Infra-Hisian Block: Difference between revisions

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===Pathophysiology of LBBB===
===Pathophysiology of LBBB===
* 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.  
* Unlike [[right bundle branch block]] ([[RBBB]]), [[left bundle branch block]] completely modifies the way of [[depolarization]] of the [[Electrical conduction system of the heart|conduction system of the heart]].  In [[Left bundle branch block|LBBB]] the [[Activation energy|activation]] of [[interventricular septum]] is from right to left due to uninterrupted [[Conductance|conduction]] in the [[Right bundle branch block|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.<ref name="pmid17385703">{{cite journal |author=Francia P, Balla C, Paneni F, Volpe M |title=Left bundle-branch block--pathophysiology, prognosis, and clinical management |journal=Clinical Cardiology |volume=30 |issue=3 |pages=110–5 |year=2007 |month=March |pmid=17385703 |doi=10.1002/clc.20034 |url=}}</ref>
* Then the electrical impulse propagates inferiorly to the left resulting in delayed depolarization and activation of the [[left ventricle]] especially the left lateral wall.<ref name="pmid17385703">{{cite journal |author=Francia P, Balla C, Paneni F, Volpe M |title=Left bundle-branch block--pathophysiology, prognosis, and clinical management |journal=Clinical Cardiology |volume=30 |issue=3 |pages=110–5 |year=2007 |month=March |pmid=17385703 |doi=10.1002/clc.20034 |url=}}</ref>
* In LBBB the right to left  activation of the septum causes a small negative deflection ([[Q wave]]) in lead V<sub>1</sub> and a positive deflection ([[R wave]]) in lead V<sub>6</sub>. Right ventricle depolarizes earlier than the left ventricle giving an R wave in lead V<sub>1</sub> and an S wave in lead V<sub>6</sub>.  Subsequent delayed depolarization of the left ventricle results in an [[S wave]] in lead V<sub>1</sub> and another R wave in lead V<sub>6</sub>.
* In LBBB the right to left  activation of the septum causes a small negative deflection ([[Q wave]]) in lead V<sub>1</sub> and a positive deflection ([[R wave]]) in lead V<sub>6</sub>. Right ventricle depolarizes earlier than the left ventricle giving an R wave in lead V<sub>1</sub> and an S wave in lead V<sub>6</sub>.  Subsequent delayed depolarization of the left ventricle results in an [[S wave]] in lead V<sub>1</sub> and another R wave in lead V<sub>6</sub>.

Revision as of 00:00, 15 May 2020

Infra-Hisian Block Microchapters

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Epidemiology and Demographics

Risk Factors

Natural History, Complications and Prognosis

Diagnosis

Treatment

Prevention

Differentiating Infra-Hisian Block from other Diseases

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Sara Mohsin, M.D.[2]

Overview

Infra-Hisian block is defined as an impaired conduction in the electrical system of the heart that occurs below the atrioventricular node.

Historical Perspective

Classification

Classification of Infra-Hisian Block
Types of Infra-Hisian Block Sub-type
Type 2 second degree heart block (Mobitz II) _
Left bundle branch block Left anterior fascicular block
Left posterior fascicular block
Right bundle branch block _

Pathophysiology

Normal Cardiac Conduction

  1. The normal cardiac conduction proceeds in a way so as to allow time for the atrium to relax during atrial diastole.
  2. The electrical impulse generated in the SA node travels through the internodal pathways towards the AV node.
  3. The conduction through the AV node is slowed down as it travels through it. This decrease in velocity of conduction allows time for the atrium to contract ahead of the ventricle so that the blood from the atria can fill up the ventricles through the atrioventricular valves.
  4. As the impulse flows through the compact AV node, it rapidly conducts through the ventricular myocardial cells. Once the depolarization is complete, the ventricle relaxes during diastole in preparation for the next impulse.

Anatomy

Conduction system of the heart
Structure of the heart's conduction system

Pathophysiology of LBBB

Pathophysiology of Mobitz type II second degree AV block

Causes

Mobitz type II second degree AV block causes

The potential etiologies of Mobitz type II second degree AV block include reversible (both pathologic and iatrogenic) and idiopathic causes that are similar to other degrees of AV block (table 1). Common potentially reversible causes include

Mobitz type II second degree AV block is rarely seen in patients without underlying heart disease. When identifiable, the reversible causes most commonly associated with Mobitz type II second degree AV block are myocardial infarction with ischemia of the AV node and medications that alter conduction through the AV node (eg, digoxin, beta blockers, calcium channel blockers). When no specific reversible cause is identified, the block is often felt to be related to idiopathic progressive cardiac conduction disease with myocardial fibrosis and/or sclerosis that affects the conduction system.

Major reversible causes of atrioventricular (AV) block
Physiologic and pathophysiologic
Increased vagal tone
  • Also known as hypervagotonia
Ischemic heart disease
Progressive cardiac conduction system disease Associated with:
Infections
Cardiomyopathy Infiltrative processes such as:

Other non-ischemic cardiomyopathies include:

Congenital AV block
Other reversible causes
Iatrogenic
Drugs (altering conduction through AV node)
Cardiac surgery
Catheter ablation of arrhythmias
Alcohol septal ablation for hypertrophic cardiomyopathy
Transcatheter closure of ventricular septal defect
Post-transcatheter aortic valve implantation

Life Threatening Causes

Life-threatening conditions can result in death or permanent disability within 24 hours if left untreated.[6]

Common Causes

Causes by Organ System

Cardiovascular Acute myocardial infarction, acute rheumatic fever, ASD, dilated cardiomyopathy, Ebstein's anomaly, hypersensitive carotid sinus syndrome, hypertension, hypertrophic cardiomyopathy, Lev's disease, myocardial bridging, myocarditis, normal variants, post aortic valve replacement, post catheter ablation for arrhythmias, post closure of a ventricular septal defect, post mitral valve replacement, tetralogy of Fallot, endocardial cushion defect, transposition of the great vessels, valvular heart disease, VSD
Chemical / poisoning No underlying causes
Dermatologic No underlying causes
Drug Side Effect Amiodarone, beta-blockers, digitalis, calcium channel blockers, cholinesterase inhibitors, disopyramide, dofetilide, dolasetron, donepezil, eslicarbazepine acetate, fesoterodine, fingolimod, flecainide, ibutilide, lacosamide, magnesium, paliperidone, pramipexole, procainamide, propafenone, propoxyphene, quinidine, sotalol, terodiline
Ear Nose Throat No underlying causes
Endocrine Hyperthyroidism, myxedema, thyrotoxic periodic paralysis
Environmental Hypothermia
Gastroenterologic Hemochromatosis
Genetic Emery-Dreifuss muscular dystrophy, Fabry disease, glycogenosis type 2b, hereditary neuromuscular disease, Kearns-Sayre syndrome
Hematologic Multiple myeloma Lymphoma[10]
Iatrogenic Post aortic valve replacement, post catheter ablation for arrhythmias, post closure of a ventricular septal defect, post mitral valve replacement
Infectious Disease Acute rheumatic fever, Chagas disease, diphtheria, Lyme disease, myocarditis, neonatal lupus erythematosus, protozoal infection, sarcoidosis, SLE, tuberculosis
Musculoskeletal / Ortho Ankylosing spondylitis, hereditary neuromuscular disease, Kearns-Sayre syndrome, mitochondrial genome inherited conditions, muscular dystrophy
Neurologic Enhanced vagal tone
Nutritional / Metabolic Fabry disease, glycogenosis type 2b
Obstetric/Gynecologic No underlying causes
Oncologic Multiple myeloma
Opthalmologic No underlying causes
Overdose / Toxicity No underlying causes
Psychiatric No underlying causes
Pulmonary Sarcoidosis
Renal / Electrolyte Hyperkalemia, hypokalemia
Rheum / Immune / Allergy Ankylosing spondylitis, dermatomyositis, rheumatoid arthritis, scleroderma, SLE
Sexual No underlying causes
Trauma No underlying causes
Urologic No underlying causes
Dental No underlying causes
Miscellaneous Amyloidosis, degenerative diseases

Causes in Alphabetical Order

Epidemiology and Demographics

Prevalence

Gender

Risk Factors

Natural History, Complications and Prognosis

Natural History

Complications

Prognosis

Diagnosis

Diagnostic Study of Choice

History and Symptoms

Physical Examination

Laboratory Findings

Patients with second degree AV block should be checked for the following laboratory tests:[26]

Electrocardiogram


Shown below is an electrocardiogram of a 12 lead EKG with a 2:1 AV block.

Copyleft image obtained, courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page


Shown below is an electrocardiogram of a type II second degree AV block (Mobitz type II).

Copyleft image obtained, courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page


Treatment

Medical therapy for Mobitz II

Contraindicated medications

Second degree AV block(except in patients with a functioning artificial pacemaker)[29][30] is considered an absolute contraindication to the use of the following medications:

Surgery for Mobitz II

Definitive treatment-Pacemaker insertion

Prevention

Primary Prevention

Differentiating Infra-Hisian Block from other Diseases


Arrhythmia Rhythm Rate P wave PR Interval QRS Complex Response to Maneuvers Epidemiology Co-existing Conditions
Atrioventricular block[35] First degree [36][37]
  • Regular



Second degree[11][38] QRS is normal but dropped as the following:
Third degree[39][40]
  • Regular
Atrial Fibrillation (AFib)[41][42]
  • Absent
Atrial Flutter[43]
Atrioventricular nodal reentry tachycardia (AVNRT)[44][45][46][47]
  • Regular
Multifocal Atrial Tachycardia[48][49]
Paroxysmal Supraventricular Tachycardia
  • Regular
  • 150 and 240 bpm
  • Absent
  • Hidden in QRS
  • Absent
Premature Atrial Contractrions (PAC)[50][51]
  • Upright
  • Usually narrow (< 0.12 s)
Wolff-Parkinson-White Syndrome[52][53]
  • Regular
Ventricular Fibrillation (VF)[54][55][56]
  • Absent
  • Absent
Ventricular Tachycardia[57][58]
  • Regular
  • > 100 bpm (150-200 bpm common)
  • Absent

References

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