Infra-Hisian Block: Difference between revisions

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* [[Mobitz type II]] [[second degree AV block]] is [[Characterization (mathematics)|characterized]] by a [[PR interval]] that remains unchanged prior to a [[P wave]] that [[Failure|fails]] to [[conduct]] to the [[ventricles]].
* [[Mobitz type II]] [[second degree AV block]] is [[Characterization (mathematics)|characterized]] by a [[PR interval]] that remains unchanged prior to a [[P wave]] that [[Failure|fails]] to [[conduct]] to the [[ventricles]].
*It almost always [[Result|results]] from a [[Conduction system disease|disease of the conduction system]] below the [[Level of measurement|level]] of [[Atrioventricular node|AV node]], occurring in the [[bundle of His]] in approximately 20% of the [[Case-based reasoning|cases]] and in the [[Bundle branch|bundle branches]] in the remainder.
*It almost always [[Result|results]] from a [[Conduction system disease|disease of the conduction system]] below the [[Level of measurement|level]] of [[Atrioventricular node|AV node]], occurring in the [[bundle of His]] in approximately 20% of the [[Case-based reasoning|cases]] and in the [[Bundle branch|bundle branches]] in the remainder.
*Depending upon the [[Location parameter|location]] of the [[Heart block|block]], [[patients]] having [[bundle branch]] involvement also have [[axis]] shifts and [[QRS]] widening.
*[[Dependent variable|Depending]] upon the [[Location parameter|location]] of the [[Heart block|block]], [[patients]] having [[bundle branch]] involvement also have [[axis]] shifts and [[QRS]] widening.
*In addition, at least two-thirds of patients with this disorder also have bifascicular or even trifascicular disease.
*In addition, at least two-thirds of the [[patients]] with this [[disorder]] also have [[Bifascicular block|bifascicular]] or even [[Trifascicular heart block|trifascicular]] [[disease]].
*Mobitz type I and Mobitz type II second degree AV block cannot be differentiated from the ECG when 2:1 AV block is present.
*Mobitz type I and Mobitz type II second degree AV block cannot be differentiated from the ECG when 2:1 AV block is present.
*In this situation, every other P wave is non-conducted and there is no opportunity to observe for the constant PR interval that is characteristic of Mobitz type II second degree AV block.
*In this situation, every other P wave is non-conducted and there is no opportunity to observe for the constant PR interval that is characteristic of Mobitz type II second degree AV block.

Revision as of 21:42, 7 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

  • Conduction delay in Mobitz type II second degree block is almost always infra-nodal (His bundle [20%], bundle branches or fascicles).
  • Usually the morphology of the QRS complex is wide, except when the site of block is the His bundle.
  • In this variant of second degree heart block the PR interval is constant with occasional dropped beats as compared to the gradually prolonging PR interval in Mobitz type I.
  • Bifascicular or trifascicular disease is seen in two thirds of the patients with Mobitz type II.[2][3]
  • Type 2 second degree AV block, also known as Mobitz II is almost always a disease of the distal conduction system (His-Purkinje System).
  • Although the terms infranodal block or infrahisian block are often applied to this disorder, they are not synonymous with it.
  • Infranodal block and infra-Hisian block are terms which refer to the anatomic location of the block, whereas
  • Mobitz II refers to an electrocardiographic pattern associated with block at these levels.[4]

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:

●Pathologic – Myocardial ischemia (acute or chronic) involving the conduction system, cardiomyopathy (eg, amyloidosis, sarcoidosis), myocarditis (eg, Lyme disease), endocarditis with abscess formation, hyperkalemia, and hypervagotonia.

●Iatrogenic – Medication-related (AV nodal blocking medications), post-cardiac surgery, post-catheter ablation, post-transcatheter aortic valve implantation.

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 causes of atrioventricular (AV) block
Physiologic and pathophysiologic
Increased vagal tone
Ischemic heart disease, including acute myocardial infarction
Progressive cardiac conduction system disease With fibrosis and/or sclerosis (Lenegre disease)
With calcification (Lev disease)
Infections (eg, viral myocarditis, Lyme carditis)
Cardiomyopathy Infiltrative processes (eg, sarcoidosis, amyloidosis, hemochromatosis, malignancy, etc)
Other non-ischemic cardiomyopathies (eg, idiopathic, infectious, etc)
Congenital AV block Related to structural congenital heart disease
As part of neonatal lupus syndrome
Other Hyperkalemia
severe hypo- or hyperthyroidism
trauma
degenerative neuromuscular diseases
Iatrogenic
Drugs Beta blockers
calcium channel blockers
digoxin
antiarrhythmic drugs
adenosine
Transcatheter aortic valve implantation
Cardiac surgery Post valvular surgery
post surgical correction of congenital heart disease
Catheter ablation of arrhythmias
Alcohol septal ablation for hypertrophic cardiomyopathy
Transcatheter closure of ventricular septal defect

Life Threatening Causes

Life-threatening conditions can result in death or permanent disability within 24 hours if left untreated.[7]

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[11]
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

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[34] First degree [35][36]
  • Regular



Second degree[12][37] QRS is normal but dropped as the following:
Third degree[38][39]
  • Regular
Atrial Fibrillation (AFib)[40][41]
  • Absent
Atrial Flutter[42]
Atrioventricular nodal reentry tachycardia (AVNRT)[43][44][45][46]
  • Regular
Multifocal Atrial Tachycardia[47][48]
Paroxysmal Supraventricular Tachycardia
  • Regular
  • 150 and 240 bpm
  • Absent
  • Hidden in QRS
  • Absent
Premature Atrial Contractrions (PAC)[49][50]
  • Upright
  • Usually narrow (< 0.12 s)
Wolff-Parkinson-White Syndrome[51][52]
  • Regular
Ventricular Fibrillation (VF)[53][54][55]
  • Absent
  • Absent
Ventricular Tachycardia[56][57]
  • Regular
  • > 100 bpm (150-200 bpm common)
  • Absent

References

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