Infra-Hisian Block

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

Overview

Infra-Hisian blocks are defined as impaired conduction in the electrical system of the heart that occur below the AV node.

Classification

Infrahisian block describes block of the distal conduction system. Types of infrahisian block include:

• Type 2 second degree heart block (Mobitz II)
• Left bundle branch block
  • Left anterior fascicular block
  • Left posterior fascicular block
• Right bundle branch block

Of these types of infrahisian block, Mobitz II heart block is considered most important because of the possible progression to complete heart block.

Pathophysiology

Mobitz type II second degree AV block Mobitz type II second degree AV block, in which the PR interval remains unchanged prior to a P wave that fails to conduct to the ventricles. It almost always results from conduction system disease below the level of the AV node, occurring in the bundle of His in approximately 20 percent of cases and in the bundle branches in the remainder. Patients with bundle branch involvement also have axis shifts and QRS widening depending upon the location of the block. In addition, at least two-thirds of patients with this disorder also have bifascicular or even 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. 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.

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.

• Acute myocardial infarction
• Acute rheumatic fever
• Bacterial endocarditis
• Myocarditis
• Severe hypothermia

Common Causes

• Acute rheumatic fever
• Bacterial endocarditis
• Calcific aortic stenosis
• Digoxin
• Dilated cardiomyopathy
• Diltiazem
• Enhanced vagal tone
• HCM
• Hypertension
• Iatrogenic after surgical correction of VSD, tetralogy of Fallot, and endocardial cushion defect
• Inferior ST elevation MI
• Massive calcification of the mitral annulus
• Myocarditis
• Normal variants
• Penetrating and non-penetrating trauma of the chest
• Sclerodegenerative disease of the electrical conduction system
• Verapamil
• β blockers

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
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

• Acute myocardial infarction
• Acute rheumatic fever
• Amyloidosis
• Ankylosing spondylitis
• ASD
• Bacterial endocarditis
• Beta-blockers
• Calcific aortic stenosis
• Calcium channel blockers
• Cardiac glycosides
• Cardiac tumors
• Chagas disease
• Cholinesterase inhibitors
• Clonidine
• Degenerative diseases
• Dermatomyositis
• Digitalis
• Digoxin
• Dilated cardiomyopathy
• Diltiazem
• Diphtheria
• Disopyramide
• Dolasetron
• Donepezil
• Ebstein's anomaly
• Electrolyte disturbances
• Emery-Dreifuss muscular dystrophy
• Endocarditis
• Enhanced vagal tone in athletes

• Eslicarbazepine acetate
• Fabry disease
• Fesoterodine
• Fingolimod
• Glycogenosis type 2b
• HCM
• Hereditary neuromuscular disease
• Hodgkin lymphoma
• Hyperkalaemia
• Hypersensitive carotid sinus syndrome
• Hyperthyroidism
• Hypokalaemia
• Hypothermia
• Ibutilide
• Ischemic heart disease
• Kearns-Sayre syndrome
• Labetalol
• Lacosamide
• Lanatoside C
• Lenegre's disease
• Lev's disease
• Lyme disease
• Mitochondrial genome inherited conditions
• Multiple myeloma
• Muscular dystrophy
• Myocardial bridging
• Myocarditis
• Myotonic dystrophy
• Myxedema

• Neonatal lupus erythematosus
• Normal variants of PR prolongation
• Paliperidone
• Post aortic valve replacement
• Post catheter ablation for arrhythmias
• Post closure of a ventricular septal defect
• Post mitral valve replacement
• Procainamide
• Propoxyphene
• Propranolol
• Protozoal infection
• Quinidine
• Quinine
• Rheumatic mitral valve disease
• Sarcoidosis
• SLE
• Systemic sclerosis
• Terodiline
• Tetralogy of Fallot
• Thyrotoxic periodic paralysis
• Tolterodine
• Transposition of the great vessels
• Vagal maneuvers
• Valsalva maneuvers
• Valvular heart disease
• Verapamil
• VSD
• X-linked inherited conditions

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