A comparison of electrocardiographic imaging based on two source types.

The aim of the study to compare the performance of two major source types involved in the imaging of the electric activity of the heart on the basis of potential differences observed on the thorax. The images depict either the timing of activation and repolarization of the myocardium or the potential field on a surface closely encompassing the myocardium. The depolarization and repolarization timing on a closed surface bounding the ventricular myocardium was derived from measured body surface potentials (BSPs), an MRI-based electric volume conductor model comprising the geometry of thorax, lungs, heart surface Sh, and cavities. The solution was constrained by using a template of the local transmembrane potentials (TMPs). The latter serve as the strength of the Equivalent Double Layer (EDL) source model (SM), which was used to compute the potential field on Sh (epicardium and endocardium). The second SM is the potential distribution on the epicardium Sp, referred to here as the Equivalent Potential Distribution (EPD). Its strength was estimated directly from the BSPs. The inflection points of the estimated electrograms (ELGs) were taken as markers of the timing of local depolarization and repolarization. The endocardial potential fields estimated using both sources exhibited qualitative similarity, as did the ELGs. With reference to the one generated by the EDL source, the magnitude of the estimated endocardial EPD field was smaller, the downslopes of the ELGs were lower. The timing of depolarization estimated from the EDL-based ELGs was highly correlated with those of the TMP templates, the EPD-based correlation was lower. For the repolarization timing the corresponding test values indicated an insufficient similarity. The EDL- and EPD-based source variants deserve to be studied alongside each other in the future development of electrocardiographic imaging.