Table 1. Criteria used to judge the level of evidence and establish the class of recommendation for AHF.

Class		Class I	Class IIa	Class IIb	Class III
Criterion		• Benefit >>> Risk	• Benefit >> Risk	• Benefit ≥ Risk	• No benefit or harm
		• Procedure/Treatment SHOULD be performed	• Additional studies with focused objectives are needed	• Additional studies with broad objectives are needed; collecting additional registry data would be helpful	• Procedure/treatment SHOULD NOT BE PERFORMED as it is not expected to be useful or may even be harmful
			• IT IS REASONABLE to perform the procedure/treatment	• Procedure/treatment MAY BE CONSIDERED
Level A
	• Multiple populations evaluated	1) Recommendation that procedure/treatment is useful/effective	1) Recommendation in favor of procedure or treatment being useful/effective	1) Recommendation's usefulness/efficacy less well-established	1) Recommendation that procedure/treatment is not useful/effective and/or may be harmful
	• Data from multiple randomized clinical trials or meta-analyses	2) Sufficient evidence from multiple randomized trials or meta-analyses	2) Some conflicting evidence from multiple randomized trials or meta-analyses	2) Greater conflicting evidence from multiple randomized trials or meta-analyses	2) Evidence from multiple randomized trials or meta-analyses
Level B
	• Limited populations evaluated	1) Recommendation that procedure/treatment is useful/effective	1) Recommendation in favor of procedure/treatment being useful/effective	1) Recommendation's usefulness/efficacy less well-established	1) Recommendation that procedure/treatment is not useful/effective or may be harmful
	• Data from a single randomized trial or non-randomized studies	2) Sufficient evidence from a single randomized trial or non-randomized studies	2) Some conflicting evidence from a single randomized trial or non-randomized studies	2) Greater conflicting evidence from a single randomized trial or non-randomized studies	2) Evidence from a single randomized trial or non-randomized studies
Level C
	• Very limited populations evaluated	1) Recommendation that procedure/treatment is useful/effective	1) Recommendation in favor of procedure/treatment being useful/effective	1) Recommendation's usefulness/efficacy less well established	1) Recommendation that procedure or treatment is not useful/effective and may be harmful
	• Only consensus expert opinions, case studies, or standards of care	2) Only expert opinions, case studies, or standards of care	2) Only diverging expert opinions, case studies, or standards of care	2) Only diverging expert opinions, case studies, or standards of care	2) Only expert opinions, case studies, or standards of care

AHF = acute heart failure.