Cardiovascular diseases are the leading causes of death globally. One contributing factor that can lead to heart failure is a myocardial infarction. When an infarct occurs, an occlusion in the tissue vasculature prevents blood flow beyond this site. It results in scar tissue formation. The scar is non-contractile and reduces the working efficiency of the heart. To compensate, left ventricular remodeling will ensue resulting in enlarging of the left ventricle. This progression of events ultimately culminates in heart failure. One approach to assist patients who have suffered a heart attack is to implant a cardiac patch. Current patches are acellular and aim to retain the geometry of the left ventricle, limiting any ventricular remodeling from occurring. While these patches provide a passive support, it is hypothesized that incorporation of cells into the patches could result in functional support that could help to restore baseline function. To be effective, a cell-populated cardiac patch would need to integrate with the host tissue functionally and mechanically. In this thesis, we developed a fibrin microthread-based composite scaffold with material properties comparable to left ventricular myocardium that promotes regional cardiomyocyte alignment and physiologically relevant contractile strains. We hypothesized that a composite material could be developed where constituents of the material would complement one another to yield a mechanically reinforced scaffold that promotes cardiomyocyte function. Through manipulation of the volume fraction of the components, we manipulated the modulus of the layer without compromising contractile strain or contractile frequency of incorporated cells. Additionally, through strategic restraint of the scaffolds, we utilized cell-mediated compaction to induce a tension pattern that increased alignment of incorporated cells. This corresponded to an increase in contractile strain magnitudes, and an anisotropic contractile wave propagation through the engineered tissue. Finally, we laminated composite layers into a patch mimicking the architecture of ventricular myocardium and found that material properties of the patch were similar to properties of the target tissue. In summary, we designed a biomimetic composite patch with material properties similar to ventricular myocardium that supports cardiomyocyte alignment and contractility to promote functional and mechanical integration upon implantation.

University of Macau / Institute of Chinese Medical Sciences

Cardiac arrest is a phenomenon in which a sudden loss of heart function leads to cessation of blood delivery to the rest of the body. It is one of the leading causes of natural death in the United States. Because its onset cannot be predicted, therapy for post-cardiac arrest victims focuses on management of moderate organ failure and neurological injury. The mortality rate of out-of-hospital cardiac arrest victims remains about 90%, but currently, there are several management techniques that reduce the incidence of sudden cardiac death. My goal is to argue that despite some of the negative effects of therapeutic hypothermia, it holds the most promise to sustain organ and neurological recovery. This study focuses on evaluating the pathophysiology of post-cardiac arrest syndrome, and referencing literature that documents the reversal techniques of therapeutic hypothermia. Despite the side effects and unwanted consequences that come with targeted temperature management, there is an imbalance between the benefits and consequences, resulting in enhanced recovery when this technique is carefully administered shortly after the cardiac arrest episode.

Increases in internal dimensions of the chambers of the heart (cardiac dilatation), mediated by right shifts in cardiac chamber diastolic pressure-volume (P-V) relations, predict mortality in patients with established heart failure. However, the mechanisms responsible for the transition from concentric cardiac hypertrophy to cardiac dilatation are unclear. Recent evidence suggests that decreases in the cross-linked properties of myocardial collagen may increase the propensity of collagen to cleavage and hence reduce cardiac myocyte tethering, thus promoting cardiac dilatation. However, decreases in myocardial collagen cross-linking may also reduce myocardial stiffness, thus explaining right shifts in cardiac diastolic P-V relations. In the present dissertation I evaluated whether right shifts in diastolic P-V relations produced by chronic β-adrenoreceptor activation (isoproterenol, a β-adrenoreceptor agonist, 0.02 mg.kg-1.day) in spontaneously hypertensive rats (SHR) with compensated cardiac hypertrophy (12 months of age), can be explained by adverse chamber remodelling or alterations in the myocardial material properties of the heart. After 7 months of daily isoproterenol administration, SHR had marked right shifts in left ventricular (LV) diastolic P-V relations as determined in isolated, perfused hearts, with increases in the volume intercept of these relations, a change that translated into increases in LV cavity diameters (echocardiography). LV dilatation was associated with reductions in LV pump function (decreases in LV endocardial fractional shortening and the slope of the LV systolic P-V relation [LV E]). The reductions in pump function were attributed to the LV dilatation rather than to alterations in intrinsic myocardial contractile properties as LV midwall fractional shortening and myocardial systolic elastance (LV En) were unchanged. Although SHR not receiving isoproterenol had increases in the LV diastolic wall thickness-to-radius ratio, a change commensurate with compensatory concentric LV hypertrophy, LV wall thickness-to-radius ratio in SHR exposed to chronic β-adrenoreceptor activation was reduced to values similar to those noted in normotensive Wistar Kyoto (WKY) control rats, despite further increases in LV weight. SHR not receiving isoproterenol had a marked increase in myocardial stiffness (slope of the linearized LV diastolic stress-strain relationship) as compared to WKY rats, a change that was associated with an increased myocardial collagen of the cross-linked phenotype. Although SHR receiving daily isoproterenol had further increases in myocardial collagen, this did not translate into changes in LV diastolic myocardial stiffness, as the further increase in myocardial collagen was of the non cross-linked phenotype. However, through a susceptibility to digestion, this collagen phenotype could have contributed to LV dilatation. In conclusion, these data suggest that LV dilatation in SHR following chronic β-adrenoreceptor activation is attributed to adverse chamber remodelling rather than to alterations in myocardial material properties as indexed by diastolic stress-strain relations.

La chirurgie cardiaque implique le plus souvent le recours à la circulation extracorporelle (CEC) en per-opératoire. Echanges gazeux et perfusion sont ainsi assurés pour les organes à l’exception du cœur, qui malgré la cardioplégie, peut présenter des signes de souffrance résultant d’une protection myocardique incomplète et génératrice d’ischémie. Les complications post-opératoires les plus souvent rencontrées sont d’une part le syndrome de réaction inflammatoire systémique (SIRS) souvent précédé d’une vasoplégie per-CEC et d’autre part la fibrillation auriculaire (FA), trouble du rythme le plus fréquemment rencontré. Les mécanismes impliqués sont multifactoriels mais l’ischémie-reperfusion myocardique engendrée par la CEC semble jouer un rôle prépondérant. Au niveau moléculaire, un acteur clé de ces désordres pourrait être l’adénosine, un nucléoside purique ubiquitaire issu de la déphosphorylation de l’ATP et libéré par nombre de cellules en cas de stress oxydatif et d’inflammation. Marqueur biologique très précoce d’hypoxie et d’ischémie globale, l’adénosine contrôle les systèmes cardiovasculaire et immunitaire par l’intermédiaire de quatre types de récepteurs avec notamment un effet vasodilatateur via le récepteur A2A et un effet pro-arythmique documenté par plusieurs études fondamentales et cliniques.Les objectifs de notre travail ont été dans un premier temps de montrer l’implication de l’adénosine dans la survenue de complications hémodynamiques et rythmiques en post-opératoire de chirurgie cardiaque sous CEC, puis dans un second temps d’évaluer l‘intérêt de la caféine, un antagoniste non spécifique des récepteurs de l’adénosine, dans la prévention de la FA. / Cardiac surgery often requires peri-operative cardiopulmonary bypass (CB). . Gas exchanges and perfusion are provided for the organs excepting the heart, which despite cardioplegia, can display stress signs resulting from an insufficient myocardial protection that generates ischemia. Most common post-surgery complications are the systemic inflammatory response syndrome (SIRS) often preceded by vasoplegia and auricular fibrillation (AF), most common rhythm disorder. Mechanisms involved are multifactorial but the CB-induced myocardial re-perfusion ischemia seems to play a major role. At a molecular level, adenosine could be a key actor, a ubiquitous glycoside derived from the dephosphorylation of ATP and released by numerous cells in case of oxidative stressor inflammation. Very early marker of hypoxemia and general ischemia, adenosine controls both cardiovascular and immune systems through 4 types of receptors most particularly with a vasodilator effect through the A2A receptor and a pro-arrhythmic effect documented by several fundamental and clinical studies.The objectives of our work were to demonstrate the involvement of adenosine in the appearance of hemodynamic and rhythmic complications in post cardiac surgery under CB and then to assess the interest of caffeine, a nonspecific antagonist of adenosine receptors, in the prevention of AF.

Die vorgestellte Arbeit analysiert an 29 Patienten die Integrität des Endothelzellverbandes der V. saphena magna in Abhängigkeit von drei unterschiedlichen, etablierten Entnahmetechniken im Rahmen einer Herz-Bypass-Operation. Darüber hinaus wird die Frequenz von Sekundärkomplikationen erfasst. Ein chirurgisch induzierter Endothelzellschaden beeinträchtigt die Offenheitsrate von Bypassgefäßen. Die minimal-invasive Operationsmethode soll neben einer schonenden Gefäßgewinnung eine reduzierte Frequenz von Wundheilungsstörungen bei einem kosmetisch verbesserten Ergebnis sowie verminderte postoperative Schmerzen nach der Venenentnahme ermöglichen. Diese Vorteile dürfen nicht zu Ungunsten der Bypassqualität bzw. eines verschlechterten Langzeitergebnis erzielt werden. Mittels lichtmikroskopischer Untersuchung von Venenproben konnten wir nachweisen, dass die minimal-invasive Entnahmetechnik mit dem SaphLITE-System zu keiner vermehrten Endothelschädigung gegenüber einer konventionellen Operationsmethode mit physiologischer Perfusion führt. Ursächlich hierfür erachten wir ein schonendes Vorgehen durch Verwedung von SaphLITE. Unsere Daten decken sich in hervorragender Weise mit Ergebnissen vorausgegangener Studien. Eine marginal verlängerte Entnahmezeit wirkt sich in der Gruppe mit der minimalinvasiven Technik nicht auf den gesamten Operationsablauf aus. Eine längere Lagerung der V. saphena magna in heparinisiertem Patientenblut bei Raumtemperatur nach Standardentnahme führt hingengen im Vergleich mit der zu einem nachweislich stärkeren Endothelschaden. Diese Praktik mit einer frühen Entnahme sollte demzufolge vermieden werden. In allen Gruppen kam es zu keinen Wundheilungsstörungen am Bein, die einer chirurgischen Intervention bedurften. Zusammengefasst bietet das SaphLITE System eine sichere Lösung zur minimal invasiven Venengewinnung zur coronaren Bypassversorgung an. Bei geringfügig verlängerten Prozedurzeiten konnte das System etwas überdurchschnittliche Protektionsergebnisse erzielen. Die Studie konnte keine SaphLITE-bedingten Komplikationen nachweisen. / 29 patients were included in 3 groups: open vein harvesting with (G1) and without (G2) storage and minimally invasive harvesting with the SaphLITE II. We have shown by microscopic examination that there was no tissue damage by the use of the SaphLITE while the storage of vein grafts did.

There is a clear need for improved methods (e.g. computer modelling, imaging) to characterize the substrate of abnormal rhythms like ventricular tachycardia (VT) developed by patients who have suffered a heart attack. Progress leading to improved disease management and treatment planning (based on predictive models) as well as outcomes assessment will have immediate impact on the quality of life in this large patient population. Prior to integration into clinical applications, the predictive models have to be properly validated using experimental techniques selected to reflect the electrophysiological phenomena at spatio-temporal scales similar to those considered in simulations. This thesis advanced us toward this goal by addressing the challenge of building more accurate models of electrophysiology for individual hearts. A novel construction of a realistic 3D cardiac model from Magnetic Resonance Images (MRI), with a long-term aim to predict propagation of the electrical impulse in normal and pathologic large hearts (translatable to human hearts), and associated inducibility of VT is described. To parameterize the model, an original evaluation method of electrophysiological (EP) characteristics of the heart tissue was used. The method combined state-of-the-art experimental physiology tools like optical fluorescence imaging using voltage-sensitive dyes and a CARTO electro-anatomical system, with a cardiac computer model generated from high resolution MR scans of explanted normal and pathologic porcine hearts. Several input model parameters (e.g., conductivity, anisotropy, restitution) were successfully adjusted using the ex-vivo measurements of action potential to yield close correspondence between model output and experiments. Moreover, a simple, fast, and macroscopic mathematical model was used with computation times less than 1h, attractive for clinical EP applications.

There is a clear need for improved methods (e.g. computer modelling, imaging) to characterize the substrate of abnormal rhythms like ventricular tachycardia (VT) developed by patients who have suffered a heart attack. Progress leading to improved disease management and treatment planning (based on predictive models) as well as outcomes assessment will have immediate impact on the quality of life in this large patient population. Prior to integration into clinical applications, the predictive models have to be properly validated using experimental techniques selected to reflect the electrophysiological phenomena at spatio-temporal scales similar to those considered in simulations. This thesis advanced us toward this goal by addressing the challenge of building more accurate models of electrophysiology for individual hearts. A novel construction of a realistic 3D cardiac model from Magnetic Resonance Images (MRI), with a long-term aim to predict propagation of the electrical impulse in normal and pathologic large hearts (translatable to human hearts), and associated inducibility of VT is described. To parameterize the model, an original evaluation method of electrophysiological (EP) characteristics of the heart tissue was used. The method combined state-of-the-art experimental physiology tools like optical fluorescence imaging using voltage-sensitive dyes and a CARTO electro-anatomical system, with a cardiac computer model generated from high resolution MR scans of explanted normal and pathologic porcine hearts. Several input model parameters (e.g., conductivity, anisotropy, restitution) were successfully adjusted using the ex-vivo measurements of action potential to yield close correspondence between model output and experiments. Moreover, a simple, fast, and macroscopic mathematical model was used with computation times less than 1h, attractive for clinical EP applications.

Cardiac hypertrophy is an adaptive response in which the heart grows to normalize output during times of increased demand. This increase in size originates from the growth of cardiomyocytes rather than cellular division. Many cellular modifications observed during hypertrophy are reminiscent of apoptosis; caspase proteases, traditionally known for their role in apoptosis, have recently been implicated in non-apoptotic settings including cardiac differentiation. Studies have reported caspase-3 inhibition limits the heart`s ability to undergo pathological hypertrophy in vivo. Data presented here indicate that inhibition of caspase-3 and caspase-8 minimizes hypertrophic growth in primary cardiomyocytes. Phenylephrine induced an increase in cell size, which was attenuated upon addition of caspase inhibitors. These data suggest these proteins may be involved in hypertrophic growth of cardiomyocytes. Furthermore, results suggest that increased caspase activity may not be directly responsible for this effect. Rather, subcellular localization of caspase proteases may contribute to the effects seen during hypertrophy.

Introduction: Cardiac hypertrophy is an adaptive response to increased myocardial workload that becomes maladaptive when hypertrophied hearts are exposed to an acute metabolic stress, such as ischemia/reperfusion. Acceleration of glycolysis occurs as part of the hypertrophic response and may be maladaptive because it enhances glycolytic metabolite accumulation and proton production. Activation of AMP-activated protein kinase (AMPK), a kinase involved in the regulation of energy metabolism, is proposed as a mechanism for the acceleration of glycolysis in hypertrophied hearts. However, this concept has not yet been proven conclusively. Additionally, several studies suggest that AMPK is involved in hypertrophic remodeling of the heart by influencing cardiac myocyte growth, a suggestion that remains controversial. Hypothesis: AMPK mediates hypertrophic remodeling in response to pressure overload. Specifically, AMPK activation is a cellular signal responsible for accelerated rates of glycolysis in hypertrophied hearts. Additionally, AMPK influences myocardial structural remodeling and gene expression by limiting hypertrophic growth. Experimental Approach: To test this hypothesis, H9c2 cells, derived from embryonic rat hearts, were treated with (1 µM) arginine vasopressin (AVP) to induce hypertrophy. Substrate utilization was measured and the effects of AMPK inhibition by either Compound C or by adenovirus-mediated transfer of dominant negative AMPK were determined. Subsequently, adenovirus-mediated transfer of constitutively active form of AMPK (CA-AMPK) was expressed in H9c2 to specifically increase AMPK activity and, thereby, further characterize the role of AMPK in hypertrophic remodeling. Results: AVP induced a metabolic profile in hypertrophied H9c2 cells similar to that in intact hypertrophied hearts. Glycolysis was accelerated and palmitate oxidation was reduced with no significant alteration in glucose oxidation. These changes were associated with AMPK activation, and inhibition of AMPK ameliorated but did not normalize the hypertrophy-associated increase in glycolysis. CA-AMPK stimulated both glycolysis and fatty acid oxidation, and also increased protein synthesis and content. Howver, CA-AMPK did not induce a pathological hypertrophic phenotype as assessed by atrial natriuretic peptide expression. Conclusion: Acceleration of glycolysis in AVP-treated hypertrophied heart muscle cells is partially dependent on AMPK. AMPK is a positive regulator of cell growth in these cells, but does not induce pathological hypertrophy when acting alone.