Normalization of the electrocardiogram by standardization of heart position and orientation

In healthy subjects, a large inter-individual variability in the ECG is present. Part of this variability is intrinsically due to physiological differences in the heart. Other causes are differences in the position and orientation of the heart relative to the chest. In the current study, research was done to reduce the variability through the latter cause. In healthy volunteers, 64-lead body surface maps (BSMs) were recorded and the inter-individual variability was determined. Pericardial potentials were calculated from the BSMs using an individual realistic torso and heart model for each subject. Then, the heart in the model was moved and rotated into a standard position and orientation. Finally, forward calculations were made using the new heart position, while keeping the pericardial potential distribution unaltered. This yielded new electrode potentials at the 64 BSM leads. The inter-individual variability of the corrected signals was calculated and compared with the original variability. The realistic models were based on magnetic resonance images of the torso, lungs and heart of four healthy volunteers. Using BSM and MRI data of 4 subjects, the authors have carried out the described procedure. The variability of the sets of BSM data was 0.28 mV. The pericardial potentials were calculated (forward simulation of the results yielded an error of 10%). The variability after shifting and rotating the hearts towards a standard position was 0.23 mV. It is concluded that a reduction of variability is indeed found when standardizing heart position and orientation. A larger number of subjects will be included in this study to substantiate this result.