Clinical guideline documents reflect the evidence supporting clinical practice, but few recommendations in cardiovascular guidelines are supported by evidence from randomized controlled trials (RCTs), the highest level of evidence. Incentives for generating evidence from RCTs differ by topic of guideline recommendation, and it is uncertain whether evidence supporting guideline recommendations differs based on the topic of the recommendation.

We abstracted recommendation statements from current ACC/AHA guideline documents (2008–2019). Two reviewers independently characterized each statement into categories based on its primary topic: pharmaceutical, device, non-invasive or minimally invasive therapeutic procedure, surgery, diagnostic invasive procedure or non-invasive imaging, laboratory, care strategies, health services or policy, history/physical examination, lifestyle or counseling. We determined the number and proportion of recommendations in each category characterized as level of evidence (LOE) A (supported by multiple RCTs), B (supported by a single RCT or observational data), and C (supported by expert opinion or limited data).

Of 2934 recommendations from 29 clinical guideline documents, 784 (26.7%) were primarily about pharmaceuticals, 503 (17.1%) diagnostic invasive procedure or non-invasive imaging, 366 (12.5%) devices, 349 (11.9%) care strategies, 274 (9.3%) surgery, 216 (7.4%) therapeutic procedures, 162 (5.5%) lifestyle interventions or counseling, 160 (5.5%) health services, care delivery, or policy, 83 (2.8%) laboratory, and 37 (1.3%) elements of the history and physical. Across all recommendations, 257 (8.8%) were characterized as LOE A, with considerable variability by topic. 25.9% of lifestyle/counseling recommendations, 16.9% of lab recommendations, and 14.7% of drug recommendations were classified as LOE A, but <8% of recommendations in all other categories, including 5.5% of device recommendations, 6.0% of therapeutic procedure recommendations, 2.6% of surgery recommendations, and 5.0% of health services or policy recommendations.

Less than 10% of current ACC/AHA guideline recommendations are supported by high quality evidence from RCTs, with substantial variability by topic and multiple areas with very few recommendations supported by high-quality evidence. Development and implementation of inexpensive methods for generating a higher volume of RCT evidence to support clinical practice are needed, especially in areas where there are not strong incentives to conduct RCTs.