To determine which of the given options can be used to measure heart rate, let's consider the commonly used intervals and segments related to the cardiac cycle seen in an electrocardiogram (ECG):
1. S-T Segment: The S-T segment represents the period when the ventricles are depolarized. It is not used to measure heart rate.
2. R-R Interval: The R-R interval is the time interval between two successive R-waves of the QRS signal on the ECG. It can be used to measure heart rate because it represents the time between heartbeats.
3. P-R Interval: The P-R interval indicates the time taken for the electrical impulse to travel from the atria to the ventricles. It is not used to measure heart rate.
4. Q-T Interval: The Q-T interval is the time from the start of the Q-wave to the end of the T-wave in the heart’s electrical cycle. It represents the total time for ventricular depolarization and repolarization but is not used directly to measure heart rate.
From this, it is clear that the R-R interval can be used to measure heart rate.
Thus, the correct answer is the R-R interval.
