Majority of clinical cardiology guidelines based on ‘less-than-optimal’ evidence

A review of American College of Cardiology and American Heart Association guidelines from 2008 and 2018 found that, despite an overall increase in the number of clinical guidelines issued over the past decade, the majority of new recommendations are highly variable and based on low-quality evidence.

Clinical practice guidelines exist to establish a standard of care in the health industry, senior author Sadeer G. Al-Kindi, MD, and colleagues wrote in a research letter published in Circulation: Cardiovascular Quality and Outcomes. They’re taken seriously, “sometimes even functioning as learned treatises in malpractice claims,” but few analyses have looked in-depth at what kind of evidence really supports what we consider best practice.

The ACC and AHA provide recommendations based on the quality (level of evidence, or LOE) and strength (class of recommendation, or COR) of research claims. Guidelines are categorized according to this simplified key:

  • COR I: Strong recommendation (intervention should be performed)
  • COR IIa: Moderate recommendation (intervention might be beneficial)
  • COR IIb: Weak recommendation (utility of intervention is unclear)
  • COR III: No-benefit recommendation (intervention neither harms nor benefits)
  • LOE A: Highest level of evidence derived from multiple randomized clinical trials or meta-analyses
  • LOE B: Recommendations based on a single randomized trial or nonrandomized studies
  • LOE C: Recommendations based on the consensus opinion of experts, case studies or standard of care

Al-Kindi, of the Harrington Heart and Vascular Institute at University Hospitals Cleveland Medical Center, et al. reviewed all guidelines published by the ACC and AHA that were active in July 2018, comparing those documents to ACC/AHA guidelines published in 2008. The authors excluded guideline update documents in their analysis.

A total of 28 guideline documents were available, comprising 3,509 individual recommendations for an average of 116.5 recommendations per document. In all, 47.3 percent of recommendations were class I, 27 percent were class IIa, 14.9 percent were class IIb and 10.8 percent were class III. A little under 9 percent of recommendations had LOE A, 46.7 percent had LOE B and 44.5 percent had LOE C.

Just 14 percent of class I recommendations were also LOE A, Al-Kindi et al. reported.

“This report demonstrates that despite an increase in the number of ACC/AHA practice guideline recommendations over the past decade and efforts to increase the portion of higher quality evidence, only a minority of current recommendations are based on highest LOE,” the authors wrote. “Additionally, only a small percentage of the strongest recommendations are based on the highest level of evidence.”

The number of guidelines between 2008 and 2018 did increase—from 17 in 2008 to 28 a decade later. The number of recommendations jumped from 3,075 to 3,509 in the same period, and the percentage of class I indications saw a slight increase from 46.4 percent to 47.3 percent.

On the other hand, recommendations based on LOE A decreased, dropping from 11.4 percent in 2008 to 8.9 percent in 2018.

“The number of recommendations based on LOE A did not increase and the number of recommendations based on LOE C increased,” Al-Kindi and co-authors said. “On a per-document basis, however, the average number of LOE C recommendations per guideline document actually decreased (from 73 to 56). The absence of clear advancements in LOE since 2008 does not indicate stagnation in cardiovascular research.”

Cardiology isn’t the only medical branch seeing these trends, the authors said—a review of Infectious Disease Society of American guidelines, for instance, found only 14 percent of professional recommendations were based on the highest level of evidence, while 37 percent were based solely on expert opinion.

“Though evidence suggests that the use of clinical practice guidelines improves outcomes, clinicians should recognize that a large portion of recommendations are derived from less-than-optimal evidence,” the team wrote. “Up-front inclusion of LOE percentages in guideline documents may help the ACC/AHA Task Force on Clinical Practice Guidelines achieve their goal of increasing the percentage of higher-quality evidence in guideline recommendations.”