[Electrocardiographic criteria for the diagnosis of the left septal fascicular block and its frequency among primarily elderly hospitalized patients].

Characteristic electrocardiographic findings of the left septal fascicular block consist of a prominent anterior QRS force. Therefore, the following criteria were proposed for the diagnosis of left septal fascicular block, based on the normal limits of the R and S waves and R/S of V1 and V2. (1) Right ventricular hypertrophy, complete right bundle branch block, preexcitation (Type A), high posterior infarction, hypertrophic cardiomyopathy and abnormality of the thorax or intrathoracic tissues which might cause marked counterclockwise rotation around the longitudinal axis of the heart, should be excluded. (2) One of the following two criteria should be satisfied. (i) R/Sv1 greater than 2, and Rv1 greater than or equal to 5 mm, (ii) R/Sv2 greater than 2, and Rv2 greater than or equal to 15 mm, or Sv2 less than 5 mm. The frequency of left septal fascicular block diagnosed by these criteria was 3.5% among all patients of a hospital mainly consisting of elderly patients. This frequency was less than that of the left anterior fascicular block or complete right bundle branch block, but it was higher than that of the complete left bundle branch block or bilateral bundle branch block.