What if there is no prospective, double blind, randomised trial?

Excerpt

Cardiology may be one of the areas in clinical medicine that is best supported by solid evidence, and the majority of recommendations in our national and international guidelines rely on data derived from randomised controlled trials (RCTs). By eliminating bias in treatment allocation, prospective RCTs form the cornerstone of our knowledge base. Nonetheless, RCTs have received their fair share of criticism, for example, that specific groups of patients may have been underrepresented, that the setting is controlled by definition and therefore may not resemble routine clinical care, and that participants in RCTs can be expected to be more motivated and adherent to therapy than may be expected in a routine care setting. …