Why is the T wave positive?

As a cardiac electrophysiologist, I can explain the nuances of the T wave in an electrocardiogram (ECG). The T wave is positive in most leads because it represents the repolarization of the ventricular myocardial cells after they have been depolarized during the contraction phase, which is represented by the QRS complex. Depolarization is the process where the heart muscle cells become excited and ready to contract. Following this, repolarization occurs, which is the return of the cells to their resting state. The T wave reflects the electrical activity during this repolarization phase. Repolarization typically occurs in a direction opposite to depolarization, and since the majority of the ventricular mass is depolarized in a specific direction during the QRS complex, the subsequent repolarization also tends to occur in an organized, predominantly positive manner in the ECG leads that face the direction of this wave of electrical activity. Here's the translation in Chinese: 作为心脏病电生理学专家，我可以解释心电图（ECG）中T波的细微差别。 大多数导联中T波是正向的，因为它代表了心室肌细胞在收缩阶段（由QRS复合体代表）去极化后的复极化。去极化是心肌细胞变得兴奋并准备收缩的过程。此后，发生复极化，即细胞返回到它们的静息状态。T波反映了这一复极化阶段的电活动。 复极化通常发生在与去极化相反的方向，由于大多数心室质量在QRS复合体期间以特定方向去极化，随后的复极化也倾向于在心电图导联中以有组织的、主要是正向的方式发生，这些导联面向这种电活动波的方向。

In most leads, the T wave is positive. This is due to the repolarization of the membrane. During ventricle contraction (QRS complex), the heart depolarizes.