Long-term cardiovascular outcomes following bariatric surgery: Reconciling seemingly conflicting evidence.

Substantial observational evidence exists in support of bariatric surgery being associated with reduction in risk for a wide range of outcomes, including cardiovascular disease (CVD) in patients with diabetes. Two recent studies, however, argued that much of that prior work suffers from various sources of underappreciated bias as well as design decisions that compromise whether one can conceive of a corresponding target trial. Furthermore, results based on analyses of claims data from Optum and electronic health record data from the Veterans Administration (VA) are presented as providing evidence of no CVD benefit for bariatric surgery in patients with diabetes. In this paper, we use data from a prior Kaiser Permanente study to emulate a trial that mimics the methods employed in the VA study. This new analysis finds a reduction in risk of CVD in patients with diabetes, consistent with pre-existing evidence. We discuss possible mechanisms by which the discrepant results can be reconciled, including issues of statistical validity that arise from small samples, whether recent work on transportability indicates that we should not always expect results to always be concordant and the role of conservatism associated with "clinical trial thinking". We conclude with a discussion of what standards should be used when considering the work of others in the literature and the role that evidence triangulation may be play in the future.