Robert Yin's work on case studies has a strong emphasis on comparative case studies, if that is what interests you: Case Study Research: Design and Methods.
We have only one randomized placebo-controlled trial dedicated to study of the the hard endpoints: Ivabradine and outcomes in chronic heart failure (SHIFT.) There were some positive effect in comparison with placebo when ivabradine was added on the top of RAAS blockers and b-blockers. Currently there are no comparative study and in my opinion nobody will give a cent for future investigation because the negative or neutral result in coronary artery disease.