Chapter 19 - Section 19.4 - Electrical and Contractile Activity of the Heart - Before You Go On - Page 728: 19

The electrocardiogram (ECG or EKG) is a graphical representation of the electrical activity of the heart over time. It consists of several waves and intervals that correspond to specific events in the cardiac cycle. Here's how each of the events you mentioned corresponds to the portions of the ECG: 1. **Atrial Depolarization:** - Portion: P wave - Description: The P wave represents the depolarization (contraction) of the atria, specifically the atrial muscle cells. This precedes atrial contraction or systole. 2. **Atrial Systole:** - Portion: From the beginning of the P wave to the beginning of the QRS complex - Description: This interval represents the time during which the atria contract and pump blood into the ventricles. 3. **Atrial Repolarization:** - Portion: Occurs during the QRS complex, so there is no distinct wave for atrial repolarization on the ECG. - Description: Atrial repolarization occurs during the depolarization of the ventricles, which masks the atrial repolarization on the ECG. 4. **Ventricular Depolarization:** - Portion: QRS complex - Description: The QRS complex represents the depolarization of the ventricles, specifically the ventricular muscle cells. This is followed by ventricular contraction or systole. 5. **Ventricular Systole:** - Portion: From the beginning of the QRS complex to the end of the T wave - Description: This interval represents the time during which the ventricles contract and pump blood into the pulmonary artery and aorta. 6. **Ventricular Repolarization:** - Portion: T wave - Description: The T wave represents the repolarization (relaxation) of the ventricles, indicating the recovery of the ventricular muscle cells. 7. **Ventricular Diastole:** - Portion: From the end of the T wave to the beginning of the next P wave - Description: This interval represents the relaxation and filling of the ventricles with blood before the next cycle begins. It's important to note that the ECG provides valuable information about the electrical activity of the heart, but it does not directly show mechanical events such as contraction and relaxation. The ECG serves as a diagnostic tool to assess the heart's rhythm, rate, and various cardiac conditions.

The electrocardiogram (ECG or EKG) is a graphical representation of the electrical activity of the heart over time. It consists of several waves and intervals that correspond to specific events in the cardiac cycle. Here's how each of the events you mentioned corresponds to the portions of the ECG: 1. **Atrial Depolarization:** - Portion: P wave - Description: The P wave represents the depolarization (contraction) of the atria, specifically the atrial muscle cells. This precedes atrial contraction or systole. 2. **Atrial Systole:** - Portion: From the beginning of the P wave to the beginning of the QRS complex - Description: This interval represents the time during which the atria contract and pump blood into the ventricles. 3. **Atrial Repolarization:** - Portion: Occurs during the QRS complex, so there is no distinct wave for atrial repolarization on the ECG. - Description: Atrial repolarization occurs during the depolarization of the ventricles, which masks the atrial repolarization on the ECG. 4. **Ventricular Depolarization:** - Portion: QRS complex - Description: The QRS complex represents the depolarization of the ventricles, specifically the ventricular muscle cells. This is followed by ventricular contraction or systole. 5. **Ventricular Systole:** - Portion: From the beginning of the QRS complex to the end of the T wave - Description: This interval represents the time during which the ventricles contract and pump blood into the pulmonary artery and aorta. 6. **Ventricular Repolarization:** - Portion: T wave - Description: The T wave represents the repolarization (relaxation) of the ventricles, indicating the recovery of the ventricular muscle cells. 7. **Ventricular Diastole:** - Portion: From the end of the T wave to the beginning of the next P wave - Description: This interval represents the relaxation and filling of the ventricles with blood before the next cycle begins. It's important to note that the ECG provides valuable information about the electrical activity of the heart, but it does not directly show mechanical events such as contraction and relaxation. The ECG serves as a diagnostic tool to assess the heart's rhythm, rate, and various cardiac conditions.