Ventricular premature beats in patterns of bi-, or trigeminy are also a common cause of group beating. The ECG strips and ladder diagrams displayed here are from 2 different patients. Both demonstrate group beating caused by ventricular premature beats occurring in patterns of trigeminy. In the upper example, the ventricular premature beats are followed by sinus P waves that are not conducted and the post-extrasystolic pause is fully compensatory. In the lower example, the non-conducted P waves that follows the ventricular premature beats are retrograde P waves. They occur earlier than the sinus P weave would have occurred and then reset the sinus node. As a result, the post-extrasystolic pause is less than fully compensatory.