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Left septal fascicular block: myth or reality?

Rex N MacAlpin1

  • 1Division of Cardiology, Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California 90095-1679, USA. rmacalpi@ucla.edu

Indian Pacing and Electrophysiology Journal
|September 1, 2006
PubMed

Insights

This study explores left septal fascicular block, a controversial conduction defect. It proposes electrocardiogram criteria for recognizing this condition, which can explain unexplained ECG abnormalities.

Area of Science:

  • Cardiology
  • Electrophysiology
  • Human Anatomy

Background:

  • The left bundle branch in the human heart typically trifurcates into anterior, posterior, and septal fascicles.
  • Electrocardiogram (ECG) interpretation commonly includes conduction abnormalities of the anterior and posterior fascicles.
  • Conduction defects of the third left fascicle, the septal or median fascicle, lack established diagnostic criteria and remain debated.

Purpose of the Study:

  • To review existing evidence regarding the septal fascicle of the left bundle branch.
  • To propose specific electrocardiogram (ECG) criteria for identifying left septal fascicular block.
  • To present illustrative cases demonstrating left septal fascicular block as a distinct entity.

Main Methods:

  • Literature review of anatomical and electrophysiological studies on left bundle branch fascicles.
  • Analysis of 12-lead electrocardiogram (ECG) patterns associated with conduction delays.
  • Development and validation of proposed ECG criteria for left septal fascicular block using case examples.

Main Results:

  • Anatomical studies confirm the trifascicular nature of the left bundle branch in most individuals.
  • Proposed electrocardiogram (ECG) criteria can identify specific conduction defects within the left septal fascicle.
  • Case studies demonstrate that left septal fascicular block can manifest as unique, previously unexplained ECG abnormalities.

Conclusions:

  • Left septal fascicular block is a recognizable clinical entity with distinct electrocardiogram (ECG) findings.
  • The proposed diagnostic criteria aid in identifying this specific conduction defect.
  • Recognition of left septal fascicular block can improve the understanding of complex electrocardiogram (ECG) abnormalities.

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