Left septal fascicular block (LSFB) is a rare electrocardiographic finding characterized by delayed or blocked conduction through the anteromedial fascicle of the left bundle branch of the His bundle.

Electrocardiographic Criteria

  • qR morphology in V1 to V4
  • R wave ≥ 15 mm in V2 and V3 or from V1, increasing toward the mid-precordial leads and decreasing from V5 to V6
  • Sudden jump in the “r” wave from V1 to V2 (“rS” in V1 to R in V2)
  • QRS duration < 120 ms
  • No deviation of the QRS electrical axis in the frontal plane
  • T waves usually negative in the right precordial leads

These diagnostic criteria were proposed by the 2022 Brazilian Guideline on Electrocardiographic Reports, in the absence of RVH, septal hypertrophy, or lateral infarction.

ECG in Left Septal Fascicular Block

Coming soon…

References

  1. Samesima N, God EG, Kruse JCL, Leal MG, et al. Diretriz da Sociedade Brasileira de Cardiologia sobre a Análise e Emissão de Laudos Eletrocardiográficos – 2022. Arq Bras Cardiol. 2022;93(3 Suppl 2):2–19.
  2. Pérez Riera AR, Ferreira C, Ferreira Filho C, Meneghini A, et al. Electrovectorcardiographic diagnosis of left septal fascicular block: Anatomic and clinical considerations. Ann Noninvasive Electrocardiol. 2011;16(2):196–207.
  3. Bayés De Luna A, Riera AP, Baranchuk A, Chiale P, et al. Electrocardiographic manifestation of the middle fibers/septal fascicle block: A consensus report. J Electrocardiol. 2012;45(5):454–60.