On an EKG tracing, the QRS complex corresponds to which cardiac event?

On an EKG tracing, the QRS complex corresponds to which cardiac event?

• A. Ventricular contraction
• B. Atrial contraction
• C. Ventricular repolarization
• D. Atrial depolarization

Answer: (A)

The key idea is that the QRS complex marks the ventricles being electrically activated, and that activation leads to ventricular contraction. When the impulse reaches the ventricles, it causes rapid depolarization, which shows up on the tracing as the QRS complex. That electrical event is what sets off the ventricles contracting to pump blood. So, in the context of the options, the best match is ventricular contraction because it reflects the mechanical effect that follows the ventricular depolarization represented by the QRS. The other waves correspond to other parts of the heart’s electrical timeline: the P wave is atrial depolarization, and the T wave is ventricular repolarization; atrial contraction is not what the QRS specifically represents.

The key idea is that the QRS complex marks the ventricles being electrically activated, and that activation leads to ventricular contraction. When the impulse reaches the ventricles, it causes rapid depolarization, which shows up on the tracing as the QRS complex. That electrical event is what sets off the ventricles contracting to pump blood. So, in the context of the options, the best match is ventricular contraction because it reflects the mechanical effect that follows the ventricular depolarization represented by the QRS. The other waves correspond to other parts of the heart’s electrical timeline: the P wave is atrial depolarization, and the T wave is ventricular repolarization; atrial contraction is not what the QRS specifically represents.