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Left Posterior Fascicular Block

Left Post Fascicular Block

A left posterior fascicular block is a very rare abnormality of the cardiac conduction system and is primarily associated with a myocardial infarction of the inferior wall and coronary artery disease. The clinical presentation significantly depends on the extent of coronary artery vessel occlusion. Electrocardiography is the single most important study for revealing a left posterior fascicular block, showing either intermediate (90° to 120°) or marked (120° and 180°) right axis deviation, alongside several other findings involving the QRS complex.


A left posterior fascicular block is an electrophysiologic abnormality that is rarely encountered in clinical practice, but it is well-known for its occurrence in the setting of coronary artery disease (CAD) [1] [2] [3] [4]. Insufficient blood flow to the left posterior fascicle, which is supplied by the right coronary artery and the anterior descending branch of the left coronary artery, causes improper conduction of the electrical signal through the heart [1] [4]. Because of blood vessel occlusion, myocardial infarction may ensue and left posterior fascicular is shown to be present in about 5% of all myocardial infarctions of the inferior wall according to isolated reports [1]. Hence, the clinical presentation of these patients is primarily related to myocardial infarction and CAD. Some reports, however (in which iatrogenic induction of this cardiac abnormality by interleukin-2 was documented) have observed patients in whom the symptoms such as chest pain, syncope, or palpitations weren't present [5]. Atrial flutter and atrial fibrillation, two very important types of arrhythmias, are known to induce the phenomenon of "axis deviation", which may promote the development of left posterior fascicular block [6].

  • QRS duration Causes of left posterior fascicular block (LPFB) Degenerative processes, ischemic heart disease, hyperkalemia, myocarditis, amyloidosis and acute cor pulmonale may all cause LPFB.[ecgwaves.com]
Heart Disease
  • It usually accompanies right bundle branch block (RBBB) or in the setting of arteriosclerotic heart diseases such as myocardial infarction.[wikidoc.org]
  • ICD-CODE.org Codes Chapters Blocks Categories Diseases of the circulatory system Other forms of heart disease I44 - Atrioventricular and left bundle-branch block I445 Code I44.5 Code: I445 Description: Left posterior fascicular block Chapter: Diseases[icd-code.org]
  • Causes of Left Posterior Fascicle Block - The left posterior fascicle has dual blood supply (LAD AV nodal artery) so if ischaemic heart disease is causing this phenomenon, it is SEVERE indeed. - Could be myocarditis or some sort nof cardiomyopathy Consequences[derangedphysiology.com]
  • MS-DRG v30.0) 308 - Cardiac Arrhythmia & Conduction Disorders W Mcc 309 - Cardiac Arrhythmia & Conduction Disorders W Cc 310 - Cardiac Arrhythmia & Conduction Disorders W/o Cc/mcc Chapter Diseases of the circulatory system (I00-I99) Block Other forms of heart[emedcodes.com]
  • The majority of those with LAFB, however, have significant heart disease.[ecgwaves.com]
Skipped Beats
  • Symptoms of arrhythmias include Fast or slow heart beat Skipping beats Lightheadedness or dizziness Chest pain Shortness of breath Sweating Your doctor can run tests to find out if you have an arrhythmia.[icdlist.com]


The diagnostic workup of patients with a left posterior fascicular block starts with a thorough clinical assessment. A detailed patient history is necessary in order to reveal possible risk factors, mainly CAD. If the abrupt clinical presentation of sudden chest pain and other typical signs seen in a myocardial infarction are noted, immediate employment of electrocardiography (ECG) is of great importance. Left posterior fascicular block can appear in association with a right bundle branch block (RBBB) or as an isolated entity, and recently proposed criteria for this abnormality state the following findings are necessary to make the diagnosis [1] [2] [5] [7]:

  • Right axis deviation - A shift of the frontal plane to 90°-180° in adults is one of the crucial findings in a left posterior fascicular block.
  • Duration of the QRS complex of < 120 milliseconds
  • A QR pattern in leads aVF and III
  • An RS pattern (a small R wave with a deep S wave) in leads aVL and I

As soon as these criteria are met, it is recommended to perform coronary angiography (and left ventricular angiography if possible), mainly because CAD in the case of left posterior fascicular block frequently affects up to 3 coronary vessels [1].

Right Axis Deviation
  • Electrocardiography is the single most important study for revealing a left posterior fascicular block, showing either intermediate (90 to 120 ) or marked (120 and 180 ) right axis deviation, alongside several other findings involving the QRS complex.[symptoma.com]
  • The ECG showed a marked right axis deviation, a QRS duration of 0.13 sec. and an rS pattern from V1 to V6. In the high right precordial leads an rsR' pattern was recorded.[ncbi.nlm.nih.gov]
  • Therefore, the latter portion of the QRS depolarizes toward the inferior myocardium, manifesting as strong right axis deviation. 2.[studymedicalphotos.blogspot.com]
  • Do not be tempted to diagnose LPFB until you have ruled out more significant causes of right axis deviation : Example: acute pulmonary embolus ; tricyclic overdose ; lateral STEMI ; and right ventricular hypertrophy .[lifeinthefastlane.com]
  • (over 45msec) in aVF - There should be absence of right ventricular hypertrophy, or any other cause of right axis deviation - Limb lead QRS voltage should be increased in summary...[derangedphysiology.com]


  • Similar electrocardiogram changes were noticed during 2 subsequent cycles of high-dose IL-2 treatment, both of which resolved spontaneously.[ncbi.nlm.nih.gov]
  • Advanced level treatment material, such as complete thrombus formation, treatment and management offers critical information for both the hospital setting and the EMS setting.[books.google.com]
  • The patient received another treatment. The endpoint was met and the procedure was successful. The left posterior fascicular block in surface ECG used as an endpoint of RF ablation to treat ILVT is effective.[ncbi.nlm.nih.gov]
  • Treatment to restore a normal heart rhythm may include medicines, an implantable cardioverter-defibrillator (ICD) or pacemaker, or sometimes surgery.[icdlist.com]


  • The development of RBBB LPFB during acute myocardial infarction is a sign of poor prognosis. RBBB LPFB has a high probability to turn into complete AV block. References Circulation 2009;119:e235-e240 Circulation 2007;115:1154-1163 ECG 1.[metealpaslan.com]
  • Prognosis of left anterior fascicular block (LAFB) Isolated LAFB is considered a benign conduction defect.[ecgwaves.com]
  • For the same reason, left posterior hemiblock carries a poorer prognosis.[cardiophile.org]
  • Questions regarding left anterior fascicular block may be very common regarding what left anterior fascicular block is, the causes, prognosis, symptoms, as well as treatments.[justanswer.com]



  • Co-authors include Mala Mandyam of the UCSF Division of Cardiology, Electrophysiology Section; Eric Vittinghoff, PhD, of the UCSF Department of Epidemiology and Biostatistics; Elsayed Z.[ucsf.edu]
Sex distribution
Age distribution


  • Canis ISSN: 2398-2942 Synonym(s): Left axis shift Contributor(s): Dan Ohad, Mark Oyama Pathophysiology The bundle branches of the cardiac conduction system arise from the bundle of His as it exits the atrioventricular node.[vetstream.com]
  • Knowledge of the anatomy and electrophysiology of the cardiac conduction system from the atrioventricular (AV) junction to the distal Purkinje fibers is essential to understanding the pathophysiology of left bundle branch (LBB) block (LBBB).[emedicine.medscape.com]
  • With the current knowledge concerning the pathophysiology of the tachycardia and modern ablation techniques, ILVT now has an excellent prognosis. References Lerman BB, Stein KM, Markowitz SM. Mechanisms of idiopathic left ventricular tachycardia.[innovationsincrm.com]


  • This type of occlusion is often called the "Widow Maker", and requires very rapid intervention to restore blood flow and prevent complicatons.[ecgguru.com]
  • Definition (MSH) A form of heart block in which the electrical stimulation of HEART VENTRICLES is interrupted at either one of the branches of BUNDLE OF HIS thus preventing the simultaneous depolarization of the two ventricles.[fpnotebook.com]
  • In addition, it prevents sudden death for patients that experience atrial fibrillation. When the atria are fibrillating, what’s to stop the ventricles from fibrillating? The AV node![ems12lead.com]
  • Committee for Practice Guidelines (Writing Committee to Develop Guidelines for Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death).[escardio.org]
  • In the diagnosis of bradyarrhythmias the identification of reversible causes is important to prevent unnecessary treatment.[textbookofcardiology.org]



  1. Godat FJ, Gertsch M. Isolated left posterior fascicular block: a reliable marker for inferior myocardial infarction and associated severe coronary artery disease. Clin Cardiol. 1993 Mar;16(3):220-6.
  2. Surawicz B, Childers R, Deal BJ, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Endorsed by the International Society for Computerized Electrocardiology. J Am Coll Cardiol. 2009 Mar 17;53(11):976-81.
  3. Patanè S, Marte F, Mancuso A, Di Bella G. Transient right axis deviation with left posterior hemiblock and junctional rhythm during acute myocardial infarction. Int J Cardiol. 2009;135(3):e69-72.
  4. Rokey R, Chahine RA. Isolated left posterior fascicular block associated with acquired ventricular septal defect. Clin Cardiol. 1984;7(6):364-369.
  5. Singla A, Denmeade SR. Left posterior fascicular block due to high-dose interleukin-2. Ann Pharmacother. 2008;42(9):1340-1343.
  6. Patanè S, Marte F, Sturiale M. Right bundle branch block with revelation of changing axis deviation at the end of atrial fibrillation. Int J Cardiol. 2009;137(3):e54-56.
  7. Ashley EA, Niebauer J. Cardiology Explained. London: Remedica; 2004. Chapter 8, Arrhythmia.

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Last updated: 2018-06-21 18:46