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Table 1 Class of recommendation and level of evidence

From: Society for Cardiovascular Magnetic Resonance/European Society of Cardiovascular Imaging/American Society of Echocardiography/Society for Pediatric Radiology/North American Society for Cardiovascular Imaging Guidelines for the use of cardiovascular magnetic resonance in pediatric congenital and acquired heart disease

Class (strength) of recommendation (COR) Level of evidence (LOE)
Class I (strong) Benefit >  >  > Risk
The procedure should be performed
Suggested phrases for recommendations:
• Is recommended
• Is indicated/useful/effective/beneficial
• Should be performed
Level A
• High quality evidence from multiple randomized clinical trials or meta-analyses
• One or more randomized clinical trials corroborated by high quality registry studies
Class IIa (moderate) Benefit >  > Risk
It is reasonable to perform the procedure. Additional studies with focused objectives needed
Suggested phrases for recommendations:
• Is resonable
• Can be useful/effective/beneficial
• Is probably recommended or indicated
Level B
• Moderate quality evidence from multiple randomized clinical trials or meta-analyses
• Moderate quality evidence from 1 or more well-designed, well-executed nonrandomized studies, observational studied or registry studies or meta-analysis of such studies
Class IIb (weak) Benefit > Risk
The procedure may be considered. Additional studies with broad objectives needed. Additional registry data would be helpful
Suggested phrases for recommendations:
• May/might be considered
• May/might be reasonable
• Useful/effectiveness is unknown/unclear/uncertain or not well established
Level C
• Randomized or nonrandomized observational or registry studies with limitations of design or execution or meta-analysis of such studies
• Physiologic or mechanistic studies in humans
• Consensus of expert opinion based on clinical experience
Class III No Benefit
The procedure is not helpful and of no proven benefit
Suggested phrases for recommendations:
• Is not recommended
• Is not indicated
• Should not be performed/administered
• Is not useful/beneficial/effective
COR and LOE are determined independently (any COR may be paired with any LOE)
Class III Harm
The procedure incurs excess cost without benefit or is harmful to patients
Suggested phrases for recommendations:
• Is potentially harmful
• Causes harm
• Associated with excess morbidity/mortality
• Should not be performed/administered
A recommendation with LOE B or C does not imply the recommendation is weak. May important clinical questions addressed in guidelines do not lend themselves to clinical trials. Although randomized clinical trials are unavailable, there may be very clear clinical consensus that a particular test is useful or effective
  1. COR, class of recommendation; LOE level of evidence