Clinicians often consult clinical practice guidelines for recommendations regarding diagnostic and treatment options. Ideally, recommendations are based on the best available evidence, with the strength of the recommendation directly linked to the strength of the evidence. This should especially apply to cardiovascular disease guidelines, considering the relatively high volume of cardiology trials published in well-respected journals and over two billion dollars of NIH research funding allocated annually. Therefore, guidelines from the American Heart Association and American College of Cardiology (AHA/ACC) and European Society of Cardiology (ESC) published over the last decade were recently analyzed to determine the level of evidence supporting the many recommendations guiding current clinical practice.

This study examined 26 AHA/ACC guidelines and 25 ESC guidelines published from 2008-2018, which together provide over 6,000 recommendations. Of the nearly 3,000 recommendation statements from the AHA/ACC, 43.4 percent receive a Class I (strongest) recommendation, yet only 14.2 percent of these Class I recommendations were based on level A evidence (supported by data from multiple randomized trials or a single, large randomized trial) according to the ACC scale. The AHA/ACC guideline with the highest percentage of Class I recommendations supported by level A evidence (the updated blood cholesterol guideline) had just 35 percent of these recommendations supported by level A evidence. Eleven percent of 188 Class I general cardiology recommendations relevant to cardiologists are supported by level C evidence (which includes consensus expert opinion, mechanistic studies, and low-quality registry data). The European guidelines performed slightly better, with 21.5 percent of the Class I recommendations supported by level A evidence. For guidelines with current and prior versions available, both the AHA/ACC and ESC had a decline in the proportion of Class I recommendations supported by level A evidence over time, suggesting a shift towards evidence on intermediate or disease-oriented outcomes. A report published in JAMA in 2014 on the durability of AHA/ACC recommendations found that recommendations based on lower quality evidence were significantly more likely to be changed over time compared to those based on higher quality evidence.

Guidelines heavily impact clinical practice, standards of care, quality measures, and reimbursement from insurers. Intuitively, one would expect Class I recommendations to be supported by level A evidence, and many likely assume that they are. Instead, it appears that although the literature has grown, guideline authors continue to base many strong recommendations on expert opinion alone. This perpetuates a cycle in which clinical practice is driven by expert opinion and a pathophysiology-reasoned approach to care rather than by recommendations derived from high-quality clinical trial evidence. At a minimum, guideline recommendations should prioritize recommendations based on the highest quality evidence, and highlight the lack of data supporting recommendations based on expert opinion.

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