ECG complexes and intervals

ECG waves are labeled alphabetically starting with the P wave, followed by the QRS complex, and the ST-T complex (ST segment and T wave). The J point is the junction between the end of the QRS and the beginning of the ST segment. The PR interval is measured from the beginning of the P wave to the first part of the QRS complex. The QT interval consists of the QRS complex which represents only a brief part of the interval, and the ST segment and T wave which are of longer duration.