The Effect of Diabetes Mellitus on In-Hospital and Long-Term Outcomes after Heart Valve Operations
Halkos ME, Kilgo P, Lattouf OM, et al.
Ann Thorac Surg 2010;90:124-30
Reviewers: Haider J Warraich, MD, Research Fellow
Harvard Medical School
Boston, MA
Feroze Mahmood, MD, Assistant Professor
Beth Israel Deaconess Medical Center
Harvard Medical School
Boston, MA
Background
Diabetes Mellitus (DM) is known to adversely affect short- and long-term outcomes after coronary artery bypass surgery (CABG). However, with regards to post-valvular surgery, published results are not as clear. The authors of this study sought to compare the in-hospital and long-term outcomes of diabetic patients who underwent valve surgery with non-diabetics.
Methods
The authors retrospectively enrolled consecutive patients who underwent isolated valve operations within the Emory Healthcare system between 1996 and 2008 excluding patients undergoing concomitant CABG surgery, aortic repairs, ventricular repairs etc. DM was defined based on a self-reported history of having diabetes. Surgical technique was as per surgeon discretion following standardized protocols. Odds ratios and hazard ratios were used to determine primary outcomes (in-hospital mortality and all-cause mortality).
Results
Over the study period a total of 2964 patients were included in the study. Of these, 14.3% (n=424) had DM. Of the diabetic patients, 29.7% (n=126) were on insulin therapy. The proportion of patients undergoing valve operations with diabetes increased from 11.6% in 1996 to 20.3% in 2007. DM was associated with reduced 10-year survival even after multivariate analysis/risk adjustment (p=0.018), in-hospital mortality was significantly higher in DM patients than in non-DM patients, and in-hospital mortality was higher in those patients who received insulin than in those who did not. The authors concluded that patients with DM have significantly worse outcomes when they undergo valvular surgery and given their worse long-term prognosis the diagnosis of DM should factor into decisions regarding their surgical management (e.g. prosthesis used, surgical technique, etc).
Reviewers' Comments
Diabetics represent a group of high-risk patients, usually presenting with multiple co-morbidities, who have a documented higher risk for adverse cardiovascular events. In various studies, DM has been identified as an independent risk factor for short-term mortality after valve operations. Valve operations performed concomitantly with CABG have been shown to have reduced survival in diabetics, but this particular study has demonstrated increased long-term mortality even in isolated valve operations alone, regardless of which valve was involved (mitral, atrial, or combined).
The study is limited by its retrospective nature which leaves it susceptible to selection bias, procedure bias, etc. DM was defined based on self-reported history of disease. However, there is a high rate of undiagnosed DM in patients presenting for cardiac procedures such as CABG (29.6%) and elective cardiac catheterization (22.9%); this undiagnosed population confounds the significance of reported results1. Furthermore, the investigators failed to evaluate factors that directly affect valvular surgery outcomes such as degree of regurgitation/stenosis, duration of valve dysfunction, prosthetic mismatch, or ventricular dysfunction. Additionally, no data regarding level of diabetic control is presented, e.g. history of ‘uncontrolled’ diabetes, HbA1c levels etc.
While this study has important implications in providing further evidence that diabetics may be at increased risk for worse outcomes, a considerable amount of information remains lacking: What level of glucose control should be maintained; what is the optimal range of glucose in patients undergoing surgery where hyperglycemia is a stress response; and whether the benefits of insulin therapy are due to its effect on glucose metabolism or of its general anabolic effects2. The benefits of preventing hyperglycemia must also be weighed against the single most important and potentially fatal complication of excessive glucose control – hypoglycemia. Long term hyperglycemia can result in a decrease in glucose transport to the cerebral tissues3, leading to symptoms of hypoglycemia even with ‘normal’ glucose levels4. More reliable data that accounts for HbA1c levels, degree of glycemic control, variability in glucose levels, degree and chronicity of valve dysfunction and other operative variables would yield more objective results. DM has been proven to predict a more adverse outcome, and in spite of the limitations of this study, there is little doubt that diabetes increases adverse events in patients with concurrent valve surgery. Nevertheless, it does not quell the long standing debate regarding the hypothesized benefits of ‘tight’ intraoperative glucose control and the mechanisms of the beneficial effects of insulin.
References
- Lauruschkat AH, Arnrich B, Albert AA, et al. Prevalence and risks of undiagnosed diabetes mellitus in patients undergoing coronary artery bypass grafting. Circulation 2005;112:2397-402.
- Siroen MP, van Leeuwen PA, Nijveldt RJ, Teerlink T, Wouters PJ, Van den Berghe G. Modulation of asymmetric dimethylarginine in critically ill patients receiving intensive insulin treatment: a possible explanation of reduced morbidity and mortality? Crit Care Med 2005;33:504-10.
- Harik SI, Gravina SA, Kalaria RN. Glucose transporter of the blood-brain barrier and brain in chronic hyperglycemia. J Neurochem 1988;51:1930-4.
- DeBrouwere R. Con: tight intraoperative glucose control does not improve outcome in cardiovascular surgery. J Cardiothorac Vasc Anesth 2000;14:479-81.
