Saturday, August 10, 2013

Medical reversal

Medical reversal is the latest hype. What is it? Here's the simple version: 1) Doctors treated based on opinion and tradition, with a lack of strong evidence or weak evidence that was rushed into implementation. 2) Really good evidence finally came along to refute said treatment. 3) Reversal of thinking resulted.

Now I'm here to tell you that it just ain't that simple. Indulge me and let's be more nuanced for a moment.

What prompted me to write this was an article and accompanying editorial in this month's Mayo Clinic Proceedings on the subject. I figured I had better weigh in before popular media outlets catch hold of it and dumb it down.

Beyond the fact that science is tentative, medical reversal takes on many forms and occurs for multiple and complex reasons. Three examples I've lived through come immediately to mind. On the surface they are similar but when examined closely hardly warrant being placed in the same category.

The latest one making the rounds is perioperative beta blockers (see here and here). Yes, it's a reversal and a big one, but not a very good example because it's an anomaly. It's an anomaly because the publications that drove the initial enthusiasm are now beset with questions of research misconduct.

Another example from a few decades ago almost fits the formula above. In the 1970s and 1980s the practice of suppressing premature ventricular contractions (PVCs) with antiarrhythmic drugs was widespread but based on weak rationale and little evidence. Then, 24 years ago today, evidence based medicine (even though we didn't call it that back then) came to the rescue in the form of the CAST results. The reversal, which ensued virtually overnight, is perhaps to this day the most widely cited example of why we needed evidence based medicine.

An example from about a decade ago concerns strict glycemic control in the ICU. Bob Wachter offered an insightful analysis on how that one bit the dust. Reversal again, but for yet a different reason. By the time strict glycemic control in critical illness came into fashion EBM was going full tilt, so a lack of EBM was not to blame. Rather, as Wachter explains, it was a misuse of the principles of EBM by turning evidence into a performance metric. (Turning the evidence based approach into performance, by the way, trumps two of the three principles of EBM but that's a topic for another post).

The authors of the Proceedings article came up with 146 examples from the past decade of what they consider to be reversals. But many of the examples were not true reversal. Some were merely examples, common in medicine, of one RCT conflicting with the results of another. Prescient clinicians have long understood the tentative nature of a single RCT and that differences in design and study populations often lead to differing results. This is not medical reversal. Other examples represented the phenomenon known as the swinging pendulum, something long known and accepted throughout the history of modern medicine. Others merely reflected later studies modifying, though not contradicting, prior research. It's a stretch to imply that any research finding that changes practice is a reversal. And some of the examples cited did not even warrant change in practice.

Accompanying the article is a video segment in which the lead author suggests that patients should do their own critical analysis of treatments offered them and consider avoiding interventions not supported by RCTs lest they find themselves harmed by a treatment later to be reversed. But many treatments now in common use which are widely regarded as life saving remain unsupported by high level RCTs. Examples include antimicrobial therapy for bacterial meningitis, and ehrlichiosis and antcoagulation for venous thromboembolism. Would the authors hesitate to administer these treatments? (Well, don't laugh).

We've long known and accepted that new research often modifies the conclusions of prior research. But the author, throughout the video, is trying to turn this into something worse. This is illustrated at 05:52 where he cites the AFFIRM study as contradicting rhythm control as a strategy in the management of atrial fibrillation. Nonsense. AFFIRM showed similar outcomes in populations teated with rate control and rhythm control. Pre-AFFIRM, clinicians used clinical judgment to determine which strategy to use. Post-AFFIRM they're doing the same. AFFIRM refined our understanding of the treatment of atrial fibrillation but it was not a game changer and it was certainly not a reversal.

The phenomenon of reversal has been widely hyped and the Proceedings article is no exception. But there are lessons we can learn from the paper. Sometimes we just need to slow down. Bob Wachter said it well:

Although many, including me, have long lamented the glacial pace of adoption of evidence-based practices in American medicine (often 5-15 years after the emergence of truly robust evidence supporting a practice), this traditional time lag did have one virtue: it allowed the literature to mature.

Maybe we're relying too much on the latest tweet and should go back to the textbook every now and then.

1 comment:

Stephen H said...

I always figured that the ability to change one's mind abut the validity of a treatment distinguishes medicine from quackery.

Basically, medicine gradually improves. Sometimes through developing better treatments (innoculations, radiotherapy), and sometimes through throwing out the garbage (leeches, Thalidomide for pregnant mothers). Quackery, however, boasts that it uses treatments that are hundreds or thousands of years old. So homoeopathy and chiropractic precede germ theory.