The reluctance to adopt FFR in the U.S. has been attributed to the need for adenosine, which can be costly and feel mildly unpleasant for patients -- or even cause bradycardia or heart block.

The reluctance to adopt FFR has been attributed in part to its reliance on adenosine that is associated with extra cost and patient discomfort.

However, FFR requires the patient to be given a drug such as adenosine to dilate blood vessels, which can cause unpleasant side effects including facial flushing and shortness of breath.