T-Vector Analysis Could Reveal Ventricular Regions with the Most Pronounced APD Changes

Introduction: Ventricular repolarization heterogeneities may serve as a functional substrate for reentrant arrhythmias. There is an intuitively clear relationship between ventricular end of repolarization gradients and vectorcardiographic T-vector components. However, the end of repolarization gradients may not coincide with action potential duration (APD) gradients due to contribution of activation pattern to repolarization sequence and T wave. Moreover, extracardiac factors may mask moderate changes of the APD distribution. The aim of this simulation study was to compare expressions of APD ventricular gradients in T-vector parameters in realistic conditions of normal and diabetic heart. Methods: Simulations were carried out in the framework of the computer model of the rabbit heart ventricles based on data obtained from epicardial and intramural electrograms recorded in normal and diabetic (alloxan model) rabbits. For any time-point, T-vector was calculated as a sum of instant action potential gradients in all model cells. Results: In normal rabbits, the main repolarization gradient was apicobasal with apical APDs being shorter than the basal APDs, whereas an anterior-posterior gradient was not significantly expressed. T-vector was oriented mainly downward. In diabetic rabbits, the most pronounced APD lengthening was found in the anterior ventricular regions, and the anterior-posterior repolarization gradient was predominant. The simulated T vector was oriented mainly backward. Thus, the changes in APD distributions in the normal and diabetic hearts were distinctly expressed in the changes of direction of the simulated T-vector. Conclusions: Extraction of the T-vector physiological content concerning ventricular repolarization gradients could be useful for identifying ventricular regions with the most pronounced APD changes which could be probably arrhythmogenic.