TABLE 4-5 Selected Examples of Evidence Hierarchies for Three Cardiology Interventions

Intervention and Organization

Quality of the Evidence

Type of Evidence

Oral anticoagulation therapy in patients with atrial fibrillation and rheumatic mitral valve disease

American Heart Association

Level B

Single randomized trial or nonrandomized studies

Scottish Intercollegiate Guidelines Network

Level 4

Expert opinion

American College of Chest Physicians

Grade C+

No RCTs (but strong RCT results can be unequivocally extrapolated) or overwhelming evidence from observational studies

Implantable cardioverter-defibrillator for cardiac arrest due to sustained ventricular fibrillation or ventricular tachycardia

American College of Cardiology/ American Heart Association

Level A

Multiple RCTs or meta-analyses

Scottish Intercollegiate Guidelines Network

Level 3/4

Nonanalytic studies, e.g., case reports and case series

European Society of Cardiology

Level B

Single RCT or large nonrandomized studies

Carotid endarterectomy for internal carotid artery stenosis or symptomatic stenosis

American College of Cardiology/ American Heart Association

Level C

Consensus opinion of experts, results of case studies, or standard of care

American Academy of Neurology

Class I/II

Class I = prospective RCT with masked outcome assessment, in a representative population*

Class II = prospective matched group cohort study in a representative population with masked outcome assessment that meets all four Class I criteria (a to d) or an RCT in a representative population that lacks one of the Class I criteria

Veterans Health Administration

Level I

At least one properly conducted randomized controlled trial

*The following are also required: (a) primary outcome(s) clearly defined; (b) exclusion and inclusion criteria clearly defined; (c) adequate accounting for dropouts and crossovers with numbers sufficiently low to have a minimal potential for bias; and (d) relevant baseline characteristics are presented and are substantially equivalent among treatment groups or there is an appropriate statistical adjustment for the differences.

SOURCE: NGC (2007); Schünemann et al. (2003).

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