Explore chapters and articles related to this topic
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 heart can be described as a double pump that distributes blood to the entire body; one pump sends blood to the lungs and the other one feeds blood to the rest of the body. Each of the two cardiac pumps consists of two chambers: one atrium and one ventricle. Therefore, the heart, as a whole, consists of two atria and two ventricles, as shown schematically in Figure 2.2. For each pumping cycle or heartbeat, the heart fills with blood (diastole) through the atria and subsequently pushes the blood out of the ventricles (systole). The sequence of steps involved in a heartbeat is carefully orchestrated by the cardiac conduction system, which consists of the sinoatrial node (SA), the atrioventricular node (AV), the common bundle, the bundle branches, and the Purkinje fibers. The SA node is known as the physiological pacemaker of the heart because it is capable of self-firing – that is, it is capable of generating an action potential without receiving an external stimulus. Overall, the SA node-firing frequency is regulated by the central nervous system (CNS), which adapts the heart rate to various physiological factors such as the breathing rhythm [8].
Heart regeneration
Published in David M. Gardiner, Regenerative Engineering and Developmental Biology, 2017
The rapid heart rate, high blood pressure, and large cardiac output of the human heart (and endotherms in general) are possible to obtain because of specialized conductive tissue (the bundle of His and the Purkinje fibers) that ensures contraction of the heart in a controlled fashion. In endotherms, depolarization starts spontaneously in the sinoatrial node, the cardiac pacemaker region, and is propagated through the right atrium and through Bachmann’s bundle to the left atrium, thus stimulating the contraction of the atria. In the atrioventricular node, conduction is delayed, facilitating a delay in atrial versus ventricular contraction before depolarization continues in the right and left branches of the bundle of His in the interventricular septum. The bundle braches taper out into numerous Purkinje fibers that finally stimulate the myocardial cells of the ventricles to contract in an apex-to-base fashion to facilitate maximal pump efficiency. In ectotherms, such as zebrafish and salamander, there is no anatomical evidence of a specific cardiac conduction system; however, they have a similar contraction pattern as described earlier but with the marked difference that the ventricular myocardium is stimulated in a base-to-apex fashion. Recently, it was suggested that the building blocks of the conduction system are similar between endothermic and ectothermic vertebrates and that the differentiated conduction system of endothermic heart, in fact, represents the primordial trabeculated myocardium of the ectothermic heart. Thus, the compact myocardial tissue of the endothermic hearts was secondarily derived to increase force production. In that sense, the base-to-apex stimulation of the bundle of His actually precisely matches that of the hearts of ectotherms (for in-depth presentation of this hypothesis, see Jensen et al. 2012, 2013).
Neuromuscular Stimulation
Published in John G Webster, Minimally Invasive Medical Technology, 2016
When the atrioventricular node fails to conduct, heart block occurs because excitation in the atria fails to conduct to the ventricles. It is possible to pace the heart using transcutaneous pacing by passing 100 mA, 2 ms pulses through large electrodes on the chest, but undesired stimulation of the intercostal muscles causes great pain. The advent of miniature implantable pacemakers has revolutionized the treatment of heart block and many other cardiac rhythm disorders (Webster 1995).
Comparison of methods for delivering cardiac resynchronization therapy: electrical treatment targets and mechanisms of action
Published in Expert Review of Medical Devices, 2023
Florentina Simader, Ahran Arnold, Zachary Whinnett
Atrial fibrillation (AF) may contribute to or be the primary cause of heart failure. It may adversely impact cardiac function via the following mechanisms: (i) loss of the contribution of atrial contraction to ventricular filling; (ii) tachymyopathy: rapid conduction of AF to the ventricles may lead to long periods of a high ventricular rate, leading to ventricular impairment; (iii) irregularity in RR interval [25]. This third mechanism of irregularity of intervals between ventricular contractions is increasingly being recognized as a trigger for developing ventricular impairment. The trigger for this harmful effect is thought to be mediated by post-extra-systolic potentiation, which refers to an increase in contractility that is associated with Ca2+ overload [26]. Tachymyopathy and RR irregularity due to AF can be treated with pacemaker implantation combined with atrioventricular node ablation and, therefore, represent a further potential electrical treatment target for pacing therapy for heart failure.
How does new-onset left bundle branch block affect the outcomes of transcatheter aortic valve repair?
Published in Expert Review of Medical Devices, 2019
Guillem Muntané-Carol, Leonardo Guimaraes, Alfredo Nunes Ferreira-Neto, Jerôme Wintzer-Wehekind, Lucia Junquera, David del Val, Laurent Faroux, François Philippon, Josep Rodés-Cabau
The proximity of the conduction system (especially bundle of His and the left bundle branch) to the base of the non-coronary and right-coronary leaflets is the main explanation of the occurrence of new-onset LBBB after TAVR (Figures 1 and 2). The atrioventricular node (AVN) is located within the triangle of Koch, which is delineated by the tendon of Todaro, the orifice of the coronary sinus, and the insertion point of the tricuspid valve septal leaflet [13,14]. Afterwards, the AVN continues as the bundle of His, penetrating the membranous septum and passing to the left through the central fibrous body. The conduction system exits immediately under the membranous septum and is positioned superficially on the crest of the interventricular septum, where it gives rise to the left bundle branch, which is related to the base of the interleaflet triangle separating the noncoronary and right coronary leaflets. Of note, some anatomical variability has been reported and there are patients who may exhibit a more right or left-sided atrioventricular bundle [15]. Patients with a more left-sided atrioventricular bundle could be at a higher risk for conduction disturbances post-TAVR.
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.