Final answer:
An ECG traces the heart's electrical activity, with the P wave representing atrial depolarization, the QRS complex indicating ventricular depolarization, and the T wave signifying ventricular repolarization. These components correlate with the mechanical events of atrial and ventricular contraction and relaxation, respectively.
Step-by-step explanation:
An electrocardiogram (ECG) is a representation of the electrical activity of the heart. The ECG tracing has several key components that correlate with specific phases in the cardiac cycle. A normal ECG tracing includes the P wave, QRS complex, and T wave, as well as the PR interval, QT interval, and ST segment.
The P wave indicates atrial depolarization, leading to atrial contraction, which is the start of systole for the atria. The QRS complex, which is larger due to the larger muscle mass of the ventricles, represents ventricular depolarization and precedes ventricular contraction. The contraction of the ventricles is considered the systolic phase for the ventricles. Lastly, the T wave signifies ventricular repolarization, marking the beginning of ventricular relaxation or diastole.
The repolarization of the atria happens during the QRS complex and is not visible on the ECG because it is masked by the larger electrical activity of the ventricular depolarization. Each of these components is essential for understanding how the electrical impulses translate into mechanical events that result in a heartbeat.