Author + information
- Fu-Shan Xue, MD∗ (, )
- Rui-Ping Li, MD,
- Gao-Pu Liu, MD and
- Chao Sun, MD
- ↵∗Department of Anesthesiology, Plastic Surgery Hospital, Chinese Academy of Medical Sciences, Peking Union Medical College, 33 Ba-Da-Chu Road, Shi-Jing-Shan District, Beijing 100144, People's Republic of China
With great interest, we read the recent article by Nyström et al. (1) assessing the relationships of preoperative glycemic control in type 1 diabetes and long-term risks of major adverse cardiovascular events (MACE) and all-cause mortality after coronary artery bypass grafting (CABG) in an observational cohort study. They showed that preoperative poor glycemic control defined by hemoglobin A1c levels was associated with increased long-term risks of MACE and all-cause mortality. The strengths of this study include the large sample of patients with a long follow-up and use of appropriate statistical methods to estimate the relationships of preoperative glycemic control with the risks of MACE and all-cause mortality. In our view, however, several issues in this study seemed not to be well addressed.
First, perioperative blood management was not included in the study design. It has been shown that preoperative anemia is common among patients undergoing CABG and is an important risk factor for early and late mortality after surgery (2). Furthermore, the combined mortality risk of pre-operative anemia and perioperative transfusion is nearly triple that of nonanemic patients not receiving transfusion. In addition, post-operative anemia is also common, with an incidence of 44% and frequently persists for months after CABG. When the postoperative hemoglobin level is considered a continuous variable, every 1-mg/dl decrease in hemoglobin level is associated with a 13% increase in MACE and a 22% increase in all-cause mortality (3). We are concerned that the existence of any imbalance in these factors among patients with the different hemoglobin A1c levels would have confounded interpretation of their results.
Second, the variables used for adjusted hazard ratios of MACE and long-term all-cause mortality in the multivariable model only included the baseline and procedural characteristics of study patients, but not important post-operative risk factors. If surgery is successful, CABG should improve postoperative cardiac function, physical health status, and quality of life in most of patients. It has been shown that established preoperative risk factors are not good predictors of adverse outcomes and long-term survival after CABG (4). Actually, late mortality is mainly attributable to many causes, not necessarily related to patients’ cardiovascular and general health before CABG. The available literature provides compelling evidence that postoperative complications and persistent vital organ dysfunctions at hospital discharge are important predictors of late mortality after cardiac surgery (5). For example, deep sternal wound infection or mediastinitis, acute myocardial and kidney injuries, pulmonary complications, dysfunction or loss of bypass grafts, new-onset atrial fibrillation, and deterioration of regional wall motion after CABG have been associated independently with increased MACE and long-term mortality. Furthermore, hemoglobin A1c is a marker of glycemic control over the previous 3 months before measurement. Can preoperative hemoglobin A1c levels exactly represent the postoperative long-term glycemic control of patients? Thus, we argue that no inclusion of important postoperative risk factors in the multivariable model for adjusted hazard ratios would have biased the true effect of preoperative glycemic control on long-term outcomes after CABG in this study.
Please note: The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- 2015 American College of Cardiology Foundation
- van Straten A.H.,
- Hamad M.A.,
- van Zundert A.J.,
- et al.
- Westenbrink B.D.,
- Kleijn L.,
- de Boer R.A.,
- et al.,
- for the IMAGINE Investigators