The patient with acute cardiovascular problems
Peate Ian, Dutton Helen in Acute Nursing Care, 2020
The middle layer of the heart is the myocardium. This is the thickest layer of the heart and is responsible for providing muscular contraction so that blood can be ejected from the chambers that it surrounds. There is a layer of myocardium around the atria and the ventricles. The muscle fibres of the myocardium are laid end-to-end so that they can contract in a wave-like motion when stimulated. The myocardium requires a constant supply of oxygenated blood which is provided by the coronary arteries.
The Cardiovascular System
Pritam S. Sahota, James A. Popp, Jerry F. Hardisty, Chirukandath Gopinath, Page R. Bouchard in Toxicologic Pathology, 2018
The sinus node (sinoatrial node; SA), or pacemaker, is located subepicardially at the junction of the cranial vena cava and the right auricle. The electrical impulse from this pacemaker causes atrial depolarization and contraction, and this impulse travels through internodal bundles to the AV node that is located in the interatrial septum, cranial to the coronary sinus just beneath the septal leaflet of the tricuspid valve. The impulse is delayed in the AV node before traveling via the AV bundle (bundle of His) to the left and right bundle branches (cura) that descend on each side of the muscular ventricular septum, terminating in the Purkinje fibers which are highly specialized, modified myocardial cells that transmit the depolarizing impulse to the ventricular myocytes. An increased concentration of Purkinje fiberlike cells has been reported in the dog as a spontaneous and incidental lesion (Ainge and Clarke 2000). This spontaneous lesion must be differentiated from histiocytoid cardiomyopathy or hamartoma, which is a developmental abnormality of the conduction system (Ainge and Clarke 2000). The cardiac wall consists of three distinct layers, the epicardium or the outer most layer; the myocardium or the middle, thick muscular layer; and the endocardium, which is the innermost layer that is continuous with the tunica intima of the great vessels entering and leaving the heart. The epicardium, also known as visceral pericardium, is continuous with the parietal pericardium. The epicardium consists of a thin layer of mesothelium, rich with elastic fibers and connective tissue that merge with that of the myocardium. The subepicardial layer that is attached to the myocardium, contains a thin layer of fibrous connective tissue and adipose tissue as well as blood vessels, nerves, and lymphatics. The cavity between the visceral and parietal pericardium contains serous fluid that lubricates the surfaces and provides frictionless cardiac motion. The myocardium is composed of cardiac myocytes that are a specialized striated muscle, embedded in a well-vascularized, connective tissue framework with nerves. Thesemyocytes are arranged in an overlapping spiral pattern that is anchored to the cardiac skeleton. Ventricular cardiac myocytes are branching, cylindrically shaped structures that vary in size, ranging from 80–100μm long and 15–20μm wide (Somner and Johnson 1979; Van Vleet et al. 2002). The individual cardiac myocytes are joined intimately at the intercalated discs allowing them to function as a unit. The end-to-end connection by the intercalated disc creates a step-like appearance that is easily visible with scanning electron microscopy using myocyte preparations that have been separated via enzymatic digestion (Van Vleet et al. 2002). Individually, each myocyte consists of a single, centrally located nucleus, mitochondria, and contractile filaments, primarily actin and myosin (Ferrans and Thiedeman 1983). Each cardiac myocyte is limited by the sarcolemma, a structure formed by the plasma membrane or plasmalemma, and the external lamina. The plasmalemma is a trilaminar structure and is of approximately 99nm wide (Somner and Johnson 1979). The external lamina is composed of a laminar coat, basement membrane, basal lamina, and glycocalyx (Borg et al. 1996). The external lamina contains the typical basement collagen proteins (I and IV) and glycoproteins. A network of invaginations of the sarcolemma is called the T system, and T tubules extend from the free surface throughout the cells in a transverse direction (Van Vleet et al. 2002).
The myocardium
Swati Gupta, Alexandra Marsh, David Dunleavy, Kevin Channer in Cardiology and the Cardiovascular System on the move, 2015
Contents: composed of specialized striated muscle fibres and makes up the bulk of the heart. Function: the myocardium provides the coordinated contractile power to circulate blood. Layers: the myocardium has a smooth surface adjoining the pericardium and a trabeculated surface underlying the endocardium. It is capable of responding (remodelling) in reaction to altered demands, either physiological or pathological:Pressure hypertrophy (the LV has the thickest myocardium and the largest diameter fibres due to the higher pressures).Volume dilatation.Hibernation: myocardium demonstrates altered contractility in response to an insult such as acute myocardial ischaemia; however, this change is potentially reversible over time and with revascularization.
The effect of hydrogel injection on cardiac function and myocardial mechanics in a computational post-infarction model
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2013
Jeroen Kortsmit, Neil H. Davies, Renee Miller, Jesse R. Macadangdang, Peter Zilla, Thomas Franz
An emerging therapy to limit adverse heart remodelling following myocardial infarction (MI) is the injection of polymers into the infarcted left ventricle (LV). In the few numerical studies carried out in this field, the definition and distribution of the hydrogel in the infarcted myocardium were simplified. In this computational study, a more realistic biomaterial distribution was simulated after which the effect on cardiac function and mechanics was studied. A validated finite element heart model was used in which an antero-apical infarct was defined. Four infarct models were created representing different temporal phases in the progression of a MI. Hydrogel layers were simulated in the infarcted myocardium in each model. Biomechanical and functional improvement of the LV was found after hydrogel inclusion in the ischaemic models representing the early phases of MI. In contrast, only functional but no mechanical restitution was shown in the scar model due to hydrogel presence.
Perfusion studies of steady flow in poroelastic myocardium tissue
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2005
E. Y. K. Ng, D. N. Ghista, R. C. Jegathese
The behaviour of the heart has always elicited interest and particularly the study of its myocardium, as 5–10% of the blood pumped by the heart is passed through the coronary arteries to the myocardium itself. An in-depth investigation of the myocardium behaviour is useful. The present work aims to investigate how myocardium perfusion is influenced by myocardial stress and diseased states, and in general by LV pumping abnormalities. LV myocardial perfusion can then serve as a possible index of the capacity of the LV to respond to its work demand, and thus of the risk of heart failure. The poroelastic analysis of the myocardium based on finite element method (FEM) for regional perfusion through a rectangular element with various physiological ranges of loading conditions was studied.
Creating the bioartificial myocardium for cardiac repair: challenges and clinical targets
Published in Expert Review of Cardiovascular Therapy, 2013
Juan C Chachques, Manuel Monleon Pradas, Antoni Bayes-Genis, Carlos Semino
The association of stem cells with tissue-engineered scaffolds constitutes an attractive approach for the repair of myocardial tissue with positive effects to avoid ventricular chamber dilatation, which changes from a natural elliptical to spherical shape in heart failure patients. Biohybrid scaffolds using nanomaterials combined with stem cells emerge as new therapeutic tool for the creation of ‘bioartificial myocardium’ and ‘cardiac wrap bioprostheses’ for myocardial regeneration and ventricular support. Biohybrids are created introducing stem cells and self-assembling peptide nanofibers inside a porous elastomeric membrane, forming cell niches. Our studies lead to the creation of semi-degradable ‘ventricular support bioprostheses’ for adaptative LV and/or RV wrapping, designed with the concept of ‘helical myocardial bands’. The goal is to restore LV elliptical shape, and contribute to systolic contraction and diastolic filling (suction mechanism). Cardiac wrapping with ventricular bioprostheses may reduce the risk of heart failure progression and the indication for heart transplantation.