Materiały źródłowe

• #1 Sinus bradycardia – UpToDate

  https://www.uptodate.com/contents/sinus-bradycardia

  Sinus bradycardia is a rhythm in which the rate of impulses arising from the sinoatrial (SA) node is lower than expected. […] The heart rate reflects a complex interplay between the sympathetic and parasympathetic nervous systems. It is affected by numerous factors, including age and physical conditioning. […] Primary sinus node dysfunction (ie, sinus node dysfunction) is discussed in detail separately. […] By conventional definition, bradycardia indicates a heart rate less than 60 beats per minute with a normal P wave vector on the surface ECG. As such, sinus bradycardia is typically thought of as sinus rhythm occurring at a rate of less than 60 beats per minute, although one professional society has advocated a rate of less than 50 beats per minute. […] A rate less than 50 beats per minute may be a more pragmatic definition, as most patients with sinus rates in the 50s are asymptomatic. It is important to note that the rate at which a patient is labeled as having bradycardia is somewhat age dependent.

• #2 Bradycardia – Wikipedia

  https://en.wikipedia.org/wiki/Bradycardia

  Bradycardia, also called bradyarrhythmia, is a resting heart rate under 60 beats per minute (BPM). While bradycardia can result from various pathological processes, it is commonly a physiological response to cardiovascular conditioning or due to asymptomatic type 1 atrioventricular block. […] Bradycardia may be associated with symptoms of fatigue, dyspnea, dizziness, confusion, and syncope due to reduced blood flow to the brain. The types of symptoms often depend on the etiology of the slow heart rate, classified by the anatomical location of a dysfunction within the cardiac conduction system. Generally, these classifications involve the broad categories of sinus node dysfunction, atrioventricular block, and other conduction tissue diseases. […] However, bradycardia can also result without dysfunction of the conduction system, arising secondarily to medications, including beta blockers, calcium channel blockers, antiarrythmics, and other cholinergic drugs. Excess vagus nerve activity or carotid sinus hypersensitivity are neurological causes of transient symptomatic bradycardia. Hypothyroidism and metabolic derangements are other common extrinsic causes of bradycardia.

• #3 Bradycardia – Wikipedia

  https://en.wikipedia.org/wiki/Bradycardia

  Bradycardia arrhythmia may have many causes, both cardiac and non-cardiac. Non-cardiac causes are usually secondary and can involve recreational drug use or abuse, metabolic or endocrine issues, especially hypothyroidism, an electrolyte imbalance, neurological factors, autonomic reflexes, situational factors, such as prolonged bed rest, and autoimmunity. […] Cardiac causes include acute or chronic ischemic heart disease, vascular heart disease, valvular heart disease, or degenerative primary electrical disease. Ultimately, the causes act by three mechanisms: depressed automaticity of the heart, conduction block, or escape pacemakers and rhythms. […] In general, two types of problems result in bradycardias: disorders of the SA node and disorders of the AV node. […] With SA node dysfunction (sometimes called sick sinus syndrome), there may be disordered automaticity or impaired conduction of the impulse from the SA node into the surrounding atrial tissue (an „exit block”). […] AV conduction disturbances (AV block; primary AV block, secondary type I AV block, secondary type II AV block, tertiary AV block) may result from impaired conduction in the AV node or anywhere below it, such as in the bundle of His.

• #4 Bradycardia | Diagnosis & Disease Information – The Cardiology Advisor

  https://www.thecardiologyadvisor.com/ddi/bradycardia/

  Bradycardia is a type of arrhythmia characterized by a reduced resting heart rate below 50 to 60 beats per minute (bpm).1 At the electrophysiologic level, bradycardia is the result of sinus node dysfunction (SND), atrioventricular (AV) block, or conduction disorders.1 […] Sinus node dysfunction (also known as sick sinus syndrome) refers to disorders of the sinoatrial (SA) node that cause abnormal electricity conduction and propagation due to intrinsic or extrinsic disease.3 Most SND is related to age-dependent fibrosis of the sinus nodal tissue and surrounding atrial tissue.1 […] Atrioventricular block (also referred to as heart block) results from interference with electrical conduction and propagation from the atria to the ventricles.4 Atrioventricular block may cause partial or complete cessation of electrical signaling. The severity of AV block ranges from mild to severe and is categorized as follows4-6:

• #5 Sinus Bradycardia: Background, Pathophysiology, Etiology

  https://emedicine.medscape.com/article/760220-overview

  The pathophysiology of sinus bradycardia is dependent on the underlying cause. […] Other causes of sinus bradycardia are related to increased vagal tone. […] Pathologic causes include, but are not limited to, inferior wall myocardial infarction, toxic or environmental exposure, electrolyte disorders, infection, sleep apnea, drug effects, hypoglycemia, hypothyroidism, and increased intracranial pressure. […] Sinus bradycardia may also be caused by the sick sinus syndrome, which involves a dysfunction in the ability of the sinus node to generate or transmit an action potential to the atria. […] Sick sinus syndrome includes a variety of disorders and pathologic processes that are grouped within one loosely defined clinical syndrome. […] The syndrome includes signs and symptoms related to cerebral hypoperfusion in association with sinus bradycardia, sinus arrest, sinoatrial (SA) block, carotid hypersensitivity, or alternating episodes of bradycardia and tachycardia.

• #6 Bradycardia pathophysiology – wikidoc

  https://www.wikidoc.org/index.php/Bradycardia_pathophysiology

  Osoby z obturacyjnym bezdechem sennym również mają bradykardię zatokową, która może być ekstremalna (30 uderzeń na minutę) podczas apne. […] Odpowiedzi wazowagalne mogą być związane z ciężką bradykardią z powodu zwiększonego zaangażowania przywspółczulnego i tłumienia współczulnego węzła SA. […] Zwiększone ciśnienie wewnątrzczaszkowe powinno być wykluczone, gdy bradykardia zatokowa pojawia się u pacjenta z dysfunkcją neurologiczną. […] Czynnikami zakaźnymi związanymi z względną bradykardią zatokową są choroby zakaźne, takie jak borelioza, choroba Chagasa, legionella, psittakoza, gorączka Q, dur brzuszny, tyfus, babeszjoza, malaria, leptospiroza, żółta febra, gorączka denga, wirusowe gorączki krwotoczne, włośnica i gorączka plamista gór Skalistych. […] Na mikroskopowej analizie histopatologicznej, u niektórych pacjentów z bradykardią zatokową mogą nie występować zmiany histopatologiczne w węźle, jednak niektóre mikroskopowe wyniki są związane z tym stanem, w tym: redukcja komórek węzłowych, komórki węzłowe i włóknienie, amyloidoza w regionie węzłowym, hipoplazja węzła zatokowego.

• #7 Sinus Bradycardia: Background, Pathophysiology, Etiology

  https://emedicine.medscape.com/article/760220-overview

  SA block occurs when the SA node fails to excite the atria uniformly. […] SA block may be associated with abnormal intrinsic nodal function, a failure of the SA junction, or a failure of propagation in the surrounding tissue. […] The 3 forms of SA block are first-, second-, and third-degree block. […] First-degree SA block is characterized by a delay in the propagation of the action potential from the SA node to the atria. […] In third-degree, or complete, SA block, the surface ECG is identical to that of sinus arrest, with absent P waves. […] Second-degree SA block is characterized by an occasional dropped P wave, reflecting the inability of the SA node to consistently transmit an action potential to the surrounding myocardium.

• #8 Bradycardia | Diagnosis & Disease Information – The Cardiology Advisor

  https://www.thecardiologyadvisor.com/ddi/bradycardia/

  Bradycardia is a type of arrhythmia characterized by a reduced resting heart rate below 50 to 60 beats per minute (bpm).1 At the electrophysiologic level, bradycardia is the result of sinus node dysfunction (SND), atrioventricular (AV) block, or conduction disorders.1 […] Sinus node dysfunction (also known as sick sinus syndrome) refers to disorders of the sinoatrial (SA) node that cause abnormal electricity conduction and propagation due to intrinsic or extrinsic disease.3 Most SND is related to age-dependent fibrosis of the sinus nodal tissue and surrounding atrial tissue.1 […] Atrioventricular block (also referred to as heart block) results from interference with electrical conduction and propagation from the atria to the ventricles.4 Atrioventricular block may cause partial or complete cessation of electrical signaling. The severity of AV block ranges from mild to severe and is categorized as follows4-6:

• #9 Bradycardia | Diagnosis & Disease Information – The Cardiology Advisor

  https://www.thecardiologyadvisor.com/ddi/bradycardia/

  Conduction disorders result from issues with the conduction system outside the SA or AV node.1 Conduction disorders include the following1: […] Most bradycardia develops in the setting of cardiac tissue damage. […] The prognosis for bradycardia varies based on the underlying cause and individual patient characteristics.7 […] Early diagnosis of symptomatic bradycardia and prompt initiation of treatment are critical to prevent serious complications and death, especially in patients with severe medical comorbidities. 7 […] Management options for bradycardia depend on individual patient characteristics, the severity of symptoms, and the type of bradycardia.1,11 […] Permanent pacing is recommended for all symptomatic patients with bradycardia attributable to AV block, regardless of type.1 […] Conduction disorders are typically managed with permanent pacing.1 According to the ACC/AHA/HRS guidelines, permanent pacing is recommended for patients with syncope, bundle branch block, and those at high risk for AV block.

• #10 Sinus bradycardia – UpToDate

  https://www.uptodate.com/contents/sinus-bradycardia

  Sinus bradycardia is a rhythm in which the rate of impulses arising from the sinoatrial (SA) node is lower than expected. […] The heart rate reflects a complex interplay between the sympathetic and parasympathetic nervous systems. It is affected by numerous factors, including age and physical conditioning. […] Primary sinus node dysfunction (ie, sinus node dysfunction) is discussed in detail separately. […] By conventional definition, bradycardia indicates a heart rate less than 60 beats per minute with a normal P wave vector on the surface ECG. As such, sinus bradycardia is typically thought of as sinus rhythm occurring at a rate of less than 60 beats per minute, although one professional society has advocated a rate of less than 50 beats per minute. […] A rate less than 50 beats per minute may be a more pragmatic definition, as most patients with sinus rates in the 50s are asymptomatic. It is important to note that the rate at which a patient is labeled as having bradycardia is somewhat age dependent.

• #11 A Mechanism of Reflexogenic Bradycardia produced by Cardiac Glycosides | Nature

  https://www.nature.com/articles/1981208b0

  IT has been accepted that the vagal factor is one of the most important factors concerning the production of bradycardia by cardiac glycosides. […] However, the bradycardia produced by cardiac glycosides was not prevented completely by bilateral vagotomy or previous administration of atropine. […] Gold et al. called the latter factor the extravagal factor, which was considered to be a direct action of cardiac glycosides on the heart. […] On the other hand, cardiac glycosides did not exert a definite negative chronotropic action on the isolated mammalian heart.

• #12 Bradycardia pathophysiology – wikidoc

  https://www.wikidoc.org/index.php/Bradycardia_pathophysiology

  Osoby z obturacyjnym bezdechem sennym również mają bradykardię zatokową, która może być ekstremalna (30 uderzeń na minutę) podczas apne. […] Odpowiedzi wazowagalne mogą być związane z ciężką bradykardią z powodu zwiększonego zaangażowania przywspółczulnego i tłumienia współczulnego węzła SA. […] Zwiększone ciśnienie wewnątrzczaszkowe powinno być wykluczone, gdy bradykardia zatokowa pojawia się u pacjenta z dysfunkcją neurologiczną. […] Czynnikami zakaźnymi związanymi z względną bradykardią zatokową są choroby zakaźne, takie jak borelioza, choroba Chagasa, legionella, psittakoza, gorączka Q, dur brzuszny, tyfus, babeszjoza, malaria, leptospiroza, żółta febra, gorączka denga, wirusowe gorączki krwotoczne, włośnica i gorączka plamista gór Skalistych. […] Na mikroskopowej analizie histopatologicznej, u niektórych pacjentów z bradykardią zatokową mogą nie występować zmiany histopatologiczne w węźle, jednak niektóre mikroskopowe wyniki są związane z tym stanem, w tym: redukcja komórek węzłowych, komórki węzłowe i włóknienie, amyloidoza w regionie węzłowym, hipoplazja węzła zatokowego.

• #13 Reflex bradycardia: Causes, symptoms, treatments, and more

  https://www.medicalnewstoday.com/articles/reflex-bradycardia

  Reflex bradycardia is a reflexive response from the autonomic nervous system that causes the heart rate to slow. Triggers may include submerging in cold water or physical pressure on certain body parts. […] Slowing down the heart rate may be the body’s way of trying to maintain balance. The autonomic nervous system is responsible for involuntary bodily processes such as heart rate, blood pressure, and breathing. […] Reflex bradycardia is when a certain stimulus triggers the heart rate to slow down, which can help the body maintain homeostasis. […] It occurs in response to stimuli that cause the parasympathetic nervous system (PSNS) to become more active. The PSNS is responsible for calming the body down. […] The main reasons for reflex bradycardia are to conserve energy and balance other changes happening within the body, such as a rise in blood pressure.

• #14 CV Physiology | Regulation of Pacemaker Activity

  https://cvphysiology.com/arrhythmias/a005

  Autonomic control of SA nodeThe SA node displays intrinsic automaticity (spontaneous pacemaker activity) at a rate of 100-110 action potentials (beats) per minute. […] Hyperkalemia induces bradycardia or can even stop SA nodal firing. […] Cellular hypoxia (usually because of ischemia) depolarizes the membrane potential, causing bradycardia. […] Various drugs used as antiarrhythmics also influence the SA nodal rhythm. Calcium-channel blockers, for example, cause bradycardia by inhibiting the slow inward Ca++ currents during phase 4 and phase 0. […] Digoxin causes bradycardia by increasing parasympathetic (vagal) activity on the SA node; however, at toxic concentrations, digitalis increases automaticity and therefore can cause tachyarrhythmias.

• #15 Reflex bradycardia: Causes, symptoms, treatments, and more

  https://www.medicalnewstoday.com/articles/reflex-bradycardia

  Reflex bradycardia is a reflexive response from the autonomic nervous system that causes the heart rate to slow. Triggers may include submerging in cold water or physical pressure on certain body parts. […] Slowing down the heart rate may be the body’s way of trying to maintain balance. The autonomic nervous system is responsible for involuntary bodily processes such as heart rate, blood pressure, and breathing. […] Reflex bradycardia is when a certain stimulus triggers the heart rate to slow down, which can help the body maintain homeostasis. […] It occurs in response to stimuli that cause the parasympathetic nervous system (PSNS) to become more active. The PSNS is responsible for calming the body down. […] The main reasons for reflex bradycardia are to conserve energy and balance other changes happening within the body, such as a rise in blood pressure.

• #16 Reflex bradycardia: Causes, symptoms, treatments, and more

  https://www.medicalnewstoday.com/articles/reflex-bradycardia

  Elevations in intracranial pressure in the skull can cause the body to produce a response called the Cushing reflex. This can, in turn, lead to bradycardia. The exact mechanism for how it leads to bradycardia is unclear. […] Exerting pressure on certain places of the body, especially where major blood vessels or nerves responsible for regulating heart rate are, can cause reflex bradycardia. […] Emotional responses, such as fear and panic, can activate the PSNS. This process may activate the vagus nerve and cause reflex bradycardia in an attempt to regulate the body’s response to stress. […] It can also lead to constriction of blood vessels in the peripheral parts of the body. Experts believe bradycardia occurs in this situation to put less pressure on the heart and limit oxygen use in the body. […] When a doctor identifies the cause of the reflex bradycardia, they may treat the condition by removing the stimulus or helping a person adjust to avoid triggering episodes.

• #17 Reflex bradycardia – Knowledge and References – Taylor & Francis

  https://taylorandfrancis.com/knowledge/Medicine_and_healthcare/Cardiology/Reflex_bradycardia/

  Reflex bradycardia is a temporary decrease in heart rate that occurs in response to stimulation of the baroreflex, which is triggered by changes in blood pressure. […] Reflex bradycardia accompanying rises in arterial pressure has traditionally been considered the result of the stimulation of a restricted reflexogenic area (Heymans and Neil, 1958). More recently, it became appreciated (Sagawa, 1983) that multiple baroreceptors send neural signals to various levels of the central nervous system and through multiple-efferent pathways to a variety of effector organs. […] Activation of the sympathetic nervous system, with reflex vasoconstriction and tachycardia, is a major compensatory adjustment during many hypotensive states. In addition, the sudden withdrawal of sympathetic drive can be a primary cause of acute, episodic hypotension with reflex bradycardia and peripheral vasodilation, which are seemingly paradoxical autonomic responses in the setting of hypotension. […] β-blocking agents, as expected, block the β-receptor activity of epinephrine, resulting in unopposed α-receptor activity. This may result in severe hypertension and reflex bradycardia. […] The increase in blood pressure may cause reflex bradycardia.

• #18 Bradycardia in Spinal Cord Injury | Spinal Cord Injury Bradycardia

  https://www.radcliffecardiology.com/articles/cardiac-bradyarrhythmias-patient-cervical-spine-injury?language_content_entity=en

  The interaction between the heart and the brain has been well established. A tragic example is the frequently seen symptomatic bradycardia following cervical spinal cord injury (CSCI). […] Severe bradycardia and hypotension as a complication of acute CSCI are common as a result of post-injury imbalance in the autonomic nervous system caused by dissociation of spinal cardiac and vasomotor sympathetic fibers, while the parasympathetic fibers that travel with vagus nerve remain intact. […] There is experimental evidence suggesting two mechanisms by which these patients may develop bradycardias. One mechanism is that of autonomic imbalance with predominance of the parasympathetic nervous system due to anatomic sympathetic denervation. A second mechanism that may have relevant long-term manifestations is autonomic dysreflexia, which causes sympathetic surges. This manifests with sudden rise in BP, which may cause activation of the baroreflex pathway resulting in vagal stimulation and resultant bradycardia.

• #19 Tachycardia-bradycardia syndrome: Electrophysiological mechanisms and future therapeutic approaches (Review)

  https://www.spandidos-publications.com/10.3892/ijmm.2017.2877

  Sick sinus syndrome (SSS) encompasses a group of disorders whereby the heart is unable to perform its pacemaker function, due to genetic and acquired causes. […] Techniques such as genetic screening and molecular diagnostics together with the use of pre-clinical models have elucidated the electrophysiological mechanisms of this condition. Dysfunction of ion channels responsible for initiation or conduction of cardiac action potentials may underlie both bradycardia and tachycardia; bradycardia can also increase the risk of tachycardia, and vice versa. […] These studies have identified the roles of different ion channels, such as hyperpolarization-activated, cyclic nucleotide-gated (HCN), Na+ and transient receptor potential (TRP) channels, ryanodine receptors (RyR) and gap junctions, as well as tissue-level mechanisms, in the pathogenesis of TBS.

• #20 Tachycardia-bradycardia syndrome: Electrophysiological mechanisms and future therapeutic approaches (Review)

  https://www.spandidos-publications.com/10.3892/ijmm.2017.2877

  TBS can be caused by genetic mutations, inflammation, ischaemia or drugs, involving both structural and electrophysiological remodeling. […] HCN4 is involved in mammalian cardiac pacemaking and is predominantly expressed in the SAN. Loss-of-function HCN4 mutations are known to cause atrioventricular (AV) block, long QT syndrome (LQTS), AF, familial TBS and non-compaction cardiomyopathy in addition to sinus bradycardia. […] A loss-of-function mutation in the Ca2+ channel gene has also been shown to cause TBS. […] Increased Ca2+ levels can arise from a number of mechanisms, such as entry via voltage-gated ion channels, receptor-operated Ca2+ entry (ROCE), store-operated Ca2+ entry (SOCE) and SR release. […] If arrhythmia persists untreated, the structure of the SAN can be modified and this remodeling can lead to fibrosis and disturbance of the electrophysiology and even apoptosis of cardiac cells.

• #21 Bradycardia associated with Hyperkalaemia – EmergencyPedia

  https://emergencypedia.com/2013/07/05/bradycardia-associated-with-hyperkalaemia/

  Bradycardia is an important cause of bradycardia. […] This relates to the cardiac pacemaker action potential a reduction in the concentration gradient (outflow) of K+ in repolarisation leads to reduced heart rate. […] The change in serum potassium affects the repolarisation part of the action potential (labelled 3 in the diagram below). Hyperkalaemia leads to a flattening of the angle of this part of the action potential which can lead to a slower heart rate.

• #22 Symptomatic sinus bradycardia due to electrolyte imbalances in syndrome of inappropriate antidiuretic hormone (SIADH) related covid-19: a case report | BMC Infectious Diseases | Full Text

  https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-021-06143-2

  Although the exact mechanism is not clear, severe hyponatremia has been associated with cardiac conduction defects through the genesis action potential. […] Low extracellular sodium could reduce inward sodium flow in the early phase of the cardiac action potential. […] Interleukin-6 (IL-6) plays an essential role in causing electrolyte imbalance by inducing the non-osmotic release of vasopressin. […] COVID-19-induced stress stimulates the hypothalamo-hypophyseal axis, or hypothalamic neuron directly, and stimulates ADH release. […] SIADH could result in dysautonomia.

• #23

  https://link.springer.com/article/10.1007/BF00380410

  The effects of acute systemic anoxia on heart rate were investigated in 46 anaesthetized, artificially ventilated and spontaneously breathing dogs. Severe anoxia produced by inhalation of 100 per cent nitrogen over a period of 1 to 3 min elicited in both groups of animals a biphasic response consisting of a primary tachycardia and secondary bradycardia. […] Bilateral cervical vagotomy, atropinization and ganglionic blockade caused consistently a considerable reduction or abolition of anoxic bradycardia. […] The intensity of bradycardia was not reduced following denervation of carotid and aortic baro- and chemoreceptors. On the contrary, denervation invariably resulted in a considerable increase of bradycardia. It is concluded that secondary anoxic bradycardia is mainly due to the increased tone of the vagal cardioinhibitory center, the local depressant action of anoxia on the heart itself being of minor importance. Increased vagal tone is opposed by the concomitant stimulation of the sympatho-adrenal system. Anoxic bradycardia cannot be regarded as resulting from stimulation of carotid and aortic receptors. It is, therefore, inferred that some other mechanism, reflex or central, is activated during acute systemic anoxia giving rise to the increased vagal discharge to the heart.

• #24

  https://www.jci.org/articles/view/110568

  To determine the characteristics of and mechanisms causing the bradycardia during sleep apnea (SA), both patients with SA and normals were studied. […] Evaluation of six consecutive SA patients demonstrated that bradycardia occurred during 95% of all apneas (central, obstructive, and mixed) and became marked with increased apnea length (P less than 0.01) and increased oxyhemoglobin desaturation (P less than 0.01). […] We conclude that the bradycardia of SA is a consistent feature of apnea and results from the combined effect of cessation of breathing plus hypoxemia.

• #25 Sinus Node Dysfunction | AAFP

  https://www.aafp.org/pubs/afp/issues/2021/0800/p179.html

  Intrinsic causes originate from structural or functional changes within the SAN. […] These changes can occur because of fibrosis, ischemia, cardiac remodeling, infiltrative disease, or ion channel dysfunction. […] Degenerative idiopathic fibrosis of the SAN is the most common cause of sinus node dysfunction. […] Ischemic heart disease and embolization of the sinus node artery may cause ischemic necrosis of the node, resulting in sinus node dysfunction. […] Cardiac remodeling following myocardial infarction, congestive heart failure, or advanced age can result in structural changes that decrease cardiac tissue voltage transmission and ultimately delay or block the SAN and result in sinus node dysfunction. […] Another result of this remodeling is the formation of bradycardia-tachycardia syndrome.

• #26 Sinus Node Dysfunction | AAFP

  https://www.aafp.org/pubs/afp/issues/2021/0800/p179.html

  Sinus node dysfunction, previously known as sick sinus syndrome, describes disorders related to abnormal conduction and propagation of electrical impulses at the sinoatrial node. […] The causes of sinus node dysfunction are intrinsic (e.g., degenerative idiopathic fibrosis, cardiac remodeling) or extrinsic (e.g., medications, metabolic abnormalities) to the sinoatrial node. […] Bradycardia-tachycardia syndrome occurs in approximately 50% of patients with sinus node dysfunction and increases the risk of stroke and death. […] To diagnose sinus node dysfunction, a combination of symptoms and documented electrical abnormalities must be present. […] Causes of sinus node dysfunction are generally categorized as intrinsic or extrinsic based on their effect on the SAN. […] It is important to note that sinus node dysfunction is usually a progressive condition and most causes are chronic and irreversible.

• #27 Sinus Node Dysfunction | AAFP

  https://www.aafp.org/pubs/afp/issues/2021/0800/p179.html

  Extrinsic causes are related to external factors causing abnormal conduction at the SAN. […] Extrinsic causes may be reversible, such as electrolyte abnormalities, hypothyroidism, metabolic abnormalities, and certain medications. […] Permanent pacemaker placement is the first-line treatment for patients with confirmed sinus node dysfunction. […] Pacemaker therapy has been found to provide symptom relief and improve quality of life, but it is unclear if it provides a mortality benefit. […] Atrial-based pacing has been established as superior because right ventricular pacing has been associated with an increased risk of arrhythmias and decreased cardiac function. […] Medication control of sinus node dysfunction is a secondary option for patients who decline permanent pacemaker placement. […] The role of oral anticoagulation in patients with sinus node dysfunction is unclear.

• #28 Sinus Bradycardia | Arrhythmias – MedSchool

  https://medschool.co/diseases/arrhythmias/sinus-bradycardia

  Sinus bradycardia is initiated by the sinus node, and occurs in the setting of reduced automaticity due to either intrinsic or extrinsic causes. […] Causes of Sinus Bradycardia […] Intrinsic […] Idiopathic degeneration […] Myocardial infarction […] Infiltrative disease – sarcoidosis, amyloidosis, haemochromatosis […] Connective tissue disease – SLE, scleroderma, RA […] Cardiac surgery – valvular surgery, correction of congenital heart disease […] Infections – Lyme disease, endocarditis […] Extrinsic […] Physiologic – sleep, athletes […] Autonomic – neurocardiogenic syncope, carotid sinus hypersensitivity […] Drugs – beta blockers, calcium channel blockers, digoxin, adenosine, flecainide, ivabradine, clonidine, acetylcholinesterase inhibitors […] Hypothyroidism […] Hypothermia […] Hyperkalaemia […] Obstructive sleep apnoea […] Raised intracranial pressure.

• #29 Bradycardia in hypothyroidism is caused by intrinsic remodelling of the sinus node – The Physiological Society

  https://www.physoc.org/abstracts/bradycardia-in-hypothyroidism-is-caused-by-intrinsic-remodelling-of-the-sinus-node/

  Bradycardia (slow heart rate) is a characteristic cardiac phenotype seen in clinical hypothyroidism. The mechanism underlying the bradycardia is unknown. Potential causes include altered autonomic nerve activity and/or intrinsic remodelling of the sinus node. […] In the HT sinus node, downregulation of HCN4, Cav1.2 and Cav3.1 coupled with significant loss of SERCA2a and RyR2 is likely to compromise the voltage- and Ca2+-clock pacemaker mechanisms. Thus, ion channel remodelling intrinsic to the sinus node is the likely cause of bradycardia in hypothyroidism.

• #30 Octreotide-induced sinus bradycardia in a male patient with acromegaly | Endocrinología y Nutrición (English Edition)

  https://www.elsevier.es/en-revista-endocrinologia-nutricion-english-edition–412-articulo-octreotide-induced-sinus-bradycardia-in-male-S217350931300161X

  Acromegaly is a disease characterized by excess growth hormone (GH), starting after the closure of the epiphyseal plates of long bones. Somatostatin is a peptide hormone with a short half-life (23min) which is synthesized in multiple tissues, including the hypothalamus, to inhibit GH secretion. This hormone mediates its actions through five receptor subtypes (SSRs), of which SSR2 and SSR5 are the most widely expressed in pituitary adenomas. Octreotide is a synthetic analog of somatostatin with an inhibitory action on the secretion of GH and various gastrointestinal and pancreatic hormones. […] The most plausible mechanism to explain the negative chronotropic effect of octreotide is the direct action of somatostatin on the heart. Somatostatin coexists with acetylcholine in presynaptic vagal endings, and may therefore be released by vagus nerve stimulation. The main cardiovascular effects of somatostatin include decreases in heart rate and myocardial contractility and a slowing of cardiac conduction velocity. Many actions of somatostatin or its analogs result from interaction with SSRs, which belong to the family of G protein-coupled receptors and whose activation causes the inhibition of adenylate cyclase with a resultant decrease in the intracellular concentration of cyclic adenosine monophosphate (cAMP) which causes decreased conduction through voltage-dependent calcium channels and increased membrane permeability to potassium.

• #31 Proposed mechanisms of relative bradycardia – PubMed

  https://pubmed.ncbi.nlm.nih.gov/30122494/

  Relative bradycardia is the term used to describe the mechanism where there is dissociation between pulse and temperature. […] We hypothesize that relative bradycardia is the central mechanism reflecting and influenced potentially by the direct pathogenic effect on the sinoatrial node as well as cross-talk between the autonomic nervous system and immune system. […] Cardiac pacemaker cells may act as a target for inflammatory cytokines leading to alteration in heart rate dynamics or their responsiveness to neurotransmitters during systemic inflammation. […] These factors account for the important role of how the host response to infectious and non-infectious causes influences the appearance of relative bradycardia.

• #32 Bradycardia pathophysiology – wikidoc

  https://www.wikidoc.org/index.php/Bradycardia_pathophysiology

  Osoby z obturacyjnym bezdechem sennym również mają bradykardię zatokową, która może być ekstremalna (30 uderzeń na minutę) podczas apne. […] Odpowiedzi wazowagalne mogą być związane z ciężką bradykardią z powodu zwiększonego zaangażowania przywspółczulnego i tłumienia współczulnego węzła SA. […] Zwiększone ciśnienie wewnątrzczaszkowe powinno być wykluczone, gdy bradykardia zatokowa pojawia się u pacjenta z dysfunkcją neurologiczną. […] Czynnikami zakaźnymi związanymi z względną bradykardią zatokową są choroby zakaźne, takie jak borelioza, choroba Chagasa, legionella, psittakoza, gorączka Q, dur brzuszny, tyfus, babeszjoza, malaria, leptospiroza, żółta febra, gorączka denga, wirusowe gorączki krwotoczne, włośnica i gorączka plamista gór Skalistych. […] Na mikroskopowej analizie histopatologicznej, u niektórych pacjentów z bradykardią zatokową mogą nie występować zmiany histopatologiczne w węźle, jednak niektóre mikroskopowe wyniki są związane z tym stanem, w tym: redukcja komórek węzłowych, komórki węzłowe i włóknienie, amyloidoza w regionie węzłowym, hipoplazja węzła zatokowego.

• #33 CV Physiology | Regulation of Pacemaker Activity

  https://cvphysiology.com/arrhythmias/a005

  Autonomic control of SA nodeThe SA node displays intrinsic automaticity (spontaneous pacemaker activity) at a rate of 100-110 action potentials (beats) per minute. […] Hyperkalemia induces bradycardia or can even stop SA nodal firing. […] Cellular hypoxia (usually because of ischemia) depolarizes the membrane potential, causing bradycardia. […] Various drugs used as antiarrhythmics also influence the SA nodal rhythm. Calcium-channel blockers, for example, cause bradycardia by inhibiting the slow inward Ca++ currents during phase 4 and phase 0. […] Digoxin causes bradycardia by increasing parasympathetic (vagal) activity on the SA node; however, at toxic concentrations, digitalis increases automaticity and therefore can cause tachyarrhythmias.

• #34 How Does Atropine Help People with Bradycardia?

  https://www.healthline.com/health/arrhythmia/atropine-for-bradycardia

  Atropine has long been used to treat abnormally slow heart rate in emergency situations by altering the way electrical signals move through the heart. […] Bradycardia is an especially slow heartbeat and a risk factor for fainting and other health problems. Atropine, an anticholinergic medication (a drug that blocks the neurotransmitter acetylcholine) used to treat a wide range of health problems, is a first-line treatment for bradycardia. […] Atropine works by blocking muscarinic receptors in the heart. Muscarinic receptors are protein receptors found throughout the body that are involved with several functions, including circulation and respiration. […] By blocking the muscarinic receptors, atropine prevents the slowing effect of acetylcholine, thereby promoting an increase in heart rate.

• #35 A Case Report of Sinus Bradycardia after the Addition of Lurasidone in a Patient with Bipolar Disorder

  https://www.cpn.or.kr/journal/view.html?uid=1502&vmd=Full

  Atypical antipsychotics are first-line drugs for schizophrenia and bipolar disorder. Although bradycardia associated with these medications is rare, previous studies have shown that several atypical antipsychotics cause bradycardia. […] The association of sinus bradycardia and lurasidone was probable based on the Naranjo adverse drug reaction (ADR) probability scale, although bradycardia was not documented in the lurasidone package insert and has not been documented previously. […] Previously reported atypical antipsychotics that cause bradycardia are known to activate 5-HT1A receptors either directly or indirectly. Similar to these antipsychotics, lurasidone has partial agonist activity at the serotonin 5-HT1A receptor. […] However, we did not consider that the adverse effects of lithium carbonate were the most likely cause of the sinus bradycardia reported in this patient.

• #36 Bradycardia – EMCrit Project

  https://emcrit.org/ibcc/bradycardia/

  Bradycardia directly pulls down the cardiac output, potentially causing shock. […] In severe bradycardia, the cardiac output must be low. This is simple math. […] Cardiogenic shock is defined as inadequate cardiac output to support organ function. Some patients can compensate for low cardiac output without developing shock. However, with increasingly severe bradycardia, there should be an increasing concern for cardiogenic shock. […] Torsade de pointes is a pause-dependent arrhythmia, which is more likely to occur at slower heart rates. Furthermore, bradycardia itself may prolong the QT interval. […] It’s possible that leaving patients in a severely bradycardic state may increase their risk of torsade.

• #37 Bradycardia Concomitant with Hypertension

  https://www.meddiscoveries.org/articles/1092.html

  Bradycardia is defined as a Heart Rate (HR) 60 beats per minute (bpm) in adults, except for well-trained athletes (studies often use a lower cut-off of 50 bpm). Multiple potential causes of bradycardia include atrioventricular block, conduction tissue disease, sick node disease, Adams-Stokes syndrome, athletes bradycardia, sleep apnea, nocturnal bradycardia, and perioperative reflex bradycardia. […] If other causes are excluded, ageing is regarded as a significant risk factor for sinus bradycardia. […] The correlation between bradycardia and hypertension can be partly explained by several mechanisms. […] Physiologically, bradycardia results in a reduction of cardiac output, that leads to brain stem hypoperfusion. […] During bradycardia (caused by a heart block) the pressures in the vena cava and jugular vein increase, which results in a sign of jugular vein dilatation, rise and that results in increased right ventricle filling.

• #38 Evaluation and Management of Acute Unstable Bradycardia | RECAPEM

  https://recapem.com/evaluation-and-management-of-acute-unstable-bradycardia/

  Progressive bradycardia is often a harbinger of death. […] Torsade de pointes is a pause-dependent arrhythmia, which is more likely to occur at slower heart rates. Moreover, bradycardia itself may prolong the QT interval. Leaving patients in a severely bradycardic state may increase their risk of torsade. […] Generally, bradydysrhythmias result from intrinsic (ie, cardiac electrical system-based) dysfunction (such as aging, infiltrative disease, ischemia, trauma, surgery) or extrinsic causes. […] Autonomic-mediated syndromes include carotid sinus stimulation or hypersensitivity, increased ICP (Cushing reflex), and vagal stimulation (coughing, micturition, defecation, vomiting). […] The principles of management of bradycardia involve the following essential concepts: Always consider the major life-threatening causes of bradycardia and evaluate the patient throughout the resuscitation to identify and correct the primary problem (e.g. hyperkalemia, drug intoxication, myocardial infarction, and neurologic catastrophe).

• #39 Evaluation and Management of Acute Unstable Bradycardia | RECAPEM

  https://recapem.com/evaluation-and-management-of-acute-unstable-bradycardia/

  Severe progressive sinus bradycardia is a common pathway of impending death from any terminal disease state. In this post, the principles of management of unstable patients with bradycardia are discussed. […] Bradycardia is defined as a heart rate of less than 50 bpm in adults (non-well-conditioned athletes). Generally severe bradycardia is more worrisome than tachycardia for the following reasons: Cardiac output is dependent on heart rate and stroke volume. In mild-moderate tachycardia, the effect of the increased heart rate predominates, and cardiac output is increased. However, in severe tachycardia, the cardiac output drops since the diastolic filling time is reduced (causing reduced stroke volume). Bradycardia can directly pull down cardiac output and cause hemodynamic instability. Theoretically, slowing down the heart rate may cause a minimal increase in diastolic filling, thereby increasing the stroke volume. However, this compensatory factor is weak and extremely limited.

• #40 Bradycardia Concomitant with Hypertension

  https://www.meddiscoveries.org/articles/1092.html

  The hypertension secondary to bradycardia is a common, but under-reported clinical problem. In this instance, the increased blood pressure is a reaction of the body to the decreased cardiac output caused by the bradycardia. The bradycardia must be chronic to permit the occurrence of hypertension. While the underlying mechanism remains undetermined, several hypotheses exist. The two most plausible mechanisms are the selfish brain hypothesis and the effects of Frank-Starling mechanism.

• #41 Bradycardia pathophysiology – wikidoc

  https://www.wikidoc.org/index.php/Bradycardia_pathophysiology

  Bradycardia generally results from sinus node dysfunction and AV node dysfunction. Jednak inne warunki patofizjologiczne mogą również prowadzić do bradykardii, takie jak ostry zawał serca, obturacyjny bezdech senny, wyolbrzymiona aktywność przywspółczulna, zwiększone ciśnienie wewnątrzczaszkowe oraz choroby zakaźne, takie jak borelioza, gorączka plamista gór Skalistych, choroba Chagasa, psittakoza, gorączka Q i dur brzuszny. […] Istnieją ogólnie dwa rodzaje problemów, które prowadzą do bradykardii: […] Zaburzenia węzła zatokowego […] Zaburzenia przewodzenia w węźle przedsionkowo-komorowym (AV) […] Bradykardia zatokowa może być również obserwowana w tych warunkach patofizjologicznych: […] Pacjenci z ostrym zawałem serca, szczególnie ci z zawałem tętnicy wieńcowej prawej, są dotknięci bradykardią, ponieważ zaopatruje ona węzeł SA.

• #42 ACLS drugs for Bradycardia | ACLS-Algorithms.com

  https://acls-algorithms.com/acls-drugs/bradycardia/

  Since new-onset Mobitz II and complete heart block are commonly associated with myocardial infarction, it is recommended to maintain a slow HR (50-60) in order to increase the diastolic filling time. […] Epinephrine and dopamine are second-line drugs for symptomatic bradycardia. They are both used as infusions in the bradycardia algorithm if atropine is ineffective. […] ACLS guidelines state that if bradycardia is unresponsive to atropine, an equally effective alternative to transcutaneous pacing is the use of an IV infusion of the beta-adrenergic agonists (dopamine or epinephrine).

• #43

  https://insight.jci.org/articles/view/91872

  Bradycardia and SAN dysfunction are common in CPVT patients. However, the mechanisms underlying these conditions are still unclear. […] The presence of RyR2R420Q produces prolonged Ca2+ sparks. This increase in Ca2+ leak, instead of accelerating the Ca2+ clock, partly inactivates ICaL, disturbing the fine tuning of the coupled clock and resulting in a reduction of the HR. […] Our study uncovers a new arrhythmogenic mechanism in a CPVT mutation located at the N-terminal portion of the channel, the RyR2R420Q. […] Thus, our data show that an aberrant gain of function of the Ca2+ clock inhibits the activity of the voltage clock by inducing a negative Ca2+-to-voltage crosstalk in RyR2R420Q CPVT SAN cells. […] The altered characteristics of Ca2+ sparks could modify the total amount of Ca2+ released through them.

• #44 Bradycardia in Spinal Cord Injury | Spinal Cord Injury Bradycardia

  https://www.radcliffecardiology.com/articles/cardiac-bradyarrhythmias-patient-cervical-spine-injury?language_content_entity=en

  Bradycardia has been reported in almost all cases of CSCI, with asystole in 15% of these patients. The time of onset is variable, but the incidence is highest in the first two to four weeks following CSCI and may decrease subsequently as the spinal shock and edema resolve. […] All patients with spinal cord injury regardless of the level and severity should be closely monitored. Treatment modalities include atropine, epinephrine, aminophylline, and pacemaker insertion. […] In the case we describe, the patient had bradycardia leading to hemodynamic collapse, thus requiring brief temporary transvenous pacing. Patients who continue to have bradyarrythmias more than two weeks after the initial injury should be considered for permanent pacemaker implantation. […] The aforementioned treatment options are based on anecdotal reports and small retrospective analyses. Currently, there are no evidence-based guidelines regarding permanent pacemaker implantation in patients similar to ours who do not have further bradycardiac episodes, at least for the time period for which he was under observation in the hospital. The decision about permanent pacemaker implantation in this situation has to be tailored on a case-by-case basis.

• #45 Bradycardia and Outcomes in COVID-19 Patients on Remdesivir: A Multicenter Retrospective Study | Umeh | Cardiology Research

  https://cardiologyres.org/index.php/Cardiologyres/article/view/1493/1451

  Bradycardia in COVID-19 patients on remdesivir has been reported in previous studies. […] The mechanism through which remdesivir causes bradycardia is unknown. One possible mechanism through which remdesivir causes bradycardia is its triphosphorylated form binding to the A1 receptor in the cardiac cells. […] Our study found that in the subset of COVID-19 patients on remdesivir, bradycardia was associated with decreased odds of mortality. […] According to a prior study, remdesivir-associated bradycardia did not increase the mortality rate in COVID-19 patients, and sudden cardiac death was not reported in the studied patients. […] One possible explanation is that COVID-19 patients with cytokine storms might be less responsive to the bradycardia effect of remdesivir due to their intense sympathetic-adrenergic stimulation and are more likely to have worse outcomes.

• #46 Symptomatic sinus bradycardia due to electrolyte imbalances in syndrome of inappropriate antidiuretic hormone (SIADH) related covid-19: a case report | BMC Infectious Diseases | Full Text

  https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-021-06143-2

  In this paper, we report a case of a 59-year-old male patient with confirmed COVID-19 initially presented with presyncope. Further investigations reveal sinus bradycardia related to COVID-19-induced SIADH. This case highlights the possibility of immuno-neuroendocrino-cardiovascular crosstalk resulting in an atypical manifestation of COVID-19: near syncope due to sinus bradycardia. […] Another possible cause of sinus bradycardia in COVID-19 is electrolyte imbalance due to COVID-19-related SIADH. […] Cardiac arrhythmias, one of which sinus bradycardia, have been noted as one of many phenotypes of COVID-19 and hypothesized to be caused by myocardial or pacemaker cell injury. […] Therefore, symptomatic sinus bradycardia in our patient may be related to other pathways rather than the abovementioned mechanism.

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