This is a Lead II rhythm strip from a patient with a biventricular pacemaker. The second and sixth beats are PVCs. In this lead, the pacemaker spikes are very difficult to see, but they are present. The pacemaker is operating in a "demand" mode for pacing the atria. Some of the P waves appear to be the patient's own, and some appear to be caused by the pacing stimulus. For example, the first beat appears to have no pacer spike before the P wave, and the second beat does have one (albeit tiny). The morphology of the P waves appears to change, also.