The American Heart Association Evidence-Based Scoring System
Classification of Recommendations
● Class I: Conditions for which there is evidence, general
agreement, or both that a given procedure or treatment is
useful and effective.
● Class II: Conditions for which there is conflicting evidence,
a divergence of opinion, or both about the usefulness/
efficacy of a procedure or treatment.
● Class IIa: Weight of evidence/opinion is in favor of
● Class IIb: Usefulness/efficacy is less well established by
● Class III: Conditions for which there is evidence, general
agreement, or both that the procedure/treatment is not useful/
effective and in some cases may be harmful.
Level of Evidence
● Level of Evidence A: Data derived from multiple randomized
● Level of Evidence B: Data derived from a single randomized
trial or nonrandomized studies
● Level of Evidence C: Consensus opinion of experts
Circulation 2006 114: 1761 – 1791.