Which interval measurement represents the complete refractory period?

The correct answer is the QT interval, as this interval encompasses both the depolarization and repolarization phases of the cardiac cycle. The QT interval begins at the beginning of the Q wave and ends at the end of the T wave. This measurement reflects the time it takes for the ventricles to contract and then recover, making it a critical component in assessing the refractory period during which the cardiac tissue cannot be stimulated to contract again.

In contrast, the PR interval reflects the time from the onset of atrial depolarization to the onset of ventricular depolarization, which does not include the full refractory period of the ventricles. The ST interval represents the time between ventricular depolarization and repolarization but does not account for the entire duration covered by the T wave. The QRS interval represents only the time taken for ventricular depolarization and does not include repolarization.

Thus, the QT interval is the most comprehensive measure for understanding the complete refractory period within the cardiac cycle.