Các thành phần của các dấu vết điện tâm đồ. Một dải nhịp điệu ở phía trên cho thấy một ghi điện tâm đồ điển hình. Một hình lớn hơn của một trong các đơn vị dạng sóng lặp đi lặp lại cho thấy làn sóng P, QRS phức tạp, và T sóng, đại diện cho quá trình khử cực khử cực tâm nhĩ, tâm thất, và tái cực thất, tương ứn | ELECTRICAL ACTIVITY OF THE HEART 27 R Q s M------M H 1 PR ST QT ----1----------1----------1----------1----------1 0 Time sec FIGURE 2-12 Components of the ECG trace. A rhythm strip at the top shows a typical ECG recording. An enlargement of one of the repeating waveform units shows the P wave QRS complex and T wave which represent atrial depolarization ventricular depolarization and ventricular repolarization respectively. The PR interval represents the time required for the depolarization wave to transverse the atria and the atrioventricular node the Q-T interval represents the period of ventricular depolarization and repolarization and the ST segment is the isoelectric period when the entire ventricle is depolarized. 80-100 m sec in duration Table 2-5 . No distinctly visible wave represents atrial repolarization in the ECG because it occurs during ventricular depolarization and is of relatively small amplitude. The brief isoelectric zero voltage period after the P wave represents the time in which the atrial cells are depolarized and the impulse is traveling within the AV node where conduction velocity is greatly reduced. The period of time from the onset of the P wave to the beginning of the QRS complex the P-R interval normally ranges from to seconds. This interval represents the time between the onset of atrial depolarization and the onset of ventricular depolarization. If the P-R interval is greater than seconds a conduction defect usually within the AV node is present . first-degree heart block . The QRS complex represents ventricular depolarization. The duration of the QRS complex is normally to seconds indicating that ventricular depolarization occurs rapidly. If the QRS complex is prolonged greater than seconds conduction is impaired within the ventricles. Impairment can occur with defects . bundle branch blocks or aberrant conduction or it can occur when an ectopic ventricular pacemaker drives ventricular
