Recent advances in the diagnosis of fascicular blocks.

The electrocardiographic criteria for the diagnosis of left fascicular blocks have been a subject of debate and speculation. Nevertheless, careful analysis of certain electropathologic studies, extrapolations from animal experiments, and studies resulting from the inadvertent section of the various fascicles and of tracings obtained at the moment that the conduction disturbances appeared or disappeared have led to the acceptance of characteristic patterns. Although the specificity and sensitivity of electrocardiographic criteria of left anterior and left posterior fascicular block still require independent confirmation, there are already some methods that appear promising in this regard.