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J Thorac Cardiovasc Surg 2004;127:1145-1150
© 2004 The American Association for Thoracic Surgery
Surgery for acquired cardiovascular disease |
a Department of Cardiothoracic Surgery, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel,
b Statistical Service, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel
Received for publication June 11, 2003; revisions received September 18, 2003; revisions received October 3, 2003; accepted for publication October 7, 2003.
* Address for reprints: Oren Lev-Ran, MD, Department of Cardiac and Thoracic Surgery, The Tel Aviv Sourasky Medical Center, 6 Weizman St, Tel Aviv 64239, Israel
orenlevran{at}hotmail.com
| Abstract |
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METHODS: Between 1996 and 2001, 515 diabetics underwent isolated left-sided skeletonized bilateral internal thoracic artery grafting. The outcome of 468 consecutive oral-treated diabetics and 47 selective insulin-treated patients was analyzed. Patients undergoing T-grafting were compared with those undergoing in situ bilateral internal thoracic artery arrangements.
RESULTS: The respective rates for early mortality and sternal infections were 2.4% and 1.9% in oral-treated diabetics and 6.3% and 4.3% in insulin-treated diabetics. Multivariate correlates of sternal infection were chronic lung disease (odds ratio, 10), obesity (odds ratio, 7), reoperation (odds ratio, 22), and a creatinine level of 2 mg/dL or more (odds ratio, 8). Five-year survival was 82%. The T-graft (n = 437) and in situ (n = 162) subgroups had comparable baseline profiles. Freedom from cardiac mortality at 6.5 years was 95.6% and 87.6% (P = .277), and freedom from repeat revascularization was 91.5% and 92.7% (P = .860), respectively. The choice of bilateral internal thoracic artery configuration did not appear as a correlate of mortality, cardiac mortality, or major adverse cardiac events. Complementary right-sided gastroepiploic artery (hazard ratio, 0.36) and sequential (hazard ratio, 0.55) grafting were identified as protective factors against the occurrence of major adverse cardiac events.
CONCLUSIONS: Routine skeletonized bilateral internal thoracic artery grafting can be implemented safely in oral-treated diabetics. This strategy is associated with a favorable late cardiac outcome and is thus recommended. Both left-sided bilateral internal thoracic artery configurations provide comparable short- and long-term outcomes.
The superiority of the internal thoracic artery (ITA) over other conduits has been established. Comparative studies have demonstrated improved resistance to the development of atherosclerosis, intimal hyperplasia, and medial calcification9,10 and maintained vasoreactive properties despite long-term diabetes.11 From a clinical standpoint, ITA use has been recognized as a strong predictor of survival in diabetic patients undergoing myocardial revascularization.1,3 Although left-sided bilateral ITA (BITA) grafting is associated with improved survival, event-free survival, and freedom from repeat revascularization in the general population,12 the application of this strategy in diabetics remains controversial because of the risk of sternal infection and subsequent lethal mediastinitis.13 To date, analysis of small datasets did not offer a clear mandate for routine BITA use in diabetics, and its long-term benefits in this group remain unclear.
Recently, skeletonized ITA harvesting14 and modifications in perioperative glucose management15 were shown to attenuate the risk of sternal infection. Reduced sternal devascularization was shown after skeletonized ITA mobilization.16
This study was designed to evaluate the risk of routine BITA grafting in diabetics. Secondary goals were to assess the long-term outcome after this strategy and to determine the left-sided BITA configuration of choice.
| Methods |
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Since 1996, we have not declined the use of skeletonized BITA in diabetic patients. All oral-treated diabetics have been regarded as eligible for BITA grafting. Excluded were patients undergoing emergency operations, patients with chronic obstructive pulmonary disease (COPD; including chronic bronchitis, emphysema, and bronchial asthma), and women with a body mass index (BMI) of 30 kg/m2 or more. Diabetics with these associated conditions, which are included in this report, were among the first enrollees who were recruited before data on their risk appeared.14 These guidelines were similar to those applied for BITA grafting in nondiabetics during this time.17 Patients were excluded from BITA grafting only when they were considered at high risk for sternal infection (detailed criteria), irrespective of the patient's cardiac or other risk factors. Therefore, there was no selection bias in patient allocation to this technique. Conversely, among insulin-treated diabetics, BITA grafting was performed selectively; other than the aforementioned criteria, this was primarily based on the surgeon's preference. Neurologically symptomatic patients or asymptomatic patients aged 65 years or older were routinely screened by carotid Doppler assays, and those who required carotid endarterectomy were excluded.
Surgical technique
Operations were performed through a midsternotomy by using standard cardiopulmonary bypass or off-pump coronary artery bypass (OPCAB). Myocardial preservation during CPB involved intermittent, antegrade, or retrograde blood cardioplegia (30°C-32°C). Coronary stabilization during OPCAB was facilitated by use of CTS stabilizers (Curpentino, Calif) or the Octopus system (Medtronic, Minneapolis, Minn). ITAs were mobilized as skeletonized vessels.17 In all cases, BITA were used to graft the left coronary system, ie, the myocardial territory supplied by the left anterior descending and circumflex arteries. Two arrangements were implemented: (1) free right ITA attached proximally on the left ITA in a T-graft configuration and (2) in situ BITA with an anteaortic crossover right ITA.17 The choice of configuration was determined by previously detailed technical considerations17 and was irrespective of the diabetic status. In case supplemental grafts to the right coronary system were necessary, the in situ right gastroepiploic artery (GEA) or saphenous vein was used. The type of conduit selected was based on the surgeon's preference; however, use of the GEA required stenosis more than 70% of the target vessel.
Preoperative and postoperative management
On admission, glucose levels were managed by continuing the patient's regimen with additional sliding-scaleguided intermittent subcutaneous insulin injections aimed at achieving serum glucose levels of 250 mg/dL or less. Postoperative treatment included intravenously administered isosorbide dinitrate (4 to 20 mg/h) for 2 days, and patients who received GEA grafts were treated with calcium channel blockers for 6 months. Glucose management was initially aimed at blood glucose levels of 250 mg/dL or less by using intermittent insulin injections and renewal of oral medication by the second postoperative day. After February 2000, glucose management was modified, and continuous intravenous insulin was administered for 48 postoperative hours to achieve target levels of 200 mg/dL or less.15 Postoperative angiography was performed selectively only in symptomatic patients (return of angina or undetermined chest pain) or in those with a positive radionuclear scan.
Definitions and data collection
Patients' data were analyzed according to the Society of Thoracic Surgeons National Cardiac Surgery Database guidelines and definitions. Causes of death were classified as cardiac or noncardiac. Cardiac mortality was defined as death occurring in relation to myocardial infarction (MI), cardiac arrhythmia, out-of-hospital sudden death, or deteriorating congestive heart failure. Undetermined causes of death were regarded as cardiac. Major adverse cardiac events (MACE) were defined as the occurrence of a nonfatal MI, the need for repeat revascularization, or cardiac mortality. Follow-up was obtained by a telephone questionnaire and the national registry database.
Data analysis
Data are expressed as mean ± SD. The
2 test and Fisher exact test were used to compare discrete variables. Actuarial survival and event-free survival curves were obtained with the Kaplan-Meier method. Statistical significance was calculated with the log-rank test. Cox analysis was used to evaluate the influence of preoperative and operative variables on late survival, freedom from cardiac mortality, and freedom from MACE. Logistic regression was used to evaluate the effect of preoperative and operative descriptors on the occurrence of sternal infection. Results of logistic regression are expressed as odds ratios (OR) with associated 95% confidence intervals (CI) and P values. Results of Cox analysis are expressed as hazard ratios (HR), 95% CI, and P values. All analyses were performed with SPSS 9 software (SPSS Inc, Chicago, Ill).
| Results |
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Five-year survival was 82% for the oral-treated group and 84.7% for the selective insulin-treated group, respectively (Kaplan-Meier). Freedom from cardiac mortality at 1, 5, and 6.5 years was 99.5%, 91.4%, and 90%, respectively (Kaplan-Meier). At 6.5 years, freedom from nonfatal MI and freedom from repeat revascularization was 94% and 93% for the oral-treated patients and 93% and 82% for insulin-treated diabetics, respectively.
Comparison between the in situ and T-graft subgroups at 6.5 years showed comparable freedom from nonfatal MI (96% and 92%, respectively; P = .514; log rank) and freedom from repeat revascularization (91.5% and 92.7%; P = .860; log rank). Correspondingly, there was no difference in cardiac mortality (95.8% and 90%; P = .277; log rank) or MACE (86.2% and 80.5%; P = .531; log rank).
Analysis of morbidity and late cardiac outcome
Significant predictors of deep sternal infection were COPD (P = .003; OR, 10.6), BMI greater than 30 kg/m2 (P = .008; OR, 7.0), female sex (P = .022; OR, 5.5), redo CABG (P = .023; OR, 22.7), and a serum creatinine level of 2 mg/dL or more (P = .025; OR, 8.2). The risk of obese women for the development of sternal infection was 22-fold (P = .042; OR, 22).
Predictors of late mortality, late cardiac mortality, and MACE are listed in Table 5. Sequential grafting (P = .047; HR, 0.55) and the use of supplemental right-sided GEA (P = .028; HR 0.36) were identified as protective factors against the occurrence of MACE. Sequential grafting also had a protective effect on cardiac mortality (P = .093; HR 0.49). The choice of left-sided BITA configuration (T-grafts or in situ) was not identified as a correlate of survival, late cardiac mortality, or the occurrence of MACE.
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| Discussion |
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Small datasets of diabetics undergoing BITA grafting did not offer a clear mandate for routine use of this strategy. This analysis of a large diabetic cohort attempted to resolve this issue. Oral- and insulin-treated diabetics were analyzed separately. Whereas the former group presented consecutive patients with no selection bias, the use of BITA in insulin-treated diabetics was selective. Nevertheless, these data are presented because of their sparsity in the literature. The observed 1.9% incidence of sternal infections among oral-treated diabetics compares with that reported after single ITA mobilization in this diabetic subset.1,18,19 Multivariate analysis validated previous observations that identified COPD and obesity (BMI
30 kg/m2) as strong predictors of sternal infection.14 The combination of being obese, diabetic, and female increased the risk by 22-fold. Severe renal dysfunction and redo CABG were further identified as correlates of sternal infection. It is our recommendation, therefore, that BITA grafting, irrespective of the mobilization technique, be avoided in these diabetic subsets. Time-frame analysis further showed that the incidence during the last 2 years was lower than in the preceding time period (1.4% vs 2.4%, respectively). This may reflect the learning curve associated with the skeletonization technique, the formation of eligibility criteria along the study,14 and adoption of a more vigilant policy of glucose control15 during this period. Evidently, this 3-armed strategy is associated with reproducible results.
The 30-day mortality (2.4%) among oral-treated diabetics was significantly lower than the Euroscore-predicted mortality and compares favorably with the 3.2% mortality in the corresponding Society of Thoracic Surgeons database oral-treated subgroup.20
It has been postulated that long-term cardiac protection is provided only by arterial grafts, whereas venous conduits undergo pathophysiologic and clinical deterioration that is similar to that from native coronary disease.21 Recent interest has focused on the use of arterial conduits in diabetics5,19; however, because surgeons are reluctant to use BITA in these patients, it may be that less-than-optimal alternative arterial grafts are used. The only conduit found to improve survival in diabetics is the ITA,1,3 and left-sided BITA grafting is the only recognized grafting pattern associated with improved survival in the general population.12 This study focuses on left-sided BITA grafting in diabetics. Our results imply that this approach may confer cardiac benefits in diabetics as well. Taking into account that the ITA attrition rate is confined to the early postoperative years,22 the 4.7% repeat revascularization rate at 6.5 years seems favorable. Although angiograms were performed selectively in prone patients (symptomatic patients or those with positive radionuclear scan; see Methods), a 92% ITA patency rate was shown. Most repeat revascularizations were required because of non-ITA graft failure or progression of disease in nongrafted vessels. This may explain the low rate of re-CABG (0.4%), because patients with a durable patent left-sided BITA retain a survival benefit from the initial CABG and would have less of a benefit from reoperation. This should be viewed in the face of a recently reported 11% mortality in re-CABG in diabetics.23 Further, the observed results (Table 2) should be viewed in face of the 11% repeat revascularizations at 7 years4 and 13% at 8 years6 reported with single ITA grafting or the 19% cardiac mortality in similar diabetic cohorts.6 Nevertheless, because this observational study does not include comparative data, the question of whether BITA grafting confers superior long-term outcome in comparison to other grafting strategies remains to be answered.
An additional conduit is often required to graft the right coronary territory when left-sided BITA is applied. In this study, the GEA or saphenous vein was used for this purpose. Complementary right-sided GEA was found by multivariate analysis to be associated with a reduced risk of MACE. This benefit was not apparent in a previous study conducted in the general population.24 Sequential grafting also showed a protective tendency with regard to cardiac-related mortality. The benefits conferred by sequential anastomoses have been previously detailed.22,25
The preferred BITA configuration remains controversial. Several clinical studies have demonstrated comparable results between in situ and T-grafts17,26; however, incidental evidence suggest incomplete relief of ischemia after T-grafting.27 It has been speculated that unique problems of T-grafts, such as competitive flow or limited flow reserve, might be exacerbated in diabetics secondary to enhanced atherosclerotic processes9,10 or altered vasoreactivity.11 This study shows that the 2 techniques are comparable with regard to short- and long-term outcome. Also, the choice of BITA configuration was not identified as a correlate of mortality, cardiac mortality, or MACE. Therefore, the choice of technique should be primarily based on technical considerations during the operation.16
Several limitations of this study need to be addressed. It is a retrospective study, and a direct comparison with other conduits would be required to determine the long-term advantage of BITA in diabetic subsets. The small number of insulin-treated patients and the low number of events negate definite conclusions with regard to the feasibility of BITA grafting in this subgroup.
In conclusion, routine skeletonized BITA grafting can be performed safely in oral-treated diabetics. This strategy is associated with favorable late cardiac outcome. Both left-sided BITA configurations (in situ and T-grafting) provide comparable short- and long-term outcome; therefore, the choice of technique should be based on technical considerations during the operation. Conclusions with regard to the safety of BITA grafting in insulin-treated diabetics should await further data.
| References |
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