This an interesting recording of nodal rhythm. The recorting shows no atrial sensing which could represent sinus node arrest and no retrograde condution or lack of sensing due to the artrial refractory period. This is the post ventricular atrial refractory period (PVARP). This refractory period which is longer than that of the ventricle is important to avoid sensing of retrograde P waves which in turn can initiate a pacemaker mediated tachycardia.