Evaluation of heart electrical axis position determination by different methods: possible reasons for the discrepancy

   Background. The position of the electrical heart axis (EHA) can be determined by various methods. In clinical practice, discrepancies often occur between physician-assessed and automated EHA estimates.

   Objective. To evaluate the significance of discrepancies between different EHA determination methods in patients with cardiovascular pathology.

   Materials and methods. We analyzed 12,323 ECGs from 9,794 patients. EHA position was determined using five methods: the Minnesota Code table (αMC), standard formulas using net voltage in leads I/III, I/II, and I/aVF (αI,III, αI,II, αI,aVF), and the mean QRS vector in leads I/II (αm). Amplitude measurements were automated and served as the single data source. Agreement was assessed using Bland – Altman analysis. Cases with maximal discrepancies underwent physician visual ECG review.

   Results. Best agreement was between αMC and αI,III. Discrepancies increased with the angle between lead III and leads aVF, II. The largest differences in number and magnitude were between αMC and αm. Visual analysis of frontal plane QRS loop morphology explained these discrepancies by differences in the angular position of the net cardiac electrical vector corresponding to maximal lead projection.

   Conclusion. Automated EHA calculation using leads I and III ensures comparability with physician assessment. Discrepancies between net voltage-based and mean vector-based EHA may have independent diagnostic value, as they characterize frontal plane QRS loop morphology and may provide information on ventricular myocardial depolarization.

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