It is well established that design and development planning is a critical component of developing safe and effective medical device software. Planning ensures that the design process is appropriately controlled and that the quality objectives are met.
However, when medical device companies adopt agile methods for software development, the planning process can be confusing and challenging. Many aspects differ with traditional waterfall approaches and the development and QA managers struggle with knowing how much planning is required.

The document at the link provided is a brief overview on this subject along with several recommendation by Brian Pate of SoftwareCPR.