In search of left septal fascicular block.
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.
MacAlpin
Rex N
RN
Division of Cardiology, Department of Medicine, University of California at Los Angeles, Los Angeles, Calif, USA. rmacalpi@ucla.edu
D002037:Bundle-Branch Block / Q000503:physiopathology*; D004562:Electrocardiography; D006346:Heart Septum / Q000503:physiopathology*; D006801:Humans