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| __NOTOC__ | | __NOTOC__ |
| {{Infobox_Disease | | | {{Left anterior fascicular block}} |
| Name = {{PAGENAME}} |
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| Image = LAFB.jpg|
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| Caption = Example of left anterior hemiblock|
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| }} | |
| {{SI}} | | {{SI}} |
| '''For patient information click [[Heart block (patient information)|here]]''' | | '''For patient information click [[Heart block (patient information)|here]]''' |
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| {{SK}} LAFB; LAHB; left anterior hemiblock | | {{SK}} LAFB; LAHB; left anterior hemiblock |
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| ==Overview== | | ==[[Left anterior fascicular block overview|Overview]]== |
| Left anterior fascicular block is caused by interruption of the anterior division of the left bundle branch. This fascicle is fragile, easily exposed to damage, and has a single blood supply (the [[left anterior descending coronary artery]]). | |
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| ==Pathophysiology== | | ==[[Left anterior fascicular block pathophysiology|Pathophysiology]]== |
| Normal activation of the left ventricle proceeds down the left bundle branch, which consist of two fascicles the left anterior fascicle and left posterior fascicle. Left anterior fascicular block (LAFB), which is also known as left anterior hemiblock (LAHB), occurs when a cardiac impulse spreads first through the left posterior fascicle, causing a delay in activation of the anterior and lateral walls of the [[left ventricle]] which are normally activated via the left anterior fascicle.<ref>Mirvis DM, Goldberger AL. Electrocardiography. In: Braunwald E, Zipes DP, Libby P, eds. Heart disease: a textbook of cardiovascular medicine, 6th edn. Philadelphia: WB Saunders; 2001:82–125.</ref>
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| Although there is a delay or block in the activation of the left anterior fascicle there is still preservation of initial left to right septal activation as well as preservation of the inferior activation of the left ventricle (preservation of septal [[Q wave]]s in I and aVL and small initial [[R wave]] in leads II, III, and aVF). The delayed and unopposed activation of the remainder of the left ventricle now results in a shift in the QRS axis leftward and superiorly, causing marked [[left axis deviation]]. This delayed activation also results in a [[wide QRS complex|widening of the QRS complex]], although not to the extent of a complete [[LBBB]]. <ref>Surawicz B, Knilans TK. Chou’s electrocardiography in clinical practice: adult and pediatric, 5th edn. Philadelphia: W.B. Saunders; 2001.</ref>
| | ==[[Left anterior fascicular block causes|Causes]]== |
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| ==Causes== | | ==[[Left anterior fascicular block differential diagnosis|Differentiating Left anterior fascicular block from other Diseases]]== |
| ==Overview==
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| ===Life Threatening Causes===
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| Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.
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| ===Common Causes=== | | ==[[Left anterior fascicular block epidemiology and demographics|Epidemiology and Demographics]]== |
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| ===Causes by Organ System===
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| {|style="width:80%; height:100px" border="1"
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| |style="height:100px"; style="width:25%" border="1" bgcolor="LightSteelBlue" |'''Cardiovascular'''
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| |style="height:100px"; style="width:75%" border="1" bgcolor="Beige" | [[Alcoholic cardiomyopathy]], [[Anomalous origins of coronary arteries|anomalous origin of the left coronary artery]], [[aortic stenosis]], [[atrial septal defect]], [[atrioventricular septal defect]], [[double outlet right ventricle]], [[hypertensive heart disease]], [[hypertrophic cardiomyopathy]], [[ischemic cardiomyopathy]], [[left ventricular hypertrophy]], [[Lev's disease]], [[postpartum cardiomyopathy]], [[restrictive cardiomyopathy]], [[single ventricle]], [[transposition of the great vessels]], [[tricuspid atresia]]
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| |- | |
| |bgcolor="LightSteelBlue"| '''Chemical/Poisoning'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Dental'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Dermatologic'''
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| |bgcolor="Beige"| [[Leopard syndrome|Lentiginosis]]
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Drug Side Effect'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Ear Nose Throat'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Endocrine'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Environmental'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Gastroenterologic'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Genetic'''
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| |bgcolor="Beige"| [[Atrial septal defect]], [[Charcot-Marie-Tooth disease]], [[double outlet right ventricle]], [[Kearns-Sayre syndrome]], [[Leopard syndrome|lentiginosis]], [[limb-girdle muscular dystrophy]]
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Hematologic'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Iatrogenic'''
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| |bgcolor="Beige"| [[Aortic valve replacement]], [[Hypertrophic cardiomyopathy septal myectomy|septal myomectomy]], [[subvalvar aortic resection]], [[Tetralogy of fallot surgical techniques|tetralogy of Fallot repair]], [[ventricular septal defect surgery]]
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Infectious Disease'''
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| |bgcolor="Beige"| [[Chagas disease]]
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Musculoskeletal/Orthopedic'''
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| |bgcolor="Beige"| [[Limb-girdle muscular dystrophy]]
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Neurologic'''
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| |bgcolor="Beige"| [[Charcot-Marie-Tooth disease]], [[Kearns-Sayre syndrome]]
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Nutritional/Metabolic'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Obstetric/Gynecologic'''
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| |bgcolor="Beige"| [[Postpartum cardiomyopathy]]
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Oncologic'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Ophthalmologic'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Overdose/Toxicity'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Psychiatric'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Pulmonary'''
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| |bgcolor="Beige"| [[Obstructive sleep apnea]]
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Renal/Electrolyte'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Rheumatology/Immunology/Allergy'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Sexual'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Trauma'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Urologic'''
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| |bgcolor="Beige"| No underlying causes
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| |-
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| |-bgcolor="LightSteelBlue"
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| | '''Miscellaneous'''
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| |bgcolor="Beige"| [[Ageing]]
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| |-
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| |}
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| ===Causes in Alphabetical Order===
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| {{col-begin|width=80%}}
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| {{col-break|width=33%}}
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| *[[Ageing]]
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| *[[Alcoholic cardiomyopathy]]
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| *[[Anomalous origins of coronary arteries|Anomalous origin of the left coronary artery]]
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| *[[Aortic stenosis]]
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| *[[Aortic valve replacement]]
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| *[[Atrial septal defect]]
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| *[[Atrioventricular septal defect]]
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| *[[Chagas disease]]
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| *[[Charcot-Marie-Tooth disease]]
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| *[[Double outlet right ventricle]]
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| *[[Hypertensive cardiomyopathy]]
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| *[[Hypertensive heart disease]]
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| *[[Ischemic cardiomyopathy]]
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| *[[Kearns-Sayre syndrome]]
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| {{col-break|width=33%}}
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| *[[Left ventricular hypertrophy]]
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| *[[Leopard syndrome|Lentiginosis]]
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| *[[Lev's disease]]
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| *[[Limb-girdle muscular dystrophy]]
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| *[[Obstructive sleep apnea]]
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| *[[Postpartum cardiomyopathy]]
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| *[[Restrictive cardiomyopathy]]
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| *[[Hypertrophic cardiomyopathy septal myectomy|Septal myomectomy]]
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| *[[Single ventricle]]
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| *[[Subvalvular aortic stenosis#Treatment|Subvalvar aortic resection]]
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| *[[Tetralogy of fallot surgical techniques|Tetralogy of Fallot repair]]
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| *[[Transposition of the great vessels]]
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| *[[Tricuspid atresia]]
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| *[[Ventricular septal defect surgery]]
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| {{col-end}}
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| ==Diagnosis== | | ==Diagnosis== |
| ===Electrocardiogram===
| | [[Left anterior fascicular block history and symptoms| History and Symptoms]] | [[Left anterior fascicular block electrocardiogram|Electrocardiogram]] |
| ====Criteria for LAHB====
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| *[[Left axis deviation]] (usually between -45° and -90°), some consider -30° to meet criteria
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| *QRS interval < 0.12 seconds
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| *qR complex in the lateral limb leads (I and aVL)
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| *rS pattern in the inferior leads (II, III, and aVF)
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| *Delayed intrinsicoid deflection in lead aVL (> 0.045 s)<ref>Mirvis DM, Goldberger AL. Electrocardiography. In: Braunwald E, Zipes DP, Libby P, eds. Heart disease: a textbook of cardiovascular medicine, 6th edn. Philadelphia: WB Saunders; 2001:82–125.</ref>
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| ====Exceptions====
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| It is important not to call LAFB in the setting of a prior inferior wall [[myocardial infarction]] which may also demonstrate left axis deviation due to the initial forces ([[Q wave]] in a Qr complex) in leads II, III, and aVF. As opposed to LAHB, the left axis shift is due to terminal forces (i.e., the S wave in an rS complex) being directed superiorly.
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| ====Effects of LAHB on Diagnosing Infarctions and Left Ventricular Hypertrophy====
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| LAHB may be a cause of poor R wave progression across the precordium causing a pseudoinfarction pattern mimicking an anteroseptal infarction. It also makes the electrocardiographic diagnosis of LVH more complicated, because both may cause a large R wave in lead aVL. Therefore to call LVH on an EKG in the setting of an LAHB you should see the presence of a “strain” pattern when you are relying on limb lead criteria to diagnose LVH.<ref>Surawicz B, Knilans TK. Chou’s electrocardiography in clinical practice: adult and pediatric, 5th edn. Philadelphia: W.B. Saunders; 2001.</ref>
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| ====EKG Examples==== | | ==Treatment== |
| Shown below is an example of an EKG demonstrating left axis deviation with rS pattern in lead III and QRS complex < 0.12 seconds indicating a left anterior hemiblock. A qR complex is also seen in lead aVL.
| | [[Left anterior fascicular block medical therapy|Medical Therapy]] | [[Left anterior fascicular block primary prevention|Primary Prevention]] |
| [[Image:Right bundle branch block 4.jpg|center|500px]] | |
| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
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| ----
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| Shown below is an example of an EKG showing rS pattern in lead III, qR complex in lead aVL and QRS complex < 0.12 seconds along with left axis deviation indicating left anterior fascicular block.
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| [[Image:LAHB.png|center|500px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
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| | ==Case Studies== |
| | [[Left anterior fascicular block case study one|Case#1]] |
| ==References== | | ==References== |
| {{Reflist|2}} | | {{Reflist|2}} |
| {{Electrocardiography}}
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| | [[Category:Crowdiagnosis]] |
| [[Category:Cardiology]] | | [[Category:Cardiology]] |
| | [[Category:Up-To-Date]] |
| | [[Category:Up-To-Date cardiology]] |
| | [[Category:Arrhythmia]] |
| [[Category:Electrophysiology]] | | [[Category:Electrophysiology]] |
| [[Category:Arrhythmia]]
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| [[Category:Emergency medicine]]
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| [[Category:Disease]] | | [[Category:Disease]] |
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