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In search of left septal fascicular block
1Division of Cardiology, Department of Medicine, University of California at Los Angeles, Los Angeles, Calif, USA. rmacalpi@ucla.edu
Insights
The existence of left septal fascicle block, a controversial electrocardiographic finding, is supported by new diagnostic criteria. This condition, found in 0.5% of ECGs, may explain unclear electrocardiogram abnormalities.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Diagnostics
Background:
- The left bundle branch in humans typically trifurcates into anterior, posterior, and septal fascicles.
- Conduction abnormalities in the anterior and posterior fascicles are well-established.
- Diagnosis of left septal fascicle block remains controversial due to a lack of consensus criteria.
Purpose of the Study:
- To investigate the existence of left septal fascicle block.
- To establish diagnostic criteria for left septal fascicle block.
- To explore the clinical significance of this condition.
Main Methods:
- A retrospective review of approximately 26,000 electrocardiograms (ECGs).
- Application of newly derived criteria for left septal fascicle block.
- Selection and analysis of illustrative ECG examples.
Main Results:
- Electrocardiograms consistent with left septal fascicle block were identified in approximately 0.5% of the reviewed tracings.
- The study presents illustrative ECG examples supporting the proposed diagnostic criteria.
- Reasons for the selection of these specific ECGs are discussed.
Conclusions:
- The findings suggest that left septal fascicle block is a real electrocardiographic entity.
- Left septal fascicle block exhibits polymorphic patterns.
- This condition may account for previously unexplained electrocardiographic abnormalities.
Background:
In most humans, the left bundle branch divides into 3 fascicles. Electrocardiographic changes resulting from conduction abnormalities of the left anterior and left posterior fascicles are well described and commonly diagnosed. Existence of conduction defects of the left septal fascicle is controversial, without generally accepted criteria for diagnosis.
Methods:
Approximately 26,000 electrocardiograms were reviewed to find examples consistent with left septal fascicle block according to criteria derived from review of the literature.
Results:
Electrocardiograms meeting proposed criteria were found in about 0.5% of tracings. Illustrative examples are shown with discussion of reasons for their selection.
Conclusions:
Left septal fascicle block seems to exist, is polymorphic, and may explain some previously inadequately understood electrocardiographic abnormalities.