How does atrial fibrillation with ventricular standstill differ from fine v-fib?

AF vs vf. Good question, they could look alike on ECG. Both would also result in cardiac arrest. As no perfusion would result, one would expect AF waves to be less visible than VF very quickly. If arrest had been present for say more than 30sec. , VF would be more likely as the AF waves should likely not be visible.