An abnormally superior vector (formerly called marked left axis deviation)

Abstract

For many years marked left axi,s deviation (mean frontal plane QRS vector of “greater” than -30”) has been considered a diagnostic aid to the diagnosis of left ventricular hypertr0phy.l There are many possible reasons for this belief, including tradition, the frequent association with left ventricular hypertrophy, and the fact that the word “left” is part of the phrase. Although in the past 15 years there has been mounting evidence that “left axis deviation” is not caused by left ventricular hypertrophy per se but by a conduction defect, the tradition appears to have continued. It is difficult to discover where the expression “axis deviation” originated, but the standard definitions defined the mean frontal plane vector in these terms : A vector from 0” to +90° was a normal axis; one of +90° to +lSO’ indicated right axis deviation; and one of 0” to -90” left axis deviation. In some terminologies, an axis between +180” and -90” (northwest) was considered an indeterminate axis since it was not clear, for example, whether $230” (-130’)’ was marked right or marked left axis deviation. Other types of axis deviation were difficult to read, such as the frequent “2 main vectors” in which the first vector was at +40”, and the second at +220” (-140”). (Is the true “axis” or mean vector +130” or --5O”?) This axis was also sometimes called in-