What does the QT interval on an ECG indicate?

The QT interval on an ECG is a crucial measurement that indicates the time taken for ventricular depolarization and repolarization. The depolarization phase is when the ventricles contract to pump blood out of the heart, followed by repolarization, during which the heart muscle resets electrically in preparation for the next heartbeat.

Understanding the QT interval is vital because its duration can vary and is influenced by factors such as heart rate, electrolyte levels, and certain medications. A prolonged or shortened QT interval can predispose individuals to arrhythmias and other cardiac issues, making it an important aspect of cardiac health monitoring.

The other options do not accurately describe the QT interval. While atrial contraction is reflected in other parts of the ECG, such as the P wave, the QT interval specifically pertains to the ventricles. Heart rate variability measures fluctuations in the time between heartbeats, which is unrelated to depolarization and repolarization timing. Although the presence of arrhythmias can be investigated through ECG analysis, the QT interval itself does not directly indicate arrhythmias but rather a potential risk for developing them if it is abnormal.