Left posterior fascicular block (LPFB)

Introduction

  • Left posterior fascicular block (LPFB) or Left posterior hemiblock (LPH) is a type of unifascicular block of left bundle branch with typical ECG pattern – right axis deviation

  • Isolated LPFB is rare and most often the cause of right-axis deviation is right ventricular hypertrophy (RVH)

  • For diagnosis of LPGB ECG and clinical characteristics of RVH and asthenic habitus must be absent

ECG features

  • Right axis deviation ≥+90 degrees
  • RS or rS pattern in I and aVL
  • qR pattern in II, III, aVF
  • QRS duration < 120 ms

Right axis deviation

  • QRS is POSITIVE (dominant R wave) in Lead II, Lead III and aVF
  • QRS is NEGATIVE (dominant S wave) in Lead I

Picture 1 Right axis deviation


ECG 1 Left posterior fascicular block (LPFB, LPH)

  • right axis deviation + 106°
  • RS pattern in lead I, rS pattern in lead aVL
  • qR pattern in II, III, aVF
  • slightly prolonged QRS duration – 110ms
  • sinus rhythm at a rate 75 bpm

Causes

  • Left bundle branch consists of two fascicles – Left anterior fascicle and Left posterior fascicle
  • Normal activation of the left-ventricular free wall spreads simultaneously from two sites. When a block in either the LAF or LPF is present, activation of the free wall proceeds from one site instead of two. This changes the waveforms of the QRS complex and produces a shift of the QRS complex axis
  • Isolated fascicular block is often benign
  • The incidence of fascicular block  in otherwise normal individuals is 2% to 5% and increases with age

References

  1. Brian Olshansky, Mina K. Chung, Steven M. Pogwizd, Nora Goldschlager, Chapter 2 - Bradyarrhythmias—Conduction System Abnormalities, Editor(s): Brian Olshansky, Mina K. Chung, Steven M. Pogwizd, Nora Goldschlager, Arrhythmia Essentials (Second Edition), Elsevier, 2017, Pages 28-86, ISBN 9780323399685, https://doi.org/10.1016/B978-0-323-39968-5.00002-0.
  2. CAMM, A. J., LÜSCHER, T. F., & SERRUYS, P. W. (2009). The ESC textbook of cardiovascular medicine. Oxford, Oxford University Press
  3. STRAUSS, David G., et al. Marriott's Practical Electrocardiography. Wolters Kluwer, 2021