: QT Interval

: What the QT Interval Measures

: Each heartbeat begins with an electrical signal that causes the heart muscle to contract and then reset for the next beat. The QT interval captures the total time from the start of ventricular activation to the end of ventricular recovery. When corrected for heart rate, it helps doctors judge whether the heart's electrical reset is happening in a normal, timely way.

: How the Test Is Done

: The QT interval is not measured from a blood sample; it is read from an electrocardiogram, a painless recording of the heart's electrical activity. Small electrodes are placed on the chest, arms, and legs, and the tracing is reviewed by a clinician. Because the interval changes with heart rate, the reading is usually adjusted (rate-corrected) for a more meaningful assessment.

: What an Abnormal Result May Mean

: A QT interval that is longer than expected can raise the concern of a rhythm problem called torsades de pointes, while a very short interval may also be significant. Many factors can affect the interval, including certain medications, electrolyte imbalances, and inherited heart conditions, so an abnormal reading is interpreted together with your history and other findings.

: What to Tell Your Care Team

: Because many medicines and some health conditions can lengthen the QT interval, be sure to share all prescription and over-the-counter drugs, supplements, and any personal or family history of fainting or heart rhythm problems. This helps your clinician interpret the ECG accurately and decide whether further testing or medication changes are needed.