The heart
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella in Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
The specialized excitation and electrical conduction system in the heart consists of: Sinoatrial nodeInteratrial pathwayInternodal pathwayAtrioventricular nodeBundle of HisBundle branchesPurkinje fibers
Cardiovascular changes with aging
Wilbert S. Aronow, Jerome L. Fleg, Michael W. Rich in Tresch and Aronow’s Cardiovascular Disease in the Elderly, 2019
The cardiac conduction system undergoes multiple changes with age that affect its electrical properties and, when exaggerated, cause clinical disease. A generalized increase in elastic and collagenous tissue commonly occurs. Fat accumulates around the sinoatrial node, sometimes creating partial or complete separation of the node from the atrial tissue. In extreme cases, this may contribute to the development of sick sinus syndrome. A pronounced decline in the number of pacemaker cells generally occurs after age 60; by age 75, less than 10% of the number seen in young adults remain. A variable degree of calcification of the left side of the cardiac skeleton, which includes the aortic and mitral annuli, the central fibrous body, and the summit of the interventricular system, is observed. Because of their proximity to these structures, the atrioventricular (AV) node, AV bifurcation, and proximal left and right bundle branches may be damaged or destroyed by this process, resulting in AV or intraventricular block.
Bradycardia
Andrea Natale, Oussama M. Wazni, Kalyanam Shivkumar, Francis E. Marchlinski in Handbook of Cardiac Electrophysiology, 2020
Bradyarrhythmias and conduction blocks are common electrocardiographic findings. These arrhythmias can result from a wide variety of disorders of the cardiac conduction system. Bradycardias are generally divided into disorders involving either the sinus node or atrioventricular conduction or as neurally mediated arrhythmias. Bradyarrhythmias may be discovered as incidental electrocardiographic abnormalities or may be found after investigation for symptoms suggestive of their presence. A wide variety of symptoms may be caused by the different etiologies of bradycardia, often times adding diagnostic difficulty to patients with coexisting medical problems.
Correlation between HCN4 gene polymorphisms and lone atrial fibrillation risk
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2019
Xiao-Hong Li, Ya-Min Hu, Guang-Li Yin, Ping Wu
Relevant studies have indicated that atrial remodelling is the main pathogenesis for AF. Atrial remodelling includes atrial electrical remodelling (AER), systolic function reconstruction and atrial structural remodelling. Close association is observed between AF and AER [9]. A part of researches show that AER is caused by AF [10,11], while, other studies suggest that AER is the reason for AF onset [12,13]. Another view regards that AF develops secondary to sustaining atrial structural and electrical remodelling which is induced by AF itself [9]. Multiple theories have been proposed to explain the pathogenesis of AF. Sinoatrial node (SA node) of the heart generates the impulse, thereby, could regulate the electrical conduction system of the heart. Potential changes of SA node cells might lead to the abnormal impulse, finally result in arrhythmia including AF.
A case of ventricular standstill in a patient with acute gastrointestinal bleeding
Published in Journal of Community Hospital Internal Medicine Perspectives, 2020
Htun Latt, Kyaw Kyaw, Nay Min Tun, Thwe Thwe Tun, Sammy San Myint Aung, Htwe Htwe Yin
Characterized by absence of ventricular activity or contraction, ventricular standstill is the result of the lack of impulse formation in ventricles (absence of idioventricular automaticity) or failure of impulse transmission to ventricles (conduction disturbance) [1]. It may happen in different age groups from a toddler to an octogenarian [3]. With intact cardiac conduction system, idioventricular pacemakers (slower rate) are suppressed by supraventricular pacemakers (faster rate), mainly the sinoatrial pacemaker. This phenomenon is termed ‘overdrive suppression’ [1,4]. Abnormally prolonged ventricular standstill can be caused by exaggerated overdrive suppression, which happens when the factors promoting overdrive suppression are enhanced or those decreasing overdrive suppression are inhibited. Sander-Jensen et al. reported that bradycardia may occur in acute hemorrhage and is mediated by increased vagal cholinergic tone [5]. Sometimes, increased vagal tone is so strong that it can block not only the AV node, but also the ventricular automaticity [6]. The finding of vagally mediated reflex bradycardia in the setting of hypotensive hemorrhage was proven in animal studies as well [7].
A meta-analysis of the relationship between anatomical variations of pulmonary veins and atrial fibrillation
Published in Acta Cardiologica, 2020
Isaac Cheruiyot, Jeremiah Munguti, Beda Olabu, Peter Gichangi
To the best of our knowledge, this is the first meta-analysis detailing the relationship between anatomical variations of the PV and AF. The results of the current study demonstrate that the presence of an accessory RMPV, as well as an increase in ostial diameters of the LCO, RSPV, LSPV, RIPV and LIPV, is significantly associated with AF. The arrhythmogenicity of the PV has been attributed to the presence of atrial myocardium in its tunica media [5,7] a feature first described by Nathan and Eliakim [23]. These striated muscles contain the pacemaker (‘P’) and Purkinje cells, similar to those native to cardiac conduction system [24,25]. These findings are supported by the fact that cells of the developing cardiac conduction system can be found in the PV prior to birth [26]. Spontaneous depolarisation of these cells is thought to result in the production of ectopic electrical impulses that disrupt the normal atrial sinus rhythm, hence the genesis of AF [27].
Related Knowledge Centers
- Bundle of His
- Cardiac Pacemaker
- Muscle Contraction
- Atrium
- Atrioventricular Node
- Circulatory System
- Heart
- Cardiac Muscle
- Cardiac Action Potential
- Sinoatrial Node
- Bundle of His