UpToDate
Official reprint from UpToDate®
www.uptodate.com ©2017 UpToDate®

Chronic bifascicular blocks

Author
William H Sauer, MD
Section Editor
N A Mark Estes, III, MD
Deputy Editor
Brian C Downey, MD, FACC

INTRODUCTION

Bifascicular block, a pattern seen on the surface electrocardiogram (ECG), results when normal physiologic activation in the His-Purkinje system is interrupted. The normal sequence of activation is altered dramatically in patients with bifascicular block, with a resultant characteristic appearance on the ECG that varies depending upon the exact fascicles which are blocked. Interruptions in conduction may result in right bundle branch block (RBBB), left anterior fascicular block (LAFB), or left posterior fascicular block (LPFB), with bifascicular block resulting when two of these three are identified from the ECG.

A 2009 American Heart Association/American College of Cardiology Foundation/Heart Rhythm Society (AHA/ACCF/HRS) scientific statement on the standardization and interpretation of the electrocardiogram recommends against using the term bifascicular block (and also trifascicular block) since these patterns do not have unique anatomic and pathologic substrates [1]. However, these terms are still widely entrenched in clinical practice and scientific literature, meriting their discussion here.

The anatomy, clinical manifestations, differential diagnosis, prognostic implications, and treatment of bifascicular block (RBBB with either LAFB or LPFB) will be reviewed here. Though technically a type of bifascicular block, complete LBBB is discussed separately, as are conduction system abnormalities involving only a single fascicle. (See "Left bundle branch block" and "Right bundle branch block" and "Left anterior fascicular block" and "Left posterior fascicular block" and "Left median (middle or septal) fascicular block".)

DEFINITIONS

Bifascicular block – The term bifascicular block most commonly refers to conduction disturbances below the atrioventricular (AV) node in which the right bundle branch and one of the two fascicles (anterior or posterior) of the left bundle branch are involved. Although this definition is used in the 2008 American College of Cardiology/American Heart Association/Heart Rhythm Society (ACC/AHA/HRS) guidelines for device-based therapy of cardiac rhythm abnormalities [2], some authors, including those of the guidelines on the management of syncope published by the European Society of Cardiology (ESC), include left bundle branch block (LBBB) in the definition of bifascicular block since LBBB, as noted, implies block in both fascicles [2,3].

Trifascicular block – The term trifascicular block is most commonly used to describe bifascicular block associated with prolongation of the PR interval (ie, first degree AV block). However, this description, though commonly used in clinical practice, is inaccurate as the conduction delay resulting in the PR interval prolongation does not usually occur in a fascicle, but in the AV node. True trifascicular block would involve block of the right bundle branch and both fascicles of the left bundle branch; this manifests as third degree (complete) heart block and is referred to as such. Sinus rhythm with alternating left/right bundle branch block or right bundle branch block (RBBB) with alternating fascicular blocks on a beat-to-beat basis is a very rare manifestation of trifascicular block, usually heralding complete AV block. (See "Third degree (complete) atrioventricular block".)

               

Subscribers log in here

To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information or to purchase a personal subscription, click below on the option that best describes you:
Literature review current through: Jul 2017. | This topic last updated: Feb 03, 2017.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2017 UpToDate, Inc.
References
Top
  1. 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. Circulation 2009; 119:e235.
  2. Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices): developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. Circulation 2008; 117:e350.
  3. Task Force for the Diagnosis and Management of Syncope, European Society of Cardiology (ESC), European Heart Rhythm Association (EHRA), et al. Guidelines for the diagnosis and management of syncope (version 2009). Eur Heart J 2009; 30:2631.
  4. Tawara S. Das Reizleitungssystem des Säuegetierherzens. Gustav Fischer, Jena 1906.
  5. Rosenbaum M, Elizari MV, Lazzari JO. The Hemiblocks. Tampa Tracings, Tampa 1970.
  6. Uhley HN. Some controversy regarding the peripheral distribution of the conduction system. Am J Cardiol 1972; 30:919.
  7. Hecht HH, Kossmann CE, Childers RW, et al. Atrioventricular and intraventricular conduction. Revised nomenclature and concepts. Am J Cardiol 1973; 31:232.
  8. Demoulin JC, Kulbertus HE. Histopathological examination of concept of left hemiblock. Br Heart J 1972; 34:807.
  9. Brignole M, Auricchio A, Baron-Esquivias G, et al. 2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA). Eur Heart J 2013; 34:2281.
  10. Englund A, Fredrikson M, Rosenqvist M. Head-up tilt test. A nonspecific method of evaluating patients with bifascicular block. Circulation 1997; 95:951.
  11. McAnulty JH, Rahimtoola SH, Murphy E, et al. Natural history of "high-risk" bundle-branch block: final report of a prospective study. N Engl J Med 1982; 307:137.
  12. Schneider JF, Thomas HE, Kreger BE, et al. Newly acquired right bundle-branch block: The Framingham Study. Ann Intern Med 1980; 92:37.
  13. Martí-Almor J, Cladellas M, Bazán V, et al. [Novel predictors of progression of atrioventricular block in patients with chronic bifascicular block]. Rev Esp Cardiol 2010; 63:400.
  14. Kalscheur MM, Donateo P, Wenzke KE, et al. Long-Term Outcome of Patients with Bifascicular Block and Unexplained Syncope Following Cardiac Pacing. Pacing Clin Electrophysiol 2016; 39:1126.
  15. Krahn AD, Morillo CA, Kus T, et al. Empiric pacemaker compared with a monitoring strategy in patients with syncope and bifascicular conduction block--rationale and design of the Syncope: Pacing or Recording in ThE Later Years (SPRITELY) study. Europace 2012; 14:1044.