2021 Coronary Revascularization Guidelines—Lessons in the Importance of Data Scrutiny and Reappraisal of Evidence

This recent JAMA Surgery editorial addresses the controversy associated with the 2021 ACC/AHA/SCAI guidelines on coronary revascularization. It underscores the importance of attention to source data and accurate characterization of evidence.
The core issue was the downgrade of CABG relative to medical therapy in patients with stable ischemic heart disease and severe three-vessel disease, with survival as the endpoint: from Class I (strong recommendation) to Class IIb (weak recommendation) in patients with normal ejection fraction; and from Class I to Class IIa (moderate recommendation) in patients with mild to moderate left ventricular dysfunction. 
There was a global outcry with rebuttals from the AATS, STS, EACTS, LACES, and multiple other professional cardiovascular associations—some of which included cardiologists among their ranks.   
Proponents of the 2021 guidelines insist that they are accurate, and that the controversy arose because of differences in the interpretation of evidence. As stated in this JAMA Surgery editorial, that is simply inaccurate. Examination of the source documents cited as “supportive evidence” to downgrade CABG in the guideline’s recommendation tables tell a different story. 
Many of the actual conclusions of the authors of the source documents are in direct contradiction to what is in the guidelines. In the synthesis of evidence, some studies were arbitrarily given more weight than others and some older studies were rendered irrelevant based solely on date of publication. The guidelines emphasized improvements in medical therapy without a balanced mention of the safety, efficacy, and durability of modern-day CABG. 
The bulk of “new evidence” was centered on trials that did not randomize patients to CABG vs. medical therapy. CABG and PCI were lumped together despite acknowledging that they are different therapies with different indications and outcomes. The new studies excluded patients with heavy atherosclerotic burden, and very few had proximal LAD lesions. A recommendation about a reasonable role for an initial conservative strategy with close follow-up in such patients would have been appropriate and compatible with available evidence. Instead, the guidelines extrapolated findings from patients with relatively favorable cardiovascular risk profiles (who typically would not be referred for CABG in the first place) to inform decision-making and erroneously weaken the CABG recommendations.
The 2021 guidelines are a perfect case study on the importance of attention to the source documents instead of blind acceptance of summary evidence. Otherwise, effective and durable therapies may be replaced by less effective therapies with diminished benefits.