Materiały źródłowe

• #1 Atrioventricular Block – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK459147/

  Atrioventricular block represents a delay or disturbance in the transmission of an impulse from the atria to the ventricles. This can be due to an anatomical or functional impairment in the hearts conduction system. […] An AV block represents a delay or disturbance in the transmission of an impulse from the atria to the ventricles. This can be due to an anatomical or functional impairment in the heart’s conduction system. […] Congenital AV block mediated by the immune system results from the transfer of maternal antibodies (anti-Ro and anti-La) across the placenta into the fetal circulation. These antibodies bind to fetal myocytes and impair cytoplasmic calcium metabolism leading to apoptotic cell death in the conduction system tissues. The result of this immune-mediated process is the fibrosis of the cardiac conduction system and surrounding myocardium.

• #1 Atrioventricular Block – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK459147/

  Acquired AV block in older individuals is characterized by degeneration and fibrosis of the His-Purkinje system. Age-related degeneration is a chronic process commonly involving the intra/infra-His conduction system, and most patients require pacemaker implantation. […] AV blocks occurring after cardiac surgery and transcatheter aortic valve replacement are primarily caused by the mechanical effects exerted on the surrounding conduction system.

• #2 Third-Degree Atrioventricular Block – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK545199/

  An atrioventricular block is a loss of the regular function of the cardiac electroconductive pathways linking the sinoatrial node (SA node) and the ventricles via conduction through the atrioventricular node (AV node). Third-degree AV block indicates a complete loss of communication between the atria and the ventricles. Without appropriate conduction through the AV node, the SA node cannot act to control the heart rate, and cardiac output can diminish secondary to loss of coordination of the atria and the ventricles. […] The underlying cause of AV blocks is varied and the same for all degrees of blocks. These causes include idiopathic fibrosis and underlying chronic cardiac diseases such as structural heart disease, acute ischemic heart disease, medication toxicity, nodal ablation, electrolyte abnormalities, and post-operative heart block, such as after surgical or transcatheter aortic valve replacement.

• #2 Third-Degree Atrioventricular Block – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK545199/

  Under its regular function, the AV node receives an impulse from the SA node. That impulse gets delayed in the AV node, assuring the contraction cycle in the atria is complete before a contraction begins in the ventricles. From the AV node, the electrical impulse passes through the His-Purkinje system to activate ventricular contraction. When there is a pathological delay in the AV nodal conduction, it is visualized on an electrocardiogram as an alteration in the PR interval. These delays present in the form of AV blocks, which are of first, second, and third-degree. […] The third-degree block is also known as complete heart block. As the name implies, no impulses from the SA node get conducted to the ventricles, leading to a complete atrioventricular dissociation. The SA node continues its activity at a set rhythm, but the ventricles activate through an escape rhythm that can be mediated by either the AV node (junctional escape), one of the fascicles (fascicular escape), or by ventricular myocytes themselves (ventricular escape rhythm). […] The heart rate will typically be less than 45 to 50 beats/min, and most patients will be hemodynamically unstable. This rhythm is unresponsive to atropine and exercise.

• #3

  https://link.springer.com/article/10.1007/BF02939856

  A METHOD of examining the conducting tissue of the heart histologically and of quantitating the histological features is described. […] Examination of the conducting tissue in nine cases of chronic heart block revealed localised lesions in two cases due to a myxomatous degeneration of the central fibrous body, and calcification extending from the base of the aortic valve. […] The only significant change found is a loss of conducting tissue in the bundle branches, with increased fibrosis. […] The clinical and electrocardiographic findings in one case with left bundle branch block and several with complete heart block supplement the histological findings to suggest that there is a transition over many years from branch blockade to bilateral bundle branch block with intermittent and later established complete heart block. […] The degenerative loss of conducting fibres with ageing is thought to be important, so accentuating previous damage of the bundle branches.

• #4 Atrioventricular Block: Practice Essentials, Background, Pathophysiology

  https://emedicine.medscape.com/article/151597-overview

  Atrioventricular (AV) block is due to the following conditions: […] Ischemia […] Degenerative changes […] Infection (myocarditis) and infiltrative processes such as Lyme disease and sarcoidosis […] Drugs (beta blockers, calcium antagonists) that slow AV nodal or block His-Purkinje (eg, procainamide, flecainide) conduction or lengthen AV node refractoriness […] Bezold-Jarisch reflex: An inferior myocardial infarction may cause a temporarily increased vagal tone leading to transient Mobitz I or complete AV block. […] Delay or lack of conduction through the atrioventricular (AV) node and below has multiple causes. Degenerative changes (eg, fibrosis, calcification, or infiltration) are the most common cause of non-ischemic AV block. Idiopathic fibrosis or calcification of the AV conduction system, commonly seen in the elderly, can cause complete AV block.

• #4 Atrioventricular Block: Practice Essentials, Background, Pathophysiology

  https://emedicine.medscape.com/article/151597-overview

  Causes of first-degree AV block include the following: […] Delayed conduction within the AV node or His-Purkinje system […] Intrinsic disease of the AV node, high vagal tone, or dual AV nodal pathways (two separate PR intervals) […] Medications that block the AV node (beta-blockers, calcium channel antagonists, digitalis, and select antiarrhythmic medications) may prolong the PR interval. […] Causes of Mobitz I second-degree AV block include the following: […] Increased vagal tone (functional block) […] Degenerative disease of the AV conduction system (commonly seen in the elderly) […] Occurs physiologically at high heart rates (especially with pacing) as a result of increased refractoriness of the AV node […] AV node-blocking medications […] Lyme disease, myocarditis, and radiofrequency ablation of the slow pathway.

• #4 Atrioventricular Block: Practice Essentials, Background, Pathophysiology

  https://emedicine.medscape.com/article/151597-overview

  Causes of Mobitz II second-degree AV block include the following: […] Degenerative disease of the His-Purkinje system […] Damage of the conduction system from coronary artery disease, valve surgery, myocardial infarction, myocarditis, infiltrative cardiomyopathies (sarcoidosis, hemochromatosis), myxedema, Lyme disease, neuromuscular disease, and AV junction ablation. […] Causes of third-degree AV block include the following: […] Reversible causes: AV node-blocking drugs and ischemia […] Pathologic causes: Include cardiomyopathy (infiltrative, idiopathic, and infarction), myocarditis (Lyme disease), endocarditis with abscess formation, and hyperkalemia […] Anterior myocardial infarction causing ischemia or infarction of the bundle branches […] Cardiac surgery, catheter ablation of the AV node, alcohol septal ablation, or neuromuscular disease.

• #5 Atrioventricular Block – Cardiovascular Disorders – Merck Manual Professional Edition

  https://www.merckmanuals.com/professional/cardiovascular-disorders/specific-cardiac-arrhythmias/atrioventricular-block

  In high-grade second-degree AV block, every second (or more) P wave is blocked. […] Patients with any form of second-degree AV block and a structural heart disorder should be considered candidates for permanent pacing unless there is a transient or reversible cause. […] In third-degree AV block, no P waves conduct to make QRS complexes. By definition, the P wave rate is greater than the QRS rate. Thus, heart block is complete in third-degree AV block. […] There is no electrical communication between the atria and ventricles and thus no relationship between P waves and QRS complexes (AV dissociation). […] AV block caused by acute inferior myocardial infarction usually reflects atrioventricular nodal dysfunction due to increased parasympathetic tone and/or local adenosine release. […] AV block caused by anterior myocardial infarction usually reflects extensive myocardial necrosis involving the His-Purkinje system and requires immediate transvenous pacemaker insertion with interim external pacing as necessary. […] Most patients with isolated congenital third-degree AV block have a junctional escape rhythm that maintains a reasonable rate, but they require a permanent pacemaker before they reach middle age.

• #5 Atrioventricular Block – Cardiovascular Disorders – Merck Manual Professional Edition

  https://www.merckmanuals.com/professional/cardiovascular-disorders/specific-cardiac-arrhythmias/atrioventricular-block

  Atrioventricular (AV) block is partial or complete interruption of impulse transmission from the atria to the ventricles. The most common cause is idiopathic fibrosis and sclerosis of the conduction system. […] The remaining cases of AV block are caused by medications (eg, beta-blockers, calcium channel blockers, digoxin, amiodarone), increased vagal tone, cardiac sarcoidosis, valvulopathy, congenital heart, genetic, or other disorders. […] Up to one-third of patients age 18 years to 60 years with new-onset Mobitz II second-degree or third-degree AV block without evident structural heart disease are diagnosed with cardiac sarcoidosis after targeted investigations. […] Transient or reversible causes of AV block can include Lyme carditis and neurologically mediated (vagal) heart blocks.

• #6 Congenital heart block: evidence for a pathogenic role of maternal autoantibodies | Arthritis Research & Therapy | Full Text

  https://arthritis-research.biomedcentral.com/articles/10.1186/ar3787

  In addition, maternal antibody deposits are found in the heart of fetuses dying of CHB and are thought to contribute to an inflammatory reaction that eventually induces fibrosis and calcification of the AV node, leading to a complete block. […] The current hypotheses for autoantibody-associated CHB development will be discussed with an emphasis on the potential molecular targets for maternal antibodies in the fetal heart before mentioning other risk factors that have recently come to light. […] Direct evidence for a pathogenic role of maternal anti-Ro/La antibodies and especially anti-Ro52 antibodies in CHB comes from experimental studies of heart block, both in vitro and in vivo. […] The presence of anti-Ro antibodies in the cardiac tissue of fetuses dying of CHB, together with deposition of complement, fibrosis, and calcification, was demonstrated over 20 years ago by several groups, providing the first link between maternal antibodies and pathogenesis of heart block by placing the antibodies at the site of injury.

• #6 Congenital heart block: evidence for a pathogenic role of maternal autoantibodies | Arthritis Research & Therapy | Full Text

  https://arthritis-research.biomedcentral.com/articles/10.1186/ar3787

  Evidence for the pathogenicity of anti-Ro/La antibodies in vivo has been gathered from animal models based on passive transfer of antibodies or active immunization of females before gestation. […] The apoptosis hypothesis postulates that maternal antibodies gain access to their target antigen when it is exposed on the surface of apoptotic cells. […] The cross-reactivity hypothesis suggests that maternal anti-Ro/La antibodies, or at least a subset of these, bind to cardiac membrane proteins involved in the control of electric signal generation or conduction or both, interfering with their function. […] A chronic effect of maternal antibodies on the fetal heart has been proposed to be mediated by binding of antibodies to calcium channels and subsequent internalization and degradation, leading to not only inefficient signal conduction but also insufficient excitation-contraction coupling and reduction of cardiac contractile function.

• #6 Congenital heart block: evidence for a pathogenic role of maternal autoantibodies | Arthritis Research & Therapy | Full Text

  https://arthritis-research.biomedcentral.com/articles/10.1186/ar3787

  During pregnancy in autoimmune conditions, maternal autoantibodies are transported across the placenta and may affect the developing fetus. Congenital heart block (CHB) is known to associate with the presence of anti-Ro/SSA and anti-La/SSB antibodies in the mother and is characterized by a block in signal conduction at the atrioventricular (AV) node. […] The molecular mechanisms leading to complete AV block are still unclear, and the existing hypotheses fail to explain all aspects of CHB in one comprehensive model. […] Autoantibodies targeting the 52-kDa component of the Ro antigen remain the antibodies most closely associated with CHB. […] In vitro experiments and animal models of CHB also point to a major role for anti-Ro52 antibodies in CHB pathogenesis and suggest that these antibodies may directly affect calcium regulation in the fetal heart, leading to disturbances in signal conduction or electrogenesis or both.

• #7 Frontiers | Prenatal Management Strategy for Immune-Associated Congenital Heart Block in Fetuses

  https://www.frontiersin.org/journals/cardiovascular-medicine/articles/10.3389/fcvm.2021.644122/full

  It is now known that there is a strong association between anti-Ro/SSAs and the occurrence of CHB. […] Ambrosi and Wahren-Herlenius proposed a biphasic model incorporating the apoptosis hypothesis and the cross-reactivity hypothesis to explain how autoantibodies from the maternal circulation lead to fetal immune-associated CHB. […] The apoptosis hypothesis suggests that antibodies may bind to the surfaces of cells undergoing programmed apoptosis after entering the fetal cycle, resulting in apoptosis fragmentation. […] The „waterfall effect” of cell factors involves the recruitment of white blood cells and complement, induces an immune inflammatory response and a fibrotic response, and ultimately leads to cardiac conductive cell damage, resulting in fetal immune-associated CHB. […] The cross-reactivity hypothesis suggests that fetal CHB is primarily associated with maladjustment of calcium channels.

• #7 Frontiers | Prenatal Management Strategy for Immune-Associated Congenital Heart Block in Fetuses

  https://www.frontiersin.org/journals/cardiovascular-medicine/articles/10.3389/fcvm.2021.644122/full

  Fetal congenital heart block (CHB) is the most commonly observed type of fetal bradycardia, and is potentially life-threatening. […] Current evidence indicates that CHB is almost universally associated with transplacental transfer of Ro and La antibodies, which causes cardiac conduction tissue damage that can occur as early as 11 GWs. To date however, the underlying molecular mechanisms of CHB pathogenesis have not been fully elucidated. […] Autoimmune-associated CHB occurs in 2–5% of pregnancies in anti-Ro/SSA and anti-La/SSB antibody-positive women. It has a recurrence rate of 12–25% in a subsequent pregnancy after the birth of a baby with neonatal lupus. […] Studies have confirmed that autoimmune-associated CHBs often co-occur in a variety of maternal autoimmune disorders, including Sjogren’s syndrome, systemic lupus erythematosus, rheumatoid arthritis, and undifferentiated connective tissue disease.

• #8 Autoimmune congenital heart block: a case report and review of the literature related to pathogenesis and pregnancy management | Arthritis Research & Therapy | Full Text

  https://arthritis-research.biomedcentral.com/articles/10.1186/s13075-023-03246-w

  A histological study of fetuses that died from ACHB revealed that apoptotic cardiomyocytes were extensively distributed in the fetal heart, especially in the sinoatrial node and atrioventricular node. […] Human fetal cardiomyocytes are prone to apoptosis, promoting the translocation of SSA and SSB antigens to the surface. […] The formation of these immune complexes inhibits apoptotic cardiomyocyte physiological clearance. […] The accumulation of apoptotic cardiomyocytes, inflammation, extensive fibrosis, calcification, and scarring play an important role in the induction of ACHB. […] Several studies have indicated that anti-Ro/SSA antibodies bind to the 1G or 1D epitopes of cardiomyocytes and inhibit L-type and T-type calcium channels, suppressing the electrophysiological activity of cardiomyocytes in fetuses with ACHB. […] Numerous studies have suggested that type I IFN may contribute to the pathogenesis of ACHB. […] ACHB may be related to viral infection. It has been reported that Ro/SSA antigens in ACHB fetal cardiomyocytes could translocate to the cell surface following cytomegalovirus infection.

• #9 Drug-Induced Complete Atrioventricular Block in an Elderly Patient: A Case Report Highlighting Digoxin-Beta Blocker Interactions and a Paradoxical State

  https://www.mdpi.com/2075-1729/15/2/215

  Moreover, a third-degree AV block can also have congenital origins, with systemic lupus erythematosus being a significant risk factor. […] Other contributing factors include hyperkalemia, which can impair conduction through the His-Purkinje system, as well as Borrelia burgdorferi infection, which may damage the heart via Lyme disease. […] Surgical procedures such as open-heart surgery, percutaneous coronary interventions, or septal alcohol infusion may also lead to AV block. […] Possible causes of CHB are intrinsic atrioventricular node disease, myocardial infarction, myocarditis, electrolyte imbalances, hypoxia and certain drugs such as beta-blockers, digitalis, calcium channel blockers, and amiodarone. […] The combination of digoxin with a beta-blocker and mild hyperkalemia may explain this.

• #9 Drug-Induced Complete Atrioventricular Block in an Elderly Patient: A Case Report Highlighting Digoxin-Beta Blocker Interactions and a Paradoxical State

  https://www.mdpi.com/2075-1729/15/2/215

  The clinical findings indicating a CHB prompted an urgent assessment, revealing a drug interaction between metoprolol and digoxin. […] Polypharmacy is more prevalent among the elderly, which increases the risk of interactions among the drugs used. […] The therapeutic management of cardiovascular conditions becomes even more complicated in the context of polypharmacy, where multiple drug interactions can occur.

• #10 Heart Block Post-Transcatheter Aortic Valve Replacement TAVR

  https://www.cfrjournal.com/articles/evaluation-and-management-heart-block-after-transcatheter-aortic-valve-replacement?language_content_entity=en

  Transcatheter aortic valve replacement (TAVR) is now the preferred strategy for aortic valve replacement in most patients with severe symptomatic aortic stenosis. […] Occasionally, injury to the conduction system during TAVR results in high-degree atrioventricular block (HAVB) necessitating permanent pacemaker (PPM) implantation. […] The relationship between AV block and deployment of TAVR prosthesis is driven by several anatomical considerations. The AV node and bundle of His lie in proximity to the aortic annulus. As the TAVR valve is inflated, there can be direct mechanical insult to the AV conduction apparatus from the AV node down to the left bundle branch itself. […] Variations in anteroposterior positioning of the AV node and the length of the penetrating bundle of His may influence a patients baseline susceptibility to post-TAVR HAVB after valve deployment.

• #10 Heart Block Post-Transcatheter Aortic Valve Replacement TAVR

  https://www.cfrjournal.com/articles/evaluation-and-management-heart-block-after-transcatheter-aortic-valve-replacement?language_content_entity=en

  Several procedural factors can influence the development of post-TAVR HAVB. […] The use of self-expanding valves over balloon-expandable valves, the degree of valve oversizing (greater than 15-20%) and lower implantation depth within the annulus have each been shown to increase the risk of HAVB after TAVR valve deployment. […] Understanding patterns in timing of HAVB post-TAVR may help identify which patients may be at risk for this complication and help to mitigate adverse events. […] Patients who develop late HAVB after discharge from TAVR hospitalisation represent a unique and growing group of patients at high risk for adverse complications of HAVB. […] Increasing awareness of the potential risk for HAVB after discharge is important to prompt development of risk stratification and monitoring protocols.

• #10 Heart Block Post-Transcatheter Aortic Valve Replacement TAVR

  https://www.cfrjournal.com/articles/evaluation-and-management-heart-block-after-transcatheter-aortic-valve-replacement?language_content_entity=en

  Additionally, pre-existing conduction abnormalities and procedural factors may influence the magnitude of injury to the conduction system. […] The most important risk factors for HAVB necessitating PPM implantation after TAVR are assessed in a preprocedural ECG. […] Specifically, pre-existing conduction defects, such as right bundle branch block (RBBB), left bundle branch block (LBBB), first-degree AVB, second-degree AVB and bifascicular block with or without first-degree AVB, have all been associated with an increased risk of HAVB after TAVR. […] Deployment of the TAVR valve may injure the left bundle due to its proximity to the aortic annulus. […] Various risk factors for post-TAVR HAVB have recently been reviewed, and while not a comprehensive list, this review highlights some of the more recognised risk factors, which can be divided into preprocedural and intraprocedural considerations.

• #11 AV Block: 2nd degree, Mobitz I (Wenckebach Phenomenon) • LITFL

  https://litfl.com/av-block-2nd-degree-mobitz-i-wenckebach-phenomenon/

  Mobitz I is usually due to reversible conduction block at the level of the AV node. […] Malfunctioning AV nodal cells tend to progressively fatigue until they fail to conduct an impulse. This is different to cells of the His-Purkinje system which tend to fail suddenly and unexpectedly (i.e. producing a Mobitz II block).

• #12 AV Block: 2nd degree, Mobitz II (Hay block) • LITFL • ECG Library

  https://litfl.com/av-block-2nd-degree-mobitz-ii-hay-block/

  Unlike Mobitz I, which is produced by progressive fatigue of the AV nodal cells, Mobitz II is an all or nothing phenomenon whereby the His-Purkinje cells suddenly and unexpectedly fail to conduct a supraventricular impulse. […] There may be no pattern to the conduction blockade, or alternatively there may be a fixed relationship between the P waves and QRS complexes, e.g. 2:1 block, 3:1 block.

• #12 AV Block: 2nd degree, Mobitz II (Hay block) • LITFL • ECG Library

  https://litfl.com/av-block-2nd-degree-mobitz-ii-hay-block/

  Mobitz II is usually due to failure of conduction at the level of the His-Purkinje system (i.e. below the AV node) […] While Mobitz I is usually due to a functional suppression of AV conduction (e.g. due to drugs, reversible ischaemia), Mobitz II is more likely to be due to structural damage to the conducting system (e.g. infarction, fibrosis, necrosis) […] Patients typically have a pre-existing LBBB or bifascicular block, and the 2nd degree AV block is produced by intermittent failure of the remaining fascicle (bilateral bundle-branch block) […] In around 75% of cases, the conduction block is located distal to the Bundle of His, producing broad QRS complexes. […] In the remaining 25% of cases, the conduction block is located within the His Bundle itself, producing narrow QRS complexes.

• #13 Third-Degree Atrioventricular Block (Complete Heart Block): Background, Pathophysiology, Etiology

  https://emedicine.medscape.com/article/162007-overview

  Third-degree AV block (complete heart block) exists when there are more P waves than QRS complexes, and there is no relationship between them (ie, no conduction). The conduction block may be at the level of the AVN, the bundle of His, or the bundle-branch Purkinje system. In most cases (approximately 61%), the block occurs below the His bundle. […] The duration of the escape QRS complex depends on the site of the block and the site of the escape rhythm pacemaker. Pacemakers above the His bundle produce a narrow QRS complex escape rhythm, whereas those at or below the His bundle produce a wide QRS complex. […] When the block is at the level of the AVN, the escape rhythm generally arises from a junctional pacemaker with a rate of 45-60 beats/min. […] Patients with third-degree AV block (complete heart block) are frequently hemodynamically unstable; as a result, they may experience syncope, hypotension, cardiovascular collapse, or death.

• #13 Third-Degree Atrioventricular Block (Complete Heart Block): Background, Pathophysiology, Etiology

  https://emedicine.medscape.com/article/162007-overview

  Third-degree AV block may be an underlying condition in patients who present with sudden cardiac death. The cause of death may often be tachyarrhythmias precipitated by the secondary changes in ventricular repolarization (QT prolongation) due to the abrupt changes in rate. […] When treated with permanent pacing, the prognosis is excellent for patients with third-degree AV block.

• #14 Third degree AV block pathophysiology – wikidoc

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

  If the site of block is the His bundle, typically a narrow QRS complex is seen. […] In short, if escape rhythm has a narrow QRS complex, the level of the block can be either AV node or His bundle, and if the QRS duration is prolonged, the level of block is in the fascicles or bundle branches. […] Block at the level of the AV node gives rise to an escape rhythm that generally arises from a junctional pacemaker with a heart rate of 45-60 beats per minute. […] Escape rhythms arise from the His bundle or bundle branch Purkinje system at rates slower than 45 beats per minute when the block is below the AV node.

• #14 Third degree AV block pathophysiology – wikidoc

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

  Normal impulse is generated in the sinoatrial node (SAN). […] Complete heart block occurs when complete block of this conduction occurs. […] In complete heart block, because the impulse is blocked, an accessory pacemaker below the level of the block will typically activate the ventricles; this is known as an escape rhythm. […] When there is no electrical connection between atria and ventricles, two independent pacemakers will generate impulse independent of SA node. […] The PR interval will be a variable that is a hallmark feature of complete heart block and with no apparent relationship between P waves and QRS complexes. […] Morphology of the QRS complex helps in determining the location at which the escape rhythms are occurring. […] If the site of complete heart block is at the level of the AV node, two-thirds of the escape rhythms have a narrow QRS complex.

• #15 Complete Heart Block in a Patient with COVID-19

  https://clinmedjournals.org/articles/iacvd/international-archives-of-cardiovascular-diseases-iacvd-5-039.php?jid=iacvd

  The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has been reported to cause cardiac complications including myocarditis, acute myocardial infarction (AMI) and various tachyarrhythmias. […] The effect on the conduction system resulting in bradyarrhythmia’s and atrioventricular blocks remains poorly understood. […] Although individuals with preexisting cardiovascular disease and COVID-19 have increased risk of mortality, the exact pathogenesis of cardiac involvement is poorly understood. […] One ongoing theory involves viral port of entry. The virus invades host cells by binding Angiotensin-converting enzyme 2 (ACE2), a protein found in high concentration in pneumocytes and cardiac myocytes involved in breaking down a proinflammatory molecule called angiotensin II.

• #15 Complete Heart Block in a Patient with COVID-19

  https://clinmedjournals.org/articles/iacvd/international-archives-of-cardiovascular-diseases-iacvd-5-039.php?jid=iacvd

  Once the virus binds ACE2, it dysregulates this protective mechanism leading to pneumocyte and myocyte injury. […] As the virus continues to replicate, a state of systemic inflammation with massive cytokine release ensues, leading to myocardial injury, ARDS and multiorgan dysfunction. […] The proposed mechanism for COVID-19-induced high degree AV block is not well understood. […] An important aspect to consider is the impact of the „cytokine storm” that is produced in response to the virus which results in elevated levels of proinflammatory molecules like TNF-, IL-1 and IL-6. […] Literature suggests inflammatory cytokines can modulate expression and function of ion channels by acting directly on cardiac myocytes and indirectly through systemic effects perhaps leading to conduction disturbances.

• #15 Complete Heart Block in a Patient with COVID-19

  https://clinmedjournals.org/articles/iacvd/international-archives-of-cardiovascular-diseases-iacvd-5-039.php?jid=iacvd

  Another plausible explanation is direct involvement of the AV node by SARS-CoV-2 as studies in animal models have shown to the presence of ACE2 receptors throughout the conduction system. […] Our patient had normal cardiac biomarkers except for elevated pro-BNP levels and normal left ventricular function which suggest against overt myocardial involvement. […] This case highlights the importance of monitoring for extrapulmonary manifestations in patients with COVID-19 infection, particularly unusual cardiovascular complications. […] We hypothesize subclinical myocarditis caused by COVID-19 resulted in AV nodal dysfunction leading to heart block. […] Whether the AV nodal dysfunction is due to direct viral involvement or the severe inflammatory response is yet to be determined.

• #16 Heart Block in the Patients with COVID-19 | medRxiv

  https://www.medrxiv.org/content/10.1101/2022.01.05.22268779v1.full-text

  According to the fast-growing availability of scientific literature on this topic, the heart appears to be one of the elective targets of the virus. […] Multiple hypotheses have been made to explain the mechanism of heart blocks in COVID-19 infection. […] In autopsy studies, SARS-CoV-2 virus and inflammatory infiltrate have been found in the myocardium, which implies direct viral invasion of the heart. […] ACE-2 downregulation decreases the action of angiotensin leading to increased synthesis of inflammatory mediators like TNF, CRP, and TGF which produces a cytokine storm. […] Troponin elevation and contractility dysfunction occur in the setting of severe hypoxia due to inflammatory damage or hypercoagulability. […] The mechanism of heart block in other cases is poorly understood.

• #16 Heart Block in the Patients with COVID-19 | medRxiv

  https://www.medrxiv.org/content/10.1101/2022.01.05.22268779v1.full-text

  Deterioration of any pre-existing diseases in the conduction system such as AV node disease, bundle branch blocks, or His-Purkinje system disorder can cause new advanced blocks, leading to poor clinical outcomes. […] The exact pathogenesis of heart block in COVID-19 patients must be further explored.

• #17 Pause-dependent paroxysmal phase-4 atrioventricular block | BMJ Case Reports

  https://casereports.bmj.com/content/2015/bcr-2015-211801

  PAVB is an under-recognised entity, and is defined as the sudden and repetitive block of atrial impulses to the ventricles. […] It is thought to occur due to spontaneous depolarisation within the diseased His-Purkinje fibres during a prolonged pause (eg, compensatory post-extrasystole pause or spontaneous slowing of sinus rate). […] The mechanism of this AV block is inactivation of sodium channels due to spontaneous depolarisation within diseased His-Purkinje fibres during a post-extrasystole compensatory pause, followed by inability to conduct electrical impulses due to a very low resting membrane potential (phase 4 of action potential).

• #18 Unexpected Recovery of 1:1 Atrioventricular Conduction in Advanced AV block: What’s the Mechanism?

  https://www.innovationsincrm.com/cardiac-rhythm-management/2013/june/467-advanced-av-block

  Unexpected paroxysmal recovery of 1:1 conduction in patients with advanced atrioventricular (AV) block can occur under specific circumstances. […] The concept of supernormal conduction as a possible mechanism is reviewed. […] These unexpected changes may be explained by supernormal conduction (SNC) in the damaged left posterior fascicle that until then was maintaining the intermittent AV propagation. […] SNC has been defined as the condition under which impulse propagation improves in relation to a supernormal phase of excitability. […] The supernormal phase of conduction has several outstanding features; a prolonged refractory period, either in the His-Purkinje system or AV accessory pathways, appears to be one of the prerequisite requirements for its occurrence. […] For 1:1 SNC to occur, prior adrenergic stimulation must precede the appropriate cycle length shortening.

• #19 Twisting interval in complete heart block, cannot be overlooked: a challenging ECG dilemma – The British Journal of Cardiology

  https://bjcardio.co.uk/2020/09/twisting-interval-in-complete-heart-block-cannot-be-overlooked-a-challenging-ecg-dilemma/

  Ventriculophasic arrhythmia (VPA) is an intriguing electrocardiogram (ECG) phenomenon, often seen in patients with complete heart block, and could sometimes pose a challenging diagnostic dilemma for physicians. […] VPA is often a tell-tale ECG finding of complete heart block. […] Complete heart block (CHB), is an abnormal heart rhythm resulting from a defect in the cardiac conduction system in which there is no conduction through the atrioventricular node (AVN), leading to complete dissociation of the atria and ventricles. […] The mechanism of VPA is still not fully understood. […] The positive chronotropic effect results in an early appearance of a P-wave following the QRS complex, which in turn causes shortening of the PP interval that contains a QRS complex. […] Two potential mechanisms have been proposed regarding the positive chronotropic effect.

• #19 Twisting interval in complete heart block, cannot be overlooked: a challenging ECG dilemma – The British Journal of Cardiology

  https://bjcardio.co.uk/2020/09/twisting-interval-in-complete-heart-block-cannot-be-overlooked-a-challenging-ecg-dilemma/

  A plausible explanation for a negative chronotropic effect involves arterial baroreceptor-mediated changes in vagal tone. […] Ventriculophasic arrhythmia is a common, but probably under-appreciated finding, associated with one-third of the patients with complete heart block. […] Several mechanisms have been postulated but no clear explanation has been agreed upon.

• #20

  https://link.springer.com/article/10.1007/s00431-016-2748-0

  Atrioventricular block is classified as congenital if diagnosed in utero, at birth, or within the first month of life. The pathophysiological process is believed to be due to immune-mediated injury of the conduction system, which occurs as a result of transplacental passage of maternal anti-SSA/Ro-SSB/La antibodies. […] Genetic variants in multiple genes have been described to date in the pathogenesis of inherited progressive cardiac conduction disorders. […] Congenital AV block can be passively acquired via an autoimmune process affecting the developing heart due to the transplacental passage of maternal anti-Ro/SSA and/or anti-La/SSB autoantibodies. Entering the fetal circulation, they can directly bind L-type calcium channels on fetal cardiomyocytes and significantly, but reversibly, inhibit the related currents. However, in some cases, for unclear reasons, the prolonged exposure to anti-Ro/SSA antibodies may induce calcium channel internalization, in turn triggering a complex and only in part mechanistically known perturbation of the cytoplasmic calcium metabolism which ultimately leads to apoptosis and cell death, and then to local inflammation. If the process is not stopped in this phase, the inflammatory damage proceeds, thus eventually resulting in fibrosis and calcification of the cardiac conduction system. This mechanistic sequence, also known as calcium channel hypothesis, is currently recognized as the more attractive theory possible explaining the pathogenesis of the disease.

• #20

  https://link.springer.com/article/10.1007/s00431-016-2748-0

  Inherited progressive cardiac conduction disease (PCCD) is diagnosed in patients less than 50 years of age with an unexplained progressive conduction abnormality but with an otherwise structurally normal heart, especially if there is a family history of PCCD. […] It is now clear that complex pathophysiological processes involving many genes and gene networks may lead to the occurrence of atrioventricular and intraventricular block.

• #21 Congenital atrioventricular heart block: From diagnosis to treatment | Revista Portuguesa de Cardiologia

  https://www.revportcardiol.org/pt-congenital-atrioventricular-heart-block-from-articulo-S0870255121005308

  Damage to the conduction system usually occurs between the 16th and 24th weeks, a period during which maternal antibodies most often cross the placenta via the trophoblast FcRn receptor. […] Maternal antibodies bind to L-type calcium channels in fetal cardiomyocytes, particularly those in the AV node, and reversibly inhibit these channels current. This results in inflammation, calcification and fibrosis of the conduction tissue, leading to irreversible damage, even in structurally normal hearts. […] The polymorphism of codon 25 in the TGFB1 gene has been associated with interindividual variability and increased risk for developing CAVB. […] Another molecular mechanism is increased levels of interferon alpha (INF-), which were found in 78% of cases in a recent study, and increase the expression of class II MHC on CD14+ monocytes.

• #21 Congenital atrioventricular heart block: From diagnosis to treatment | Revista Portuguesa de Cardiologia

  https://www.revportcardiol.org/pt-congenital-atrioventricular-heart-block-from-articulo-S0870255121005308

  Analysis of umbilical cord blood showed that levels of C-reactive protein, N-terminal pro-B-type natriuretic peptide (NT-proBNP), matrix metalloproteinases (particularly type 2), plasminogen and urokinase plasminogen activator are increased in cases of neonatal lupus with severe cardiac damage. This is further evidence for the hypothesis that immune-mediated inflammation and fibrosis are associated with these alterations.

• #22 Heart Block | Cedars-Sinai

  https://www.cedars-sinai.org/health-library/diseases-and-conditions/h/heart-block.html

  Electrical signals control the beating of your heart. They tell your heart muscle when to contract, a process known as conduction. When you have heart block, there is interference with the electrical signals that usually travel from the atria to the ventricles. This is known as a conduction disorder. If the electrical signals cant move from your atria to your ventricles, they cant tell your ventricles to contract and pump blood correctly. […] For most people, heart block develops as you get older. It happens when the electrical signals that connect the top and bottom of the heart develop fibrosis and eventually fail. Sometimes this may happen because of advancing age. Any process that can damage these electrical signals can result in heart block. Coronary artery disease with and without a heart attack is 1 of the most common causes of heart block. Diseases that weaken the heart muscle (cardiomyopathies) can also damage the electrical signals. Heart block can also be caused by any disease that can affect the heart, such as sarcoidosis and certain cancers, or any disease that results in heart inflammation. This can be an autoimmune disease or infection. Electrolyte problems, such as high potassium levels, can also result in heart block. Additionally, some heart surgeries can damage the conduction pathway leading to heart block. Certain heart medicines can also cause varying degrees of heart block. […] Heart block occurs when the electrical signals from the top chambers of your heart dont conduct correctly to the bottom chambers of your heart.

• #23

  https://www.omim.org/entry/234700

  An obvious viral candidate is a Coxsackie virus, since these viruses are common causes of myocarditis, show sequence homology with some intracellular proteins, and may persist in connective tissue diseases such as dermatomyositis. […] Orth et al. (1996) found increased autoantibody titers against human calreticulin (109091) in infants with complete congenital heart block. […] Cooley et al. (1997) described 2 pairs of monozygotic twins discordant for congenital complete heart block. Both mothers were positive for anti-Ro 52 and anti-Ro 60 antibodies, and neither had anti-La antibody on immunoblot. These cases demonstrated that there can be discordance in the development of congenital complete heart block despite identical genetics and presumably very similar exposure to anti-Ro antibody.

• #24 Atrioventricular block – Wikipedia

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

• #25 Heart Block: Types, Symptoms & Causes

  https://my.clevelandclinic.org/health/diseases/17056-heart-block

  The result is a heart that may not work well. Your heart may beat slowly or skip beats. In severe cases, heart block can affect your hearts ability to pump blood, causing low blood flow to your entire body. […] Other names for heart block are atrioventricular (AV) block or a conduction disorder. […] Heart blocks can range from mild to severe, depending on whether the electrical signal can get through, and how often. Heart block types are: […] Third-degree heart block: This is a complete blockage of the electrical signal from your atria to your ventricles. Third-degree block negatively affects your hearts ability to pump blood out to your body. This form of heart block is serious and usually requires a pacemaker for treatment. […] Causes of heart block include: Heart attack. Coronary artery disease (CAD). Heart muscle disease (cardiomyopathy). Heart valve diseases. Scarring in your conduction system from an unknown cause. Issues with your hearts structure (since birth). Heart damage during open heart surgery. Medication side effects (from beta-blockers, digitalis and calcium channel blockers). Exposure to toxins. Obstructive sleep apnea. Thyroid disease. Infections like Lyme disease. Autoimmune diseases. Genetic anomalies.

• #25 Heart Block: Types, Symptoms & Causes

  https://my.clevelandclinic.org/health/diseases/17056-heart-block

  The complications can be life-threatening and include: Heart failure. Arrhythmia (irregular heartbeat). Heart attack. Sudden cardiac arrest. […] Heart block treatment varies from person to person. A provider may admit you to the hospital to monitor your heart. To manage your condition, your cardiologist will consider: Which type of heart block you have. The severity of your heart block. How it affects your hearts ability to function. The symptoms youre having. […] Sometimes, making changes to medicines or treatment for heart disease stops heart block. Other people may need a temporary or permanent pacemaker that sends electrical pulses to their hearts. […] If you need a pacemaker, your provider will talk to you about the details, the type thats best for you, and what to expect before, during and after you get your pacemaker. […] You may be able to prevent some causes of heart block, like heart disease. […] Heart blocks can be serious. Without treatment, severe heart block can cause sudden cardiac arrest. But most commonly, untreated heart block can cause lightheadedness or fainting spells.

• #26 Analysis of the independent risk factors of second-degree atrioventric | IJGM

  https://www.dovepress.com/analysis-of-the-independent-risk-factors-of-second-degree-atrioventric-peer-reviewed-fulltext-article-IJGM

  The pathogenesis of AF is relatively complex, and increasing evidence suggests that the occurrence of AF is related to sudden cardiac death, cerebral infarction, and congestive heart failure. […] AVB is an abnormal conduction along the atrioventricular node or Hipper system, and different etiologies may lead to different outcomes. […] The results showed that smoking history, LAD, R-R interval, and ventricular rate were all influencing factors of AF combined with II AVB. […] Smoking remains the main risk factor for cardiovascular disease. […] The R-R interval exceeding 1.5 seconds and the appearance of escape rhythm are important features of atrial fibrillation. […] In this study, potential confounding factors such as hypertension and coronary heart disease were controlled by multivariate Logistic regression to ensure the independence of risk factors.

• #27 Mechanisms of Heart Block after Transcatheter Aortic Valve Replacement – Cardiac Anatomy, Clinical Predictors and Mechanical Factors that Contribute to Permanent Pacemaker Implantation | AER Journal

  https://www.aerjournal.com/articles/mechanisms-heart-block-after-transcatheter-aortic-valve-replacement-cardiac-anatomy?language_content_entity=en

  However, the benefit of this procedure comes at the cost of a substantially increased risk of high-grade heart block that necessitates the placement of a permanent pacemaker. […] A number of mechanical and clinical features have been implicated as risk factors for PPM placement after TAVR, including usage of the larger profile CoreValve device, deeper implantation within the LVOT (CoreValve), prosthesis to LVOT diameter ratio (SAPIEN valve), and pre-existing RBBB. […] These predictors are meaningful in this context, since it is well-established that the aortic root complex is intimately related to the AV node and its distal conduction fibres.

• #28 Heart Block (AV Block) – Symptoms, Causes and Treatment

  https://en.taylanakgun.com/what-is-a-heart-block

  Another important aspect of treatment is identifying and addressing any underlying conditions that are causing the heart block. For example, certain medications can cause heart block, in which case discontinuing or changing the medication may be necessary. Similarly, imbalances in electrolytes or infections in the body can lead to heart block and should be treated accordingly. […] Untreated heart block can lead to serious complications. Especially in the case of complete block, the heart may not be able to pump enough blood to the body, increasing the risk of organ damage, fainting, and sudden cardiac arrest.

• #29 Unusual course of congenital complete heart block in an adult: A case report

  https://www.wjgnet.com/2307-8960/full/v10/i19/6602.htm

  In contrast to patients with acquired heart block, who frequently have severe cardiac dysfunction largely secondary to structural heart disease and fatal ventricular arrhythmias due to unstable pacemaker site, patients with CCHB often have normal myocardial function and ventricular rate increases with activities seldom complicated by severe ventricular arrhythmias. […] Furthermore, in CCHB, slow heart rate is often ascertained at an early age in the absence of any infection that might cause heart block; notably, diphtheria, rheumatic fever, chorea, and congenital syphilis. […] Accordingly, the excellent outcome of our patient is more supportive of the notion that CCHB in adults even complicated by Adams-Stoke episodes may not always require permanent pacemaker implantation. […] Overall, our patient had a better clinical course than that of the prior case in the absence of treatment.

• #30

  https://consensus.app/questions/av-heart-block/

  Acquired AV block can result from various etiologies, including ischemic heart disease, cardiomyopathies, and the use of certain medications. For instance, catheter ablation for ventricular arrhythmias can induce AV block, particularly in patients with nonischemic cardiomyopathy or those undergoing transcoronary ethanol ablation. Additionally, first-degree AV block, characterized by a prolonged PR interval, can progress to higher degrees of block, especially in patients with marked prolongation of the PR interval. […] Animal models, such as the rat model of complete heart block, have been developed to study the pathophysiology and treatment of AV block. These models help in understanding the hemodynamic changes and myocardial damage associated with AV block, providing insights for future therapeutic interventions. […] Congenital atrioventricular block occurs in 1 in 15,000 to 1 in 20,000 births and is caused by immune-mediated injury to the conduction system.

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