ISO 13485 and QSR are very similar. However, it's my experience that the QSR has additional requirements that are clearly spelled out in the regulations. But they have the same QMS processes (e.g design control, CAPA which falls under measurement and analysis ). I would start with ISO as a baseline and do a gap analysis with QSR. Complete your SOPs based on ISO and incorporate the additional FDA elements. There are also some terminology differences. For example, DHF and DMR are FDA terms. In ISO 13485:2016, what is known as the medical device file is similar to the DMR (and there has been a debate about the distinction between DMR and MDF; just search around on Elsmar). Also, both QSR and ISO 2016 are risk-based. I hope this makes sense.