration into the infarcted myocardium, especially areas with microvascular obstruction. Markers of eosinophil maturation and survival (interleukin-5), degranulation (eosinophil cationic protein) and migration (eotoxin-1) were detected in the blood of patients, and in porcine myocardium. Eosinophil infiltration was detected in autopsies from chronic MI patients.ConclusionEosinopenia post-MI was associated with an impaired cardiac structure and adverse events. The decay in circulating eosinophils soon after reperfusion mirrors their migration into the infarcted myocardium, as reflected by their presence in heart samples from swine and patients. Further studies are needed to understanding this unexplored pathway and its therapeutic implications.

The Effect of Immersion Agents on the Weight and Geometric Parameters of Myocardial Tissue in Vitro

Abstract—The effect of 40%-glucose solution and 60%-glycerol solution on the weight and geometric parameters of the myocardium was studied in vitro in order to improve the accuracy of estimating the glucose and glycerol diffusion coefficients in the myocardium by including changes in the geometry and water content of a tissue sample in a mathematical algorithm. The temporal kinetics of the weight, thickness, area, and volume were measured using porcine myocardium samples during their immersion in 60%-glycerol solution or 40%-glucose solution in vitro. All parameters started to decrease immediately after placing myocardium samples in immersion agents (tissue shrinkage). The weight and geometric parameters of the sample then increased gradually (tissue swelling), leading to tissue saturation in almost all cases. By approximating the temporal kinetics, the degree of dehydration and the characteristic times of transverse and longitudinal shrinkage and swelling of the myocardium were determined. More significant and rapid dehydration of myocardial tissue was observed case of using 60%-glycerol solution, while a stronger and faster swelling of the myocardium was observed when 40%-glucose solution was applied.

Compressibility and Anisotropy of the Ventricular Myocardium: Experimental Analysis and Microstructural Modeling.

While the anisotropic behavior of the complex composite myocardial tissue has been well characterized in recent years, the compressibility of the tissue has not been rigorously investigated to date. In the first part of this study, we present experimental evidence that passive-excised porcine myocardium exhibits volume change. Under tensile loading of a cylindrical specimen, a volume change of 4.1±1.95% is observed at a peak stretch of 1.3. Confined compression experiments also demonstrate significant volume change in the tissue (loading applied up to a volumetric strain of 10%). In order to simulate the multiaxial passive behavior of the myocardium, a nonlinear volumetric hyperelastic component is combined with the well-established Holzapfel-Ogden anisotropic hyperelastic component for myocardium fibers. This framework is shown to describe the experimentally observed behavior of porcine and human tissues under shear and biaxial loading conditions. In the second part of the study, a representative volumetric element (RVE) of myocardium tissue is constructed to parse the contribution of the tissue vasculature to observed volume change under confined compression loading. Simulations of the myocardium microstructure suggest that the vasculature cannot fully account for the experimentally measured volume change. Additionally, the RVE is subjected to six modes of shear loading to investigate the influence of microscale fiber alignment and dispersion on tissue-scale mechanical behavior.

Acute stimulation of the soluble guanylate cyclase does not impact on left ventricular capacitance in normal and hypertrophied porcine hearts in vivo.

Experimental data indicate that stimulation of the nitric oxide-soluble guanylate cyclase(sGC)-cGMP-PKG pathway can increase left ventricular (LV) capacitance via phosphorylation of the myofilamental protein titin. We aimed to test whether acute pharmacological sGC stimulation with BAY 41-8543 would increase LV capacitance via titin phosphorylation in healthy and deoxycorticosteroneacetate (DOCA)-induced hypertensive pigs. Nine healthy Landrace pigs and 7 pigs with DOCA-induced hypertension and LV concentric hypertrophy were acutely instrumented to measure LV end-diastolic pressure-volume relationships (EDPVRs) at baseline and during intravenous infusion of BAY 41-8543 (1 and 3 μg·kg-1·min-1 for 30 min, respectively). Separately, in seven healthy and six DOCA pigs, transmural LV biopsies were harvested from the beating heart to measure titin phosphorylation during BAY 41-8543 infusion. LV EDPVRs before and during BAY 41-8543 infusion were superimposable in both healthy and DOCA-treated pigs, whereas mean aortic pressure decreased by 20-30 mmHg in both groups. Myocardial titin phosphorylation was unchanged in healthy pigs, but total and site-specific (Pro-Glu-Val-Lys and N2-Bus domains) titin phosphorylation was increased in DOCA-treated pigs. Bicoronary nitroglycerin infusion in healthy pigs ( n = 5) induced a rightward shift of the LV EDPVR, demonstrating the responsiveness of the pathway in this model. Acute systemic sGC stimulation with the sGC stimulator BAY 41-8543 did not recruit an LV preload reserve in both healthy and hypertrophied LV porcine myocardium, although it increased titin phosphorylation in the latter group. Thus, increased titin phosphorylation is not indicative of increased in vivo LV capacitance. NEW & NOTEWORTHY We demonstrate that acute pharmacological stimulation of soluble guanylate cyclase does not increase left ventricular compliance in normal and hypertrophied porcine hearts. Effects of long-term soluble guanylate cyclase stimulation with oral compounds in disease conditions associated with lowered myocardial cGMP levels, i.e., heart failure with preserved ejection fraction, remain to be investigated.

Induced Pluripotent Stem Cell (iPSC)-Derived Exosomes for Precision Medicine in Heart Failure.

In the United States, heart failure (HF) is the leading cause of hospital admission and a major public health problem.1 Ischemic cardiomyopathy is the primary pathogenesis of advanced HF.1 More than 5 million people experience HF, with an annual incidence of 300 000 patients.1 Despite significant therapeutic advances during the past 3 decades, the 5-year survival remains at a dismal 50%.2 Clinical studies have confirmed that the high morbidity and mortality of HF are because of left ventricular arrhythmias and dilatation.1,2 Patients with a history of acute myocardial infarction and left ventricular dysfunction have a 6-month mortality of >10% of which one third is attributed to sudden cardiac death.3 Although implantable cardioverter defibrillators reduced mortality from left ventricular arrhythmia, patients with acute myocardial infarction do not qualify under the current guideline. An important trigger for ventricular arrhythmias and dilatation is the tissue heterogeneity in the peri-infarct region (PIR), which is independent of the actual infarct size.4–7 An effective targeted therapy to salvage the injured and vulnerable myocardium in the PIR is urgently needed to reduce the high mortality of patients with HF.7,8 Promising discoveries of induced pluripotent stem cell (iPSC) biology may restore the PIR.9,10 The initial theory for the regeneration of the myocardium hypothesized that the transplanted stem cells would differentiate into cardiomyocytes, engraft into the host myocardium, and augment the cardiac function through synchronized electromechanical integration. However, de novo cardiac differentiation of transplanted stem cells was rare and mostly led to teratoma.9,10 Similarly, ex vivo differentiated cardiac stem cells demonstrate transient in vivo engraftment and functional restoration.9,10 Other controversial studies examined the cardiac progenitor cells, a multipotent population of cardiac, vascular, and endothelial cells in the …

Construction of a vascularized hydrogel for cardiac tissue formation in a porcine model.

Replacing cardiac tissues lost to myocardial infarction remains a therapeutic goal for regenerative therapy in recovering cardiac function. We assessed the feasibility of constructing a macrosized human cardiac tissue construct using pluripotent stem cell-derived cardiomyocytes or control fibroblasts infused fibrin/collagen hydrogel and performed ectopic implantation in peripheral vascular system of a porcine model for 3weeks. Finally, an optimized vascularized cardiac construct was explanted and grafted onto porcine myocardium for 2weeks. Myocardial-grafted human cardiac constructs showed a nascent tissue-like organization with aligned cardiomyocytes within the remodelled collagen matrix. Nevertheless, no significant changes in intraconstruct density of cardiomyocytes were observed in the myocardial-grafted constructs (human embryonic stem cell [hESC]-derived cardiomyocyte [n=4]: 70.5±22.8 troponin I+ cardiomyocytes/high power field [HPF]) as compared to peripherally implanted constructs (hESC-derived cardiomyocyte [n=4]: 59.0±19.6 troponin I+ cardiomyocytes/HPF; human induced pluripotent stem cell-derived cardiomyocyte [n=3]: 50.9±8.5 troponin I+ cardiomyocytes/HPF, p=ns). However, the myocardial-grafted constructs showed an increased in neovascularization (194.4±24.7 microvessels/mm2 tissue, p<.05), microvascular maturation (82.8±24.7 mature microvessels/mm2 , p<.05), and tissue-like formation whereas the peripherally implanted constructs of hESC-derived cardiomyocyte (168.3±98.2 microvessels/mm2 tissue and 68.1±33.4 mature microvessels/mm2 ) and human induced pluripotent stem cell-derived cardiomyocyte (86.8±57.4 microvessels/mm2 tissue and 22.0±32.7 mature microvessels/mm2 ) were not significantly different in vascularized response when compared to the control human fibroblasts (n=3) constructs (65.6±34.1 microvessels/mm2 tissue and 30.7±20.7 mature microvessels/mm2 ). We presented results on technical feasibility and challenges of grafting vascularized centimetre-sized human cardiac construct that may spur novel approaches in cardiac tissue replacement strategy.

Effects of salts on ultrasonic extraction of protein from porcine myocardium

The porcine myocardium is a valuable protein source. However, it is generally not utilized owing to inefficient processing methods, e.g., protein extraction requires a complicated process and a high concentration of salt (>0.2M NaCl). In the present study, the extraction method was improved by simplifying the pre-treatment process and reducing the amount of salt used. The effects of three salts used as food additives (NaCl, sodium phosphate, and sodium pyrophosphate) on the protein extraction efficiency were compared. The extraction yield was the greatest for sodium pyrophosphate, followed by sodium phosphate and NaCl. An extraction yield of 91.5% w/w was achieved only with 5mM pyrophosphate and 80min of ultrasonication. The physiological properties of extracted proteins were assessed by measuring Na2+- and Ca2+-ATPase activities, and digestion properties were examined using pepsin. Ultrasonic treatment in sodium pyrophosphate enhanced the extraction of proteins and digestibility by promoting the structural collapse of the myocardium. Accordingly, the developed extraction method can be used to recover proteins from the porcine myocardium and may contribute for the posterior application of this meat by-product in a nutritional supplement.

Protein/polysaccharide-based scaffolds mimicking native extracellular matrix for cardiac tissue engineering applications.

Tissue engineering has emerged as a viable approach to treat disease or repair damage in tissues and organs. One of the key elements for the success of tissue engineering is the use of a scaffold serving as artificial extracellular matrix (ECM). The ECM hosts the cells and improves their survival, proliferation, and differentiation, enabling the formation of new tissue. Here, we propose the development of a class of protein/polysaccharide-based porous scaffolds for use as ECM substitutes in cardiac tissue engineering. Scaffolds based on blends of a protein component, collagen or gelatin, with a polysaccharide component, alginate, were produced by freeze-drying and subsequent ionic and chemical crosslinking. Their morphological, physicochemical, and mechanical properties were determined and compared with those of natural porcine myocardium. We demonstrated that our scaffolds possessed highly porous and interconnected structures, and the chemical homogeneity of the natural ECM was well reproduced in both types of scaffolds. Furthermore, the alginate/gelatin (AG) scaffolds better mimicked the native tissue in terms of interactions between components and protein secondary structure, and in terms of swelling behavior. The AG scaffolds also showed superior mechanical properties for the desired application and supported better adhesion, growth, and differentiation of myoblasts under static conditions. The AG scaffolds were subsequently used for culturing neonatal rat cardiomyocytes, where high viability of the resulting cardiac constructs was observed under dynamic flow culture in a microfluidic bioreactor. We therefore propose our protein/polysaccharide scaffolds as a viable ECM substitute for applications in cardiac tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 769-781, 2018.

Protein Extraction from Porcine Myocardium Using Ultrasonication.

Porcine myocardium is regarded as a byproduct in slaughterhouses and is rarely used as a food source due to its unsuitability for processing and consumption. In this study, we sought to develop an efficient ultrasonication method to extract protein from porcine myocardium. Comparisons of protein yield using various ultrasonication conditions with porcine myocardium revealed that treatment with 0.2 M NaCl, with pH 8.0, at an extraction temperature of less than 40 °C and an amplitude of 60% to 80% was optimal, yielding an extraction rate of 90%. In addition, SDS-PAGE analysis showed that increasing the time interval for ultrasonication increased the presence of myosin heavy chain and actin protein content. Functional analysis of the physiological properties of the isolated proteins using an ATPase assay showed that Ca and Mg ATPase activity was virtually undetectable in the early stages of ultrasonic treatment and that the proteins denatured rapidly. An analysis of protein digestion also showed that the digestive capacity of proteins treated by ultrasonication methods was greater. These results demonstrate that the ultrasonication method is effective for high-yield protein extraction from cardiac myofibrils of porcine myocardium with low salt concentrations, low Ca and Mg ATPase activities, and high digestive capacities.

Application of swine iPS cell transplantation in porcine myocardial infarction model

Objective To observe the therapeutic effect of porcine myocardium against porcine myocardial infarction (MI) by porcine myocardial infarction model with connexin-43/zonula occludens-1 (CX43/ZO-1) double gene induced pluripotent stem cells (iPS) transplantation. Methods Porcine myocardial infarction model was established by balloon occlusion. One week later, 1640 culture medium, CX43 gene ips cells and CX43/ZO-1 gene ips cells were injected into the different coronary arteries. After 3 months, electron microscopy and color Doppler ultrasonography were used to evaluate the curative effect. Results Compared to ips group of CX43 and 1640 culture group, in CX43/ZO-1 gene ips group, electron microscope showed a large number of island-like cardiomyocytes, blood vessels and intact intercalated discs in the infarct area and normal myocardial junction area structure, color Doppler echocardiography showed left ventricular end diastolic diameter reduced, and ejection fraction was significantly increased (P<0.05). Conclusions Transfection of CX43/ZO-1 double gene ips cells can promote cardiomyocyte regeneration and cardiac function recovery in porcine myocardial infarction model. Key words: Multipotent stem cells/TR; Connexin 43; Desmin; Myocardial infarction/SU; Models, animal

Prevascularization of Decellularized Porcine Myocardial Slice for Cardiac Tissue Engineering.

Prevacularization strategies have been implemented in tissue engineering to generate microvasculature networks within a scaffold prior to implantation. Prevascularizing scaffolds will shorten the time of functional vascular perfusion with host upon implantation. In this study, we explored key variables affecting the interaction between decellularized porcine myocardium slices (dPMSs) and reseeded stem cells toward the fabrication of prevascularized cardiac tissue. Our results demonstrated that dPMS supports attachment of human mesenchymal stem cells (hMSCs) and rat adipose derived stem cells (rASCs) with high viability. We found that cell seeding efficiency and proliferation are dPMS thickness dependent. Compared to lateral cell seeding, bilateral cell seeding strategy significantly enhanced seeding efficiency, infiltration, and growth in 600 μm dPMS. dPMS induced endothelial differentiation and maturation of hMSCs and rASCs after 1 and 5 days culture, respectively. These results indicate the potential of dPMS as a powerful platform to develop prevascularized scaffolds and fabricate functional cardiac patches.

Biaxial quantification of passive porcine myocardium elastic properties by region

Biaxial quantification of passive porcine myocardium elastic properties by region

Anisotropic engineered heart tissue made from laser-cut decellularized myocardium.

We have developed an engineered heart tissue (EHT) system that uses laser-cut sheets of decellularized myocardium as scaffolds. This material enables formation of thin muscle strips whose biomechanical characteristics are easily measured and manipulated. To create EHTs, sections of porcine myocardium were laser-cut into ribbon-like shapes, decellularized, and mounted in specialized clips for seeding and culture. Scaffolds were first tested by seeding with neonatal rat ventricular myocytes. EHTs beat synchronously by day five and exhibited robust length-dependent activation by day 21. Fiber orientation within the scaffold affected peak twitch stress, demonstrating its ability to guide cells toward physiologic contractile anisotropy. Scaffold anisotropy also made it possible to probe cellular responses to stretch as a function of fiber angle. Stretch that was aligned with the fiber direction increased expression of brain natriuretic peptide, but off-axis stretches (causing fiber shear) did not. The method also produced robust EHTs from cardiomyocytes derived from human embryonic stem cells and induced pluripotent stem cells (hiPSC). hiPSC-EHTs achieved maximum peak stress of 6.5 mN/mm2 and twitch kinetics approaching reported values from adult human trabeculae. We conclude that laser-cut EHTs are a viable platform for novel mechanotransduction experiments and characterizing the biomechanical function of patient-derived cardiomyoctyes.

AdVEGF-B186 and AdVEGF-DΔNΔC induce angiogenesis and increase perfusion in porcine myocardium

ObjectiveCoronary heart disease remains a significant clinical problem, and new therapies are needed especially for patients with refractory angina for whom the current therapies do not provide sufficient relief. The...

Impact of decellularization on porcine myocardium as scaffold for tissue engineered heart tissue.

Decellularized myocardium has been proposed to construct tissue engineered heart tissue, providing the advantage of natural extracellular architecture. Various decellularization protocols have been developed, but the impact of individual decellularization reagent in the protocol remains unclear. The aim of this study is to evaluate the structural impact of three commonly used decellularization reagents on the porcine myocardium. We decellularized porcine heart tissue with trypsin, Triton X-100 or SDS, and analyzed the morphological characteristics of the remaining tissue by SEM, AFM and two-photon LSM. We further recellularized the scaffold with rat myocardial fibroblasts and cardiomyocytes separately. According to the H&E staining and DNA quantification, SDS decellularized more efficiently in comparison to the other two reagents. Moreover, we found distinct surface microarchitecture differences among groups. The changed structure of tissue might result in varied proliferation myocardial fibroblasts and biophysical performance of the engineered heart tissue. This study demonstrated that the microstructure of decellularized porcine heart tissue vary with decellularization agents. Compared to trypsin and Triton X-100, SDS not only decellularized more efficiently but also preserved the biocompatible microstructure of ECM for recellularization.

Initial and Secondary ST-T Alternans During Acute Myocardial Ischemia in the In-Situ Pig Heart.

The factors responsible for the ST-T wave alternans (STTA) and associated arrhythmias during acute ischemia have not been clarified.In acutely ischemic porcine myocardium, we recorded transmural unipolar and bipolar electrocardiograms and mid-myocardial extracellular K(+) ([K(+)]e) from the center of the ischemic zone during 8-minute episodes of ischemia. Two different STTAs occurred. The initial STTA, which occurred at 4 minutes 15 seconds ± 12 seconds of ischemia during sinus rhythm, was most prominent in the subendocardium, independent of [K(+)]e and activation block, and heart rate dependent. It occurred in 13/19 (68%) occlusions at heart rates ≤ 100 bpm and in 22/23 (96%) at > 100 bpm. The second STTA was more obvious and greatest in the subepicardium. It began in the later phase of ischemia and was also heart rate dependent (5/19 [26%] occlusions at heart rates ≤ 100 bpm and 10/23 [44%] at > 100 bpm). This STTA was consistently associated with 2:1 change in the bipolar electrogram morphology, possibly due to 2:1 conduction block. Ventricular fibrillation (VF) occurred only at > 100 bpm.The initial STTA may be independent of conduction abnormalities and represent primary repolarization alternans. The second STTA may be secondary to and indicative of 2:1 activation block or marked alternans of the action potential amplitude/duration. The associated VF most likely reflects the underlying conduction abnormality.

Polarimetric assessment of healthy and radiofrequency ablated porcine myocardial tissue

Radiofrequency (RF) ablation offers a potential treatment for cardiac arrhythmia, where properly titrated energy delivered at critical sites can destroy arrhythmogenic foci. The resulting ablation lesion typically consists of a core (coagulative necrosis) surrounded by a rim of mixed viable and non-viable cells. The extent of the RF lesion is difficult to delineate with current imaging techniques. Here, we explore polarization signatures of ten ex-vivo samples from untreated (n=5) and RF ablated porcine hearts (n=5), in backscattered geometry through Mueller matrix polarimetry. Significant differences (p<0.01) in depolarization, ΔT , were observed between the healthy, RF ablated and rim regions. Linear retardance, δ, was significantly lower in the core and rim regions compared to healthy regions (p<0.05). The results demonstrate a novel application of polarimetry, namely the characterization of RF ablation extent in myocardium, including the visualization of the important lesion rim region. White light photo (top) of porcine myocardium tissue with radiofrequency ablation lesion and corresponding depolarization map (bottom). Depolarization is useful for visualizing the lesion core and rim.

Inducible NO synthase is constitutively expressed in porcine myocardium and its level decreases along with tachycardia-induced heart failure.

The adverse effects of oxidative stress and the presence of proinflammatory factors in the heart have been widely demonstrated mainly on rodent models. However, larger clinical trials focusing on inflammation or oxidative stress in heart failure (HF) have not been carried out. This may be due to differences in the anatomy and physiology of the cardiovascular system between small rodents and large mammals. Thus, we investigated myocardial inflammatory factors, such as inducible NO synthase (iNOS) and oxidative stress indices in female pigs with chronic tachycardia-induced cardiomyopathy. Homogenous female siblings of Large White breed swine (n=15) underwent continuous right ventricular (RV) pacing at 170bpm, whereas five sham-operated subjects served as controls. In the course of RV pacing, animals developed a clinical picture of HF and were euthanized at subsequent stages of the disease: mild, moderate and severe HF. Left ventricle (LV) sections were examined with electron microscopy. The relative expression of iNOS in LV was determined by quantitative PCR. The protein level of iNOS was determined by Western blotting and immunohistochemistry. The level of the S-nitrosylated (S-NO) protein in LV was determined after S-NO moieties were substituted by biotin, followed by a colorimetrical detection with streptavidin. Malondialdehyde (MDA), a marker of lipid peroxidation, was evaluated in the LV and serum using thiobarbituric acid. The aconitase activity (based on measurement of the concomitant formation of NADPH from NADP(+)), a marker of oxidative stress, was analyzed in mitochondrial and cytosolic LV fractions. The concentration of interleukin-1β (IL-1β) was measured in LV homogenates using enzyme-linked immunosorbent assay. RV pacing resulted in an impairment of LV systolic function, LV dilatation and neurohormonal activation. The electron microscopy revealed abnormalities within the cardiomyocytes of failing hearts, i.e. swollen mitochondria and myofibril derangement. iNOS was expressed in the control LV myocardium. The development of HF was accompanied by a decrease in iNOS mRNA (P<.05), which was also reflected at a protein level, and a decrease in the protein S-nitrosylation (P<.05). Both iNOS mRNA and S-NO relative moiety levels were inversely related to the dilatation of the LV (P<.05). There was no difference in the concentration of MDA in the LV and serum. Similarly, no differences in the concentration of IL-1β LV were found between diseased and healthy animals. Aconitase activity was decreased only in the LV mitochondrial fraction of pigs with severe HF. iNOS was shown to be constitutively expressed within porcine LV. Its level decreases during the progression of systolic nonischemic HF in the pig model. Thus, it can be assumed that an up-regulation of proinflammatory factors is not involved in porcine tachycardia-induced cardiomyopathy and that the impact of oxidative stress may be restricted to the mitochondria in this HF model.

Thermal expansion imaging for monitoring lesion depth using M-mode ultrasound during cardiac RF ablation: in vitro study.

We demonstrate a novel method for automatic direct lesion depth (LD) tracking during coagulation from time series of a single A-mode ultrasound (US) transducer custom fit at the tip of a RFA catheter. This method is named thermal expansion imaging (TEI). A total of 35 porcine myocardium samples were ablated (LD 0.5-5 mm) while acquiring US, electrical impedance (EI) and contact force (CF) data. US images are generated in real time in terms of echo intensity (M-mode) and phase (TEI). For TEI, displacements between US time series are estimated with time-domain cross-correlation. A modified least squares strain estimation with temporal and depth smoothing reveals a thermal expansion boundary (TEB)--negative zero-crossing of temporal strain--which is associated to the coagulated tissue front. M-mode does not reliably delineate RFA lesions. TEI images reveal a traceable TEB with RMSE = 0.50 mm and R2 = 0.85 with respect to visual observations. The conventional technique, EI, shows lower R2 = 0.7 and > 200 % variations with CF. The discontinuous time progression of the TEB is qualitatively associated to tissue heterogeneity and CF variations, which are directly traceable with TEI. The speed of sound, measured in function of tissue temperature, increases up to a plateau at 55°C , which does not explain the observed strain bands in the TEB. TEI successfully tracks LD in in vitro experiments based on a single US transducer and is robust to catheter/tissue contact, ablation time and even tissue heterogeneity. The presence of a TEB suggests thermal expansion as the main strain mechanism during coagulation, accompanied by compression of the adjacent non-ablated tissue. The isolation of thermally induced displacements from in vivo motion is a matter of future research. TEI is potentially applicable to other treatments such as percutaneous RFA of liver and high-intensity focused ultrasound.