[Tall R waves in the right precordial leads as a possible expression of left septal fascicular block].

Histological, physiological and pathophysiological studies have shown that the left bundle branch mainly divides into three fascicles, and a septal (middle) fascicle is present in over half of human hearts. Electrocardiographic criteria for the diagnosis of the block of this fascicle have been suggested by some authors: tall R waves in lead V2 and sometimes in V1 in the absence of a right bundle branch block pattern or a well evident jump of R waves from V1 to V2, absence of initial septal q waves and/or possible small q waves in the right precordial leads, normal QRS duration and normal QRS axis. At present, this intraventricular block can only be suspected but not diagnosed with certainty even after clinical/instrumental exclusion of pathological situations associated with tall R waves in leads V1 and V2 (right ventricular hypertrophy, lateral infarction, severe septal hypertrophy) because of the marked variability of normal ECG and the potential presence of confounding diseases.