QT interval
Also calledQT · Q-T interval
Definition
The time from the onset of the QRS complex to the end of the T wave, spanning ventricular depolarization and repolarization. It lengthens as the heart rate slows, so it is usually corrected for rate (QTc). With simultaneously recorded leads it runs from the earliest QRS onset to the latest T-wave end; when measured in single leads, the lead with the longest QT is used (usually V2 or V3). U waves are excluded: if a U wave merges with the T wave, the QT is measured in leads without U waves (often aVR and aVL) or the end of the T wave is found with the tangent method, where a line along the steepest part of the T-wave downslope meets the baseline.
Sources
- Rautaharju PM, Surawicz B, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part IV: the ST segment, T and U waves, and the QT interval. Circulation. 2009;119(10):e241-e250. doi.org/10.1161/CIRCULATIONAHA.108.191096
- Samesima N, God EG, Kruse JCL, et al. Brazilian Society of Cardiology guidelines on the analysis and issuance of electrocardiographic reports - 2022. Arq Bras Cardiol. 2022;119(4):638-680. doi.org/10.36660/abc.20220623
- Meek S, Morris F. ABC of clinical electrocardiography. Introduction. II: Basic terminology. BMJ. 2002;324(7335):470-473. doi.org/10.1136/bmj.324.7335.470
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.