You go to your doctor and she recommends a certain procedure for treating cardiovascular disease. Showing up for your next annual appointment, you mention having followed her guidelines and she stares at you blankly for a moment before explaining that another different procedure is now considered the way to go. Although you understand that medical knowledge has been expanding exponentially in recent years — by IBM's estimates, medical information is doubling every five years — part of you feels vaguely indignant... and definitely confused. Which recommendations do I trust? you ask yourself.
In a new study, Penn Medicine researchers examined recommendations published by the American College of Cardiology (ACC) and the American Heart Association (AHA) between 1998 and 2007 and found that one out of every five Class I recommendations was reversed, omitted, or downgraded over time. "Clinical practice guidelines are used by health care providers to make decisions about treatments for individual patients, and by hospitals, regulators, and insurers to develop quality measures," Dr. Mark D. Neuman, assistant professor of Anesthesiology and Critical Care, said in a press release. “Our study provides new information about the durability of guideline recommendations over time.”
To better understand how cardiology recommendations change over time, Neuman and his team of researchers looked at editions of ACC/AHA guidelines and analyzed over 600 Class I guidelines, each a strong endorsement of a particular treatment or procedure related to cardiovascular disease. The authors observed that four out of five Class I recommendations remained valid across two guideline editions, whereas one out of every five recommendations did not stand the test of time.
In fact, Neuman found the odds of a downgrade, reversal, or omission to be more than three times greater for recommendations based on expert opinion, retrospective studies, or case reports.
By contrast, guidelines supported by multiple, randomized controlled trials were the most stable and least likely to change over time. Randomized controlled trials are considered the gold standard among researchers. In such experiments, researchers randomly divide all carefully selected participants into two groups and then treat both groups identically except for the experimental therapy, such as a new drug, being tested. Often, the participants themselves remain unaware of any difference in treatment until the study is completed.
The real surprise comes with the reasons behind guideline reversals. The study was not designed to examine the reasons why an individual recommendation might be downgraded or reversed, still the researchers observed that the many downgrades did not usually result from a new study contradicting old medical information. Instead, many of the downgrades arose from changes in how physicians interpreted existing medical research.
Source: Neuman MD, Schwartz JS, Goldstein JN, Cirullo MA. Durability of Class I American College of Cardiology/American Heart Association Clinical Practice Guideline Recommendations. JAMA. 2014.