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Assessing and responding to sudden deterioration in the adult
Published in Nicola Neale, Joanne Sale, Developing Practical Nursing Skills, 2022
Electrical impulses precede cardiac muscle (myocardium) contraction, so this electrical impulse is captured and recorded in an ECG. Waveforms vary in different leads placed on the person’s body, and the ECG records the conduction of electrical impulses through the heart from different points. Think of taking a picture with a camera and obtaining a 360° view of the person’s heart from various positions around their bed. For more detail about the physiology underpinning ECGs and their interpretation, refer to your physiology textbook and specialist cardiology books (e.g. Iaizzo 2015). This section focuses on the practice of recording an ECG; Box 14.51 provides key practice points for recording ECGs.
Functional Neurology
Published in James Crossley, Functional Exercise and Rehabilitation, 2021
To create movement, a single electrical impulse passes through the motor nerve, referred to as an action potential. A single action potential stimulates a ‘twitch response’, a single muscle contraction in the muscle fibers it innervates. A single twitch response is not enough to generate sufficient force for movement, so increased effort, referred to as ‘neural drive’, is required to trigger a greater frequency of action potentials and more twitch responses. With increasing neural drive, twitch responses start to aggregate and superimpose, producing ever-increasing levels of force. This process is known as summation.
Critical care, neurology and analgesia
Published in Evelyne Jacqz-Aigrain, Imti Choonara, Paediatric Clinical Pharmacology, 2021
Evelyne Jacqz-Aigrain, Imti Choonara
In most mammalian muscles, each muscle fibre has a single area of contact with the axon of the motor neurone that supplies it. This specialised structure is the neuromuscular junction, which facilitates transmission of the electrical impulse from the nerve terminal to the motor end plate of the muscle. This is achieved by the transmission of acetylcholine molecules across the 60–100 nanometre synaptic cleft. Acetylcholine binds to receptors on the motor end plate, causing depolarisation and contraction of the muscle fibre. After acetylcholine dissociates from the receptor, it is degraded by acetylcholinesterase into acetate and choline, which is reabsorbed into the nerve terminal for recycling into further acetylcholine [1].
Relationship between P-wave duration and the risk of atrial fibrillation
Published in Expert Review of Cardiovascular Therapy, 2018
Krupal J. Hari, Thong P. Nguyen, Elsayed Z. Soliman
The right and left atrium are composed of overlapping myocytes in the form of myocardial fibers that come together and create the atrial walls [8]. Within the right atrium resides the sinus node, a specialized cardiomyocyte aggregate and the primary electrical impulse generator of the heart. As the current is generated, it travels in a nonuniform anisotropic fashion depolarizing the right and left atria [9]. The left atrium is relatively irregular in its arrangement of myocytes compared to the right; however, the myocytes of both chambers run parallel to the atrioventricular grooves. The organization of myocytes in a parallel arrangement helps facilitate conduction of electrical currents in a uniform fashion [10]. Multiple organized bundles of myocytes help allow for depolarization of the atria, with the Bachmann’s bundle considered the most important of the inter-atrial connections [9,11,12]. The atrial current ultimately reaches the atrioventricular node, a slower conducting specialized cardiomyocyte aggregate just above the ventricles [9].
Optimal site selection and image fusion guidance technology to facilitate cardiac resynchronization therapy
Published in Expert Review of Medical Devices, 2018
Benjamin J. Sieniewicz, Justin Gould, Bradley Porter, Baldeep S Sidhu, Jonathan M Behar, Simon Claridge, Steve Niederer, Christopher A. Rinaldi
Scar prevents effective transmission of the electrical impulse, resulting in prolonged activation. Electrical activation in regions of fibrosis is characterized by localized delays and fractionated, low-amplitude extracellular electrograms [49]. This has been attributed to changes in patterns of excitation and conduction due to altered ion channel activity [50] and decreased cellular connectivity [51] compounded by tortuous conduction through areas of surviving myocytes. This delay in LV activation results in less hemodynamic improvement during BiV pacing [52]. Electrical stimulation in regions of scar can also be pro-arrhythmic [53,54] and is associated with increased morbidity and mortality [8,55]. Unsurprisingly, the presence of myocardial scar at the site of LV stimulation during CRT is associated with non-response [8,56].
A model of lipid rearrangements during pore formation in the DPPC lipid bilayer
Published in Journal of Liposome Research, 2018
This assumption seems appropriate for the proposed model as our theoretical considerations focus on the reversible pore created during EP, i.e. the membrane spontaneously returns to its initial pre-EP pore-free state after removal of the external electric field. This can be observed in the experimental work carried out on the model lipid bilayers assembled in vitro (e.g. Black Lipid Membranes or liposomes) (Portet et al.2009), which are being widely used in electroporation research. In a few cases this assumption may not hold true, for instance as previously mentioned when the external electrical field is applied with specially selected parameter values (intensity or exposure duration). During the electroporation process in the giant unilamellar vesicle (GUV) formed from the DOPC lipids with the electrical field intensity from 235 to 360 V/cm lasting for 5 ms, some lipid molecules are pulled away from the lipid bilayer, outside the GUV (Portet et al.2009). With every electrical impulse, a portion of the lipid molecules is removed. However, no such effects were observed for the DPPC GUV treated with the electric field pulses of 6 × 105 V/m intensity and lasting 300 μs (Dimova et al.2007).