Definitions of class of recommendation and supporting level of evidence used in European Society of Cardiology (ESC) guidelines4
| Recommendations | ||
| Class of Recommendation | Definition | Wording used |
| Class I | Evidence and/or general agreement that a given treatment or procedure is beneficial, useful, effective | It is recommended or indicated |
| Class II | Conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of the given treatment or procedure | |
| Class IIa | Weight of evidence/opinion is in favour of usefulness/efficacy | Should be considered |
| Class IIb | Usefulness/efficacy is less well established by evidence/opinion | May be considered |
| Class III | Evidence or general agreement that the given treatment or procedure is not useful/effective and in some cases may be harmful | It is not recommended |
| Levels of evidence | ||
| Levels | Definition | |
| A | Data derived from multiple randomised clinical trials or meta-analyses | |
| B | Data derived from a single randomised clinical trial or large non-randomised studies | |
| C | Consensus of opinion of the experts and/or small studies, retrospective studies, registries | |