QRS complex

ABSTRACT

The QRS complex is a group of waves in the electrocardiogram (ECG), and represents ventricular activation. It usually consists of three wave forms. The Q wave is an initial negative wave at the onset of the QRS complex. The R wave is the first positive wave in the QRS complex, and appears at the onset of the QRS complex or following a Q wave. The S wave is a second negative wave in the QRS complex. The morphology of the QRS complex is useful in interpreting a 12-lead ECG because it provides clinical information regarding heart rate, QRS axis, heart position, rotation, and abnormal conduction in the ventricles.