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

usefulness/efficacy.

● Class IIb: Usefulness/efficacy is less well established by

evidence/opinion.

● 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

clinical trials

● 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.