My qualitative approach to your research question would read something similar to; What barriers do underserved populations face when participating in cardiac rehabilitation? Brian provided this initial insight into his response to your post in referencing the hurdles that individuals may face to access. It would seem that identifying these hurdles could serve to substantiate any recommendations that you may have if you are leaning towards a positivist emphasis in your research.
One approach to this enquiry in a qualitative sense would be to use a grounded theory framework to provide some insight on the issue of cardiac rehabilitation attendance. As outlined in our readings for this past week, this approach is intended to capture