Table 2 Class of recommendation and level of evidence as defined in the ESC guidelines

I

Evidence and/or general agreement that a given treatment or procedure is beneficial, useful, effective

II

Conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of the given treatment or procedure

IIa

Weight of evidence/opinion is in favor of usefulness/efficacy

IIb

Usefulness/efficacy is less well established by evidence/opinion

III

Evidence or general agreement that the given treatment or procedure is not useful/effective, and in some cases may be harmful

A

Data derived from multiple randomized clinical trials or meta-analyses

B

Data derived from a single randomized clinical trial or large non-randomized studies

C

Consensus of opinion of the experts and/ or small studies, retrospective studies, registries