Comparison of scalar with vectorial electrocardiogram in axis determination

Axis deviation is one of the variables most commonly sought for in Electrocardiography (ECG). Although no one doubts the superiority of vector cardiography (VCG) as the most accurate in axis determination, most clinicians adopt the Hexaxial Reference System (HRS) of the 12-Lead ECG (12LS) as the most accessible for routine use. The question therefore arises: How accurate is the HRS? The 12LS and Orthogonal (Frank Lead) ECG (OLS) were recorded in 664 adult Nigerians without heart or metabolic diseases. Their VCG were constructed manually for the QRS complexes. On each subject, QRS axis was determined by three methods: the HRS for the 12LS, the trigonometric method for the OLS and the direction of the maximum deflection vector for the VCG. Axes by the three modalities were analysed and compared statistically as applicable to paired samples. The frontal plane (FP) QRS axis ranged between O degree and +90 degrees in 98.2% of cases by VCG, 96% by the OLS and 93.6% by the 12LS. There was excellent correlation between axes obtained by VCG and OLS (r = 0.85; P < 0.0001). It was lower but highly significant between VCG and the 12LS (r = 0.70; P < 0.0001). In the horizontal plane (HP), the 97 per centile distribution ranged from 240 degrees through 0 degree to 30 degrees; that is, posteriorly and to the left. In the left sagittal plane (LSP), the 95 per centile distribution ranged from 60 degrees counter-clockwise to 210 degrees; that is inferiorly and posteriorly. In a sample of healthy adult Nigerians, the QRS axis by VCG was located posteriorly, inferiorly and to the left. Axis determination by the 12LS is limited to the FP only, and it bears a good correlation with VCG. This commends the H RS as a condonable tool for estimating wave axis routinely and for epidemiologic studies.