Preoperative Aspirin-dosing Strategy and Mortality After Coronary Artery Bypass Graft Surgery

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To the Editor:
In a retrospective analysis assessing association between preoperative aspirin dosing strategy and 30-day all-cause mortality after coronary artery bypass graft (CABG) surgery, Deng and colleagues1 showed that low-dose aspirin use within 24 hours of CABG surgery was independently associated with decreased early postoperative mortality. Strengths of this study include a large sample of patients, with multivariable and propensity matching analyses to adjust influences of potential confounders on study endpoints. Other than the limitations described in the discussion, however, we note other issues of this study making interpretation of their results questionable.
First, the perioperative hemoglobin levels were not provided, though they are routinely monitored in cardiac surgical patients. It has been shown that preoperative anemia is common among patients undergoing CABG surgery and is an important risk factor for early and late mortality.2,3 Furthermore, the combined mortality risk of anemia and transfusion is nearly triple that of a nonanemic patient not receiving transfusion.2 Similarly, hemodilution anemia (a hematocrit of <24%) during cardiopulmonary bypass has been associated with increased mortality after CABG surgery.4 In addition, postoperative anemia is also common, frequently persists for months after CABG surgery, and is associated with an impaired postoperative outcome. When postoperative hemoglobin level is considered as a continuous variable, every 1 mg/dL decrease in hemoglobin level is associated with a 22% increase in all-cause mortality.5 Thus, we cannot exclude the possibility that existence of imbalance in the perioperative hemoglobin levels between groups would have confounded interpretation of their results.
Second, if surgery is successful without severe postoperative complications, CABG surgery should improve cardiac function, physical health status, and quality of life in most patients.6 Furthermore, it has been shown that the majority of predictors of short-term mortality and morbidity after CABG surgery are cardiac-related variables.7 In this study, no inclusion of postoperative cardiac variables in multivariable and propensity matching analyses would have tampered with inferences of adjustments for postoperative short-term mortality.
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