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Ann Thorac Surg 2007;83:1002-1006
© 2007 The Society of Thoracic Surgeons

Original Articles: Cardiovascular

Use of Both Internal Thoracic Arteries in Diabetic Patients Increases Deep Sternal Wound Infection

Edward B. Savage, MDa,*, Joshua D. Grab, MSb, Sean M. O’Brien, PhDb, Aman Ali, MDc, Eric J. Okum, MDc, R. Anthony Perez-Tamayo, MDc, Daniel S. Eiferman, MDc, Eric D. Peterson, MDb,d, Fred H. Edwards, MDe, Robert S.D. Higgins, MDc

a Department of Surgery, St. John’s Mercy Medical Center, St. Louis, Missouri
b Duke Clinical Research Institute, Durham, North Carolina
c Department of Cardiovascular-Thoracic Surgery, Rush University, Chicago, Illinois
d Department of Medicine, Duke University, Durham, North Carolina
e Department of Surgery, University of Florida, Jacksonville, Florida

Accepted for publication September 28, 2006.

* Address correspondence to Dr Savage, 621 S. New Ballas Rd, Suite R-7049, 625 South New Ballas Rd, St. Louis, MO 63141 (Email: chstcutter{at}aya.yale.edu).


   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 References
 
Background: Use of both internal thoracic arteries has been limited in diabetic patients fearing an increased incidence of deep sternal wound infection. We analyzed this concern by querying The Society of Thoracic Surgeons Database.

Methods: Diabetic patients who had isolated coronary artery bypass graft surgery during 2002 to 2004 were included if they had no prior bypass surgery, two or more distal bypasses, and a left internal thoracic artery bypass. Group B (both internal thoracic arteries) was compared with group L (left internal thoracic artery only).

Results: The incidence of deep sternal wound infection for all patients undergoing isolated first-time bypass surgery was less than 1%. Of these, 120,793 patients met criteria for inclusion: group B, 1.4% (1732); and group L, 98.6% (119,061). Group B had a higher crude (unadjusted) deep sternal wound infection rate of 2.8% (49) versus 1.7% (1969; p = 0.0005) in group L, with an estimated odds ratio of 2.23 (95% confidence interval, 1.69 to 2.96). Group B had a similar crude mortality rate of 1.7% (30) versus 2.3% (2785; p = NS) in group L, with an estimated odds ratio of 1.110 (95% CI, 0.78 to 1.59; p = NS). Patients in group B were younger, mostly male, had a lower serum creatinine level, and were more often current smokers; less commonly, they were insulin dependent, diagnosed with pulmonary or vascular disease, or on dialysis. Other risk factors for deep sternal would infection included female gender, insulin dependence, peripheral vascular disease, recent infarction, body mass index exceeding 35 kg/m2, and use of blood products.

Conclusions: There is a significant increase in the incidence of deep sternal would infection in diabetic patients. This is further increased with the use of both internal thoracic arteries with no apparent short-term mortality difference.


   Introduction
Top
 Abstract
 Introduction
Material and Methods
 Results
 Comment
 References
 
Deep sternal wound infection (DSWI) is a major cause of morbidity, mortality, and increased cost in patients undergoing cardiac surgery [1]. Prior analysis of patients entered into The Society of Thoracic Surgery (STS) National Cardiac Database demonstrated that patients with diabetes mellitus undergoing coronary artery bypass grafting (CABG) surgery are at increased risk for infections [2]. Reported risk factors for DSWI include longer operation time, obesity, blood usage, diabetes, and age [3–5]. Gansera and colleagues [6] noted an increase in sternal complications with the use of both internal thoracic arteries that was compounded in diabetic patients.

Numerous studies have shown that the use of both internal thoracic arteries increases long-term survival relative to the use of the left internal thoracic artery and saphenous vein grafts [7–9]. Use of two internal thoracic arteries is increasingly recommended either as bilateral pedicled grafts, free grafts from the aorta, or as a composite graft, which is a free graft originating off a pedicled graft as an extension or in a branched configuration. However, the concern that diabetes leads to an increased risk of DSWI has limited the use of both internal thoracic arteries to nondiabetic patients. This may lead to the denial of the long-term benefits of the use of both internal thoracic arteries from diabetic patients.

We sought to answer three questions based on the large amount of information available from the STS National Cardiac Database:

1 Is the incidence of DSWI higher in diabetic patients?
2 Is there a higher incidence of DSWI in diabetic patients if both internal thoracic arteries are used instead of just the left internal thoracic artery?
3 Is there a difference in perioperative mortality with the use of both internal thoracic arteries?


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 References
 
Data Source
The STS National Cardiac Database was established in 1989 to report surgical outcomes after cardiothoracic surgical procedures [10,11]. The database currently captures clinical information from nearly two thirds of all CABG procedures in the United States from more than half of all centers performing adult cardiac surgery. Sites enter patient data using uniform definitions (available online at http://www.sts.org) and certified software systems. This information is sent semi-annually to the STS Data Warehouse and Analysis Center at the Duke Clinical Research Institute. A series of data quality checks are performed at the institute before a site’s data are aggregated into the national sample. Data completeness in the STS database is high and highly accurate [12]. Research performed at the Duke Clinical Research Institute on the STS database is approved by the Duke University Institutional Review Board and was granted a waiver of informed consent and Health Insurance Portability and Accountability Act authorization.

Patient Population
A subset of diabetic patients who underwent isolated CABG surgery during 2002 to 2004 was included in this study. Records during this time span were included only if collected on versions 2.41 or 2.52 of the standard data collection form to ensure consistency in the data definitions. Patients with prior CABG surgery, fewer than two distal anastomoses, without diabetes, or those whose procedure did not involve use of the left internal thoracic artery were excluded from analysis. Patients in whom both internal thoracic arteries (group B) were used were compared with those in whom only the left internal thoracic artery (group L) was used.

Clinical End Point
The primary end point was the diagnosis of a DSWI. The secondary end point was operative mortality, defined as death occurring during the hospitalization in which the operation was performed, even if after 30 days; or death occurring after discharge from the hospital, but within 30 days of the procedure, unless the cause of death was clearly unrelated to the operation.

Statistical Analysis
Group B patients were compared with group L patients for the two outcome variables of DSWI and operative mortality. Univariable differences between the two groups were assessed using generalized score tests that account for clustering of study subjects within hospitals. Adjusted odds ratios comparing group B with group L were estimated by fitting separate logistic regression models for DSWI and operative mortality. Predictor variables were identified from previous STS risk-prediction models for DSWI and clinical judgement. The parameters of the logistic regression model were estimated by using generalized estimating equations methodology to adjust for correlation between patient outcomes within the same hospital or surgeon group.


   Results
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 Abstract
 Introduction
 Material and Methods
 Results
Comment
 References
 
From the entire group of 331,081 patients that underwent isolated first-time coronary artery bypass surgery during the period 2002 to 2004, 120,793 diabetic patients met criteria for inclusion. Of these, 1.4% were in group B and 98.6% were in group L (Table 1).


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  		Table 1 Populations Studied (2002 to 2004)
 
The demographics and risk factors of the two study groups are compared in Table 2. Patients in group B were younger, more predominantly male, had a lower baseline serum creatinine level, and were more often current smokers; less commonly, they were insulin dependent, diagnosed with pulmonary or peripheral vascular disease, or on dialysis. In general, group B patients had fewer defined morbidity and mortality risk factors.


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  		Table 2 Demographics and Risk Factors a
 
For nondiabetic patients satisfying all other study criteria, the incidence of DSWI for patients undergoing isolated first time CABG surgery was less than 1%. For the diabetic patients included in this study, the incidence of DSWI was 1.7% (2018), significantly higher than the 0.66% (1392) for those without diabetes (p < 0.0001). The incidence of DSWI and mortality in the study group is detailed in Table 3. Group B patients had a higher crude (unadjusted) rate of DSWI and an insignificantly lower crude operative mortality rate. By multivariable analysis, group B had a significantly increased DSWI outcome, with no difference in the mortality outcome.


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  		Table 3 Incidence of Deep Sternal Wound Infection and Mortality a
 
Other independent risk factors for DSWI are outlined in Table 4 and include female gender, insulin dependence, peripheral or cerebrovascular disease, recent myocardial infarction, excessive perfusion time, body mass index exceeding 35 kg/m2, the use of blood products and postoperative ventilation time exceeding 24 hours.


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  		Table 4 Other Independent Risk Factors For Deep Sternal Wound Infection
 

   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
References
 
The STS National Cardiac Database represents a unique resource for the evaluation of clinical questions; however, the limitations of its application should be clearly understood before the interpretation of data drawn from it. Unlike most published studies, data from the STS National Cardiac Database should most accurately reflect the current practice and results across a broad spectrum in the United States. It must be remembered that participation in the database is voluntary, and accuracy of the data is dependent on the rigorousness of collection by the contributing institutions. Nevertheless, the data are considered to be highly accurate [12].

By its nature, the database only allows retrospective analysis, and data sets may be incomplete. Although theoretically possible, "going back" to seek a more complete data set or make additional comparisons is not practical. Instead, questions that cannot be answered by the current data set (eg, Was the internal thoracic artery skeletonized? or How tightly were glucose level controlled perioperatively?) are more practically incorporated into future data sets.

The definition of DSWI is another limitation of the STS database. DSWI represents a spectrum of illness, from a sternitis to profound mediastinitis with associated sepsis, but no data are available to stratify the severity of the infection.

A final important limitation is that no long-term survival data are currently available within the database to assess the overall impact of the use of one or both internal thoracic arteries. We are thus limited in the questions that can be answered by the current study, but this study will help guide future data collection.

The improved durability and survival benefit of multiarterial grafting has been clearly demonstrated. This is best documented with the use of both internal thoracic arteries [13]. Within the past 10 years, however, the use of the radial artery as a free graft has gained popularity. Whether the free radial graft will be as durable as a pedicled internal thoracic artery graft is unanswered. An important variable in the selection of a conduit for multiarterial grafting is the associated morbidity. Very few major complications have been reported with proper use of the free radial artery [14]. In contrast, the use of both internal thoracic arteries has been associated with a higher incidence of sternal wound infection [15].

Gansera and colleagues [6] compared outcomes in 4462 patients in which both internal thoracic arteries were used with 4204 patients in which a single internal thoracic artery was used. They noted that in all patients, the use of both internal thoracic arteries increased the incidence of sternal instability (1.4% versus 0.6%) and mediastinitis (0.7% versus 0.2%). The incidence of mediastinitis in diabetic patients increased to 1.0% with use of both and 0.2% with a single internal thoracic artery. Gansera and colleagues [6] present important results from one center, but they do not represent results noted in general practice; their incidence of DSWI in diabetic patients is significantly lower than that reported in the STS database.

This study sought to assess the relationship and impact of diabetes and the use of both internal thoracic arteries through the unique size and capacity of the STS database. Diabetes is an independent risk factor for the development of a deep sternal wound infection; in this study, it was 0.66% for nondiabetic patients versus 1.7% for those with diabetes. The use of both internal thoracic arteries further increases this risk in diabetic patients, 1.7% with the use of one versus 2.8% with the use of both internal thoracic arteries. There was no associated increase in short-term mortality.

These data should be interpreted with caution, because the diabetic group in which both internal thoracic arteries were used had fewer risk factors for morbidity and mortality than the other group and may have been able to better endure and survive a DSWI. Internal thoracic artery usage may reflect the bias of surgeons who are less likely to use both internal thoracic arteries in patients who are older, obese, and insulin-dependent, with pulmonary, renal, or vascular disease.

Skeletonization of the internal thoracic artery, defined here as dissection leaving the muscle attached to the chest wall, thus minimizing sternal devascularization, compared with removal with an attached muscle pedicle, might reduce the risk of DSWI. Khuri [16] recently reviewed results of the use of skeletonization and noted that nonrandomized observational studies suggest that skeletonization results in less reduction of sternal perfusion and an associated reduction in sternal wound infection, but no randomized studies have been reported to date [17, 18]. Although this information would be useful and informative, it cannot be determined for this patient group because it was not collected as part of the data set.

Furnary and colleagues [19] have shown that aggressive use of insulin for perioperative glucose control greatly reduces mortality and infectious complications. Whether better treatment of diabetes perioperatively would lessen the difference between the two groups studied here is unknown. Data on perioperative glucose control are not available for the data set analyzed. This is an important area for future investigation.

According to these results, the diagnosis of diabetes mellitus should not preclude the use of both internal thoracic arteries. The increase in the risk of DSWI, in the absence of an associated increased short-term mortality risk, does not justify routine denial of the long-term mortality benefit potentially derived from the use of both internal thoracic arteries. There is, however, clear evidence that the use of both internal thoracic arteries in diabetic patients at particular risk for DSWI, specifically women and those with insulin dependence, vascular disease, recent myocardial infarction and excessive body mass index, may not be indicated and alternative arterial grafts may be a better option.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 References
 

  1. Loop FD, Lytle BW, Cosgrove DM, et al. Sternal wound complications after isolated coronary artery bypass grafting: early and late mortality, morbidity, and cost of care Ann Thorac Surg 1990;49:179-187.[Abstract]
  2. Carson JL, Carson JL, Scholz PM, et al. Diabetes mellitus increases short-term mortality and morbidity in patients undergoing coronary artery bypass graft surgery J Am Coll Cardiol 2002;40:418-423.[Abstract/Free Full Text]
  3. The Parisian Mediastinitis Study Group Risk factors for deep sternal wound infection after sternotomy: a prospective, multicenter study J Throac Cardiovasc Surg 1996;111:1200-1207.[Abstract/Free Full Text]
  4. Blanchard A, Hurni M, Ruchat P, Stumpe F, Fischer A, Sadeghi H. Incidence of deep and superficial sternal infection after open heart surgery: a ten years retrospective study from 1981 to 1991 Eur J Cardiothorac Surg 1995;9:53-57.
  5. Ottino G, De Paulis R, Pansini S, et al. Major sternal wound infection after open-heart surgery: a multivariate analysis of risk factors in 2,579 consecutive operative procedures Ann Thorac Surg 1987;44:173-179.[Abstract]
  6. Gansera B, Schmidtler F, Gillrath G, et al. Does bilateral ITA grafting increase perioperative complications?Outcome of 4462 patients with bilateral versus 4204 patients with single ITA bypass. Eur J Cardiothorac Surg 2006;30:318-323.[Abstract/Free Full Text]
  7. Lytle BW, Blackstone EH, Loop FD, et al. Two internal thoracic artery grafts are better than one J Thorac Cardiovasc Surg 1999;117:855-872.[Abstract/Free Full Text]
  8. Lytle BW, Blackstone EH, Sabik JF, Houghtaling P, Loop FD, Cosgrove DM. The effect of bilateral internal thoracic artery grafting on survival during 20 postoperative years Ann Thorac Surg 2004;78:2005-2012.[Abstract/Free Full Text]
  9. Rizzoli G, Schiavon L, Bellini P. Does the use of bilateral internal mammary artery (IMA) grafts provide incremental benefit relative to the use of a single IMA graft?A meta-analysis approach. Eur J Cardiothorac Surg 2002;22:781-786.[Abstract/Free Full Text]
  10. Ferguson Jr TB, Dziuban Jr SW, Edwards FH, et al. The STS National Database: current changes and challenges for the new millennium Ann Thorac Surg 2000;69:680-691.[Abstract/Free Full Text]
  11. Edwards FH, Clark RE, Schwartz M. Practical considerations in the management of large multiinstitutional databases Ann Thorac Surg 1994;58:1841-1844.[Abstract]
  12. Welke KF, Ferguson Jr TB, Coombs LP, et al. Validity of the Society of Thoracic Surgeons National Adult Cardiac Surgery Database Ann Thorac Surg 2004;77:1137-1139.[Free Full Text]
  13. Lytle BW, Blackstone EH, Loop FD, et al. Two internal thoracic artery grafts are better than one J Thorac Cardiovasc Surg 1999;117:855-872.[Abstract/Free Full Text]
  14. Nezic DG, Knezevic AM, Milojevic PS, et al. The fate of the radial artery conduit in coronary artery bypass grafting surgery Eur J Cardiothorac Surg 2006;30:341-346.[Abstract/Free Full Text]
  15. Kouchoukos NT, Wareing TH, Murphy SF, Pelate C, Marshall WG. Risk of bilateral mammary artery bypass grafting Ann Thorac Surg 1990;49:210-217.[Abstract]
  16. Khuri SF. To skeletonize the internal thoracic artery or not?Is that the question?. Circulation 2006;114:754-756.[Free Full Text]
  17. De Paulis R, de Notaris S, Scaffa R, et al. The effect of bilateral internal thoracic artery harvesting on superficial and deep sternal infection: the role of skeletonization J Thorac Cardiovasc Surg 2005;129:536-543.[Abstract/Free Full Text]
  18. Peterson MD, Borger MA, Rao V, Peniston CM, Feindel CM. Skeletonization of bilateral internal thoracic artery grafts lowers the risk of sternal infection in patients with diabetes J Thorac Cardiovasc Surg 2003;126:1314-1319.[Abstract/Free Full Text]
  19. Furnary AP, Gao G, Grunkemeier GL, et al. Continuous insulin infusion reduces mortality in patients with diabetes undergoing coronary artery bypass grafting J Thorac Cardiovasc Surg 2003;125:1007-1021.[Abstract/Free Full Text]

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