This is AV pacing. The ventricular pacemaker stimulus did not alter the QRS morphology. So, what is seen is a narrow QRS complex. This means the pacer stimulus occurred after the normal depolarization of the ventricles has started. This is called PSEUDOFUSION and the machine functioning normally.
Bonnow et al. 2014. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 10th Edition. PA.Saunders