QT interval

Abstract

The electrocardiogram records the electrical activity of the heart, the depolarization and repolarization of the atria and ventricles. Deflections are all shown by the single features of the electrocardiogram: the P wave, the QRS complex, the T wave, the U wave, the PR interval and the QT. The QT interval represents the entire electrical activity of the left ventricle: it begins with the onset of ventricular depolarization (start of the Q wave) and is completed when ventricular repolarization ends (at the end of the T wave). Measurement of the QT interval is important because of the useful information it provides on the electrical activity of the heart; the length of the interval depends on various pathophysiological conditions, changes in electrolyte concentration, and the pharmacological action of toxic substances.