Materiały źródłowe

• #1 Bundle branch block – Symptoms & causes – Mayo Clinic

  https://www.mayoclinic.org/diseases-conditions/bundle-branch-block/symptoms-causes/syc-20370514

  Bundle branch block is a condition in which there’s a delay or blockage along the pathway that electrical impulses travel to make the heart beat. […] The delay or blockage can occur on the pathway that sends electrical impulses either to the left or the right side of the bottom chambers (ventricles) of the heart. […] Electrical impulses that cause your heart to beat (contract) start in the heart’s upper right chamber (right atrium) and travel to the lower chambers (ventricles). In bundle branch block, the pathway these impulses follow is delayed or blocked. The pathway includes two branches the left and the right bundles. If one bundle is damaged, the ventricles rely on the other bundle to receive and respond to signals from the right atrium. If both bundles are blocked, the heart may beat very slowly, which can require a pacemaker.

• #2 Bundle branch block – Wikipedia

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

  A bundle branch block is a partial or complete interruption in the flow of electrical impulses in either of the bundle branches of the heart’s electrical system. […] When a bundle branch or fascicle becomes injured (by underlying heart disease, myocardial infarction, or cardiac surgery), it may cease to conduct electrical impulses appropriately. This results in altered pathways for ventricular depolarization. Since the electrical impulse can no longer use the preferred pathway across the bundle branch, it may move instead through muscle fibers in a way that both slows the electrical movement and changes the directional propagation of the impulses. As a result, there is a loss of ventricular synchrony, ventricular depolarization is prolonged, and there may be a corresponding drop in cardiac output. […] In more severe cases, a pacemaker may be required to restore an optimal electrical supply to the heart muscle.

• #3 Understanding Bundle Branch Blocks

  https://medictests.com/units/bundle-branch-blocks-right-left-complete-vs-incomplete

  A bundle branch block (BBB) is a block of the right or the left bundle branches that propagate depolarizations from the Sino-Atrial node to and through the ventricles. The signal is conducted first through the healthy branch, and then it is distributed to the damaged side. This skewing of one ventricle taking longer than the other widens the QRS complex abnormally. […] COMPLETE BUNDLE BRANCH BLOCKS are full obstructions along the pathway that electrical impulses travel to get to the ventricles. […] INCOMPLETE BUNDLE BRANCH BLOCKS are partial obstructions or delays along the pathway that electrical impulses travel to get to the ventricles and can be either right-sided or left-sided. […] Right bundle branch blocks are either delays or partial obstructions (incomplete bundle branch blocks) or full obstructions along the pathway that electrical impulses travel to get to the right ventricle and are evidenced by wider than normal QRS segments in normal ECGs, and require 12-lead acquisition for further differentiation.

• #4 Bundle Branch and Fascicular Blocks | Concise Medical Knowledge

  https://www.lecturio.com/concepts/bundle-branch-and-fascicular-blocks/

  Bundle branch and fascicular blocks arise due to obstruction of electrical current through the His-Purkinje system and are named on the basis of the location of that disruption. […] Impairment in a bundle causes disruption of downward cardiac impulse transmission. […] This subsequently causes the impulse to be conducted through the opposite branch. […] The contralateral ventricle will depolarize first. […] The ipsilateral ventricle will depolarize later (electrical impulse travels slowly through the muscle, reaching the conduction system below the block). […] This will appear as prolongation of the QRS interval on ECG. […] The pathophysiology is similar to that of bundle branch blocks, though the bundle branch is not completely affected; depolarization of the left ventricle is dependent on the opposite fascicle.

• #5 Bundle branch block – Symptoms & causes – Mayo Clinic

  https://www.mayoclinic.org/diseases-conditions/bundle-branch-block/symptoms-causes/syc-20370514

  Bundle branch block is a condition in which there’s a delay or blockage along the pathway that electrical impulses travel to make the heart beat. […] The delay or blockage can occur on the pathway that sends electrical impulses either to the left or the right side of the bottom chambers (ventricles) of the heart. […] Electrical impulses that cause your heart to beat (contract) start in the heart’s upper right chamber (right atrium) and travel to the lower chambers (ventricles). In bundle branch block, the pathway these impulses follow is delayed or blocked. The pathway includes two branches the left and the right bundles. If one bundle is damaged, the ventricles rely on the other bundle to receive and respond to signals from the right atrium. If both bundles are blocked, the heart may beat very slowly, which can require a pacemaker.

• #6 Right Bundle Branch Block – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK507872/

  Right bundle branch block (RBB) is an electrocardiogram finding resulting in a widened QRS and electrocardiographic vector changes. […] Right bundle branch block is associated with structural changes from stretch or ischemia to the myocardium. […] A right bundle branch block is typically caused by disease processes that change the myocardium of the right bundle branch, for example, structural changes, trauma, and infiltrative processes. […] When the right bundle branch is interrupted, electrical stimuli from the atrioventricular (AV) node conducts to the bundle of His and down the left bundle branch. […] In patients with cardiovascular disease, right bundle branch block is an independent risk factor for all-cause mortality.

• #7 Left Bundle Branch Block – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK482167/

  Left bundle branch block (LBBB) is a cardiac conduction disorder that affects the left bundle branch of the heart’s conduction system, leading to delayed or abnormal electrical impulses through the ventricles. This condition is commonly associated with structural heart diseases such as ischemic heart disease, cardiomyopathies, and valvular disorders. […] New-onset LBBB, especially in the context of acute coronary syndromes, is considered an ST-segment elevation equivalent, indicating a potential risk of myocardial infarction. LBBB is also linked to an increased likelihood of developing heart failure and arrhythmias, such as atrial fibrillation or ventricular tachycardia. […] Left bundle branch block (LBBB) is an intraventricular conduction abnormality usually caused by ischemic or mechanical factors affecting the cardiac conduction system’s left bundle branch. The condition can be seen in association with structural heart diseases, such as ischemic or valvular heart disease, and cardiomyopathies, including dilatation, hypertrophic, fibrotic, or infiltrative cardiomyopathies. […] A complete LBBB results in an abnormal left ventricular activation sequence and diffuse slowing of cardiac conduction.

• #8 A case of rate dependent bundle branch block presented with atypical course of the disease – MedCrave online

  https://medcraveonline.com/MOJCR/a-case-of-rate-dependent-bundle-branch-block-presented-with-atypical-course-of-the-disease.html

  Rate dependent bundle branch block is a common phenomenon. […] The condition is associated with bad cardiac prognosis and needs close follow up with a cardiologist. […] The phenomenon known as „intermittent (rate dependent or transient) bundle branch block (RDBBB) was first described by Lewis in 1913 and demonstrated experimentally by Drury and Mackenzie in 1934. […] In most cases, RDBBB occurs when a critical heart rate is exceeded, and has been attributed to a prolongation of recovery in the diseased bundle branch. […] Several hypotheses have been proposed to explain these phenomena, including concealed conduction, hypoxia, vagal effects and super normality of the affected bundle. […] Recently, Singer et al. demonstrated that depolarization of depressed Purkinje fibers can lead to propagation impairment and can produce slow conduction or even blockade.

• #9 Right Bundle Branch Block (RBBB) • LITFL • ECG Library Diagnosis

  https://litfl.com/right-bundle-branch-block-rbbb-ecg-library/

  In normal cardiac conduction, impulses travel equally down the left and right bundles, with the septum activated from left to right and the formation of small Q waves in lateral leads […] In RBBB, the left ventricle is activated normally, thus the early part of the QRS complex correlating to septal depolarisation is unchanged […] There is delayed activation of the right ventricle as depolarisation originates from the left ventricle across the septum. This produces a secondary R wave (R) in the precordial leads, and a wide, slurred S wave in lateral leads […] Normal activation of the left ventricle means that cardiac axis remains normal in isolated RBBB […] There is increasing literature suggesting that in the context of chest pain, a new RBBB is highly concerning for OMI and a potential indication for immediate reperfusion therapy. The right bundle branch is supplied by LAD perforators in most patient populations and thus occlusion of this branch may manifest as a new RBBB +/- LAFB.

• #10 Right bundle branch block – Wikipedia

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

  A right bundle branch block (RBBB) is a heart block in the right bundle branch of the electrical conduction system. […] During a right bundle branch block, the right ventricle is not directly activated by impulses traveling through the right bundle branch. However, the left bundle branch still normally activates the left ventricle. These impulses can then travel through the myocardium of the left ventricle to the right ventricle and depolarize the right ventricle this way. As conduction through the myocardium is slower than conduction through the bundle of His-Purkinje fibres, the QRS complex is seen to be widened. The QRS complex often shows an extra deflection that reflects the rapid depolarisation of the left ventricle, followed by the slower depolarisation of the right ventricle. […] Common causes include normal variation, changes in bundle branch structure – such as mechanical stretching, chest trauma, right ventricular hypertrophy or strain, congenital heart disease such as atrial septal defect, and ischemic heart disease.

• #11 Right Bundle Branch Block (RBBB) • LITFL • ECG Library Diagnosis

  https://litfl.com/right-bundle-branch-block-rbbb-ecg-library/

  In normal cardiac conduction, impulses travel equally down the left and right bundles, with the septum activated from left to right and the formation of small Q waves in lateral leads […] In RBBB, the left ventricle is activated normally, thus the early part of the QRS complex correlating to septal depolarisation is unchanged […] There is delayed activation of the right ventricle as depolarisation originates from the left ventricle across the septum. This produces a secondary R wave (R) in the precordial leads, and a wide, slurred S wave in lateral leads […] Normal activation of the left ventricle means that cardiac axis remains normal in isolated RBBB […] There is increasing literature suggesting that in the context of chest pain, a new RBBB is highly concerning for OMI and a potential indication for immediate reperfusion therapy. The right bundle branch is supplied by LAD perforators in most patient populations and thus occlusion of this branch may manifest as a new RBBB +/- LAFB.

• #12 Right Bundle Branch Block (RBBB) • LITFL • ECG Library Diagnosis

  https://litfl.com/right-bundle-branch-block-rbbb-ecg-library/

  In normal cardiac conduction, impulses travel equally down the left and right bundles, with the septum activated from left to right and the formation of small Q waves in lateral leads […] In RBBB, the left ventricle is activated normally, thus the early part of the QRS complex correlating to septal depolarisation is unchanged […] There is delayed activation of the right ventricle as depolarisation originates from the left ventricle across the septum. This produces a secondary R wave (R) in the precordial leads, and a wide, slurred S wave in lateral leads […] Normal activation of the left ventricle means that cardiac axis remains normal in isolated RBBB […] There is increasing literature suggesting that in the context of chest pain, a new RBBB is highly concerning for OMI and a potential indication for immediate reperfusion therapy. The right bundle branch is supplied by LAD perforators in most patient populations and thus occlusion of this branch may manifest as a new RBBB +/- LAFB.

• #13 Right bundle branch block (RBBB): ECG, criteria, definitions, causes & treatment – The Cardiovascular

  https://ecgwaves.com/topic/right-bundle-branch-block-rbbb-ecg-criteria-treatment/

  Right bundle branch block (RBBB) is due to an anatomical or functional dysfunction in the right bundle branch, such that the electrical impulse is blocked. […] In right bundle branch block (RBBB), the right ventricle depolarizes after the left ventricle, allowing its electrical vectors to become evident. These vectors manifest in the later part of the QRS complex as an R wave (pronounced R prime), which is directed anteriorly and rightward. […] Due to the abnormal depolarization sequence of the right ventricle in RBBB, repolarization is also abnormal, leading to secondary ST-T changes, which appear on the ECG as discordant ST-T segments. […] Right bundle branch block does not affect the electrical axis of the heart. […] The prevalence of right bundle branch block (RBBB) in healthy individuals varies by age, gender, and diagnostic criteria, ranging from 0.2% to 8% in the general population.

• #14 Pediatric Right Bundle Branch Block: Background, Pathophysiology, Etiology

  https://emedicine.medscape.com/article/894927-overview

  Exercise-induced right bundle branch block has been rarely noted and appears to be benign. […] Three types of right bundle branch block have been identified in electrophysiologic studies. Proximal, or central, right bundle branch block occurs when a conduction block is present just distal to the bundle of His in the superior aspect of the right bundle branch. This generally occurs when the proximal bundle is injured during surgery for lesions with an inlet or membranous ventricular septal defect (VSD). […] In general, surgically induced right bundle branch block results in no clinically significant acute hemodynamic consequences and has a benign course over the long term. In rare cases, a progression to complete heart block and sudden death is a concern, particularly if the right bundle branch block pattern is accompanied by additional evidence of substantial injury to the His-Purkinje system (eg, left anterior hemiblock, first-degree AV block).

• #15 Structural Causes of Right Bundle Branch Block—Time for a Closer Look?

  https://opencardiovascularmedicinejournal.com/VOLUME/4/PAGE/105/?doi=10.1126/sciadv.adg2248

  In this study a third cause of RBBB is proposed neither proximal, nor distal, but one caused by increased conduction to the left ventricle by a subaortic muscular tendon in this way causing a pseudo RBBB. […] In this study, it is proposed that there exists a third type of right bundle branch block neither proximal, nor distal, but one caused by an increased velocity of conduction to the left ventricle, effected by a muscular sub-aortic tendon coursing between the sub-aortic portion of the interventricular septum and the apex of the left ventricle, in this way leading to a relative RBBB as conduction in the right ventricle lags behind the increased conduction in the left ventricle. […] Thus, in the assessment of structural causes for right bundle branch block it is suggested that it is time to take a closer look at endoventricular structures and specifically at muscular structures traversing the cavity of the left ventricle.

• #16 Complete right bundle branch block of unique behavior: What is the mechanism? | Akerström | Cardiology Journal

  https://journals.viamedica.pl/cardiology_journal/article/view/CJ.2013.0036/32158

  Complete right bundle branch block of unique behavior: What is the mechanism? […] Intermittent bundle branch block may be caused by several mechanisms namely tachycardia-dependent (phase 3) block, acceleration-dependent block, bradycardia-dependent (phase 4) block and concealed conduction. […] Normally, as the heart rate accelerates, the His-Purkinje system (HPS) effective refractory period shortens thereby preserving normal conduction. Acceleration-dependent block occurs at critically increasing heart rates (but still below the action potential duration) when the action potential of the, often diseased, bundle branch fails to shorten in response to heart rate acceleration. […] A probable mechanism would be an atypical Wenckebach-type second-degree block in the RBB. […] Another plausible underlying mechanism for the intermittent RBBB observed might be tachycardia-dependent (phase 3) block.

• #17 Rate dependent bundle branch block

  https://www.cardioscan.co/harrys-corner/rate-dependent-bundle-branch-block

  This is a rate dependent bundle branch block. […] There are lesions in the bundle branch which result in altered conduction and are rate dependent. […] At least for the left bundle, the reported prognosis of a rate dependent bundle branch block can be poor as it is often associated with septal ischaemia. […] A bradycardia dependent bundle branch block is a rare ECG finding.

• #18 Left Bundle Branch Block (LBBB) • LITFL • ECG Library Diagnosis

  https://litfl.com/left-bundle-branch-block-lbbb-ecg-library/

  In normal cardiac conduction, impulses travel equally down the left and right bundles, with the septum activated from left to right and the formation of small Q waves in lateral leads […] In LBBB, conduction delay means that impulses travel first via the right bundle branch to the RV, and then to the LV via the septum […] Septal activation is thus reversed eliminating lateral Q waves […] The overall depolarisation vector from the right to left ventricle produces tall R waves in lateral leads (I, V5-6) and deep S waves in the right precordial leads (V1-3). The delay between activation of the RV and LV produces the characteristic M-shaped R wave seen in lateral leads […] Delayed overall conduction time to the LV extends the QRS duration to 120 ms […] It is unusual for LBBB to exist in the absence of organic disease. Causes are varied and include: Aortic stenosis, Ischaemic heart disease, Hypertension, Dilated cardiomyopathy, Anterior MI, Lengre-Lev disease: primary degenerative disease (fibrosis) of the conducting system, Hyperkalaemia, Digoxin toxicity

• #19 Left bundle branch block pathophysiology – wikidoc

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

  Unlike right bundle branch block (RBBB), left bundle branch block completely modifies the way of depolarization of the conduction system of the heart. In LBBB the activation of the interventricular septum is from right to left due to uninterrupted conduction in the RBB. […] Then the electrical impulse propagates inferiorly to the left resulting in delayed depolarization and activation of the left ventricle especially the left lateral wall. […] In LBBB the right to left activation of the septum causes a small negative deflection (Q wave) in lead V1 and a positive deflection (R wave) in lead V6. Right ventricle depolarizes earlier than the left ventricle giving an R wave in lead V1 and an S wave in lead V6. Subsequent delayed depolarization of the left ventricle results in an S wave in lead V1 and another R wave in lead V6.

• #20 Left Bundle Branch Block (LBBB) • LITFL • ECG Library Diagnosis

  https://litfl.com/left-bundle-branch-block-lbbb-ecg-library/

  In normal cardiac conduction, impulses travel equally down the left and right bundles, with the septum activated from left to right and the formation of small Q waves in lateral leads […] In LBBB, conduction delay means that impulses travel first via the right bundle branch to the RV, and then to the LV via the septum […] Septal activation is thus reversed eliminating lateral Q waves […] The overall depolarisation vector from the right to left ventricle produces tall R waves in lateral leads (I, V5-6) and deep S waves in the right precordial leads (V1-3). The delay between activation of the RV and LV produces the characteristic M-shaped R wave seen in lateral leads […] Delayed overall conduction time to the LV extends the QRS duration to 120 ms […] It is unusual for LBBB to exist in the absence of organic disease. Causes are varied and include: Aortic stenosis, Ischaemic heart disease, Hypertension, Dilated cardiomyopathy, Anterior MI, Lengre-Lev disease: primary degenerative disease (fibrosis) of the conducting system, Hyperkalaemia, Digoxin toxicity

• #21 Left bundle branch block (LBBB): ECG criteria, causes, management – The Cardiovascular

  https://ecgwaves.com/topic/left-bundle-branch-block-lbbb-ecg-criteria-treatment/

  Left bundle branch block (LBBB) results from anatomical or functional impairment of the left bundle branch (LBB), leading to a blockage of electrical impulse conduction through this bundle. Consequently, depolarization of the left ventricle is achieved by impulses spreading from the right ventricle. […] In left bundle branch block, depolarization of the septum occurs via impulses spreading from the right ventricle. Consequently, the small r-waves in V1V2 and small q-waves in V5V6 are either diminished or disappeared. Depolarization continues slowly towards the left ventricular free wall, and the vector is continuously directed leftward. This causes a wide S-wave in V1V2 (referred to as QS complex if the r-wave is absent) and a broad and notched R-wave in V5V6. […] Due to the abnormal left ventricular depolarization sequence in LBBB, the repolarization process is also abnormal, leading to secondary ST-T changes that become apparent. In LBBB, it is expected that ST segment depressions and T-wave inversions exist in left-sided leads (V5, V6, I and aVL). Simultaneously, V1V3 typically display ST-segment elevation and large S-waves.

• #22 LB-NICM: New Approach | AER Journal

  https://www.aerjournal.com/articles/left-bundle-branch-block-associated-cardiomyopathy-new-approach?language_content_entity=en

  Left bundle branch block (LBBB) is frequently associated with structural heart disease, and predicts higher rates of morbidity and mortality. […] In the absence of any other known aetiology, LBBB-associated cardiomyopathy represents a potentially reversible form of cardiomyopathy, with the majority of the patients having reverse remodelling after CRT by left bundle branch pacing. This review provides the mechanism, published evidence and role of conduction system pacing for patients with LBBB-associated cardiomyopathy. […] The electrophysiological abnormality resulting in LBBB could be a conduction defect into the left bundle rather than within the left bundle. […] Understanding the activation of the left His-Purkinje system during complete LBBB is important, as those patients with conduction block into LBBB could be corrected by conduction system pacing, while those with intact Purkinje activation may not be amenable to conduction system pacing.

• #23 Defining Left Bundle Branch Block Patterns in Cardiac Resynchronisation Therapy: A Return to His Bundle Recordings

  https://www.aerjournal.com/articles/defining-left-bundle-branch-block-patterns-cardiac-resynchronisation-therapy-return-his?language_content_entity=en

  Left bundle branch block (LBBB) is associated with improved outcome after cardiac resynchronisation therapy (CRT). […] The ability to normalize wide QRS patterns with His bundle pacing (HBP) has called this notion into question. […] During a novel extension of the classical EPS to involve left-sided recordings, we found that conduction block associated with the LBBB pattern is most often proximal, usually within the left-sided His fibres, and these patients are the most likely to demonstrate QRS correction with HBP for resynchronisation. […] Future EPS are required to determine the impact of newer approaches to conduction system pacing, including intraseptal or left ventricular septal pacing. […] The physiology of conduction system disease is highly individualised and requires therapy directed at the patients underlying pathophysiology; traditional LV lead placement into an available tributary of the coronary sinus might not meet the needs of an individual patient.

• #24 Defining Left Bundle Branch Block Patterns in Cardiac Resynchronisation Therapy: A Return to His Bundle Recordings

  https://www.aerjournal.com/articles/defining-left-bundle-branch-block-patterns-cardiac-resynchronisation-therapy-return-his?language_content_entity=en

  Identifying patients who might achieve physiological resynchronisation, however, can be challenging. […] In CRT, a precise diagnosis of the level and extent of conduction system pathology could improve technology selection, lead delivery and outcomes of physiological pacing. […] His bundle pacing (HBP) is a promising method to achieve electromechanical resynchronisation, as pacing utilising this strategy recruits the intrinsic specialised conduction system. […] Until recently, the underlying mechanism of how HBP (delivered proximally in the conduction system) corrects LBBB patterns (a distal defect) had not been well understood. […] The findings of complete conduction block at the level of the left-sided His fibres or the proximal LBBB are consistent with the theory of longitudinal dissociation, in that the inferred site of pathology is a proximal lesion within the branching His bundle, but differs significantly from this proposed theory because left bundle activation was not asynchronous relative to the right bundle, but completely blocked.

• #25 LB-NICM: New Approach | AER Journal

  https://www.aerjournal.com/articles/left-bundle-branch-block-associated-cardiomyopathy-new-approach?language_content_entity=en

  LBBB is characterised by delayed activation of the left ventricular posterolateral wall and significantly prolonged LV activation time resulting in interventricular and intra-ventricular dyssynchrony. […] There is a global discoordination of the contraction/relaxation process designated as intraventricular and interventricular dyssynchrony. […] Hence, the loss of septal contribution to LV function, as well as excessive workload on the lateral wall, results in LV lateral wall hypertrophy and thinning of the septum in the majority of the patients with long-standing LBBB. […] The mechanism of functional mitral regurgitation includes increased subvalvular traction due to papillary muscle displacement, mitral annular dilatation and slow closure of the mitral valve due to poor LV contraction.

• #26 LB-NICM: New Approach | AER Journal

  https://www.aerjournal.com/articles/left-bundle-branch-block-associated-cardiomyopathy-new-approach?language_content_entity=en

  LBBB is characterised by delayed activation of the left ventricular posterolateral wall and significantly prolonged LV activation time resulting in interventricular and intra-ventricular dyssynchrony. […] There is a global discoordination of the contraction/relaxation process designated as intraventricular and interventricular dyssynchrony. […] Hence, the loss of septal contribution to LV function, as well as excessive workload on the lateral wall, results in LV lateral wall hypertrophy and thinning of the septum in the majority of the patients with long-standing LBBB. […] The mechanism of functional mitral regurgitation includes increased subvalvular traction due to papillary muscle displacement, mitral annular dilatation and slow closure of the mitral valve due to poor LV contraction.

• #27 Left bundle branch block-induced cardiomyopathy: A review and pooled analysis of pathophysiology, diagnosis and clinical management

  https://www.oatext.com/left-bundle-branch-block-induced-cardiomyopathy-a-review-and-pooled-analysis-of-pathophysiology-diagnosis-and-clinical-management.php

  The mechanisms of LBBB-associated LV dysfunction is an altered pattern of ventricular activation and contraction. […] The presence of LBBB alters this synchronous activation and contraction. […] The contraction of the LV free wall causes ejection of blood into the aorta. However, since the septum represents about a third of the LV mass, the loss of a large portion of the septal contribution to LV function adds substantial workload on the LV lateral wall (energy-inefficient contraction), which is a major stimulus to adverse remodelling in HF patients with LBBB. […] The current proposed role of LBBB in the pathogenesis of CM is mechanical dyssynchrony on ventricular contraction. […] The remarkable response to CRT is the key finding identifying LBBB as a reversible cause of CM.

• #28 Left bundle branch block-induced dilated cardiomyopathy: Definitions, pathophysiology, and therapy | Revista Portuguesa de Cardiologia

  https://www.revportcardiol.org/pt-left-bundle-branch-block-induced-dilated-articulo-S0870255124000817

  Left bundle branch block (LBBB) is a frequent finding in patients with heart failure (HF), particularly in those with dilated cardiomyopathy (DCM). […] However, a total recovery of left ventricular (LV) function after cardiac resynchronization therapy (CRT), observed in patients with LBBB and DCM, has led to increasing acknowledgement of LBBB-induced dilated cardiomyopathy (LBBB-iDCM) as a specific pathological entity. […] At present, there are no definitive diagnostic criteria enabling the universal identification of LBBB-iDCM, and no defined therapeutic approach in this subgroup of patients. […] This review compiles the main findings about LBBB-iDCM pathophysiology and the current proposed diagnostic criteria and therapeutic approach. […] The relationship between LBBB and DCM is well known, particularly the traditional concept of LBBB development as a consequence of DCM progression.

• #29 Left bundle branch block-induced dilated cardiomyopathy: Definitions, pathophysiology, and therapy | Revista Portuguesa de Cardiologia

  https://www.revportcardiol.org/pt-left-bundle-branch-block-induced-dilated-articulo-S0870255124000817

  However, the excellent response to CRT reported in many patients with LBBB and concomitant DCM has contributed to the recognition of LBBB-iDCM as a distinct entity. […] Accordingly, LBBB may appear in the natural course of DCM, and present as a marker of disease severity, or it may play a causative role in LV dysfunction development. […] The latter corresponds to the increasingly recognized LBBB-iDCM entity, also known as dessynchronopathy. […] Left bundle branch block leads to a dyssynchronous activation and contraction of the LV. […] The mechanical dyssynchrony induced by LBBB can ultimately lead to LV hypertrophy, dilatation, and systolic dysfunction. […] Not all patients with LBBB develop DCM, raising an emerging question about the existence of certain characteristics that might determine this evolution in some patients and not in others.

• #30 Left bundle branch block-induced dilated cardiomyopathy: Definitions, pathophysiology, and therapy | Revista Portuguesa de Cardiologia

  https://www.revportcardiol.org/pt-left-bundle-branch-block-induced-dilated-articulo-S0870255124000817

  However, the excellent response to CRT reported in many patients with LBBB and concomitant DCM has contributed to the recognition of LBBB-iDCM as a distinct entity. […] Accordingly, LBBB may appear in the natural course of DCM, and present as a marker of disease severity, or it may play a causative role in LV dysfunction development. […] The latter corresponds to the increasingly recognized LBBB-iDCM entity, also known as dessynchronopathy. […] Left bundle branch block leads to a dyssynchronous activation and contraction of the LV. […] The mechanical dyssynchrony induced by LBBB can ultimately lead to LV hypertrophy, dilatation, and systolic dysfunction. […] Not all patients with LBBB develop DCM, raising an emerging question about the existence of certain characteristics that might determine this evolution in some patients and not in others.

• #31 Left bundle branch block-induced dilated cardiomyopathy: Definitions, pathophysiology, and therapy | Revista Portuguesa de Cardiologia

  https://www.revportcardiol.org/pt-left-bundle-branch-block-induced-dilated-articulo-S0870255124000817

  However, the excellent response to CRT reported in many patients with LBBB and concomitant DCM has contributed to the recognition of LBBB-iDCM as a distinct entity. […] Accordingly, LBBB may appear in the natural course of DCM, and present as a marker of disease severity, or it may play a causative role in LV dysfunction development. […] The latter corresponds to the increasingly recognized LBBB-iDCM entity, also known as dessynchronopathy. […] Left bundle branch block leads to a dyssynchronous activation and contraction of the LV. […] The mechanical dyssynchrony induced by LBBB can ultimately lead to LV hypertrophy, dilatation, and systolic dysfunction. […] Not all patients with LBBB develop DCM, raising an emerging question about the existence of certain characteristics that might determine this evolution in some patients and not in others.

• #32 LB-NICM: New Approach | AER Journal

  https://www.aerjournal.com/articles/left-bundle-branch-block-associated-cardiomyopathy-new-approach?language_content_entity=en

  LBBB may lead to significant myocardial injury beyond conduction system disease. […] The effect of LBBB on cardiac function varies between significant reduction in LV function in some patients to minimal effect in others. […] However, the real challenge is to establish a cause-and-effect relationship between LBBB and LV dysfunction. […] This would suggest that in patients with LBBB and dilated cardiomyopathy, the conduction abnormality is the causative factor for the development of cardiomyopathy. […] Given the evidence that LBBB is the primary aetiology for cardiomyopathy and potentially reversible after CRT, it is essential to identify this subset of patients with LIC as a distinct entity to initiate early device therapy. […] The conduction disease in LB-NICM is fixed, progressive and amenable to complete correction by conduction system pacing.

• #33 Left bundle branch block-induced dilated cardiomyopathy: Definitions, pathophysiology, and therapy | Revista Portuguesa de Cardiologia

  https://www.revportcardiol.org/pt-left-bundle-branch-block-induced-dilated-articulo-S0870255124000817

  This highlights the need for longitudinal studies enrolling patients with isolated and idiopathic LBBB without structural or functional dysfunction, to evaluate and characterize this progression to DCM, and whether it can be prevented in clinical practice, focusing on the search for possible predisposition/predicting factors. […] Considering all this information, recent evidence points to the possible need for a close follow-up of LBBB patients with preserved LVEF. […] The optimal manner for stratification and surveillance (best technique and periodicity) of these asymptomatic LBBB carriers has not yet been established.

• #34 Left Bundle Branch Block – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK482167/

  The clinical significance of LBBB in asymptomatic individuals is controversial. LBBB often appears in the setting of other cardiovascular diseases, such as hypertension, coronary artery disease, or cardiomyopathy. […] The presence of this rhythm abnormality in middle-aged and older individuals is associated with an increased risk of adverse cardiovascular events, such as heart failure, sudden cardiac death, and cardiovascular mortality. […] LBBB can develop gradually or suddenly. New-onset LBBB in the appropriate clinical context is considered an ST-segment elevation equivalent. […] In cases of structural heart disease, the presence of LBBB can exacerbate dyssynchrony in ventricular contraction, further impairing cardiac function. […] LBBB arises from various factors and conditions that can affect the electrical conduction system. The underlying causes can be broadly categorized into structural heart disease, degenerative changes, and other less common factors. […] Recent evidence suggests that several genes are implicated in the pathogenesis of LBBB. Affected genes include HCN4, SCN5A, LMNA, GATA4, and ANK2.

• #35 Left Bundle Branch Block | Treatment & Management | Point of Care

  https://www.statpearls.com/point-of-care/18700

  LBBB arises from various factors and conditions that can affect the electrical conduction system. The underlying causes can be broadly categorized into structural heart disease, degenerative changes, and other less common factors. […] A LBBB results from direct damage to the LBB as a result of conduction delay within the HPS and into the myocardium or a combination of both. With LBBB, the right ventricle is activated first, followed by a right-to-left septal transmission and activation of the left ventricular endocardium at the level of the midseptum. […] Recent evidence suggests that several genes are implicated in the pathogenesis of LBBB. Affected genes include HCN4, SCN5A, LMNA, GATA4, and ANK2.

• #36 Structural Causes of Right Bundle Branch Block—Time for a Closer Look?

  https://opencardiovascularmedicinejournal.com/VOLUME/4/PAGE/105/?doi=10.1126/sciadv.adg2248

  Right bundle branch block is an electrocardiographic phenomenon with specific criteria. […] Currently, two specific forms of right bundle branch block are acknowledged, a proximal and a distal variant. A vast array of pathologies can cause proximal, distal or even combined forms of right bundle branch block. […] In this study it is suggested that a third type of right bundle branch block exist: one caused by a subaortic muscular tendon in the left ventricle, leading to an increased velocity of conduction in the left ventricle, with a resultant relative right bundle branch block. It is concluded that it is necessary (and time) to take a closer look at endoventricular structures in the assessment of structural causes of right bundle branch block. […] RBBB is the electrocardiographic reflection of delayed conduction in the right ventricle, caused by sclerosis (Lenegre`s disease), fibrosis (Lev`s disease) or necrosis of the right bundle branch.

• #37

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

  A study of the ageing changes in the conducting tissue in 44 hearts (aged 289 years) shows that there is a significant loss of conducting fibres, and a relative increase in the amount of elastic tissue. […] 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. […] When the histological features of the different parts of the AV conducting tissue in patients with heart block are compared statistically as a group with similarly aged cases with normal conduction, the only significant change found is a loss of conducting tissue in the bundle branches, with increased fibrosis. […] The fibrosis of the bundle branches in some of these cases is similar to that seen in cases with complete heart block.

• #38 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. Block within the AV node accounts for approximately one fifth of all cases, whereas block within the His bundle accounts for slightly fewer than one fifth of all cases. […] AV block results from various pathologic states causing infiltration, fibrosis, or loss of connection in portions of the healthy conduction system. Third-degree AV block can be either congenital or acquired. […] 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.

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

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

  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 a junctional pacemaker frequently are hemodynamically stable, and their heart rate increases in response to exercise and atropine. When the block is below the AVN, the escape rhythm arises from the His bundle or the bundle-branch Purkinje system at rates slower than 45 beats/min. These patients generally are hemodynamically unstable, and their heart rate is unresponsive to exercise and atropine.

• #40

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

  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.

• #41 Bundle branch block – Symptoms & causes – Mayo Clinic

  https://www.mayoclinic.org/diseases-conditions/bundle-branch-block/symptoms-causes/syc-20370514

  Electrical impulses within the heart muscle cause it to beat (contract). These impulses travel along a pathway, including two branches called the right and the left bundles. If one or both of these branch bundles are damaged due to a heart attack, for example the electrical impulses can become blocked. As a result, the heart beats irregularly. […] The cause for bundle branch blocks can differ depending on whether the left or the right bundle branch is affected. Sometimes, there is no known cause. […] If both the right and the left bundles are blocked, the main complication is a complete blockage of the electric signaling from the upper to the lower chambers of the heart. The lack of signaling can slow the heart rate. A slowed heart rate may lead to fainting, irregular heart rhythms and other serious complications. […] Because bundle branch block affects the electrical activity of the heart, it can sometimes complicate the accurate diagnosis of other heart conditions, especially heart attacks. It may lead to delays in proper management of those heart conditions.

• #42 Bundle Branch Block: Causes, Symptoms & Treatment

  https://my.clevelandclinic.org/health/diseases/22938-bundle-branch-block

  Right bundle branch block may also result from lung diseases including: Chronic obstructive pulmonary disease (COPD). Pulmonary embolism. Pulmonary hypertension (PH). […] A left bundle branch block may be the first sign of a complete heart block. […] If you have other conditions that affect your heart, BBB may make your heart deteriorate faster and worsen your symptoms.

• #43 Right bundle branch block – Wikipedia

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

  In addition, a right bundle branch block may also result from Brugada syndrome, Chagas disease, pulmonary embolism, rheumatic heart disease, myocarditis, cardiomyopathy, or hypertension. […] Causes for incomplete right bundle branch block (IRBBB) often involve exercise-induced right ventricular remodeling, increased right ventricular (RV) free wall thickness, especially in athletes due to prolonged endurance exercise. […] The criteria to diagnose a right bundle branch block on the electrocardiogram: The heart rhythm must originate above the ventricles (i.e., sinoatrial node, atria or atrioventricular node) to activate the conduction system at the correct point. The QRS duration must be more than 100 ms (incomplete block) or more than 120 ms (complete block). There should be a terminal R wave in lead V1 (often called „R prime,” and denoted by R, rR’, rsR’, rSR’, or qR). There must be a prolonged S wave in leads I and V6 (sometimes referred to as a „slurred” S wave). […] The underlying condition may be treated by medications to control hypertension or diabetes, if they are the primary underlying cause. If coronary arteries are blocked, an invasive coronary angioplasty may relieve the impending RBBB.

• #44 Right bundle branch block (RBBB): ECG, criteria, definitions, causes & treatment – The Cardiovascular

  https://ecgwaves.com/topic/right-bundle-branch-block-rbbb-ecg-criteria-treatment/

  While traditionally considered benign in asymptomatic individuals, recent evidence suggests that RBBB may be linked to an increased cardiovascular risk. […] Key predictors of incident RBBB included male sex, older age, high systolic blood pressure, and the presence of incomplete RBBB. […] Complete RBBB was associated with increased all-cause mortality (1.3-fold higher relative risk) and cardiovascular mortality (1.9-fold higher relative risk), as well as an elevated risk of myocardial infarction (1.7-fold higher relative risk) and pacemaker implantation (2.2-fold higher relative risk). […] The findings suggest that RBBB in asymptomatic individuals may signal increased cardiovascular risk, challenging the perception of its benign nature. […] Causes of right bundle branch block (RBBB) include idiopathic fibrosis or degeneration in the right bundle branch, congenital heart disease, ischemic heart disease (coronary artery disease), acute cor pulmonale (pulmonary embolism), chronic obstructive pulmonary disease, cardiac surgery, PCI, cardiomyopathy, and aberrant ventricular conduction. […] The right bundle branch block does not interfere with the diagnosis of ischemia/infarction.

• #45 Left Bundle Branch Block – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK482167/

  Left bundle branch block (LBBB) is a cardiac conduction disorder that affects the left bundle branch of the heart’s conduction system, leading to delayed or abnormal electrical impulses through the ventricles. This condition is commonly associated with structural heart diseases such as ischemic heart disease, cardiomyopathies, and valvular disorders. […] New-onset LBBB, especially in the context of acute coronary syndromes, is considered an ST-segment elevation equivalent, indicating a potential risk of myocardial infarction. LBBB is also linked to an increased likelihood of developing heart failure and arrhythmias, such as atrial fibrillation or ventricular tachycardia. […] Left bundle branch block (LBBB) is an intraventricular conduction abnormality usually caused by ischemic or mechanical factors affecting the cardiac conduction system’s left bundle branch. The condition can be seen in association with structural heart diseases, such as ischemic or valvular heart disease, and cardiomyopathies, including dilatation, hypertrophic, fibrotic, or infiltrative cardiomyopathies. […] A complete LBBB results in an abnormal left ventricular activation sequence and diffuse slowing of cardiac conduction.

• #46 Left Bundle Branch Block: Causes, Symptoms & Treatment

  https://my.clevelandclinic.org/health/diseases/23287-left-bundle-branch-block

  Left bundle branch block occurs when something blocks or disrupts the electrical impulse that causes your heart to beat. This block leads to an abnormal heart rhythm. A diagnosis of left bundle branch block often means that you have an underlying heart condition. […] Left bundle branch block often results from heart damage. Conditions that can cause LBBB include: Heart attack (myocardial infarction), Heart disease (coronary artery disease), Heart failure, Heart infection (myocarditis), Heart valve disease, High blood pressure (hypertension), Weakened or stiffened heart muscle (cardiomyopathy), Congenital heart defects. […] Sometimes, left bundle branch block has no known cause. It can occur in people whose hearts otherwise function normally and who have no underlying conditions.

• #47 Left Bundle Branch Block | Arrhythmias – MedSchool

  https://medschool.co/diseases/arrhythmias/left-bundle-branch-block

  Left bundle branch block occurs due to failure of conduction down the left bundle branch, resulting in depolarisation of the left ventricle after the right ventricle. […] Causes of Left Bundle Branch Block include Ischaemic heart disease, Hypertension, Dilated cardiomyopathy, Rheumatic heart disease, Aortic stenosis.

• #48 Left bundle branch block after sutureless, transcatheter, and stented biological aortic valve replacement for aortic stenosis | EuroIntervention

  https://eurointervention.pcronline.com/article/left-bundle-branch-block-after-sutureless-transcatheter-and-stented-biological-aortic-valve-replacement-for-aortic-stenosis

  Aims: Conventional aortic valve replacement (AVR), sutureless AVR (su-AVR) and transcatheter aortic valve implantation (TAVI) for severe aortic stenosis (AS) are associated with conduction abnormalities. The aim of the present study was to assess the incidence of left bundle branch block (LBBB) after su-AVR and TAVI, in comparison to conventional AVR. […] Su-AVR and TAVI were associated with higher risk of developing postoperative LBBB compared to conventional AVR, after adjusting for age, preoperative heart rate and QRS duration. […] One of the complications that may occur after TAVI and surgical AVR is new-onset left bundle branch block (LBBB). […] New-onset LBBB after AVR can be related to compression by the prosthesis on the conduction system. […] The bundle branch initiates at the base of the interleaflet triangle between the non-coronary and right coronary cusps, located at the aortic annulus.

• #49 Left bundle branch block after sutureless, transcatheter, and stented biological aortic valve replacement for aortic stenosis | EuroIntervention

  https://eurointervention.pcronline.com/article/left-bundle-branch-block-after-sutureless-transcatheter-and-stented-biological-aortic-valve-replacement-for-aortic-stenosis

  Stented biological prostheses are placed supra-annular, whereas the su-AVR and TAVI prostheses are placed intra-annular, close to the bundle branch, which may lead to an increased risk of damage of the conduction system. […] Besides the position of the valve, the size of the implanted prosthesis relative to the annulus size is important in the pathophysiology of conduction abnormalities. […] However, excessive oversizing can result in increased compression of the conduction system and aortic annulus rupture. […] Another factor responsible for the occurrence of LBBB after AVR might be related to the expandable property of the su-AVR and TAVI prostheses. […] The present study showed a significantly higher incidence of new-onset LBBB after su-AVR and TAVI in comparison to conventional AVR.

• #50 Left bundle branch block after sutureless, transcatheter, and stented biological aortic valve replacement for aortic stenosis | EuroIntervention

  https://eurointervention.pcronline.com/article/left-bundle-branch-block-after-sutureless-transcatheter-and-stented-biological-aortic-valve-replacement-for-aortic-stenosis

  Aims: Conventional aortic valve replacement (AVR), sutureless AVR (su-AVR) and transcatheter aortic valve implantation (TAVI) for severe aortic stenosis (AS) are associated with conduction abnormalities. The aim of the present study was to assess the incidence of left bundle branch block (LBBB) after su-AVR and TAVI, in comparison to conventional AVR. […] Su-AVR and TAVI were associated with higher risk of developing postoperative LBBB compared to conventional AVR, after adjusting for age, preoperative heart rate and QRS duration. […] One of the complications that may occur after TAVI and surgical AVR is new-onset left bundle branch block (LBBB). […] New-onset LBBB after AVR can be related to compression by the prosthesis on the conduction system. […] The bundle branch initiates at the base of the interleaflet triangle between the non-coronary and right coronary cusps, located at the aortic annulus.

• #51 Left bundle branch block after sutureless, transcatheter, and stented biological aortic valve replacement for aortic stenosis | EuroIntervention

  https://eurointervention.pcronline.com/article/left-bundle-branch-block-after-sutureless-transcatheter-and-stented-biological-aortic-valve-replacement-for-aortic-stenosis

  Stented biological prostheses are placed supra-annular, whereas the su-AVR and TAVI prostheses are placed intra-annular, close to the bundle branch, which may lead to an increased risk of damage of the conduction system. […] Besides the position of the valve, the size of the implanted prosthesis relative to the annulus size is important in the pathophysiology of conduction abnormalities. […] However, excessive oversizing can result in increased compression of the conduction system and aortic annulus rupture. […] Another factor responsible for the occurrence of LBBB after AVR might be related to the expandable property of the su-AVR and TAVI prostheses. […] The present study showed a significantly higher incidence of new-onset LBBB after su-AVR and TAVI in comparison to conventional AVR.

• #52 Bundle branch block – Wikipedia

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

  A bundle branch block is a partial or complete interruption in the flow of electrical impulses in either of the bundle branches of the heart’s electrical system. […] When a bundle branch or fascicle becomes injured (by underlying heart disease, myocardial infarction, or cardiac surgery), it may cease to conduct electrical impulses appropriately. This results in altered pathways for ventricular depolarization. Since the electrical impulse can no longer use the preferred pathway across the bundle branch, it may move instead through muscle fibers in a way that both slows the electrical movement and changes the directional propagation of the impulses. As a result, there is a loss of ventricular synchrony, ventricular depolarization is prolonged, and there may be a corresponding drop in cardiac output. […] In more severe cases, a pacemaker may be required to restore an optimal electrical supply to the heart muscle.

• #53 Left bundle branch block (LBBB): ECG criteria, causes, management – The Cardiovascular

  https://ecgwaves.com/topic/left-bundle-branch-block-lbbb-ecg-criteria-treatment/

  Left bundle branch block is always a pathological finding. It affects left ventricular contractility (systolic function) and is associated with adverse cardiovascular outcomes. […] In LBBB, activation of the left ventricle relies on electrical impulses spreading from the right ventricle, leading to slow and abnormal depolarization of the left ventricle. This abnormal depolarization produces an atypical QRS complex. […] LBBB may be caused by ischemia/infarction: An acute myocardial infarction (particularly anterior STEMI) may cause LBBB. Hence, an acute myocardial infarction may result in LBBB, which then conceals the ischemic ST-T changes on ECG. […] Incomplete left bundle branch block is less common than the complete form. In this condition, conduction through the left bundle branch is preserved but occurs at a reduced capacity compared to a normal bundle branch. Thus, the initial depolarization of the left ventricle occurs via impulses spreading from the right ventricle, but after a while, the impulse passes the block in the left bundle branch and executes the remained of ventricular depolarization normally.

• #54

  https://link.springer.com/article/10.1007/BF03164901

  Patients with left bundle branch block (LBBB) often show abnormal images on exercise thallium (Tl)-201 scintigraphy without evidence of significant coronary stenosis. […] In conclusion, these results suggest that abnormal Tl-201 SPECT images of the septum in patients with LBBB are partially caused by impaired septal wall thickening during systole. Such an abnormal wall motion may reduce blood flow demands to the septum, resulting in reduction of coronary blood flow with little ischemia.

• #55 Bundle branch block – Symptoms & causes – Mayo Clinic

  https://www.mayoclinic.org/diseases-conditions/bundle-branch-block/symptoms-causes/syc-20370514

  Electrical impulses within the heart muscle cause it to beat (contract). These impulses travel along a pathway, including two branches called the right and the left bundles. If one or both of these branch bundles are damaged due to a heart attack, for example the electrical impulses can become blocked. As a result, the heart beats irregularly. […] The cause for bundle branch blocks can differ depending on whether the left or the right bundle branch is affected. Sometimes, there is no known cause. […] If both the right and the left bundles are blocked, the main complication is a complete blockage of the electric signaling from the upper to the lower chambers of the heart. The lack of signaling can slow the heart rate. A slowed heart rate may lead to fainting, irregular heart rhythms and other serious complications. […] Because bundle branch block affects the electrical activity of the heart, it can sometimes complicate the accurate diagnosis of other heart conditions, especially heart attacks. It may lead to delays in proper management of those heart conditions.

• #56 Bundle branch block – Symptoms & causes – Mayo Clinic

  https://www.mayoclinic.org/diseases-conditions/bundle-branch-block/symptoms-causes/syc-20370514

  Electrical impulses within the heart muscle cause it to beat (contract). These impulses travel along a pathway, including two branches called the right and the left bundles. If one or both of these branch bundles are damaged due to a heart attack, for example the electrical impulses can become blocked. As a result, the heart beats irregularly. […] The cause for bundle branch blocks can differ depending on whether the left or the right bundle branch is affected. Sometimes, there is no known cause. […] If both the right and the left bundles are blocked, the main complication is a complete blockage of the electric signaling from the upper to the lower chambers of the heart. The lack of signaling can slow the heart rate. A slowed heart rate may lead to fainting, irregular heart rhythms and other serious complications. […] Because bundle branch block affects the electrical activity of the heart, it can sometimes complicate the accurate diagnosis of other heart conditions, especially heart attacks. It may lead to delays in proper management of those heart conditions.

• #57 Bundle Branch Block: Causes, Symptoms & Treatment

  https://my.clevelandclinic.org/health/diseases/22938-bundle-branch-block

  Right bundle branch block may also result from lung diseases including: Chronic obstructive pulmonary disease (COPD). Pulmonary embolism. Pulmonary hypertension (PH). […] A left bundle branch block may be the first sign of a complete heart block. […] If you have other conditions that affect your heart, BBB may make your heart deteriorate faster and worsen your symptoms.

• #58 Right Bundle Branch Block – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK507872/

  Right bundle branch block (RBB) is an electrocardiogram finding resulting in a widened QRS and electrocardiographic vector changes. […] Right bundle branch block is associated with structural changes from stretch or ischemia to the myocardium. […] A right bundle branch block is typically caused by disease processes that change the myocardium of the right bundle branch, for example, structural changes, trauma, and infiltrative processes. […] When the right bundle branch is interrupted, electrical stimuli from the atrioventricular (AV) node conducts to the bundle of His and down the left bundle branch. […] In patients with cardiovascular disease, right bundle branch block is an independent risk factor for all-cause mortality.

• #59 Right bundle branch block (RBBB): ECG, criteria, definitions, causes & treatment – The Cardiovascular

  https://ecgwaves.com/topic/right-bundle-branch-block-rbbb-ecg-criteria-treatment/

  While traditionally considered benign in asymptomatic individuals, recent evidence suggests that RBBB may be linked to an increased cardiovascular risk. […] Key predictors of incident RBBB included male sex, older age, high systolic blood pressure, and the presence of incomplete RBBB. […] Complete RBBB was associated with increased all-cause mortality (1.3-fold higher relative risk) and cardiovascular mortality (1.9-fold higher relative risk), as well as an elevated risk of myocardial infarction (1.7-fold higher relative risk) and pacemaker implantation (2.2-fold higher relative risk). […] The findings suggest that RBBB in asymptomatic individuals may signal increased cardiovascular risk, challenging the perception of its benign nature. […] Causes of right bundle branch block (RBBB) include idiopathic fibrosis or degeneration in the right bundle branch, congenital heart disease, ischemic heart disease (coronary artery disease), acute cor pulmonale (pulmonary embolism), chronic obstructive pulmonary disease, cardiac surgery, PCI, cardiomyopathy, and aberrant ventricular conduction. […] The right bundle branch block does not interfere with the diagnosis of ischemia/infarction.

• #60 Bundle Branch Block and Fascicular Block – Cardiovascular Disorders – MSD Manual Professional Edition

  https://www.msdmanuals.com/professional/cardiovascular-disorders/specific-cardiac-arrhythmias/bundle-branch-block-and-fascicular-block

  Bundle branch block is partial or complete interruption of impulse conduction in a bundle branch; fascicular block is similar interruption in a hemifascicle of the left bundle. The disorders often coexist. Conduction blocks can be caused by many heart disorders, including intrinsic degeneration without another associated heart disorder. RBBB can occur in people with no evidence of heart disease. It may also occur with anterior myocardial infarction, indicating substantial myocardial injury. The presence of RBBB should prompt a search for underlying cardiac pathology, but often none is found. Although RBBB distorts the QRS complex, it does not significantly interfere with ECG criteria of past myocardial infarction. In the absence of evidence of a heart disorder or more advanced interventricular conduction disturbance, RBBB does not appear to indicate a higher risk of future cardiovascular events. Also, isolated RBBB produces no symptoms. Thus, isolated RBBB requires no specific therapy. LBBB is associated with a structural heart disorder more often than is RBBB and, in contrast to RBBB, LBBB is associated with a higher risk of future cardiac events and mortality. The presence of LBBB should prompt a search for underlying cardiac pathology, which is present more often than in patients with RBBB. Isolated left anterior hemiblock is more common and does not appear to be independently associated with an increased risk of future cardiac events or mortality. The associations between hemiblocks and a structural heart disorder are the same as for LBBB. Presence of bifascicular or trifascicular block after myocardial infarction implies extensive cardiac damage. Nonspecific intraventricular conduction defects are diagnosed when the QRS complex is prolonged, but the QRS pattern is not typical of LBBB or RBBB. The conduction delay may occur beyond the Purkinje fibers and result from slow cell-to-cell myocyte conduction. Risk of subsequent cardiac events and mortality with nonspecific intraventricular conduction defect is similar to that of a LBBB.

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