Second degree AV block causes: Difference between revisions

Jump to navigation Jump to search
No edit summary
 
(15 intermediate revisions by 5 users not shown)
Line 1: Line 1:
__NOTOC__
__NOTOC__
{{Second degree AV block}}
{{Second degree AV block}}
{{CMG}}; {{AE}} {{CZ}} {{MS}}
{{CMG}}; {{AE}} {{CZ}}; {{MS}}


==Overview==
==Overview==
Atrioventricular (AV) block is defined as an interruption in the transmission of an impulse, either transient or permanent, from the atria to the ventricles due to an anatomic or functional impairment in the conduction system.  In second degree AV block, some atrial impulses fail to reach the ventricles.  Wenckebach described progressive delay between atrial and ventricular contraction and the eventual failure of an atrial beat to reach the ventricles.  Mobitz subsequently divided second degree AV block into two subtypes, as determined by the findings on the [[electrocardiogram]].  In Mobitz type I AV block, progressive PR interval prolongation precedes a non-conducted P wave.  While in Mobitz type II AV block, the PR interval remains unchanged prior to a P wave that suddenly fails to conduct to the ventricles.
Common causes of second degree [[AV block]] include acute [[myocardial ischemia]] or [[infarction]], [[infiltrative]] diseases, [[collagen vascular disease]], [[surgical trauma]], [[endocrine]] abnormalities, [[autonomic]] effects, [[neuromuscular ]] disorders, and [[medication]]s.


==Causes==
==Causes==
===Life Threatening Causes===
===Life Threatening Causes===
Life-threatening conditions  can result in death or permanent disability within 24 hours if left untreated.
Life-threatening conditions  can result in death or permanent disability within 24 hours if left untreated<ref name="pmid29493981">{{cite journal |vauthors=Mangi MA, Jones WM, Napier L |title= |journal= |volume= |issue= |pages= |date= |pmid=29493981 |doi= |url=}}</ref>.
* [[Acute myocardial infarction]]
* [[Acute myocardial infarction]]<ref name="pmid30227965">{{cite journal |vauthors=Misumida N, Ogunbayo GO, Kim SM, Abdel-Latif A, Ziada KM, Elayi CS |title=Frequency and Significance of High-Degree Atrioventricular Block and Sinoatrial Node Dysfunction in Patients With Non-ST-Elevation Myocardial Infarction |journal=Am. J. Cardiol. |volume=122 |issue=10 |pages=1598–1603 |date=November 2018 |pmid=30227965 |doi=10.1016/j.amjcard.2018.08.001 |url=}}</ref><ref name="pmid23224264">{{cite journal |vauthors=Barold SS, Herweg B |title=Second-degree atrioventricular block revisited |journal=Herzschrittmacherther Elektrophysiol |volume=23 |issue=4 |pages=296–304 |date=December 2012 |pmid=23224264 |doi=10.1007/s00399-012-0240-8 |url=}}</ref>
* [[Acute rheumatic fever]]
* [[Acute rheumatic fever]]
* [[Bacterial endocarditis]]
* [[Bacterial endocarditis]]
Line 17: Line 17:
===Common Causes===  
===Common Causes===  
* [[Acute rheumatic fever]]
* [[Acute rheumatic fever]]
* [[Bacterial endocarditis]]
* [[Bacterial endocarditis]]<ref name="pmid27585419">{{cite journal |vauthors=Kamatani T, Akizuki A, Kondo S, Shirota T |title=Second-Degree Atrioventricular Block Occurring After Tooth Extraction |journal=Anesth Prog |volume=63 |issue=3 |pages=156–9 |date=Fall 2016 |pmid=27585419 |pmc=5011958 |doi=10.2344/15-00042.1 |url=}}</ref>
* [[aortic stenosis|Calcific aortic stenosis]]
* [[aortic stenosis|Calcific aortic stenosis]]
* [[Degenerative disease]]
* [[Digoxin]]
* [[Digoxin]]
* [[Dilated cardiomyopathy]]
* [[Dilated cardiomyopathy]]
* [[Diltiazem]]
* [[Diltiazem]]
* [[vagus nerve|Enhanced vagal tone]]
* [[Vasovagal syncope#Cardioinhibitory Response|Enhanced vagal tone]]
* [[HCM]]
* [[HCM]]
* [[Hypertension]]
* [[Hypertension]]
Line 30: Line 29:
* [[mitral valve sclerosis|Massive calcification of the mitral annulus]]
* [[mitral valve sclerosis|Massive calcification of the mitral annulus]]
* [[Myocarditis]]
* [[Myocarditis]]
* [[PR interval|Normal variants]]
* [[PR interval|Normal variants]]<ref name="pmid8445186">{{cite journal |vauthors=Wogan JM, Lowenstein SR, Gordon GS |title=Second-degree atrioventricular block: Mobitz type II |journal=J Emerg Med |volume=11 |issue=1 |pages=47–54 |date=1993 |pmid=8445186 |doi=10.1016/0736-4679(93)90009-v |url=}}</ref>
* [[chest trauma|Penetrating and non-penetrating trauma of the chest]]
* [[chest trauma|Penetrating and non-penetrating trauma of the chest]]
* [[Lev's disease|Sclerodegenerative disease of the electrical conduction system]]
* [[Lev's disease|Sclerodegenerative disease of the electrical conduction system]]
Line 39: Line 38:
{|style="width:80%; height:100px" border="1"
{|style="width:80%; height:100px" border="1"
|style="height:100px"; style="width:25%" border="1" bgcolor="LightSteelBlue" | '''Cardiovascular'''
|style="height:100px"; style="width:25%" border="1" bgcolor="LightSteelBlue" | '''Cardiovascular'''
|style="height:100px"; style="width:75%" border="1" bgcolor="Beige" |[[Acute myocardial infarction]], [[acute rheumatic fever]], [[ASD]], [[dilated cardiomyopathy]], [[Ebstein's anomaly]], [[Carotid sinus hypersensitivity|hypersensitive carotid sinus syndrome]], [[hypertension]], [[hypertrophic cardiomyopathy]], [[Lev's disease]], [[myocardial bridging]], [[myocarditis]], [[Aortic valve replacement|post aortic valve  replacement]], [[catheter ablation|post catheter ablation for arrhythmias]], [[ventricular septal defect surgery|post closure of a ventricular septal defect]], [[mitral valve replacement|post mitral valve replacement]], [[tetralogy of Fallot]], [[endocardial cushion defect]], [[transposition of the great vessels]], [[valvular heart disease]], [[VSD]]
|style="height:100px"; style="width:75%" border="1" bgcolor="Beige" | [[Acute myocardial infarction]], [[acute rheumatic fever]], [[ASD]], [[dilated cardiomyopathy]], [[Ebstein's anomaly]], [[Carotid sinus hypersensitivity|hypersensitive carotid sinus syndrome]], [[hypertension]], [[hypertrophic cardiomyopathy]], [[Lev's disease]], [[myocardial bridging]], [[myocarditis]], [[PR interval|normal variants]], [[Aortic valve replacement|post aortic valve  replacement]], [[catheter ablation|post catheter ablation for arrhythmias]], [[ventricular septal defect surgery|post closure of a ventricular septal defect]], [[mitral valve replacement|post mitral valve replacement]], [[tetralogy of Fallot]], [[endocardial cushion defect]], [[transposition of the great vessels]], [[valvular heart disease]], [[VSD]]
|-
|-
|-bgcolor="LightSteelBlue"
|-bgcolor="LightSteelBlue"
Line 51: Line 50:
|-bgcolor="LightSteelBlue"
|-bgcolor="LightSteelBlue"
| '''Drug Side Effect'''
| '''Drug Side Effect'''
|bgcolor="Beige"| [[Amiodarone]], [[beta-blockers]], [[digitalis]], [[calcium channel blockers]], [[cholinesterase inhibitor|cholinesterase inhibitors]], [[disopyramide]], [[dofetilide]], [[dolasetron]], [[donepezil]], [[eslicarbazepine acetate]], [[fesoterodine]], [[fingolimod]], [[flecainide]], [[ibutilide]], [[lacosamide]], [[magnesium]], [[paliperidone]], [[procainamide]], [[propafenone]], [[propoxyphene]], [[quinidine]], [[sotalol]], [[terodiline]]
|bgcolor="Beige"| [[Amiodarone]], [[beta-blockers]], [[digitalis]], [[calcium channel blockers]], [[cholinesterase inhibitor|cholinesterase inhibitors]], [[disopyramide]], [[dofetilide]], [[dolasetron]], [[donepezil]], [[eslicarbazepine acetate]], [[fesoterodine]], [[fingolimod]], [[flecainide]], [[ibutilide]], [[lacosamide]], [[magnesium]], [[paliperidone]], [[pramipexole]], [[procainamide]], [[propafenone]], [[propoxyphene]], [[quinidine]], [[sotalol]], [[terodiline]]
|-
|-
|-bgcolor="LightSteelBlue"
|-bgcolor="LightSteelBlue"
Line 75: Line 74:
|-bgcolor="LightSteelBlue"
|-bgcolor="LightSteelBlue"
| '''Hematologic'''
| '''Hematologic'''
|bgcolor="Beige"| [[Multiple myeloma]]
|bgcolor="Beige"| [[Multiple myeloma]] [[Lymphoma]]<ref name="pmid27200273">{{cite journal |vauthors=Menicagli F, Lanza A, Sbrocca F, Baldi A, Spugnini EP |title=A case of advanced second-degree atrioventricular block in a ferret secondary to lymphoma |journal=Open Vet J |volume=6 |issue=1 |pages=68–70 |date=2016 |pmid=27200273 |pmc=4833871 |doi=10.4314/ovj.v6i1.10 |url=}}</ref>
|-
|-
|-bgcolor="LightSteelBlue"
|-bgcolor="LightSteelBlue"
Line 87: Line 86:
|-bgcolor="LightSteelBlue"
|-bgcolor="LightSteelBlue"
| '''Musculoskeletal / Ortho'''
| '''Musculoskeletal / Ortho'''
|bgcolor="Beige"| [[Ankylosing spondylitis]], [[Neuromuscular disease|hereditary neuromuscular disease]], [[Kearns-Sayre syndrome]], [[mitochondrial DNA|mitochondrial genome inherited conditions]], [[muscular dystrophy]]
|bgcolor="Beige"| [[Ankylosing spondylitis]], [[Neuromuscular disease|hereditary neuromuscular disease]], [[Kearns-Sayre syndrome]], [[mitochondrial DNA|mitochondrial genome inherited conditions]], [[muscular dystrophy]]
|-
|-
|-bgcolor="LightSteelBlue"
|-bgcolor="LightSteelBlue"
| '''Neurologic'''
| '''Neurologic'''
|bgcolor="Beige"| No underlying causes
|bgcolor="Beige"| [[Vasovagal syncope#Cardioinhibitory Response|Enhanced vagal tone]]
|-
|-
|-bgcolor="LightSteelBlue"
|-bgcolor="LightSteelBlue"
Line 147: Line 146:
|-bgcolor="LightSteelBlue"
|-bgcolor="LightSteelBlue"
| '''Miscellaneous'''
| '''Miscellaneous'''
|bgcolor="Beige"|  [[Amyloidosis]], [[degenerative diseases]],  [[vagus nerve|Enhanced  vagal tone]], [[PR interval|normal variants]], [[pain]], [[sleep ]], [[trauma]]
|bgcolor="Beige"|  [[Amyloidosis]], [[degenerative diseases]]
|-
|-
|}
|}
Line 178: Line 177:
* [[Dolasetron]]
* [[Dolasetron]]
* [[Donepezil]]
* [[Donepezil]]
* [[Drugs]]
* [[Ebstein's anomaly]]
* [[Ebstein's anomaly]]
* [[Electrolyte disturbances]]
* [[Electrolyte disturbances]]
* [[Emery-Dreifuss muscular dystrophy]], [[sex linkage|x-linked]]
* [[Emery-Dreifuss muscular dystrophy]]
* [[Endocarditis]]
* [[Endocarditis]]
* [[vagus nerve|enhanced vagal tone in athletes]]  
* [[vagus nerve|Enhanced vagal tone in athletes]]  
{{col-break|width=33%}}
* [[Eslicarbazepine acetate]]
* [[Eslicarbazepine acetate]]
{{col-break|width=33%}}
* [[Fabry disease]]
* [[Fabry disease]]
* [[Fesoterodine]]
* [[Fesoterodine]]
Line 191: Line 189:
* [[Glycogenosis type 2b]]
* [[Glycogenosis type 2b]]
* [[HCM]]
* [[HCM]]
* [[Neuromuscular disease|hereditary neuromuscular disease]]
* [[Neuromuscular disease|Hereditary neuromuscular disease]]
* [[Hodgkin lymphoma]]
* [[Hodgkin lymphoma]]
* [[Hyperkalaemia]]
* [[Hyperkalaemia]]
Line 199: Line 197:
* [[Hypothermia]]
* [[Hypothermia]]
* [[Ibutilide]]
* [[Ibutilide]]
* [[Ischaemic heart disease]]
* [[Ischemic heart disease]]
* [[Kearns-Sayre syndrome]]
* [[Kearns-Sayre syndrome]]
* [[Labetalol]]
* [[Labetalol]]
Line 214: Line 212:
* [[Myotonic dystrophy]]
* [[Myotonic dystrophy]]
* [[Myxedema]]
* [[Myxedema]]
* [[neonatal lupus erythematosus]]
{{col-break|width=33%}}
* [[prolonged PR interval|Normal variants of PR prolongation]]
* [[Neonatal lupus erythematosus]]
* [[Pain]]
* [[prolonged PR interval|Normal variants of PR prolongation]]
* [[Paliperidone]]
* [[Paliperidone]]
{{col-break|width=33%}}
* [[aortic valve  replacement|Post aortic valve replacement]]
* [[aortic valve  replacement|Post aortic valve replacement ]]
* [[catheter ablation|Post catheter ablation for  arrhythmias]]
* [[catheter ablation|Post catheter ablation for  arrhythmias]]
* [[Ventricular septal defect surgery|Post closure of a  ventricular septal defect]]
* [[Ventricular septal defect surgery|Post closure of a  ventricular septal defect]]
* [[mitral valve  replacement|Post mitral valve  replacement]]
* [[mitral valve  replacement|Post mitral valve  replacement]]
* [[Procainamide ]]
* [[Procainamide]]
* [[Propoxyphene]]
* [[Propoxyphene]]
* [[Propranolol]]
* [[Propranolol]]
Line 232: Line 229:
* [[Sarcoidosis]]
* [[Sarcoidosis]]
* [[SLE]]
* [[SLE]]
* [[Sleep ]]
* [[Systemic sclerosis]]
* [[Systemic sclerosis]]
* [[Terodiline]]
* [[Terodiline]]
* [[Tetralogy of fallot]]
* [[Tetralogy of Fallot]]
* [[periodic  paralysis|Thyrotoxic periodic paralysis]]
* [[periodic  paralysis|Thyrotoxic periodic paralysis]]
* [[Tolterodine]]
* [[Tolterodine]]
* [[Transposition of the great vessels]]
* [[Transposition of the great vessels]]
* [[Trauma]]
* [[vagus nerve|Vagal maneuvers]]
* [[vagus nerve|Vagal maneuvers]]
* [[Valsalva manouevre]]
* [[Valsalva maneuvers]]
* [[Valvular heart disease]]
* [[Valvular heart disease]]
* [[Verapamil]]
* [[Verapamil]]
Line 247: Line 242:
* [[sex linkage|X-linked inherited  conditions]]
* [[sex linkage|X-linked inherited  conditions]]
{{col-end}}
{{col-end}}
===Contraindicated medications===
{{MedCondContrAbs
|MedCond = Second degree AV block (except in [[patients]] with a functioning artificial [[pacemaker]])<ref name="pmid26115830">{{cite journal |vauthors=Brignole M, Deharo JC, Guieu R |title=Syncope and Idiopathic (Paroxysmal) AV Block |journal=Cardiol Clin |volume=33 |issue=3 |pages=441–7 |date=August 2015 |pmid=26115830 |doi=10.1016/j.ccl.2015.04.012 |url=}}</ref><ref name="pmid11229299">{{cite journal |vauthors=Kelkar PN |title=Atenolol induced high grade AV block |journal=J Assoc Physicians India |volume=46 |issue=8 |pages=748, 751 |date=August 1998 |pmid=11229299 |doi= |url=}}</ref>|Adenosine|Atenolol|Betaxolol|Bisoprolol|Brimonidine tartrate and Timolol maleate|Carteolol|Diltiazem|Disopyramide|Dronedarone|Fingolimod|Flecainide|Metoprolol|Mexiletine|Nadolol|Nebivolol|Penbutolol|Pindolol|Propranolol|Sotalol|Timolol|Labetalol}}<ref name="pmid15234417">{{cite journal |vauthors=Zeltser D, Justo D, Halkin A, Rosso R, Ish-Shalom M, Hochenberg M, Viskin S |title=Drug-induced atrioventricular block: prognosis after discontinuation of the culprit drug |journal=J. Am. Coll. Cardiol. |volume=44 |issue=1 |pages=105–8 |date=July 2004 |pmid=15234417 |doi=10.1016/j.jacc.2004.03.057 |url=}}</ref>


==References==
==References==
{{Reflist|2}}
{{Reflist|2}}


{{WikiDoc Help Menu}}
{{WikiDoc Sources}}
[[Category:Electrophysiology]]
[[Category:Cardiology]]
[[Category:Cardiology]]
[[Category:Disease]]
[[Category:Up-To-Date]]
[[Category:Up-To-Date]]
[[Category:Up-To-Date cardiology]]
[[Category:Up-To-Date cardiology]]
[[Category:Arrhythmia]]
[[Category:Arrhythmia]]
 
[[Category:Electrophysiology]]
[[Category:Disease]]
[[Category:Disease]]


[[Category:Primary care]]
{{WikiDoc Help Menu}}
{{WikiDoc Sources}}

Latest revision as of 05:40, 12 July 2021

Second degree AV block Microchapters

Home

Patient Information

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Second degree AV block from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications and Prognosis

Diagnosis

Diagnostic Study of Choice

History and Symptoms

Physical Examination

Laboratory Findings

Electrocardiogram

EKG Examples

Chest X Ray

Echocardiography

Other Imaging Findings

Other Diagnostic Studies

Treatment

Medical Therapy

Surgery

Primary Prevention

Secondary Prevention

Cost-Effectiveness of Therapy

Future or Investigational Therapies

Case Studies

Case #1

Second degree AV block causes On the Web

Most recent articles

Most cited articles

Review articles

CME Programs

slides

Images

American Roentgen Ray Society Images of Second degree AV block causes

All Images
X-rays
Echo & Ultrasound
CT Images
MRI

Ongoing Trials at Clinical Trials.gov

US National Guidelines Clearinghouse

NICE Guidance

FDA on Second degree AV block causes

CDC on Second degree AV block causes

Second degree AV block causes in the news

Blogs on Second degree AV block causes

Directions to Hospitals Treating Second degree AV block

Risk calculators and risk factors for Second degree AV block causes

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Mahmoud Sakr, M.D. [3]

Overview

Common causes of second degree AV block include acute myocardial ischemia or infarction, infiltrative diseases, collagen vascular disease, surgical trauma, endocrine abnormalities, autonomic effects, neuromuscular disorders, and medications.

Causes

Life Threatening Causes

Life-threatening conditions can result in death or permanent disability within 24 hours if left untreated[1].

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[6]
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

Contraindicated medications

Second degree AV block (except in patients with a functioning artificial pacemaker)[7][8] is considered an absolute contraindication to the use of the following medications:

References

  1. Mangi MA, Jones WM, Napier L. PMID 29493981. Missing or empty |title= (help)
  2. Misumida N, Ogunbayo GO, Kim SM, Abdel-Latif A, Ziada KM, Elayi CS (November 2018). "Frequency and Significance of High-Degree Atrioventricular Block and Sinoatrial Node Dysfunction in Patients With Non-ST-Elevation Myocardial Infarction". Am. J. Cardiol. 122 (10): 1598–1603. doi:10.1016/j.amjcard.2018.08.001. PMID 30227965.
  3. Barold SS, Herweg B (December 2012). "Second-degree atrioventricular block revisited". Herzschrittmacherther Elektrophysiol. 23 (4): 296–304. doi:10.1007/s00399-012-0240-8. PMID 23224264.
  4. Kamatani T, Akizuki A, Kondo S, Shirota T (Fall 2016). "Second-Degree Atrioventricular Block Occurring After Tooth Extraction". Anesth Prog. 63 (3): 156–9. doi:10.2344/15-00042.1. PMC 5011958. PMID 27585419.
  5. Wogan JM, Lowenstein SR, Gordon GS (1993). "Second-degree atrioventricular block: Mobitz type II". J Emerg Med. 11 (1): 47–54. doi:10.1016/0736-4679(93)90009-v. PMID 8445186.
  6. Menicagli F, Lanza A, Sbrocca F, Baldi A, Spugnini EP (2016). "A case of advanced second-degree atrioventricular block in a ferret secondary to lymphoma". Open Vet J. 6 (1): 68–70. doi:10.4314/ovj.v6i1.10. PMC 4833871. PMID 27200273.
  7. Brignole M, Deharo JC, Guieu R (August 2015). "Syncope and Idiopathic (Paroxysmal) AV Block". Cardiol Clin. 33 (3): 441–7. doi:10.1016/j.ccl.2015.04.012. PMID 26115830.
  8. Kelkar PN (August 1998). "Atenolol induced high grade AV block". J Assoc Physicians India. 46 (8): 748, 751. PMID 11229299.
  9. Zeltser D, Justo D, Halkin A, Rosso R, Ish-Shalom M, Hochenberg M, Viskin S (July 2004). "Drug-induced atrioventricular block: prognosis after discontinuation of the culprit drug". J. Am. Coll. Cardiol. 44 (1): 105–8. doi:10.1016/j.jacc.2004.03.057. PMID 15234417.


Template:WikiDoc Sources