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