What can the QT interval in an ECG signify?

The QT interval on an ECG signifies the time taken for the heart to reset electrically after each heartbeat. Specifically, it measures the duration from the beginning of the Q wave (the initial downward deflection) to the end of the T wave (the final upward deflection) in a single cardiac cycle. This interval encompasses both ventricular depolarization (when the ventricles contract) and repolarization (when the ventricles reset electrically in preparation for the next contraction).

A prolonged or shortened QT interval can indicate underlying health issues, such as electrolyte imbalances or the effects of certain medications, and can lead to various arrhythmias. Understanding the QT interval is crucial in clinical settings as it provides insight into the electrical activity and stability of the heart.

The other options do not accurately represent what the QT interval signifies. For instance, the duration from atrial depolarization to ventricular depolarization relates to a different measurement, while overall heart rate and blood flow through the heart are related to different cardiac parameters.