ACC AHA guidelines classification scheme
Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
The Class designation is used to indicate whether a therapy is recommended or not and the certainty surrounding that recommendation.
Classification of Recommendations
Class I: Benefit >>> Risk
Conditions for which there is evidence and/or general agreement that a given procedure or treatment is beneficial, useful, and effective.
Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment.
Class IIa: Benefit >> Risk
Weight of evidence/opinion is in favor of usefulness/efficacy.
Class IIb: Benefit ≥ Risk
Usefulness/efficacy is less well established by evidence/opinion.
Conditions for which there is evidence and/or general agreement that a procedure/treatment is not useful/effective and in some cases may be harmful.
Class III: No Benefit
Is not recommended, not indicated, should not be performed/ administered/ other. Is not useful/beneficial/effective.
Class III: Harm
Potentially harmful, causes harm, associated with excess morbidity/mortality. Should not be performed/administered/other.
Use the Level of Evidence designation to indicate the strength of the data associated with that recommendation.
Level of Evidence
Level of Evidence A:
Data derived from multiple randomized clinical trials or meta-analyses of such studies.
Level of Evidence B:
- Level of Evidence B-R: Data derived from one or more randomized trials or meta-analysis of such studies.
- Level of Evidence B-NR: Data derived from one or more non-randomized trials or meta-analysis of such studies.
Level of Evidence C:
- Level of Evidence C-LD:: Non randomized observational studies with limitations in design or execution or Metanalysis of such studies.
- Level of Evidence C-EO: Consensus opinion of experts based on clinical experience.
Applying Classification of Recommendations and Level of Evidence
2016 Classification of Recommendations and Level of Evidence
2014 Classification of Recommendations and Level of Evidence