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Table 1 American college of cardiology/American heart association recommendation system

From: Clinical practice recommendations on the management of perioperative cardiac arrest: A report from the PERIOPCA Consortium

Class (strength) of recommendation  
Class I (Strong)—Benefit >>> Risk  
Suggested phrases for writing recommendations:  
 Is recommended
 Is indicated/useful/effective/beneficial
 Should be performed/administered/other
 Comparative-Effectiveness Phrases
 
  Treatment/strategy A is recommended/indicated in preference to treatment B
  Treatment A should be chosen over treatment B
Class IIa (Moderate)—Benefit >> Risk  
Suggested phrases for writing recommendations:  
 Is reasonable
 Can be useful/effective/beneficial
 Should be performed/administered/other
 Comparative-Effectiveness Phrases
  Treatment/strategy A is probably recommended/indicated in preference to treatment B
  It is reasonable to choose treatment A over treatment B
Class IIb (Weak)—Benefit ≥ Risk  
Suggested phrases for writing recommendations:  
 May/might be reasonable
 May/might be considered
 Usefulness/effectiveness is unknown/unclear/uncertain or not well established
Class III: No Benefit (Moderate)—Benefit = Risk  
Suggested phrases for writing recommendations:  
 Is not recommended
 Is not indicated/useful/effective/beneficial
 Should not be performed/administered/other
Class III: Harm (Strong)—Benefit < Risk  
Suggested phrases for writing recommendations:  
 Potentially harmful
 Causes harm
 Associated with excess morbidity/mortality
 Should not be performed/administered/other
 
Level (Quality) of evidence  
Level A  
 High-quality evidence from more than 1 RCT
 Meta-analyses of high-quality RCTs
 One or more RCTs corroborated by high-quality registry studies
 
Level B-R (randomized)  
 Moderate-quality evidence from 1 or more RCTs
 Meta-analyses of moderate-quality RCTs
 
Level B-NR (nonrandomized)  
 Moderate-quality evidence from 1 or more well-designed, well-executed nonrandomized studies, observational studies, or registry studies
 Meta-analyses of such studies
 
Level C-LD (limited data)  
 Randomized or nonrandomized observational or registry studies with limitations of design or execution
 Meta-analyses of such studies
 Physiological or mechanistic studies in human subjects
 
Level C-EO (expert opinion)  
 Consensus of expert opinion based on clinical experience  
  1. COR class of recommendation, EO expert opinion, LD limited data, LOE level of evidence, NR nonrandomized, R randomized and RCT randomized clinical trial
  2. COR and LOE are determined independently (any COR may be paired with any LOE). A recommendation with LOE C does not simply imply that the recommendation is weak. Many important clinical questions addressed in guidelines do not lend themselves to clinical trials. Although RCTs are unavailable, there may be a very clear clinical consensus that a particular test or therapy is useful or effective
  3. Modified from reference [17]