Simulation of T wave based on cardiac model of electrical activity: effects of anisotropy of myocardium and inhomogeneity of ventricular gradient on QRS-T angle.

To investigate the effects of the excitation propagation and the inhomogenous distribution of action potential duration (APD) on QRS-T angle and T wave polarity, mathematical analysis and computer simulation of QRS-T wave were performed in a cardiac model of the electrical activity. A rectangular solid model with the conduction system on the subendocardial surface simulated a part of the free wall of the left ventricle. In our previous studies we assumed isotropy of the myocardium and linear ventricular gradient. In the present study, we obtained the quantitative relationship between the ventricular gradient (beta) (intramural gradient of action potential duration) and the QRS-T angle (theta) in the models with anisotropy of the myocardium and inhomogenous ventricular gradient. The directions of progress of depolarization and repolarization were different between with presence and absence of anisotropy. However, the beta-theta relationship was minimally influenced by anisotopy. Furthermore, the present study demonstrated that the total T vector is determined by the difference of APD between endocardium and epicardium, and is not influenced by the inhomogeneity of APD in the middle layer of the ventricular wall. These results support the validity of our previous cardiac model in which we assumed isotropy of the myocardium and the homogenous ventricular gradient. Moreover we demonstrated that the propagation velocity and the cardiac hypertrophy may largely influence the T wave polarity by the simulation study of electrocardiograms.