参考答案：

P wave: atrial depolarization (2`);

QRS complex: depolarization of ventricles (2`);

T wave: repolarization of ventricles (2`);

PR interval is the interval from the beginning of atrial activation to the beginning of ventricular activation (2`);

QT interval is required for ventricular depolarization and repolarization. (1`);

ST-segment: potential of myocardial cell in each part of ventricle is equal to each other and located at the platform period of AP (1`).