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Division of Cardiac Surgery, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada
Accepted for publication September 28, 2009.
* Address correspondence to Dr Imtiaz Ali, Queen Elizabeth II Health Sciences Centre, 1796 Summer St, Room 2263, Halifax, Nova Scotia, B3H 3A7, Canada (Email: imtiaz.ali{at}dal.ca).
| ADULT CARDIAC SURGERY:
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Abstract |
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Methods: Data were prospectively collected on all first-time isolated CABG and combined valve/CABG with saphenous vein graft between 1998 and 2007 at a single center. Patients having traditional "open" vein harvest (OVH) were compared with patients having EVH. Multivariate models were used to examine the risk-adjusted impact of EVH on postoperative leg infection, composite in-hospital adverse events, and individual and composite midterm adverse events.
Results: The study included 5,825 patients, of whom 2,004 (34.4%) had EVH. Patients having EVH were more likely to have ejection fraction less than 50% (32.0% versus 29.3%, p = 0.04), recent myocardial infarction (24.2% versus 18.3%, p < 0.0001), and left main disease (26.0% versus 22.1%, p = 0.0009). Median follow-up was 2.6 years. After risk adjustment, EVH was associated with reduced rates of leg infection (odds ratio 0.48, p = 0.003) but had no association with either in-hospital (odds ratio 0.93, p = 0.56) or midterm adverse outcomes (hazard ratio 0.93, p = 0.22). Endoscopic saphenous vein harvest was associated with reduced readmission to hospital for unstable angina (odds ratio 0.74, p = 0.01).
Conclusions: Endoscopic saphenous vein harvest is associated with a lower rate of leg infection and is not an independent predictor of in-hospital or midterm adverse outcomes. Endoscopic saphenous vein harvest is a safe alternative to OVH for patients undergoing CABG with saphenous vein.
Autologous saphenous vein remains the most commonly used conduit for coronary artery bypass graft surgery (CABG). Minimally invasive endoscopic vein harvest (EVH) techniques have been developed to decrease vein harvest morbidity. Compared with traditional open vein harvest (OVH), several studies have reported decreased wound related complications, improved patient satisfaction, shorter hospital stay, and reduced postoperative pain at the harvest site with EVH [1-11]. Despite these reported benefits, uptake of EVH among surgeons has been variable. Criticism of this technique centers on the risk of injury at the time of harvest with its potential detrimental effect on vein graft patency and clinical outcomes. While 6-month angiographic patency rates were found to be similar after EVH and OVH [12] and veins harvested by either technique had similar histology [7, 13], analysis of the Project of Ex-Vivo Vein Graft Engineering via Transfection (PREVENT IV) trial demonstrated EVH to be an independent predictor of vein graft failure at 1 year [14, 15], and endothelial injury has been observed after EVH [16].
The midterm safety and efficacy of EVH are unknown. Studies to date have had small sample sizes with limited follow-up and were not adequately powered to assess intermediate-term clinical outcomes. Given the paucity of clinical data available, it was the objective of this study to assess the impact of EVH on short-term and midterm clinical outcomes after CABG. We hypothesized that EVH would lead to reduced graft patency and worse mid-term outcomes.
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Material and Methods |
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Endoscopic Versus Open Saphenous Vein Harvest
Patients undergoing CABG or combined valve/CABG with EVH and OVH were differentiated from each other in the MHCCSR as of the start of the study period. The OVH was performed by either a continuous, longitudinal incision, or through multiple smaller incisions (open, bridging technique) under direct vision. An experienced surgeon or nurse practitioner performed EVH using the Guidant Vasoview system (Boston Scientific, Natick, MA) with sealed carbon dioxide insufflation. The vein was harvested through a subcutaneous tunnel with endoscopic bipolar cautery scissors to divide side branches. Surgeons were at liberty to choose EVH or OVH for each case. Factors influencing their decision may have included availability of equipment and skilled vein harvesting personnel, time constraints, and preconceptions regarding the safety and efficacy of either technique. Patients receiving veins using both EVH and OVH were excluded, and conversions from EVH to OVH were classified as EVH.
Data Collection and Variable Definitions
The MHCCSR is a detailed clinical registry that has prospectively collected perioperative data on all patients undergoing cardiac surgery at the Queen Elizabeth II Health Sciences Centre from March 1, 1995, until the present. For the purposes of tracking midterm survival and readmission to hospital, clinical data from the MHCCSR are linked to administrative data from Vital Statistics and the Canadian Institute for Health Information discharge abstract databases. A subgroup of cases from June 1, 1998, through September 30, 2005, was included in the link to administrative data, allowing a minimum of 6 months of follow-up.
Several baseline demographic and clinical variables were considered: age, sex, body mass index greater than 35, hypertension, diabetes mellitus, dyslipidemia, smoking history (any tobacco use in the past), cerebrovascular disease (history of transient ischemic attack, cerebrovascular accident, cerebrovascular surgery, or carotid disease), peripheral vascular disease (history of aneurysm or occlusive vascular disease, or both), renal insufficiency (preoperative serum creatinine greater than 176 µmol/L [1.99 mg/dL]), chronic obstructive pulmonary disease, ejection fraction less than 50%, recent myocardial infarction (within 21 days preceding surgery), left main disease (more than 50% stenosis), and operative urgency (emergent or urgent versus elective). Intraoperative variables of interest included the number of bypasses, cross-clamp and bypass times, need for an intra-aortic balloon pump, and whether the patient left the operating room on intravenous inotropic therapy.
The short-term outcomes of interest included leg infections (leg incision site opened with excision of tissue, positive wound cultures, or treatment with antibiotics), in-hospital mortality, and a composite outcome consisting of in-hospital mortality, perioperative myocardial infarction (documented by electrocardiogram or biochemical changes), reoperation before discharge from hospital, permanent or disabling stroke, deep sternal wound infection, and sepsis (requires positive blood cultures). The midterm outcomes were all-cause mortality; readmission to hospital for cardiac catheterization, repeat revascularization, unstable angina, myocardial infarction, or heart failure; and a composite outcome consisting of all-cause mortality and readmission to hospital for a cardiac cause.
Statistical Analysis
Patients who underwent CABG or combined valve/CABG surgery with EVH were compared with patients undergoing OVH using t tests and Kruskal-Wallis tests for continuous variables and 
2 tests for categorical variables. The association of clinical characteristics with each outcome was assessed univariately, and relevant variables with 2
p values less than 0.20 were included in fully adjusted multivariable models; additional variables deemed clinically important were included in the models regardless of univariate p value. Logistic regression was used to examine the association of EVH with leg infections and the in-hospital composite outcome after fully adjusting for clinically relevant preoperative variables. Predictive accuracy of each logistic model was assessed by the receiver operating characteristics curve. The association between EVH and the intermediate individual and composite outcomes of interest was analyzed by Cox proportional hazards models fully adjusted for preoperative variables. Observations were censored at the date of last known follow-up, the time of death, or at the time of readmission to hospital for cardiac catheterization, repeat revascularization, unstable angina, myocardial infarction, or heart failure. To assess the proportional hazards assumption, a time-dependent covariate was created for each predictor as a function of survival time, and tests of proportionality were applied. For variables that did not satisfy the assumption of proportional hazards, time-dependent covariates were included in the models.
All analyses were performed using SAS version 8.2 (SAS Institute, Cary, NC). Authors had full access to all data and take responsibility for the integrity of data. All authors have read and agree with the contents of the article as written.
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Results |
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Clinical Characteristics
The baseline characteristics of patients who underwent CABG or combined valve/CABG with EVH or OVH are shown in Table 1. Compared with patients undergoing surgery with OVH, patients undergoing surgery with EVH were more likely to have ejection fraction less than 50% (32.0% versus 29.3%, p = 0.04), recent myocardial infarction (24.2% versus 18.3%, p < 0.0001), left main disease (26.0% versus 22.1%, p = 0.0009), and dyslipidemia (91.1% versus 85.7 %, p < 0.0001). Intraoperatively, patients undergoing CABG with EVH received a slightly greater mean number of distal anastomoses (3.12 versus 2.97, p < 0.0001) and had longer median cross-clamp times (71 versus 66 minutes, p < 0.0001; Table 1).
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Comment |
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Minimally invasive endoscopic harvest techniques are used in 80% of cardiac surgery centers, and the consensus panel of the International Society of Minimally Invasive Cardiothoracic Surgery recommends EVH as the standard of care for patients requiring saphenous vein grafts for coronary revascularization [10]. The short-term benefits of EVH are well documented. A meta-analysis of 11 randomized controlled trials reported a significant reduction in wound infection using an endoscopic technique (OR 0.22, 95% CI: 0.14 to 0.37, p < 0.00001), for a number needed to treat of 14 [3]. The International Society of Minimally Invasive Cardiothoracic Surgery consensus group reviewed 36 randomized and nonrandomized trials and found a 69% reduction in the risk of wound complications by EVH (OR 0.31, 95% CI: 0.23 to 0.41) [11]. Noninfective wound healing disturbances of hematoma, edema, skin necrosis, wound dehiscence, drainage, and seroma are also significantly reduced with EVH [17]. Several studies have demonstrated improved quality of life indices, including postoperative length of stay, time to mobilization, and patient satisfaction [4, 6, 7]. Finally, an economic analysis has reported EVH to be more cost effective than OVH [18].
In contrast to the abundant evidence demonstrating improved short-term and wound-related outcomes after EVH, there is a paucity of data regarding graft patency or clinical outcomes after open or minimally invasive saphenous vein harvest. Yun and colleagues [12] randomized 200 patients to EVH or OVH and reported 6-month overall occlusion rates of 21.7% for EVH and 17.6% for OVH (OR 1.15, p = 0.63). In contrast, the PREVENT IV multicenter CABG trial assessed 1-year patency rates in more than 4,000 saphenous vein grafts and found EVH to be an independent predictor of graft failure as compared with OVH (OR 1.35, p < 0.001) [15]. In this trial, the harvest technique used was left to the discretion of the surgeon, and details regarding the EVH technique were not specified. Macroscopic, histologic, and functional quality of veins harvested by EVH and OVH has been reported. Surgeon-assessed macroscopic quality was reviewed in a meta-analysis of 32 trials, and does not differ between veins harvested by EVH or OVH [19]. Histologic quality as assessed by light and scanning electron microscopy also does not differ between the two techniques [4]. One recent study reported damaged endothelium after EVH; however, the clinical sequelae of these structural and functional changes are unclear [16]. In addition, the majority of studies examining the functional characteristics of venous grafts, including cytokine levels, expression of adhesion molecules, vascular reactivity, and endothelial function found no difference between open and endoscopic techniques [20-24]. Along with potential injury to the vessel wall at the time of harvest, Brown and colleagues [25] observed that residual luminal clot is common if EVH is performed without systemic heparinization therapy, or with sealed carbon dioxide insufflation.
The clinical impact of these observations remains to be determined. Five-year freedom from death, myocardial infarction, or recurrent angina has been reported by Allen and colleagues [26] and was similar between the two groups (75% versus 74%, p = 0.85); however, the number of patients in each group of this randomized study was small (EVH, n = 54; OVH, n = 58). More recently, in a secondary analysis of the PREVENT IV trial, Lopes and colleagues [14] found an association of EVH with higher rates of vein graft failure and adverse clinical outcomes including higher mortality. The purpose of the trial was to assess ex vivo treatment of vein grafts with the E2F transcription factor decoy, edifoligide. It was conducted at 107 sites between 2002 and 2003, and the percentage of cases performed with EVH differed greatly across centers. The variability in experience levels and technique between centers and the overall low number of cases per institution should be considered when interpreting these findings. Despite the lack of angiographic data in our study, we included all patients undergoing CABG with a vein graft at a single institution during the study period.
In this study, we found no association between EVH and midterm freedom from death, and/or readmission to hospital for cardiac catheterization, repeat revascularization, acute coronary syndromes, or heart failure. We did find an association of EVH with reduced readmission to hospital for unstable angina and a trend towards improved freedom from the composite outcome. Although these observations are interesting, there is little biological rationale for improved outcomes after EVH, and the presence of unmeasured confounders may account for these findings. It is reassuring, however, that there is no trend towards harm and suggests that although subtle changes to the venous conduit may be identified after endoscopic harvest, these may not translate to clinically relevant adverse outcomes.
This study has certain limitations. Despite considering a wide array of clinical predictors of EVH in our analyses, our study was observational in nature, thus allowing for bias from unmeasured confounders. In addition, the decision to use endoscopic or open technique was largely dependent on surgeon's preference and the availability of trained assistants facile with the EVH technique. This may have introduced a selection bias as to which patients received a particular harvest technique. Finally, the lack of angiographic patency data should be noted, as a difference in graft patency may clinically manifest later than the duration of our study. We were reassured, however, by a hazard ratio of 0.93 and no evidence of divergence of the event-free survival curves in Figure 2. Despite these limitations, this study provides valuable data that have been largely lacking regarding the midterm safety of EVH. Further studies reporting 5- and 10-year clinical outcomes are necessary.
In conclusion, patients undergoing CABG or combined valve/CABG surgery with EVH presented with worse systolic function and more recent myocardial infarction. After adjusting for baseline differences, no independent association between EVH and short-term or midterm adverse outcomes was found. Endoscopic saphenous vein harvest was associated with reduced readmission to hospital for acute coronary syndromes. Consistent with previous reports, EVH was found to be protective against postoperative leg wound infections. Endoscopic saphenous vein harvest is a safe alternative to OVH for patients undergoing CABG with saphenous vein.
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M. Ouzounian, K. J. Buth, and I. S. Ali Reply Ann. Thorac. Surg., November 1, 2010; 90(5): 1744 - 1744. [Full Text] [PDF]
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M. Ouzounian, K. J. Buth, and I. S. Ali Reply Ann. Thorac. Surg., November 1, 2010; 90(5): 1743 - 1743. [Full Text] [PDF]
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