• Healthcare registry
• coronary angiography
• percutaneous coronary intervention
• mortality
• randomised clinical trial

Registries in cardiovascular medicine in general, and within interventional cardiology in particular, have gained more attention in medical journals over the past few years. By consecutive enrolment of complete patient populations, the methodology is a powerful tool for describing healthcare, including the complications and benefits of different therapies. However, it is very important to be cautious in the interpretation of the comparison of outcomes between different treatment alternatives in observational studies and always consider them non-definitive and hypothesis generating. In order to avoid selection bias, randomisation of patients may be included within a clinical registry, combining some of the most important features of a prospective randomised trial with the key strengths of a large scale clinical registry. Thereby prospective use of quality registries could potentially revolutionise clinical trials by the fast inclusion of large patient numbers, focus on hard endpoints and complete follow-up, and at a fraction of the costs of today's randomised controlled trials.

Good clinical practice should be based on sound evidence derived from well-conducted studies. The highest levels of scientific clinical evidence stem from prospective randomised clinical trials. The European Society of Cardiology and other guideline committees and authorities generally require more than one adequate prospective randomised study for giving the procedure the highest class of recommendation reflecting the need for independent confirmation of experimental results. A single clinical experimental finding of efficacy, unsupported by other independent evidence, is not considered adequate scientific support for a definitive conclusion of efficacy. In the medical field and particularly within cardiology, an increasing number of pharmaceutical agents, medical devices and clinical procedures are tested in appropriately designed prospective randomised trials. Despite this, only about half the recommendations given in international guidelines are class one recommendations based on prospective randomised trials,1 and a large proportion of recommendations are based on …