What does "QT interval" refer to in an ECG?

The QT interval in an ECG represents the time from the start of the Q wave to the end of the T wave. This interval reflects the total time it takes for the heart's ventricles to depolarize and then repolarize, which is crucial for understanding the electrical activity of the heart and assessing the heart's rhythm.

Measuring the QT interval is important for identifying potential arrhythmias, as a prolonged QT interval can indicate an increased risk of ventricular tachycardia or other heart rhythm disorders. The timing of the QT interval indicates how well the heart is able to recover after each heartbeat, making it a vital parameter in cardiovascular monitoring.

Other options relate to different phases of the ECG cycle. For instance, the time from the beginning of the P wave to the end of the QRS complex pertains to the PR interval, and the timing between two consecutive P waves refers to the rate of atrial depolarization, while the QRS complex alone does not involve the repolarization captured by the T wave. Thus, option A accurately encapsulates the definition of the QT interval within the context of cardiovascular physiology.