Chapter 19 - Section 19.4 - Study Guide - Assess Your Learning Outcomes - Page 740: 7

Electrocardiograms (ECGs or EKGs) are graphical representations of the electrical activity of the heart over time. ECGs consist of a series of waves and intervals that correspond to different events occurring during the cardiac cycle. Here's what happens in the heart during each ECG wave: **1. P Wave:** - Represents atrial depolarization, which is the electrical activation of the atria as the electrical impulse spreads from the sinoatrial (SA) node. - Atrial contraction (atrial systole) follows shortly after the P wave, leading to the emptying of blood into the ventricles. **2. PR Interval:** - This interval measures the time it takes for the electrical impulse to travel from the SA node to the atrioventricular (AV) node. - During this interval, the atria contract and push blood into the ventricles. The ventricles are in diastole, preparing to contract. **3. QRS Complex:** - Represents ventricular depolarization, which is the electrical activation of the ventricles. - Atrial repolarization occurs during this time but is usually masked by the larger QRS complex. - Ventricular contraction (ventricular systole) follows after the QRS complex, leading to the ejection of blood from the ventricles. **4. ST Segment:** - This segment represents the time between ventricular depolarization and repolarization. - It's an isoelectric period where the ventricles are depolarized, and the heart is preparing for the next phase of the cardiac cycle. **5. T Wave:** - Represents ventricular repolarization, which is the recovery of the ventricles following contraction. - Ventricular relaxation (ventricular diastole) occurs during this phase, allowing the ventricles to fill with blood. **6. QT Interval:** - This interval measures the time from ventricular depolarization (beginning of QRS) to ventricular repolarization (end of T wave). - It reflects the total time taken for ventricular contraction and relaxation. It's important to note that the electrical events represented by the ECG waves are closely associated with the mechanical events of the cardiac cycle. The electrical depolarization of the heart leads to contraction, and repolarization leads to relaxation. The coordinated sequence of electrical and mechanical events ensures efficient pumping and circulation of blood throughout the body.

Electrocardiograms (ECGs or EKGs) are graphical representations of the electrical activity of the heart over time. ECGs consist of a series of waves and intervals that correspond to different events occurring during the cardiac cycle. Here's what happens in the heart during each ECG wave: **1. P Wave:** - Represents atrial depolarization, which is the electrical activation of the atria as the electrical impulse spreads from the sinoatrial (SA) node. - Atrial contraction (atrial systole) follows shortly after the P wave, leading to the emptying of blood into the ventricles. **2. PR Interval:** - This interval measures the time it takes for the electrical impulse to travel from the SA node to the atrioventricular (AV) node. - During this interval, the atria contract and push blood into the ventricles. The ventricles are in diastole, preparing to contract. **3. QRS Complex:** - Represents ventricular depolarization, which is the electrical activation of the ventricles. - Atrial repolarization occurs during this time but is usually masked by the larger QRS complex. - Ventricular contraction (ventricular systole) follows after the QRS complex, leading to the ejection of blood from the ventricles. **4. ST Segment:** - This segment represents the time between ventricular depolarization and repolarization. - It's an isoelectric period where the ventricles are depolarized, and the heart is preparing for the next phase of the cardiac cycle. **5. T Wave:** - Represents ventricular repolarization, which is the recovery of the ventricles following contraction. - Ventricular relaxation (ventricular diastole) occurs during this phase, allowing the ventricles to fill with blood. **6. QT Interval:** - This interval measures the time from ventricular depolarization (beginning of QRS) to ventricular repolarization (end of T wave). - It reflects the total time taken for ventricular contraction and relaxation. It's important to note that the electrical events represented by the ECG waves are closely associated with the mechanical events of the cardiac cycle. The electrical depolarization of the heart leads to contraction, and repolarization leads to relaxation. The coordinated sequence of electrical and mechanical events ensures efficient pumping and circulation of blood throughout the body.