Bundle Branch and Fascicular Blocks (Clinical)

Classification and Epidemiology

Classification^[8,9]

Bundle branch and fascicular blocks Fascicular Blocks Bundle branch and fascicular blocks occur when the normal electrical activity in the His-Purkinje system is interrupted. These blocks can be due to many etiologies that may affect the structure of the heart or the conduction system directly. Bundle Branch and Fascicular Blocks are classified on the basis of where the disruption occurs within the His-Purkinje system.

• Bundle branch blocks Bundle Branch Blocks Bundle branch and fascicular blocks occur when the normal electrical activity in the His-Purkinje system is interrupted. These blocks can be due to many etiologies that may affect the structure of the heart or the conduction system directly. Bundle Branch and Fascicular Blocks:
  • Right bundle branch block Right bundle branch block Bundle Branch and Fascicular Blocks ( RBBB RBBB Bundle Branch and Fascicular Blocks)
  • Left bundle branch block Left bundle branch block Bundle Branch and Fascicular Blocks ( LBBB LBBB Bundle Branch and Fascicular Blocks)
• Fascicular blocks Fascicular Blocks Bundle branch and fascicular blocks occur when the normal electrical activity in the His-Purkinje system is interrupted. These blocks can be due to many etiologies that may affect the structure of the heart or the conduction system directly. Bundle Branch and Fascicular Blocks:
  • Left anterior fascicular block Left anterior fascicular block Bundle Branch and Fascicular Blocks or hemiblock ( LAFB LAFB Bundle Branch and Fascicular Blocks)
  • Left posterior fascicular block Left posterior fascicular block Bundle Branch and Fascicular Blocks or hemiblock ( LPFB LPFB Bundle Branch and Fascicular Blocks)

Epidemiology^[2‒5]

• RBBB RBBB Bundle Branch and Fascicular Blocks:
  • Prevalence Prevalence The total number of cases of a given disease in a specified population at a designated time. It is differentiated from incidence, which refers to the number of new cases in the population at a given time. Measures of Disease Frequency:
    • In the general population: < 1%
    • Increases with age
  • Can occur in young, healthy people
• LBBB LBBB Bundle Branch and Fascicular Blocks:
  • Prevalence Prevalence The total number of cases of a given disease in a specified population at a designated time. It is differentiated from incidence, which refers to the number of new cases in the population at a given time. Measures of Disease Frequency:
    • In the general population: < 1%
    • Increases with age
  • Occurs infrequently in young, healthy people
• LAFB LAFB Bundle Branch and Fascicular Blocks:
  • Prevalence Prevalence The total number of cases of a given disease in a specified population at a designated time. It is differentiated from incidence, which refers to the number of new cases in the population at a given time. Measures of Disease Frequency in the general population: 1%–2.5%
  • Prevalence Prevalence The total number of cases of a given disease in a specified population at a designated time. It is differentiated from incidence, which refers to the number of new cases in the population at a given time. Measures of Disease Frequency increases with age
• LPFB LPFB Bundle Branch and Fascicular Blocks:
  • An isolated LPFB LPFB Bundle Branch and Fascicular Blocks is rare.
  • Prevalence Prevalence The total number of cases of a given disease in a specified population at a designated time. It is differentiated from incidence, which refers to the number of new cases in the population at a given time. Measures of Disease Frequency: 0.1%–0.6%
  • Often occurs in association with RBBB RBBB Bundle Branch and Fascicular Blocks

Etiology

RBBB RBBB Bundle Branch and Fascicular Blocks^[2,6]

• Structural disease:
  • Includes conditions resulting in right ventricular pathology:
    • Hypertrophy Hypertrophy General increase in bulk of a part or organ due to cell enlargement and accumulation of fluids and secretions, not due to tumor formation, nor to an increase in the number of cells (hyperplasia). Cellular Adaptation
    • ↑ Pressure
    • Dilation
    • Injury
    • Inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation/infiltration
  • Examples:
    • Pulmonary hypertension Pulmonary Hypertension Pulmonary hypertension (PH) or pulmonary arterial hypertension (PAH) is characterized by elevated pulmonary arterial pressure, which can lead to chronic progressive right heart failure. Pulmonary hypertension is grouped into 5 categories based on etiology, which include primary PAH, and PH due to cardiac disease, lung or hypoxic disease, chronic thromboembolic disease, and multifactorial or unclear etiologies. Pulmonary Hypertension and cor pulmonale Cor Pulmonale Cor pulmonale is right ventricular (RV) dysfunction caused by lung disease that results in pulmonary artery hypertension. The most common cause of cor pulmonale is chronic obstructive pulmonary disease. Dyspnea is the usual presenting symptom. Cor Pulmonale
    • Pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism
    • Myocardial ischemia Myocardial ischemia A disorder of cardiac function caused by insufficient blood flow to the muscle tissue of the heart. The decreased blood flow may be due to narrowing of the coronary arteries (coronary artery disease), to obstruction by a thrombus (coronary thrombosis), or less commonly, to diffuse narrowing of arterioles and other small vessels within the heart. Coronary Heart Disease or infarction ( MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction)
    • Myocarditis Myocarditis Myocarditis is an inflammatory disease of the myocardium, which may occur alone or in association with a systemic process. There are numerous etiologies of myocarditis, but all lead to inflammation and myocyte injury, most often leading to signs and symptoms of heart failure. Myocarditis
    • Cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Cardiomyopathy: Overview and Types
    • Valvular disease
    • Atrial septal defect Atrial Septal Defect Atrial septal defects (ASDs) are benign acyanotic congenital heart defects characterized by an opening in the interatrial septum that causes blood to flow from the left atrium (LA) to the right atrium (RA) (left-to-right shunt). Atrial Septal Defect (ASD)
    • Chagas disease Chagas disease Infection with the protozoan parasite trypanosoma cruzi, a form of trypanosomiasis endemic in central and south america. It is named after the brazilian physician carlos chagas, who discovered the parasite. Infection by the parasite (positive serologic result only) is distinguished from the clinical manifestations that develop years later, such as destruction of parasympathetic ganglia; chagas cardiomyopathy; and dysfunction of the esophagus or colon. Trypanosoma cruzi/Chagas disease
• Idiopathic Idiopathic Dermatomyositis cardiac conduction disease (Lenegre or Lev disease)
• Iatrogenic Iatrogenic Any adverse condition in a patient occurring as the result of treatment by a physician, surgeon, or other health professional, especially infections acquired by a patient during the course of treatment. Anterior Cord Syndrome trauma to the conduction system:
  • Right-heart catheter insertion
  • Septal reduction therapy with ethanol Ethanol A clear, colorless liquid rapidly absorbed from the gastrointestinal tract and distributed throughout the body. It has bactericidal activity and is used often as a topical disinfectant. It is widely used as a solvent and preservative in pharmaceutical preparations as well as serving as the primary ingredient in alcoholic beverages. Ethanol Metabolism ablation
  • Cardiac surgery Cardiac surgery Cardiac surgery is the surgical management of cardiac abnormalities and of the great vessels of the thorax. In general terms, surgical intervention of the heart is performed to directly restore adequate pump function, correct inherent structural issues, and reestablish proper blood supply via the coronary circulation. Cardiac Surgery
• Can also occur in those with no heart disease

LBBB LBBB Bundle Branch and Fascicular Blocks^[3,6]

• Structural disease:
  • Includes conditions resulting in left ventricular pathology:
    • Hypertrophy Hypertrophy General increase in bulk of a part or organ due to cell enlargement and accumulation of fluids and secretions, not due to tumor formation, nor to an increase in the number of cells (hyperplasia). Cellular Adaptation
    • ↑ Pressure
    • Dilation
    • Injury
    • Inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation/infiltration
  • Examples:
    • MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction/ ischemia Ischemia A hypoperfusion of the blood through an organ or tissue caused by a pathologic constriction or obstruction of its blood vessels, or an absence of blood circulation. Ischemic Cell Damage (most common)
    • Cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Cardiomyopathy: Overview and Types
    • Hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
    • Endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis (particularly with abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease)
    • Myocarditis Myocarditis Myocarditis is an inflammatory disease of the myocardium, which may occur alone or in association with a systemic process. There are numerous etiologies of myocarditis, but all lead to inflammation and myocyte injury, most often leading to signs and symptoms of heart failure. Myocarditis
    • Valvular disease
    • Congenital Congenital Chorioretinitis defects
• Idiopathic Idiopathic Dermatomyositis cardiac conduction disease
• Iatrogenic Iatrogenic Any adverse condition in a patient occurring as the result of treatment by a physician, surgeon, or other health professional, especially infections acquired by a patient during the course of treatment. Anterior Cord Syndrome:
  • Septal myectomy Septal myectomy Hypertrophic Cardiomyopathy
  • Transcatheter aortic valve implantation Transcatheter aortic valve implantation Surgical treatment for severe aortic valve stenosis. Transcatheter aortic valve replacement (TAVR) is used as an alternative option in patients who are deemed at high risk or inoperable for traditional open-heart surgery. Aortic Stenosis

LAFB LAFB Bundle Branch and Fascicular Blocks and LPFB LPFB Bundle Branch and Fascicular Blocks^[4,5]

These fascicular blocks Fascicular Blocks Bundle branch and fascicular blocks occur when the normal electrical activity in the His-Purkinje system is interrupted. These blocks can be due to many etiologies that may affect the structure of the heart or the conduction system directly. Bundle Branch and Fascicular Blocks can occur because of many of the same causes of RBBB RBBB Bundle Branch and Fascicular Blocks or LBBB LBBB Bundle Branch and Fascicular Blocks, most notably:

• Aortic valvular disease ( LAFB LAFB Bundle Branch and Fascicular Blocks)
• Myocardial ischemia Myocardial ischemia A disorder of cardiac function caused by insufficient blood flow to the muscle tissue of the heart. The decreased blood flow may be due to narrowing of the coronary arteries (coronary artery disease), to obstruction by a thrombus (coronary thrombosis), or less commonly, to diffuse narrowing of arterioles and other small vessels within the heart. Coronary Heart Disease or MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction
• Cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Cardiomyopathy: Overview and Types
• Hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
• Chagas disease Chagas disease Infection with the protozoan parasite trypanosoma cruzi, a form of trypanosomiasis endemic in central and south america. It is named after the brazilian physician carlos chagas, who discovered the parasite. Infection by the parasite (positive serologic result only) is distinguished from the clinical manifestations that develop years later, such as destruction of parasympathetic ganglia; chagas cardiomyopathy; and dysfunction of the esophagus or colon. Trypanosoma cruzi/Chagas disease
• Infiltrative and inflammatory diseases
• Congenital Congenital Chorioretinitis defects
• Idiopathic Idiopathic Dermatomyositis cardiac conduction disease

Pathophysiology

Normal physiology^[2‒5]

• The cardiac impulse is generated by pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias cells in the sinoatrial (SA) node and moves through the atria → depolarization Depolarization Membrane Potential → atrial contraction
• Transmitted to the atrioventricular (AV) node → His-Purkinje system → depolarization Depolarization Membrane Potential → ventricular contraction
• His-Purkinje system:
  • Provides rapid electrical conduction for the ventricles → synchronized ventricular depolarization Depolarization Membrane Potential and contraction
  • Contains:
    • Bundle of His Bundle of His Small band of specialized cardiac muscle fibers that originates in the atrioventricular node and extends into the membranous part of the interventricular septum. The bundle of his, consisting of the left and the right bundle branches, conducts the electrical impulses to the heart ventricles in generation of myocardial contraction. Heart: Anatomy
    • The bundle splits in 2 → right and left bundles branches
    • Left bundle branch splits → left anterior fascicle and left posterior fascicle
    • Purkinje fibers Purkinje fibers Modified cardiac muscle fibers composing the terminal portion of the heart conduction system. Heart: Anatomy

Bundle branch blocks Bundle Branch Blocks Bundle branch and fascicular blocks occur when the normal electrical activity in the His-Purkinje system is interrupted. These blocks can be due to many etiologies that may affect the structure of the heart or the conduction system directly. Bundle Branch and Fascicular Blocks^[2‒5,9]

• 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 ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG).

Fascicular blocks Fascicular Blocks Bundle branch and fascicular blocks occur when the normal electrical activity in the His-Purkinje system is interrupted. These blocks can be due to many etiologies that may affect the structure of the heart or the conduction system directly. Bundle Branch and Fascicular Blocks^[4‒6]

• The pathophysiology is similar to that of bundle branch blocks Bundle Branch Blocks Bundle branch and fascicular blocks occur when the normal electrical activity in the His-Purkinje system is interrupted. These blocks can be due to many etiologies that may affect the structure of the heart or the conduction system directly. Bundle Branch and Fascicular Blocks, though the bundle branch is not completely affected → depolarization Depolarization Membrane Potential of the left ventricle is dependent on the opposite fascicle
• This causes axis deviation, but has less effect on QRS duration.

Clinical Presentation and Diagnosis

Clinical presentation^[9,10,14]

• Usually asymptomatic
• Most people are unaware.
• Rarely, may cause syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope or presyncope Presyncope Syncope (may have associated AV block AV block Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. Atrioventricular block (AV block))
• A split S1 S1 Heart Sounds is common in RBBB RBBB Bundle Branch and Fascicular Blocks.
• A split S2 S2 Heart Sounds can also be noted:
  • Persistent in RBBB RBBB Bundle Branch and Fascicular Blocks → delayed pulmonic valve closure (due to delayed activation of the right ventricle)
  • Paradoxical in LBBB LBBB Bundle Branch and Fascicular Blocks → delayed aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy closure (due to delayed activation of the left ventricle)

Audio:

This audio clip is an example of a split S2 S2 Heart Sounds in the setting of an RBBB RBBB Bundle Branch and Fascicular Blocks. The 2 sounds occurring during S2 S2 Heart Sounds result from delayed closure Delayed Closure Gastroschisis of the pulmonic valve in relation to the aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy.

Right bundle branch block Right bundle branch block Bundle Branch and Fascicular Blocks on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)^[8,14]

• QRS duration ≥ 120 msec
• Leads V1 and V2:
  • Rsr′, rsR’ or rSR’ (many variations)
  • The R’ or r’ deflection is usually wider than the initial R wave.
  • Appears as “rabbit ears”
• Leads I and V6 will have an S wave that is:
  • Deep
  • Of longer duration
  • Slurred 
• T waves tend to be discordant to the terminal QRS vector.

LBBB LBBB Bundle Branch and Fascicular Blocks on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)^[8,9]

• QRS duration > 120 msec in adults
• Broad notched (R,R’) or slurred R wave in leads I, aVL, V5, and V6
• Absent Q waves in lateral leads
• Large S wave in V1 and V2
• ST segments and T waves are usually discordant to QRS complex QRS complex Electrocardiogram (ECG).

Incomplete RBBB RBBB Bundle Branch and Fascicular Blocks and LBBB LBBB Bundle Branch and Fascicular Blocks^[8,9,14]

A bundle branch block Bundle branch block A form of heart block in which the electrical stimulation of heart ventricles is interrupted at either one of the branches of bundle of His thus preventing the simultaneous depolarization of the two ventricles. Bundle Branch and Fascicular Blocks may be considered incomplete if the usual RBBB RBBB Bundle Branch and Fascicular Blocks or LBBB LBBB Bundle Branch and Fascicular Blocks pattern is seen but the QRS duration is 110–119 msec.

Left anterior fascicular block Left anterior fascicular block Bundle Branch and Fascicular Blocks on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)^[8,10]

• QRS duration < 120 msec
• Left-axis deviation (approximately 45–90 degrees)
• R-peak time ≥ 45 msec in lead aVL (measured from the start of the Q wave to the peak of the R wave)
• qR complexes in leads I and aVL
• rS complexes in leads II, III, and aVF

Left posterior fascicular block Left posterior fascicular block Bundle Branch and Fascicular Blocks on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)^[8,10]

• QRS duration < 120 msec
• Right-axis deviation (90–180 degrees)
• qR complexes in leads II, III, and aVF
• rS complexes in leads I and aVL

Management

Management may vary depending on practice location and is generally guided by cardiology consultation. The following information is based on the most recent US and European guidelines. 

RBBB RBBB Bundle Branch and Fascicular Blocks^[12,14]

• Most individuals are asymptomatic and require no treatment.
• Treat underlying cause if present (e.g., myocardial ischemia Myocardial ischemia A disorder of cardiac function caused by insufficient blood flow to the muscle tissue of the heart. The decreased blood flow may be due to narrowing of the coronary arteries (coronary artery disease), to obstruction by a thrombus (coronary thrombosis), or less commonly, to diffuse narrowing of arterioles and other small vessels within the heart. Coronary Heart Disease).
• Pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias placement may be needed for:
  • Recurrent syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope 
  • Concurrent RBBB RBBB Bundle Branch and Fascicular Blocks and high-degree atrioventricular block Atrioventricular block Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. Atrioventricular block (AV block)
• New-onset RBBB RBBB Bundle Branch and Fascicular Blocks:
  • Evaluate for potential causes of right heart strain.
  • Echocardiography Echocardiography Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues. The standard approach is transthoracic. Tricuspid Valve Atresia (TVA) is warranted.
• In patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR), cardiac resynchronization therapy (CRT) may be considered on an individual basis (appears to be less beneficial than in LBBB LBBB Bundle Branch and Fascicular Blocks).^[16,17]

LBBB LBBB Bundle Branch and Fascicular Blocks^[9]

• Newly diagnosed:
  • Isolated LBBB LBBB Bundle Branch and Fascicular Blocks no longer considered a STEMI equivalent by itself
  • Strong association with preexisting structural heart disease
  • Screen with echocardiography Echocardiography Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues. The standard approach is transthoracic. Tricuspid Valve Atresia (TVA).
  • Subsequent testing for coronary artery Coronary Artery Truncus Arteriosus disease done based on clinical judgment Judgment The process of discovering or asserting an objective or intrinsic relation between two objects or concepts; a faculty or power that enables a person to make judgments; the process of bringing to light and asserting the implicit meaning of a concept; a critical evaluation of a person or situation. Psychiatric Assessment
• Painful LBBB LBBB Bundle Branch and Fascicular Blocks syndrome:
  • Episodic chest pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways correlating with intermittent LBBB LBBB Bundle Branch and Fascicular Blocks (without myocardial ischemia Myocardial ischemia A disorder of cardiac function caused by insufficient blood flow to the muscle tissue of the heart. The decreased blood flow may be due to narrowing of the coronary arteries (coronary artery disease), to obstruction by a thrombus (coronary thrombosis), or less commonly, to diffuse narrowing of arterioles and other small vessels within the heart. Coronary Heart Disease)
  • Consider beta-blocker therapy, CRT, or His bundle pacing. 
• New-onset LBBB LBBB Bundle Branch and Fascicular Blocks following transcatheter aortic valve replacement Aortic valve replacement Aortic Stenosis (TAVR):
  • Postoperative high-grade atrioventricular block Atrioventricular block Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. Atrioventricular block (AV block) may develop in the 1st 48‒72 hours.
  • Observe patient in cardiac telemetry Telemetry Transmission of the readings of instruments to a remote location by means of wires, radio waves, or other means. Crush Syndrome unit or cardiac intensive care unit postoperatively.
  • After 72 hours, if prolonged QRS (> 150 msec), consider permanent pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias implantation Implantation Endometrial implantation of embryo, mammalian at the blastocyst stage. Fertilization and First Week.
• LBBB LBBB Bundle Branch and Fascicular Blocks and heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR):^[9,11‒13]
  • Left ventricular ejection fraction Ejection fraction Cardiac Cycle (LVEF) < 35% and LBBB LBBB Bundle Branch and Fascicular Blocks show mortality Mortality All deaths reported in a given population. Measures of Health Status benefits with CRT:
    • Consider if QRS > 120 msec.
    • Definite benefit for prolonged QRS interval ≥ 150 msec 
    • Women may benefit at narrower QRS intervals.
  • CRT may benefit patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with LBBB LBBB Bundle Branch and Fascicular Blocks and LVEF between 35% and 50%.

LAFB LAFB Bundle Branch and Fascicular Blocks and LPFB LPFB Bundle Branch and Fascicular Blocks

• Isolated ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG) finding with no symptoms does not require workup.^[10]
• Neuromuscular disorders and LAFB LAFB Bundle Branch and Fascicular Blocks or LPFB LPFB Bundle Branch and Fascicular Blocks:^[10]
  • Consider pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias.
  • Higher likelihood of rapid progression of conduction delays
• LAFB LAFB Bundle Branch and Fascicular Blocks:^[10]
  • Higher risk of developing heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR) and atrial fibrillation Atrial fibrillation Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation
  • Counsel patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship on symptoms of these conditions.
  • Further cardiac workup is indicated. 
• Bifascicular block ( RBBB RBBB Bundle Branch and Fascicular Blocks + LAFB LAFB Bundle Branch and Fascicular Blocks or LPFB LPFB Bundle Branch and Fascicular Blocks):^[10,15]
  • Look for reversible causes ( myocardial ischemia Myocardial ischemia A disorder of cardiac function caused by insufficient blood flow to the muscle tissue of the heart. The decreased blood flow may be due to narrowing of the coronary arteries (coronary artery disease), to obstruction by a thrombus (coronary thrombosis), or less commonly, to diffuse narrowing of arterioles and other small vessels within the heart. Coronary Heart Disease and conduction delaying medications).
  • No apparent reversible cause:
    • No symptoms → no treatment required
    • Presyncope Presyncope Syncope or syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope of cardiac origin → permanent pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias

Differential Diagnosis

• Hyperkalemia Hyperkalemia Hyperkalemia is defined as a serum potassium (K+) concentration >5.2 mEq/L. Homeostatic mechanisms maintain the serum K+ concentration between 3.5 and 5.2 mEq/L, despite marked variation in dietary intake. Hyperkalemia can be due to a variety of causes, which include transcellular shifts, tissue breakdown, inadequate renal excretion, and drugs. Hyperkalemia: increased serum potassium Potassium An element in the alkali group of metals with an atomic symbol k, atomic number 19, and atomic weight 39. 10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the water-electrolyte balance. Hyperkalemia concentration due to abnormal movement out of cells, decreased renal excretion, or increased intake. Hyperkalemia Hyperkalemia Hyperkalemia is defined as a serum potassium (K+) concentration >5.2 mEq/L. Homeostatic mechanisms maintain the serum K+ concentration between 3.5 and 5.2 mEq/L, despite marked variation in dietary intake. Hyperkalemia can be due to a variety of causes, which include transcellular shifts, tissue breakdown, inadequate renal excretion, and drugs. Hyperkalemia may present with muscle weakness and dangerous cardiac toxicity Toxicity Dosage Calculation, such as ventricular fibrillation Ventricular fibrillation Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular Fibrillation (V-fib) or asystole Asystole No discernible electrical activity, flatline on electrocardiogram (P waves and QRS complexes are not present). Cardiac Arrest (if severe). Diagnosis is by serum potassium Potassium An element in the alkali group of metals with an atomic symbol k, atomic number 19, and atomic weight 39. 10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the water-electrolyte balance. Hyperkalemia measurement. Appearance on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG) can be similar to RBBB RBBB Bundle Branch and Fascicular Blocks or LBBB LBBB Bundle Branch and Fascicular Blocks because of depressed conduction in the His-Purkinje system. Acute management includes insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin, sodium Sodium A member of the alkali group of metals. It has the atomic symbol na, atomic number 11, and atomic weight 23. Hyponatremia bicarbonate Bicarbonate Inorganic salts that contain the -HCO3 radical. They are an important factor in determining the ph of the blood and the concentration of bicarbonate ions is regulated by the kidney. Levels in the blood are an index of the alkali reserve or buffering capacity. Electrolytes, albuterol Albuterol A short-acting beta-2 adrenergic agonist that is primarily used as a bronchodilator agent to treat asthma. Sympathomimetic Drugs, calcium gluconate Calcium gluconate The calcium salt of gluconic acid. The compound has a variety of uses, including its use as a calcium replenisher in hypocalcemic states. Hypocalcemia, cation exchangers, and/or dialysis Dialysis Renal replacement therapy refers to dialysis and/or kidney transplantation. Dialysis is a procedure by which toxins and excess water are removed from the circulation. Hemodialysis and peritoneal dialysis (PD) are the two types of dialysis, and their primary difference is the location of the filtration process (external to the body in hemodialysis versus inside the body for PD). Peritoneal Dialysis and Hemodialysis.
• Wolff-Parkinson-White syndrome Wolff-Parkinson-White Syndrome A form of ventricular pre-excitation characterized by a short PR interval and a long QRS interval with a delta wave. In this syndrome, atrial impulses are abnormally conducted to the heart ventricles via an accessory conducting pathway that is located between the wall of the right or left atria and the ventricles, also known as a bundle of kent. The inherited form can be caused by mutation of prkag2 gene encoding a gamma-2 regulatory subunit of amp-activated protein kinase. Supraventricular Tachycardias: congenital Congenital Chorioretinitis preexcitation condition in which antegrade conduction occurs over an accessory pathway. Individuals may present with tachypnea Tachypnea Increased respiratory rate. Pulmonary Examination, chest pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways, palpitations Palpitations Ebstein’s Anomaly, and difficulty breathing due to tachyarrhythmia Tachyarrhythmia A tachyarrhythmia is a rapid heart rhythm, regular or irregular, with a rate > 100 beats/min. Tachyarrhythmia may or may not be accompanied by symptoms of hemodynamic change. Tachyarrhythmias. Appearance on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG) can be similar to LBBB LBBB Bundle Branch and Fascicular Blocks but with a shortened PR interval PR interval Electrocardiogram (ECG). Treatment is by radiofrequency ablation Radiofrequency ablation Removal of tissue using heat generated from electrodes delivering an alternating electrical current in the frequency of radio waves. Hepatocellular Carcinoma (HCC) and Liver Metastases and antiarrhythmic medications.
• Ventricular tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children: ≥ 3 ventricular beats at a rate of ≥ 120 beats/min. Symptoms of ventricular tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children are duration-dependent and vary from no symptoms to palpitations Palpitations Ebstein’s Anomaly to hemodynamic instability and death. Diagnosis is by ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG), which can appear similar to LBBB LBBB Bundle Branch and Fascicular Blocks or RBBB RBBB Bundle Branch and Fascicular Blocks because of the QRS widening. However, there will be AV dissociation Dissociation Defense Mechanisms and extreme axis deviation. Treatment of acute episodes is with cardioversion Cardioversion Atrial Fibrillation or antiarrhythmic drugs. Long-term treatment is with an implantable cardioverter-defibrillator. 
• Ventricular pacing: due to an implanted cardiac pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias. ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG) can appear similar to LBBB LBBB Bundle Branch and Fascicular Blocks (rarely RBBB RBBB Bundle Branch and Fascicular Blocks). However, pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias spikes are usually also seen preceding the QRS complex QRS complex Electrocardiogram (ECG).