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Bariatric Surgery and CVD Outcomes in Nonalcoholic Fatty Liver Disease
Quick Takes
- In this retrospective database study, in a large cohort of obese patients (BMI >40 kg/m2) with nonalcoholic fatty liver disease, those who underwent bariatric surgery showed a nearly 50% reduction in incident cardiovascular disease and composite cardiovascular adverse events compared to those who did not undergo bariatric surgery.
- Although inverse probability treatment weighting was used in an effort to balance the baseline covariates in the surgical and nonsurgical groups, unmeasured confounding may be more likely in an administrative database where access to detailed clinical data may be limited.
Study Questions:
Nonalcoholic fatty liver disease (NAFLD) is a known independent risk factor for cardiovascular disease (CVD) and CVD-related mortality. Although previous studies indicate that lifestyle modifications such as weight loss and exercise improve steatosis and metabolic markers of dyslipidemia, their effectiveness in reducing CVD risk may be limited, possibly because the level of effort needed to attain significant improvement may be difficult to maintain over time. Elsaid and colleagues state that the relationship between bariatric surgery and improved CVD outcome has not been fully explored in the obese population across a broad spectrum of NAFLD. Does bariatric surgery reduce the risk of subsequent adverse cardiovascular events among obese patients with NAFLD?
Methods:
From the MarketScan Commercial Claims and Encounters database between January 1, 2007–December 31, 2017, insured patients between 18-64 years of age with a diagnosis of NAFLD and severe obesity (BMI >40 kg/m2) were identified. Patients with prior bariatric surgery before the study period, excess alcohol use, or previously diagnosed liver disease unrelated to NAFLD were excluded. Among the remaining cohort, the subset who underwent bariatric surgery (sleeve gastrectomy or Roux-en-Y) during the study period were referred to as the surgical group, and the subset not undergoing bariatric surgery during the study period were identified as the nonsurgical group.
The primary composite outcome was myocardial infarction, heart failure, or stroke. The secondary composite outcome included ischemic cardiovascular and cerebrovascular events, CVD, and atherosclerosis. Bariatric surgery, modeled as a time-varying variable, was examined against all outcomes using Cox proportional hazards modeling with inverse probability treatment weighting.
Results:
A total of 86,964 patients meeting inclusion criteria were included for analysis. During the study period, 30,300 (34.8%) received bariatric surgery, and 56,664 (65.2%) did not receive bariatric surgery. Inverse probability treatment weighting was applied to balance all baseline covariates available in the database and used in the analysis.
Incident composite cardiovascular events occurred in 1,568 over 57,061.4 person-years in the surgical group, versus in 7,215 over 96,150.1 person-years in the nonsurgical group. Incident difference was greater in the nonsurgical group by 4.8 events per 100 person-years (95% confidence interval, 4.5-5.0 events per 100 person-years).
Compared to nonsurgical patients, the surgical patients had lower adjusted hazards of myocardial infarction (0.80 [0.63, 1.00], p = 0.05); heart failure (0.39 [0.34, 0.45], p < 0.001); and ischemic stroke (0.79 [0.66, 0.94], p = 0.01).
By the end of the study period, the surgical group had a 49% lower risk of any CVD outcome (adjusted hazard ratio [aHR], 0.51 [0.48-0.54]) versus the nonsurgical group. Compared to the nonsurgical group, the bariatric surgical group had primary composite CVD outcome reduction of 47% (aHR, 0.53 [0.48, 0.59]), and secondary composite CVD outcome reduction of 50% (aHR, 0.50 [0.46, 0.53]).
Sensitivity analyses examining the likelihood that unmeasured confounders could alter the statistical conclusions confirmed a consistent and robust relationship between bariatric surgery and improved clinical outcomes. However, the E-value analysis suggested that an unmeasured confounder with HR ≥2.56 could provide an alternate explanation for the study’s main findings.
Conclusions:
In this large, retrospective database study of severely obese adult patients with NAFLD over an average follow-up of 21 months, those undergoing bariatric surgery had roughly 50% lesser incidence of CVD compared to patients who did not undergo bariatric surgery. The lower CVD incidence was associated with significant reduction in both primary and secondary composite outcomes.
Perspective:
Although these data show a strong association between bariatric surgery and improved cardiovascular outcome in obese patients with NAFLD, any retrospective observational study using claims data may be subject to allocation bias and numerous unmeasured confounders, so these apparently robust results should still be interpreted with caution.
Clinical Topics: Cardiovascular Care Team, Diabetes and Cardiometabolic Disease, Dyslipidemia, Heart Failure and Cardiomyopathies, Prevention, Vascular Medicine, Acute Heart Failure, Exercise
Keywords: Atherosclerosis, Bariatric Surgery, Body Mass Index, Cardiovascular Diseases, Dyslipidemias, Exercise, Gastrectomy, Heart Failure, Ischemic Stroke, Life Style, Metabolic Syndrome, Myocardial Infarction, Non-alcoholic Fatty Liver Disease, Obesity, Morbid, Primary Prevention, Risk Factors, Vascular Diseases, Weight Loss
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