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Noninvasive Diagnosis Using Sounds Originating from within the Body
Published in Robert B. Northrop, Non-Invasive Instrumentation and Measurement in Medical Diagnosis, 2017
Another cardiac defect that can be diagnosed by hearing the S2 sound “split” is a left or right bundle branch block. The synchronization of the contraction of the muscle of the left and right ventricles is accomplished by the wave of electrical depolarization that propagates from the AV node, down the bundle of His, which bifurcates into the left and right bundle branches which run down on each side of the ventricular septum. Near the apex of the heart, the bundle branches branch extensively into the Purkinje fibers which invade the inner ventricular cardiac muscle syncytium, carrying the electrical activity that triggers ventricular contraction. See Figure 3.7 for a schematic, cut-away view of the heart, and Figure 3.8 for a time-domain schematic of where certain heart sounds occur in the cardiac cycle.
Electrophysiological Amplifier
Published in Mesut Sahin, Howard Fidel, Raquel Perez-Castillejos, Instrumentation Handbook for Biomedical Engineers, 2020
Mesut Sahin, Howard Fidel, Raquel Perez-Castillejos
The contraction of the heart starts with the firing of the SA node, which produces an action potential that spreads across the atria (also known as auricles) and into the AV node. The atria contract upon receiving the trigger signal from the SA node and push the blood into the ventricles through the cardiac valves. Then the AV node fires a pulse into the common bundle, the bundle branches, and ultimately, the Purkinje fibers that cause the contraction of the ventricles and the delivery of the blood outside of the heart into the bodily organs [9]. Cells in each one of the components of the cardiac conduction system fire at a different time and produce an action potential with a distinctive shape or signature (Figure 2.2). The waveform that we are used to seeing in ECGs is the combination of the action potentials produced by each one of the cells in the heart. The cardiac conduction system, despite its key role in the function of the heart, contributes only a small portion of the volume and the cells of the entire heart. By comparison, the muscle cells in the atria and the ventricles are much more numerous than the cells in the conduction system and as a result, the main factor for the recorded ECG signal is the firing of the muscle cells in atria and ventricles. The P wave in the ECG corresponds to the depolarization of the atria. The QRS complex, a component of the ECG waveform, arises from the depolarization of the ventricles; the repolarization of the atria also occurs during the time of the QRS complex, but the atrial signal is much weaker than that produced by the ventricles. The T wave is the result of the repolarization of the ventricles. Finally, the U waves are related to the repolarization of the Purkinje fibers although these waves are frequently not visible in ECGs. The ECG feature resulting from combining waves P through U is commonly referred to as electrical systole whereas the rest of the ECG between one U wave and the following P wave is known as electrical diastole.
Mechanotransduction of Cardiovascular Development and Regeneration
Published in Juhyun Lee, Sharon Gerecht, Hanjoong Jo, Tzung Hsiai, Modern Mechanobiology, 2021
Quinton Smith, Justin Lowenthal, Sharon Gerecht
A small and specific subpopulation of cardiomyocytes of the myocardium, termed “pacemaker cells,” has the ability to generate action potentials locally in the sinoatrial [30]. Once initiated this depolarization signal is propagated, traveling down the atrium, to the AV node, where it is able to pass into the bundle of His and finally into the subendocardium via a specialized collection of conducting tissue called the “Purkinje fibers.” The Purkinje fibers are essential to heart conduction, maintaining a consistent rhythm, as they are able to conduct cardiac action potentials more efficiently and faster than their smaller cardiomyocyte counterparts [31]. This is due to their unique structural organization. In comparison to cardiomyocytes, Purkinje fibers have a larger number of mitochondria and fewer myofibrils. Electrocardiography serves as a medical tool to monitor patterns in heart conduction and can be broken down into four distinct phases: the P wave, representing atrial depolarization; a QRS complex, which is characteristic of ventricular depolarization; the T wave, which shows ventricular repolarization; and finally the U wave, a pattern that denotes papillary muscle (ventricle muscles) repolarization [21, 31]. Diastolic and systolic cycles act in concert for blood perfusion. The left and right atria of the heart are filled by veins in the first stage of diastole, while the left and right ventricles are relaxed. In the second stage, contraction of the right and left atria by the myocardium results in the pumping of blood into the right and left ventricles via the AV valves. In the first stage of systole, both ventricles contract simultaneously, pushing blood, where pulmonary arteries are fed by the right ventricle, while the aorta is fed by the left ventricle. Systolic and diastolic blood pressure are measured from the second stage of the systole and the diastole, or the pressure of the heart at rest. Normal systolic and diastolic pressure ranges are between 80–120 and 60–80, respectively [32].
Predicting the cardiac toxicity of drugs using a novel multiscale exposure–response simulator
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2018
Francisco Sahli Costabal, Jiang Yao, Ellen Kuhl
Our baseline excitation profile of the left and right ventricles in Figure 5 agrees well with the excitation sequence in healthy human hearts. Critical to this sequence is the Purkinje fiber network that quickly and reliably transmits the signal from the atrioventricular node down to the apex of the heart to excite the heart from the bottom up (Sahli Costabal et al. 2016). There is a general agreement that, within the healthy activation sequence, the posterior basal region of the right ventricle is the last region to activate (Durrer et al. 1970), which agrees well with our predicted excitation profile at 60 ms. The timing of repolarization and depolarization also agree well with those of healthy human hearts, where complete the activation takes between 62 and 80 ms (Durrer et al. 1970), compared to 72 ms in our model.
Spatiotemporal regularization for inverse ECG modeling
Published in IISE Transactions on Healthcare Systems Engineering, 2020
Cardiac electrical signal is initiated by the sinoatrial (SA) node, i.e. the pacemaker of the heart, and then propagates through the right and left atria toward the atrioventricular node (AVN). The electric impulse further travels through the bundle of His and Purkinje fibers, and enter the left and right ventricles, which completes the cardiac cycle. As shown in Figure 2, the forward ECG problem denotes the prediction of electric potentials on the body surface based on the excitation and propagation of space-time electrodynamics in the heart. The objective of the inverse ECG problem is to estimate cardiac electrical sources from electrical signals (e.g. BSPMs) measured on the body surface.