1. Department of Cardiovascular Diseases, Mayo Clinic, Rochester, MN, USA
Randomised clinical trials help to study the science of what can be done and what can be accomplished. While these studies suffer from “entry” bias which dictates that there must be validated equipoise between the two approaches to be studied, they form the basis of the most highly controlled and highest levels of evidence in studying specific patient scenarios1,2. In contrast to randomised clinical trials, registries tell us what we are actually doing and have greater relevance to clinical practice at large. Both sides of the coin give very valuable, albeit different, data3,4.