Guidelines Recommendations Still Largely Based on Expert Opinion

In 2009, a review of clinical practice guidelines found that only 11% of recommendations had a level of evidence (LOE) of A (i.e., evidence based on data from a single large randomized trial or multiple randomized trials). Now, a team including some of the same investigators studying whether reliance on high-quality evidence has improved in the intervening years performed a systematic review of the American College of Cardiology/American Heart Association (ACC/AHA) and European Society of Cardiology (ESC) guidelines and their precursors.

The investigators abstracted information from 26 current ACC/AHA guidelines (2930 recommendations) published between 2008 and 2018 and 25 current ESC guidelines (3399 recommendations) published between 2003 …