title: Evolution of the American College of Cardiology/American Heart Association Clinical Guidelines.
abstract: BACKGROUND
  The American College of Cardiology (ACC) and the American Heart Association (AHA) have been developing clinical guidelines to assist practicing clinicians.
  
  
  OBJECTIVE
  The goal of this study was to evaluate changes in ACC/AHA guideline recommendations between 2008 and 2014.
  
  
  METHODS
  The previous and current ACC/AHA guideline documents that were updated between 2008 and June 2014 were compared to determine changes in Class of Recommendation (COR) and Level of Evidence (LOE). Each recommendation was classified as new, dropped, revised, or unchanged, and the changes in evidence were examined.
  
  
  RESULTS
  During the study period, 11 guideline documents (9 disease based and 2 interventional procedure based) were updated. The total number of recommendations decreased from 2,067 to 1,869 (321 fewer recommendations in disease-based guidelines and 123 additional recommendations in interventional procedure-based guidelines). The recommendation class distribution of the updated guidelines was 50.1% Class I (previously 50.8%), 39.4% Class II (previously 35.4%), and 10.4% Class III (previously 13.8%) (p = 0.001). The LOE distribution among updated versions was 15.0% for LOE: A (previously 13.3%), 50.8% for LOE: B (previously 41.4%), and 34.2% for LOE C (previously 45.3%) (p < 0.001). Among all guidelines, 859 recommendations were new, 1,339 were dropped, 881 were unchanged in COR and LOE, and 129 were revised. Of the revised guidelines, 75 recommendations had an increase in LOE (the majority from LOE: C to LOE: B); 34 recommendations had a decrease in LOE; and 20 recommendations had class changes. LOE increases were justified by introduction of new randomized controlled trials, new studies, and new meta-analyses.
  
  
  CONCLUSIONS
  The ACC/AHA guideline recommendations are undergoing significant changes, becoming more evidence based and scientifically robust with a tendency to exclude recommendations with insufficient scientific evidence.
authors.affiliation: VA North Texas Healthcare System and University of Texas Southwestern Medical Center at Dallas, Dallas, Texas.
authors.forename: Henry
authors.initials: H
authors.lastname: Han
authors.affiliation: VA North Texas Healthcare System and University of Texas Southwestern Medical Center at Dallas, Dallas, Texas.
authors.forename: Howard
authors.initials: H
authors.lastname: Chao
authors.affiliation: VA North Texas Healthcare System and University of Texas Southwestern Medical Center at Dallas, Dallas, Texas.
authors.forename: Andres
authors.initials: A
authors.lastname: Guerra
authors.affiliation: VA North Texas Healthcare System and University of Texas Southwestern Medical Center at Dallas, Dallas, Texas.
authors.forename: Alan
authors.initials: A
authors.lastname: Sosa
authors.affiliation: VA North Texas Healthcare System and University of Texas Southwestern Medical Center at Dallas, Dallas, Texas.
authors.forename: Georgios
authors.initials: G
authors.lastname: Christopoulos
authors.affiliation: VA North Texas Healthcare System and University of Texas Southwestern Medical Center at Dallas, Dallas, Texas.
authors.forename: Georgios E
authors.initials: GE
authors.lastname: Christakopoulos
authors.affiliation: VA North Texas Healthcare System and University of Texas Southwestern Medical Center at Dallas, Dallas, Texas.
authors.forename: Bavana V
authors.initials: BV
authors.lastname: Rangan
authors.affiliation: University of Heraklion, Heraklion, Greece.
authors.forename: Spyros
authors.initials: S
authors.lastname: Maragkoudakis
authors.affiliation: Baylor College of Medicine and Michael E. DeBakey VA Medical Center, Houston, Texas.
authors.forename: Hani
authors.initials: H
authors.lastname: Jneid
authors.affiliation: VA North Texas Healthcare System and University of Texas Southwestern Medical Center at Dallas, Dallas, Texas.
authors.forename: Subhash
authors.initials: S
authors.lastname: Banerjee
authors.affiliation: VA North Texas Healthcare System and University of Texas Southwestern Medical Center at Dallas, Dallas, Texas. Electronic address: esbrilakis@gmail.com.
authors.forename: Emmanouil S
authors.initials: ES
authors.lastname: Brilakis
mesh_terms: D000572:American Heart Association; D002309:Cardiology; D019317:Evidence-Based Medicine; D017408:Guidelines as Topic; D012955:Societies, Medical; D014481:United States
keywords: cardiovascular diseases; clinical guidelines; evolution; scientific evidence