What does the QRS complex of an ECG represent?

The QRS complex of an ECG represents ventricular contraction. This complex indicates the time it takes for electrical impulses to travel through the ventricles, leading to their depolarization and subsequent contraction. The QRS complex is a critical component of the cardiac cycle, as it directly correlates with the heart's ability to pump blood effectively to the lungs and the rest of the body.

The complex is characterized by three distinct waves: the Q wave, the R wave, and the S wave. When these waves are seen on an ECG, they signify that the ventricles are contracting, which is crucial for maintaining adequate blood flow. Therefore, understanding the significance of the QRS complex is essential for interpreting heart rhythms and diagnosing various cardiac conditions. In contrast, the other choices either pertain to activities associated with different phases of the cardiac cycle, such as atrial events, or do not specifically convey the mechanical aspect of contraction.