A physiological assessment of mean QRS axis in an Indian sub-population using two methods of axis calculation

Abstract

Background and Aim: The interpretation of the electrocardiographic deflection in terms of mean QRS axis (MQRSA) direction and deviation constitutes one of the most important diagnostic aids for the accurate and deductive evaluation of the electrocardiogram. This study was undertaken to assess the MQRSA in an Indian sub-population free of any cardiac illness using the hexaxial reference system and a formula tan θ = (I + 2III)/√3 I. Methods: The present work is a hospital based cross-sectional study. After getting consent, data was collected from 162 subjects (91 males and 71 females). Electrocardiogram of the subjects studied were taken using Marquette 2000 portable electrocardiographs. Chi-square test was used for comparision of data between the two methods. Results: MQRSA of 162 adult subjects with no any past or present history of cardiac illness was found to be directed within a narrow range between +40° and +60°. Hundred and forty-two had their mean electrical axis between 0° and +90° and 18 had their mean electrical axis between −90° and 0°. Of the 104 subjects >50 years, 16 (15%) have a statistically significant left axis deviation. The results obtained by both the graph and formula methods tallied perfectly. Conclusion: This investigation confirms that a majority of the subjects had their MQRSA lying in the range 0°-90°, which is the accepted normal range. The formula can be reliably used for a bedside axis calculation.