Preoperative Atrial Fibrillation and Elevated C-Reactive Protein Levels as Predictors of Mediastinitis After Coronary Artery Bypass Grafting
Elenbaas TW, Soliman Hamad MA, Schönberger JP, Martens EJ, van Zundert AA, vanStraten AH.
Ann Thorac Surg 2010 Mar; 89(3):704-9.
Reviewers: Farheen Khan, Research Assistant; Feroze Mahmood, MD, Assistant Professor
Beth Israel Deaconess Medical Center
Harvard Medical School
After receiving coronary artery bypass grafting (CABG), patients often develop a serious complication consisting of a deep sternal wound infection, called mediastinitis. The authors of this study analyzed several risk factors for developing postoperative mediastinitis, in a large group of patients, between January 1998 and December 2008, who underwent CABG at Catharina Hospital, Eindhoven, The Netherlands. They used univariate as well as multivariate logistic regression analyses to discover the effect of biomedical variables which increased the chances of developing mediastinitis. The results showed that out of 11,748 patients, 100 developed mediastinitis. Independent predictors of this infection included: preoperative arterial fibrillation [odds ratio = 4.26 (2.26 to 8.02)] and an increase in preoperative C-reactive protein levels, due to surgical trauma [odds ratio = 1.013 (1.007 to 1.020)]. Other noted factors were: age, chronic obstructive pulmonary disease, diabetes, morbid obesity, use of extracorporeal circulation, use of bilateral internal mammary arteries, reexploration for ischemia, and preoperative myocardial infarction. The authors concluded that preoperative atrial fibrillation and elevated C-Reactive protein level were major contributors to the development of mediastinitis in patients who underwent CABG.
Several factors are known to contribute to the development of mediastinitis after coronary artery bypass grafting (CABG) surgery, including: morbid obesity, diabetes, and chronic obstructive pulmonary disease. The researchers studied other risk factors such as preoperative atrial fibrillation (AF) and the use of amiodarone. They specifically focused on preoperative, operative, and postoperative risk factors for the development of mediastinitis in a large group of patients at Catharina Hospital.
Patients and Methods
In this study, all the patients who underwent isolation at the Catharina Hospital, between January 1998 and December 2008, were studied. Data collected included clinical data, demographic data, risk factors, and complications.
From January 1998 to December 2008, 11,748 patients received CABG. Patients who developed mediastinitis after surgery were older, had more chronic obstructive pulmonary disease (COPD), peripheral vascular disease (PVD), diabetes, AF, a BMI > 35 kg/m2 and a higher preoperative CRP level.
Patients with postoperative mediastinitis had fewer off-pump surgical approaches, received more time for extracorporeal circulation (ECC), reexploration for bleeding or ischemia was more frequent, the number of transfusions of red blood cells was higher, the need for intraaortic balloon pump support was higher and the incidence of preoperative myocardial infarction was higher. In-hospital mortality was 22% for patients who developed mediastinitis versus only 2% in those who did not have mediastinitis.
Multivariate analyses showed the following independent risk factors: PVD, age, COPD, diabetics, BMI, preoperative AF, and preoperative CRP level. The highest odds ratio was for preoperative AF. Univariate analyses demonstrated the following risk factors: use of ECC, duration of ECC, use of bilateral internal mammary arteries (BIMA), reexploration for bleeding, reexploration for ischemia, number of transfused red blood cell units, need for intraaortic balloon pump support, and perioperative myocardial infarction.
This study found that preoperative AF was an important factor for the development of mediastinitis after CABG. They also found that elevated preoperative CRP level was associated with a higher chance of developing postoperative mediastinitis. Over the 10 years of the study, mediastinitis remained stable—around 1%. Surgical trauma gives rise to elevated CRP. Fransen, and his colleagues, described this phenomenon showing a correlation between CRP levels and all postoperative infections, including mediastinitis. Further studies need to be conducted to investigate possible interventions which will lower postoperative CRP levels, and perhaps decrease the incidences of postoperative mediastinitis.
Elevated CRP levels were also found in patients with chronic AF. Analysis determined that both CRP and AF are independent predictors of the development of mediastinitis. Patients with AF had fourfold chance of developing mediastinitis. There is no clear explanation for this finding and it should be noted that there were several limitations to the study. First and foremost, this was a retrospective study and the authors were not able to determine if the preoperative AF was paroxysmal, persistent, or permanent. Preoperative atrial fibrillation and an elevated C-reactive protein level may be important predictors of mediastinitis, but whether they actually cause mediastinitis cannot be determined from a retrospective study. However, knowing these associations may help physicians in better modulating other potential risk factors for mediastinitis (e.g., glucose control) in patients with pre-existing atrial fibrillation or elevated CRP as they may be considered at higher risk for developing this complication.