: QT Interval

: What the QT Interval Measures

: The QT interval represents the total time from the start of electrical activation of the heart's ventricles (the lower chambers) to the end of their electrical recovery. On an ECG tracing, it spans from the beginning of the QRS complex to the end of the T wave. Because the interval changes with heart rate, it is often adjusted (corrected) to account for how fast or slow the heart is beating.

: How the Test Is Done

: This is not a blood test; the QT interval is measured from an ECG, a painless recording of the heart's electrical activity using electrodes placed on the chest and limbs. The ECG tracing is then reviewed by a clinician or computer software to determine the interval length.

: Why It May Be Measured

: Your clinician may assess the QT interval as part of a routine ECG, when evaluating palpitations, fainting, or an irregular heartbeat, or when you are taking medications that can affect the heart's electrical activity. It can also be checked if there is a family history of certain heart rhythm conditions.

: What Results Can Mean

: A QT interval that is longer or shorter than expected may suggest an increased chance of certain abnormal heart rhythms. Results are interpreted alongside heart rate, your symptoms, medications, and other ECG findings. A single measurement is rarely interpreted alone, and repeat or follow-up testing may be recommended.