Was balloon angioplasty subjected to randomized and double-blinded clinical trials before becoming approved as an effective treatment for heart disease?
No, because the doctor performing the procedure needs to be aware of what he or she is doing. The nature of the procedure is such that he or she is aware of whether or not they are holding an angioplasty catheter, whether or not they see it in the correct spot in the circulatory system through the scanner and whether or not they see the balloon expand correctly.
Since I believe the most common alternative is medication, the patient is also aware that they are undergoing surgery. Well, hopefully aware before and after, not during, but you know what I mean.
These types of procedures are usually evaluated by comparing two (or more) populations of patients with similar symptoms and outcomes on existing treatments and then seeing how a population responds to the new treatment. There are statistical analyses that can be made and a decision to approve the procedure comes after sufficient data to suggest an improvement in a significant portion of the population is obtained. While random, double-blind studies are the gold standard for things like tablets and other drug products, there are other scientifically valid ways of studying treatments where the people involved are aware of the procedure/treatment.