Effects of anisotropy and transmural heterogeneity on the T-wave polarity of simulated electrograms

The major determinants of the T wave polarity in electrocardiograms (ECGs) are still a debated issue. The aim of this work is to investigate the effects of tissue anisotropy, cellular action potential duration (APD) heterogeneities and excitation wavefront shape on the T wave polarity in unipolar and bipolar ECGs, simulated in a conducting medium surrounding the cardiac tissue at some distance fom endo to epicardium. The study is based on three-dimensional anisotropic Monodomain simulations of the entire depolarization and repolarization phases of propagating action potentials in a parallelepipedal slab. The results show that the T wave of unipolar ECGs is positive at all sites explored and its shape and polarity are mainly determined by the anisotropy of the cardiac tissue, irrespective of cellular APD heterogeneities and shape of the excitation wavefront. On the other hand, bipolar ECGs are mainly affected by their isotropic component and their T wave turns out to be positive for single site stimulations in the presence of transmural APD heterogeneity, while it becomes always negative in case of multiple sites stimulation generating large activation wavefronts, regardless of the considered cellular APD heterogeneities.