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Ann Thorac Surg 1998;66:2051-2055
© 1998 The Society of Thoracic Surgeons

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Original Articles

Does bilateral internal thoracic artery grafting increase surgical risk in diabetic patients?¹

^a Department of Cardiac Surgery, Hôpital Saint Joseph, Paris, France

Accepted for publication June 20, 1998.

Address reprint requests to Dr Sousa Uva, Hospital Cruz Vermelha rua Duarte Galvao n° 54, 1500 Lisboa, Portugal

	Abstract

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
Background. The purpose of this study was to determine whether, with appropriate techniques, diabetic patients could benefit from the advantages of double internal thoracic artery (ITA) coronary bypass without an increased hospital risk.

Methods. Between January 1990 and December 1996, 207 consecutive diabetic patients underwent coronary artery bypass graft operations. In 74 patients both arteries (bilateral ITA group) were used, whereas 133 patients received one ITA and vein grafts or vein grafts alone (nonbilateral group). Patients in the bilateral ITA group were younger (p < 0.0001), predominantly male (p < 0.0001), and were operated on more electively. The internal thoracic arteries were harvested by skeletonization without electrocautery, and strict glycemic control was pursued.

Results. No death was observed in the bilateral ITA group, whereas 7 patients died in the nonbilateral ITA group (p < 0.05). Deep sternal wound infection was observed in 2 patients in the nonbilateral ITA group (1.5%) and in none of the bilateral ITA group (p = NS). There was no significant difference in the morbidity rate between the two groups except for greater blood losses in the bilateral ITA group.

Conclusion. Double ITA coronary revascularization in young diabetic patients was performed without increased morbidity and mortality. The low rate of sternal wound infections may be related to ITA harvesting by a skeletonization technique, but larger studies are required to confirm these data.

	Introduction

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
Diabetes mellitus is a major independent risk factor for coronary artery disease. Atherosclerosis accounts for about 80% of all deaths from diabetes, of which three-quarters are from coronary heart disease [1].

Percutaneous coronary angioplasty in diabetic patients is associated with a lower completeness of revascularization, an increased risk of restenosis, and a greater need for additional revascularization procedures [2]. The BARI study showed that in diabetic patients with multivessel disease, operative procedures achieved a significantly higher 5-year survival rate than angioplasty [3].

The indisputable survival benefit of grafting one internal thoracic artery (ITA) on the left anterior descending coronary artery is because of its superior long-term patency [4] and the benefit is at least as great in diabetic as in nondiabetic patients [5]. The superior performance of this conduit led to an increase in the use of both internal thoracic arteries in an attempt to avoid late saphenous venous graft closure and improve the event-free survival. However, bilateral internal thoracic artery grafting has been associated with a four- to 20-fold increase in the incidence of sternal wound infections in diabetic patients [6, 7]. If the use of two internal thoracic arteries in diabetics is associated with higher morbidity and mortality, one could question the wisdom of using bilateral ITA grafting for a potential long-term benefit that would be neutralized by an increased early risk.

The aim of this study was to test the hypothesis that, with appropriate patient selection and adequate surgical technique, bilateral ITA grafting could be performed in diabetic patients, with a limited hospital risk and a low rate of complications.

	Patients and methods

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
Between January 1990 and December 1996, 1,098 consecutive patients underwent first-time coronary artery bypass grafting in our unit. Among these, we identified 207 diabetic patients, defined by a preoperative plasma fasting glucose greater than 1.25 mg/dL (7.0 mmol/L). Diabetes was either insulin dependent (n = 19; 9.2%) or treated by oral hypoglycemic agents or diet (n = 188; 90.8%). Patients with temporary postoperative hyperglycemia were not included. In 74 patients the two internal thoracic arteries (ITA) were used (bilateral ITA group). In 133 patients (nonbilateral ITA group) either one ITA with vein grafts (n = 120) or vein grafts alone (n = 13) were used. No attempt to match the two groups was made in this retrospective study. In the bilateral ITA group patients were younger, there were fewer women, and patients were operated on more electively (Table 1). The two groups and status at operation had similar incidences of hypertension, smoking, extent of coronary artery disease, left ventricular function, and completeness of revascularization. These demographic differences reflect a selective policy of indications for using bilateral ITA. In diabetics, as in the nondiabetic population, coronary revascularization with two ITA has been our method of choice in nonobese patients younger than 70 years of age operated on a nonemergent basis. There was no significant difference in the incidence of insulin-dependent diabetes between the two groups (6 of 74, 9.4% versus 14 of 133, 10.5%). There was also no difference between the two groups regarding the incidence of prior myocardial infarction (41 of 133 versus 30 of 74). Demographics of the two groups are summarized in Table 1.

The mean number of distal anastomoses per patient was 2.7 ± 0.7 in the bilateral ITA group and 2.6 ± 0.8 in the nonbilateral ITA group (p = NS).

Normothermic perfusion was used and myocardial protection was achieved by cold crystaloid cardioplegia until 1995; we used antegrade warm blood cardioplegia thereafter. Cross-clamp times were 54 ± 13 minutes and 54 ± 17 minutes in the bilateral ITA and the nonbilateral ITA groups, respectively (p = NS). Cardiopulmonary bypass times were 70 ± 24 minutes and 95 ± 29 minutes in the bilateral ITA and the nonbilateral ITA groups, respectively (p < 0.0001). The longer cardiopulmonary bypass time in the nonbilateral ITA group was related to vein graft aortic implantation. The sternum was closed with interrupted 6–8 stainless steel wires, interrupted double-layer polydiaxone musculofascial sutures, and polydioxanone absorbable continuous dermal suture.

After surgery all patients had blood glucose determinations at 3-hour intervals and continuously adapted insulin infusion to a blood glucose target level of 150 to 200 mg/dL until postoperative day 2. Thereafter, either subcutaneous insulin or the oral hypoglycemic agents were resumed.

Definitions
Deep sternal wound infection was defined by infection involving tissues beneath the subcutaneous tissue with at least one of the following: positive mediastinal culture; evidence of mediastinitis at operation; or fever, chest pain, or sternal instability, as well as either purulent drainage from the mediastinum or a positive blood culture or culture of mediastinal drainage.

Superficial wound infection involved only skin or subcutaneous tissue below the incision with either purulent drainage, organism isolated, or incision opened by the surgeon. Nosocomial pneumonia was defined by the association of fever, pulmonary infiltrate, and a distal bronchial positive culture.

Follow-up
Patients were examined by the surgeon or the referring cardiologist 2 months after operation.

Statistical methods
Data were expressed as the mean ± standard deviation. Statistical analysis was performed using Fischer’s exact test and ² test for discrete variables and unpaired t test for continuous variable comparisons. Statistical significance was established at a p value less than 0.05.

	Results

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
Mortality
There was no in-hospital death in the bilateral ITA group, whereas 7 patients (5.2%) died in the nonbilateral ITA group (p < 0.05). Causes of death were cardiac related in 6 patients and septicemia in 1 patient.

Morbidity
Complications were not increased in the bilateral ITA group, compared with the nonbilateral ITA group, and are summarized in Table 2.

The incidences of nosocomial pneumonia were identical in the two groups. However, intubation time was longer in the nonbilateral ITA group (53 ± 78 hours versus 31 ± 51 hours in the bilateral ITA group; p < 0.05) despite a similar incidence of phrenic nerve paresis (1.5% versus 1.3%). Total amount of blood loss was significantly greater in the bilateral ITA group (Table 2), although the incidence of reexploration for bleeding was identical (3 patients [4%] in the bilateral ITA group versus 5 patients [3.7%] in the nonbilateral ITA group).

The number of patients taking inotropes (including dosage < 5 µg/Kg/min) was 49 (66%) in the bilateral ITA group and 117 (88%) in the nonbilateral ITA group (p < 0.01). Three patients (2.2%) developed neurologic complications in the nonbilateral ITA group (two cases of reversible neurologic deficits and one stroke) versus none in the bilateral ITA group (p = NS). Duration of stay in the intensive care unit (3.4 ± 1.5 days in the bilateral ITA group versus 4.6 ± 3.4 days in the nonbilateral ITA group) and hospital stay (14.1 ± 4 days in the bilateral ITA group versus 14.5 ± 7 days in the nonbilateral ITA group) were not statistically different between the two groups.

	Comment

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
This retrospective study showed that with appropriate surgical technique and patient selection, bilateral ITA could be used in diabetics without increased morbidity or mortality. Diabetes is an independent major risk factor for coronary atherosclerosis. Patients with diabetes are at increased risk of myocardial infarction and have more extensive and severe coronary artery disease than the general population [1]. Angioplasty in diabetic patients with multivessel disease is associated with a less complete revascularization than that obtained by operation. Moreover, there is excess neointimal hyperplasia after angioplasty in diabetic patients. This process is not prevented by stent deployment, resulting in a higher intrastent restenosis rate than in nondiabetic patients [8]. Clearly, whatever the type of therapy, the 5-year survival probability for diabetic patients is worse than that for nondiabetic patients [3]. All things considered, however, the available evidence favors operation rather than percutaneous transluminal coronary angioplasty for patients with treated diabetes in terms of overall and cardiac mortality [9]. The rationale for coronary revascularization with both ITA is based on the superior durability of this conduit and the reduction in the rate of adverse cadiac events [10, 11]. However, there is still no firm consensus on whether bilateral ITA grafting provides a long-term survival benefit, compared with use of one ITA [12, 13]. Recently, Pick and colleagues [14] showed better 10-year survival in patients having two ITA grafts although multivariate analysis revealed that this was the result of the greater prevalence of diabetes in patients having only one ITA graft [14]. On the other hand, patient-related factors such as comorbidity, chronic blood glucose levels, hypercholesterolemia, and other risk factors for atherosclerosis could be more relevant in terms of event-free survival than the choice of conduits.

If the long-term benefit of the use of bilateral ITA grafting in a diabetic population is to be seen, there must be no increase in the early risk. The objective of this study was to determine precisely whether a trade-off was being made, ie, increasing early risks for a potential late benefit. Diabetes, either treated by insulin or not, increases the risk of surgical wound infection whatever the type of operation. Several studies have shown diabetes to be a risk factor for sternal wound infection either independently or in association with other factors such as obesity, age, or respiratory disease [6, 15, 16].

Diabetic patients are more prone to wound infections through the combination of several physiologic derangements. The intracellular bactericidal activity of leukocytes is decreased, as is the capacity of immunoglobulins to fix the complement [17]. Moreover, the detrimental effects of associated microvascular complications and neuropathy contribute to impairment of the local circulation, which may delay prompt host inflammatory response to infection, retard wound healing, and impede delivery of antimicrobial agents to the involved area.

Mobilization of the ITA leads to devascularization of the ipsilateral hemisternum; if both arteries are mobilized the entire sternum is significantly devascularized [18]. Because devascularization itself is a risk factor for infection or wound dehiscence, bilateral ITA take-down in diabetic patients could be considered hazardous. In this study, the incidence of deep sternal wound infection was zero in the bilateral ITA group and 1.5% in the nonbilateral ITA group. The explanation for these results may lie, at least partially, in the use of skeletonization for ITA harvesting, without the use of electrocautery and meticulous wound closure. Parish and associates [19] have shown in a canine model that the hemisternum from which the ITA was harvested by skeletonization had a significantly higher residual sternal blood flow than that dissected as a pedicle [19]. De Jesus and Acland [20], in a microdissection study, showed three types of collateral vessels with the potential to carry blood to the sternum after mobilization of the ITA. For these collaterals to remain functional after ITA take-down their short common origin must remain intact. Skeletonization using accurate and atraumatic ligation of branches as close as possible to the ITA itself ensures maximum residual collateral blood flow to the sternum. Using sternal radionuclide tomography Carrier and coworkers [21] showed that bilateral ITA mobilization caused an important but transient decrease in the sternal blood supply. It is therefore paramount that sternal closure ensures secure contact between the two sternal halves, as devascularization and poor bone immobilization carry a high risk of wound dehiscence.

Although we believe that with skeletonization dissection both internal thoracic arteries can be used for coronary artery bypass grafting in patients with diabetes mellitus without increased morbidity and mortality, skeletonization is more technically demanding and requires patience and experience.

It could be argued that the relatively low incidence of insulin-dependent diabetes (9.2%) in the present series may partially explain the fact that we did not observe any case of deep sternal wound infections in the bilateral ITA patients. However, it has not been demonstrated that insulin-dependent diabetes carries a greater risk for soft tissue or sternal wound infections than non–insulin-dependent diabetes [22, 23]. In fact, associated factors such as obesity, quality of the chronic glycemic control (as assessed by glycosylated hemoglobin), and blood glucose control during the perioperative period could be more relevant than the type of diabetes mellitus. Indeed, a direct correlation was found between the prevalence of infections and mean plasma glucose levels, as was a decrease in the incidence of deep sternal wound infection after tight control of blood glucose levels [23].

Development of a preoperative risk score for sternal wound infection by multivariate analysis in a large multicenter prospective study is theoretically appealing, for it could help in selecting patients who would benefit from the superior long-term patency of bilateral ITA grafting without incurring the negative impact of mediastinitis [24]. However, to be able to identify institution-dependent risk factors, such a study would require the difficult task of recording a myriad of operative technical details as well as organizational factors and is therefore hard to undertake.

In this series, bilateral ITA revascularization was used with careful assessment of indications. In general, patients older than 75 years of age, or those with major respiratory function impairment, obesity, or who required emergent revascularization did not undergo double mammary artery grafting. Indeed, age, emergency status, duration of operation, and obesity were all found to be risk factors for operative mortality or wound complications in bilateral ITA grafting [6, 7, 15, 16, 24]. Using this policy, mortality rate and cardiac, neurologic, and respiratory morbidity were low in patients who received bilateral ITA grafts. Similar to the findings of Cosgrove and associates [6], we found a slight increase in total blood loss in the bilateral ITA group but no difference in the percentage of patients reoperated for bleeding.

Limitations
There was an intentional selection process between patients who received two ITA and those receiving one, therefore comparisons between groups should be considered within these limitations. These results were achieved through the conjunction of various factors, including ITA harvesting technique, meticulous wound closure, operating room organization, and continuous aggressive blood glucose control throughout the perioperative period. Therefore, only intrainstitution review of practices and results can determine whether or not this policy may be generalized and advised for coronary artery bypass grafting in diabetic patients. Finally, the number of patients studied is relatively small and larger studies will be required to confirm these data.

The quest for the best treatment strategy in diabetic patients with multivessel coronary artery disease is not over. From this study we conclude that with appropriate surgical technique and selection, bilateral internal thoracic coronary artery grafting in diabetic patients does not carry an increased operative risk. The advantage of this policy in terms of event-free survival remains to be confirmed by long-term follow-up.

	Footnotes

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
¹ This article has been selected for the open discussion forum on the STS Web site: http://www.sts.org/annals

	References

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 

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