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Ann Thorac Surg 2007;83:1666-1671
© 2007 The Society of Thoracic Surgeons

Original Articles: Cardiovascular

Long-Term Results of Bilateral Internal Thoracic Artery Grafting in Dialysis Patients

Masashi Kai, MDa, Hitoshi Okabayashi, MD, PhDb,*, Michiya Hanyu, MD, PhDa, Yoshiharu Soga, MD, PhDa, Takuya Nomoto, MD, PhDa, Jota Nakano, MDa, Takehiko Matsuo, MDa, Eitaro Umehara, MDa, Masahide Kawato, MDa

a Department of Cardiovascular Surgery, Kokura Memorial Hospital, Kitakyusyu City, Fukuoka, Japan
b Department of Cardiovascular Surgery, Iwate Medical University Memorial Heart Center, Morioka, Iwate, Japan

Accepted for publication December 6, 2006.

* Address correspondence to Dr Okabayashi, Department of Cardiovascular Surgery, Iwate Medical University Memorial Heart Center, Chuodori 1-2-1, Morioka, Iwate 020-8505, Japan (Email: cardiovascsurg{at}siren.ocn.ne.jp).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 References
 
Background: We evaluated the perioperative and long-term results of bilateral internal thoracic artery grafting in dialysis patients.

Methods: One hundred one consecutive patients on chronic dialysis who underwent isolated coronary artery bypass grafting were retrospectively compared according to the surgical technique, bilateral internal thoracic artery (BITA) grafting (n = 76) or single internal thoracic artery (SITA) grafting (n = 25).

Results: Hospital mortality was 5.3% in the BITA group and 8.0% in the SITA group (p = not significant). The incidence of mediastinitis was not different (7.9% in the BITA group and 8.0% in the SITA group). The median duration of follow-up was 3.1 years (range, 0.1 to 10.9). Survival and freedom from cardiac mortality were not different between the two groups, but the BITA group had a trend toward better results. Freedom from cardiac events (including cardiac-related death, myocardial infarction, pecutaneous coronary intervention, redo coronary artery bypass grafting, and congestive heart failure) was superior in the BITA group (p = 0.03). Calcification of the ascending aorta, peripheral vascular disease, insulin-dependent diabetes mellitis, and age were the independent risk factors of late death.

Conclusions: Perioperative results of BITA grafting in dialysis patients were not different from the results of SITA grafting. However, the long-term results of BITA grafting in dialysis patients were better than the results of SITA grafting. Overall, our results support the continued use of BITA grafting in dialysis patients.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 References
 
It has been shown that an internal thoracic artery (ITA) graft to the left anterior descending artery (LAD) has superior long-term patency and leads to better survival and freedom from cardiac events than a saphenous vein graft. The left internal thoracic artery (LITA) is now widely accepted as the standard conduit for revascularization of the LAD [1–3].

Although the issue is still controversial, there have been several recent reports indicating that bilateral internal thoracic artery (BITA) grafting gives better results than single internal thoracic artery (SITA) grafting in terms of survival and cardiac events, especially among diabetic patients [4–7].

Several studies have reported the long-term results of coronary artery bypass grafting (CABG) for dialysis patients [8–14]. Use of the ITA for revascularization has been shown to increase the survival of dialysis patients [14]. However, there are few reports about the early and long-term results of BITA grafting in dialysis patients. The possible increased risk of mediastinitis is a concern when BITA grafting is used in dialysis patients. We have been actively using BITA for dialysis patients for a long time. The objective of the present study was to evaluate the perioperative risks and the long-term efficacy of BITA grafting by means of comparison with SITA grafting in dialysis patients.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 References
 
Between September 1992 and December 2005, 116 consecutive patients with end-stage renal failure maintained on chronic dialysis underwent isolated CABG at Kokura Memorial Hospital. Among them, 76 consecutive patients undergoing BITA grafting and 25 consecutive patients undergoing SITA were retrospectively analyzed. Permission to use the denominated database was obtained from the Review Board of Kokura Memorial Hospital, and informed consent was obtained from each participant. The patients’ preoperative characteristics are summarized in Table 1.


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  		Table 1 Patients’ Characteristics
 
Surgical Technique
Table 2 demonstrates the operative data. All operations were performed through a midsternotomy by using cardiopulmonary bypass or off-pump coronary artery grafting surgery (OPCABG). Myocardial preservation during cardiopulmonary bypass involved intermittent, antegrade warm cardioplegia. Off-pump CABG was introduced in January 2000, and was used in 77 consecutive patients except for one redo case. Coronary stabilization during OPCABG was facilitated by using stabilizers such as the Octopus system. The ITAs were harvested in a pedicled manner before January 2000 and in a skeletonized manner thereafter. Bilateral ITA grafting had been used actively since 2002.


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  		Table 2 Operative Data
 
Table 3 shows the destination of the ITA. Before 2001, in situ right ITA (RITA) with anteaortic crossover anastomosed to the LAD and in situ LITA to the circumflex artery had been one of our surgical choices. However, we changed our method to prevent injury of the RITA in resternotomy cases. From 2001, LITA was singly or sequentially anastomosed to the LAD. The in situ RITA was routed through the transverse sinus and anastomosed to the major branches of the circumflex artery. In cases when the in situ RITA did not reach the major branches of the circumflex artery, a Y graft was constructed by attaching the free RITA proximally to the LITA in an end-to-side manner. This technique was used in 21 patients (27.6%) BITA group. Dialysis was usually performed on the first postoperative morning before extubation. Postoperative angiography had been routinely performed about 2 weeks after surgery. However, starting in 2005, it was canceled owing to possible complications, especially cerebrovascular accidents, and multidimensional computed tomography was used instead for evaluation of graft patency.


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  		Table 3 Internal Thoracic Artery Destination
 
Late Follow-Up
Follow-up was performed between December 2005 and May 2006 and ascertained for 100% of the patients. The median duration of follow-up was 3.1 ± 2.1 years and ranged from 1 month to 10.9 years. Follow-up information was collected at the time of the patient’s most recent clinical visit, supported by telephone interview with dialysis physicians or patients. If patients had suffered late death or cardiac-related events, the hospital records were examined to gain further information.

Statistical Methods
Data are expressed as mean ± SD. Unrelated two-group comparisons were done with unpaired, two-tailed Student’s t tests for continuous variables and {chi}2 or Fisher’s exact test for categorical data. The logistic regression models were used to determine the influence of patients’ characteristics on mediastinitis. Survival curve, freedom from cardiac mortality curve, and freedom from cardiac events free curve were estimated using the Kaplan-Meier method. Statistical significance was calculated with the log-rank test. Cox proportional hazard models were used to determine the influence of patients’ characteristics and operative data on late survival. Hazard ratios, 95% confidence intervals, and levels of statistical significance (p value) were calculated. All data were analyzed with StatView version 5.0 (SAS Institute, Cary, North Carolina).


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 References
 
Perioperative Data
Patients who underwent CABG with BITA grafting had more distal anastomosis. More patients in the BITA group underwent ITA grafting in an off-pump and skeletonized manner.

Early Results
Table 4 shows early results. Of 4 in-hospital deaths in the BITA group, 3 were due to mediastinitis and 1 was due to mesenteric ischemia. Of 2 in-hospital deaths in the SITA group, 1 was due to mediastinitis and 1 was due to pyothorax. Postoperative angiography was performed on 64 patients (84.2%) in the BITA group. The patency rate was 97.9%.


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  		Table 4 Early Results
 
There were 8 patients having mediastinitis. The predictors of mediastinitis are shown in Table 5. There was no significant difference between the SITA group (8%) and the BITA group (7.9%).


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  		Table 5 Predictors of Mediastinitis
 
Late Results
There were 25 late deaths in the BITA group, 5 of them due to cardiac causes, namely, congestive heart failure (n = 4) and sudden death (n = 1). The other 20 deaths were due to noncardiac causes: sepsis (n = 8), cerebrovascular disease (n = 4), renal failure (n = 3), pneumonia (n = 2), liver cirrhosis (n = 1), cancer (n = 1), and mesenteric ischemia (n = 1). Kaplan-Meier 1-year, 3-year, and 5-year survivals for the BITA group were 88.6% ± 3.8%, 67.0% ± 6.6%, and 54.7% ± 7.8%, respectively (excluding hospital deaths), as illustrated in Figure 1.


Figure 1
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  		Fig 1. Kaplan-Meier survival. A trend toward better survival was noted in the bilateral internal thoracic artery (BITA) group (dotted line) compared with the single internal thoracic artery (SITA) group (solid line), but it was not statistically significant (p = 0.42).

 
There were 15 late deaths in the SITA group, 4 of them due to cardiac causes, namely, sudden death (n = 2), congestive heart failure (n = 1), and acute myocardial infarction (n = 1). The other 11 deaths were due to noncardiac causes: sepsis (n = 5), cerebrovascular disease (n = 3), renal failure (n = 2), and cancer (n = 1). Kaplan-Meier 1-year, 3-year, and 5-year survivals for the SITA group were 91.3% ± 5.9%, 60.9% ± 10.2%, and 40.9% ± 10.7%, respectively (excluding hospital deaths). The Kaplan-Meier curves for the two groups were not statistically different (p = 0.421, log rank).

The freedom from cardiac-related mortality is demonstrated in Figure 2. The 1-year, 3-year, and 5-year freedom from cardiac-related mortality for the BITA group was 97.0% ± 2.1%, 91.9% ± 4.2%, and 91.9% ± 4.2%, respectively (excluding hospital deaths). The 1-year, 3-year, and 5-year freedom from cardiac-related mortality for the SITA group was 95.7% ± 4.3%, 84.0% ± 8.6%, and 84.0% ± 8.6%, respectively (excluding hospital deaths). These results are not statistically different between the two groups (p = 0.420).


Figure 2
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  		Fig 2. Freedom from cardiac-related mortality. A trend toward better freedom from cardiac-related mortality was noted for the bilateral internal thoracic artery (BITA) group (dotted line) compared with the single internal thoracic artery (SITA) group (solid line), but it was not statistically significant (p = 0.42).

 
The freedom from cardiac-related events (including cardiac-related death, myocardial infarction, pecutaneous coronary intervention, redo CABG, and congestive heart failure) are demonstrated in Figure 3. The 1-year, 3-year, and 5-year freedom from cardiac-related events for the BITA group was 95.4% ± 2.6%, 83.5% ± 6.2%, and 78.0% ± 7.9%, respectively (excluding hospital deaths). The 1-year, 3-year, and 5-year freedom from cardiac-related events for the SITA group was 91.1% ± 6.0%, 67.7% ± 11.1%, and 59.2% ± 12.5%, respectively (excluding hospital deaths). The BITA group did better than the SITA group (p = 0.030).


Figure 3
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  		Fig 3. Freedom from cardiac-related events (including cardiac-related death, myocardial infarction, pecutaneous coronary intervention, redo coronary bypass artery grafting, and congestive heart failure). Better results results were noted for the bilateral internal thoracic artery (BITA) group (dotted line) compared with the single internal thoracic artery (SITA) group (solid line; p = 0.02).

 
Cox proportional hazard models (Table 6) were used to assess the effect of confounding factors on late death. For the total group, significant predictors of late death included calcification of the ascending aorta, peripheral vascular disease, insulin-dependent diabetes mellitus, and age. For the BITA group, significant predictors of late death included calcification of the ascending aorta, peripheral vascular disease, and age. Dialysis duration or type and OPCABG were not significant predictors.


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  		Table 6 Cox Proportional Hazard Model for Death at Long-Term Follow-Up
 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
References
 
This retrospective study showed long-term survival is not different between BITA grafting and SITA grafting in dialysis patients. Our 5-year survival rate of 55% for the BITA group and 41% for the SITA group is discouraging and fits within the widely variable range of previous reports, although we did not have large numbers of patients beyond 5 years. Several studies have reported poor survival of dialysis patients after CABG. Five-year survival rates are reported to range from 32% to 71% [8–14]. Dialysis patients are 3.2 times more likely to die than other CABG patients over a 5-year period [19]. The main causes of death are diseases other than cardiac ones such as infection and cerebrovascular disease. Our analysis identified calcification of the aorta, peripheral vascular disease, insulin-dependent diabetes, and age as independent risk factors for late death. These findings indicate that severe systemic atherosclerosis is a risk factor for late death.

Compared with patients undergoing SITA grafting, however, dialysis patients undergoing BITA grafting have significantly better long-term results with regard to cardiac-related events. Additionally, freedom from cardiac mortality for the BITA group is at least comparable with the results of other previous studies using bilateral ITAs, even though the patients examined in these previous studies were not specifically dialysis patients [4–7, 15–18]. That could be explained by the high resistance of the ITA to atherosclerosis, even in dialysis patients. The superiority of the ITA over other grafts has been well established by numerous studies that have demonstrated better resistance to the development of atherosclerosis, intimal hyperplasia, and medial calcification [19, 20]. Even though dialysis patients often have calcification of the coronary arteries, aorta, or other peripheral arteries, the minimal impact of chronic renal failure on atherosclerotic changes in the ITA has also been documented [21].

Not all cardiac-related events are avoidable even if the bilateral ITAs is used. Some cardiac-related events can occur because of progression of native coronary artery disease in areas distal to the graft anastomosis site or other nonbypassed branches of the coronary artery [22]. In our series, no ITA occlusion was observed during follow-up. We think that the relative resistance of the ITA to atherosclerosis can explain the beneficial long-term cardiac outcomes of BITA grafting in dialysis patients. By using two internal thoracic arteries, better survival could be expected if the size of the study were bigger and the follow-up period longer. However, dialysis patients have poor survival, especially having coronary artery disease [23]. It might be difficult to achieve longer duration of follow-up to reach the statistical difference between BITA grafting and SITA grafting with regard to survival.

This study showed no significant difference between the BITA group and the SITA group in the incidence of mediastinitis and hospital death. This finding indicates that BITA grafting can be safely performed in dialysis patients. Our results revealed that ITAs harvested in a skeletonized manner led to a favorable outcome in terms of wound infection compared with ITAs harvested in a pedicled manner, although that was not significantly different (p = 0.10). We believe ITA harvesting in a skeltonized manner is a useful technique to avoid the devastating complication of mediastinitis.

In a previous report of dialysis patients having OPCABG, longevity was significantly worse than it was for patients having on-pump CABG who survived the perioperative period. A possible explanation was the fewer grafts and incomplete revascularization in the off-pump patients due to technical demands [13]. Early studies demonstrated decreased perioperative and long-term survival with incomplete revascularization [24]. In our study, OPCABG was not a risk factor for late death. Eighty-two percent of patients underwent BITA grafting in an OPCABG manner, with an average number of distal anastomoses of 3.7 per patient. We think that even in dialysis patients, revascularization can be done in an OPCABG manner with good anastomosis quality.

We realize that this is a retrospective review of a small number of patients and that the characteristics of the two groups have some differences. A comparative prospective randomized trial is required to validate our results.

In conclusion, there is no difference in terms of hospital deaths and the incidence of mediastinitis between the SITA group and the BITA group. Patients having BITA grafting have better long-term results with regard to cardiac-related events than do patients having SITA grafting. We continue to use BITA for dialysis patients.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 References
 

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