Table 1.

Definitions of class of recommendation and supporting level of evidence used in European Society of Cardiology (ESC) guidelines4

Class of RecommendationDefinitionWording used
Class IEvidence and/or general agreement that a given treatment or procedure is beneficial, useful, effectiveIt is recommended or indicated
Class IIConflicting evidence and/or a divergence of opinion about the usefulness/efficacy of the given treatment or procedure
Class IIaWeight of evidence/opinion is in favour of usefulness/efficacyShould be considered
Class IIbUsefulness/efficacy is less well established by evidence/opinionMay be considered
Class IIIEvidence or general agreement that the given treatment or procedure is not useful/effective and in some cases may be harmfulIt is not recommended
Levels of evidence
AData derived from multiple randomised clinical trials or meta-analyses
BData derived from a single randomised clinical trial or large non-randomised studies
CConsensus of opinion of the experts and/or small studies, retrospective studies, registries