Eur J Cardiothorac Surg 2007;32:718-723. doi:10.1016/j.ejcts.2007.08.001
Copyright © 2007, European Association for Cardio-thoracic Surgery. Published by Elsevier. All rights reserved.
Influence of vein graft use on postoperative 1-year results after off-pump coronary artery bypass surgery
Kwang Ree Choa,
Dong Seop Jeongb,
Ki-Bong Kimb,*
a Department of Thoracic and Cardiovascular Surgery, Halla General Hospital, Jeju-City, Jeju-Do, Korea
b Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital, Seoul, Korea
Received 14 May 2007;
received in revised form 27 July 2007;
accepted 1 August 2007.
* Corresponding author. Address: Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital, 28, Yeongeon-dong, Jongno-gu, Seoul 110-744, Korea. Tel.: +82 2 2072 3482; fax: +82 2 747 5245. (Email: kimkb{at}snu.ac.kr).
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Abstract
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Objective: We studied the postoperative 1-year results after off-pump coronary artery bypass surgery (OPCAB) with one or more saphenous vein grafts. Methods: We compared the clinical and angiographic results of 833 patients who underwent OPCAB between 1998 and 2004. Group 1 patients (n
= 135) received one or more vein grafts. Group 2 patients (n
= 698) received total arterial grafts. Coronary angiographies were performed early postoperatively (n
= 804, 1.6 ± 1.5 days), and 1 year postoperatively (n
= 671, 12.1 ± 4.2 months). Results: There were no significant differences in patient characteristics, operative mortalities, and morbidities between the two groups (p
= ns). Both the early postoperative and 1-year angiographies demonstrated significantly lower overall graft patency rates in group 1 than in group 2 (early: 90.9% vs 99.1%, p
< 0.001; 1 year: 78.8% vs 95.1%, p
< 0.001), which might be affected by the lower vein graft patency rates in group 1 (early: 86.4%; 1 year: 67.9%). There was no difference in the 1-year patency of internal thoracic arteries between the two groups (94.3% vs 95.6%, p
= 0.402). Multivariate analysis demonstrated the use of vein graft (Odds ratio = 5.204, p
< 0.001) as an independent predictor of graft failure during the first postoperative year. Target vessel revascularization rate during the postoperative 1 year was significantly higher in group 1 than in group 2 (7.4% vs 2.0%, p
= 0.002). Conclusions: Our study revealed that saphenous vein graft use in OPCAB independently predicted the graft failure while increasing the target vessel revascularization rate during the first postoperative year. Exclusive arterial revascularization would be a preferable strategy in OPCAB.
Key Words: Coronary artery bypass grafting • Off-pump CABG • Graft patency
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1. Introduction
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The surgical results of coronary artery bypass grafting (CABG) have demonstrated that the long-term patency of a saphenous vein graft is lower than that of an internal thoracic artery (ITA) graft [1,2]. However, the saphenous vein graft is still the most widely used graft because of its accessibility and ease of use. With resurgent interest in off-pump coronary artery bypass surgery (OPCAB), a favorable composite of death, stroke, and myocardial infarction was demonstrated in patients undergoing OPCAB [3]. With regard to graft patency, however, patients undergoing OPCAB demonstrated a lower graft patency than patients undergoing conventional CABG [4,5], and concerns have been raised about the further lowered patency of saphenous vein grafts in patients undergoing OPCAB compared with patients undergoing conventional CABG [6,7].
The aims of this study were: (1) to compare the clinical and angiographic results of the OPCAB patients who received saphenous vein grafts with those who received arterial grafts, based on the postoperative early and 1-year follow-up angiographies, and (2) to elucidate the predictors for graft failure during the first postoperative year after OPCAB.
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2. Materials and methods
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2.1 Patients
Of the 962 patients who underwent isolated CABG between January 1998 and December 2004, 833 patients who underwent OPCAB were studied. We compared the clinical and angiographic results of 135 patients who received one or more saphenous vein grafts (group 1) with those of 698 patients who received total arterial grafts (group 2). There were no differences between the two groups in terms of age, preoperative risk factors, ratio of unstable to stable angina, and urgent or emergent operations. The proportion of female gender was a little higher in group 1 (Table 1
). A computer-based patient database system was used for this retrospective analysis. The study protocol was reviewed by the Institutional Review Board and approved as a minimal-risk retrospective study (Approval Number; H-0603-042-170) that did not require individual consent based on the institutional guidelines for waiving consent.
2.2 Surgical technique
The basic surgical procedures and principles of OPCAB have been previously described [8].
The grafts used for distal anastomoses in 833 patients were left ITA (n
= 797), right ITA (n
= 538), right gastroepiploic artery (n
= 420), radial artery (n
= 15), and saphenous vein (n
= 135). To increase the length of graft, composite graft was constructed as a Y-fashion (n
= 480; free arterial graft to in-situ arterial graft in 471, saphenous vein to in-situ arterial graft in 7, and free arterial graft to saphenous vein graft in 2) or I-fashion (n
= 73; free arterial graft to in-situ arterial graft in 67 and saphenous vein graft to in-situ arterial graft in 6). Of the total 2427 distal anastomoses, 448 side-to-side sequential anastomoses (417 arterial and 31 venous) were performed. Sequential anastomoses were performed 12.5% and 19.8% of distal anastomoses in groups 1 and 2, respectively (p
= 0.001). The average number of distal anastomoses per patient was 2.9 ± 1.0. When the coronary arteries were classified as anterior (left anterior descending artery, diagonal branches, ramus intermedius, and proximal or middle right coronary artery), posterior (obtuse marginal branches), and inferior (distal right coronary artery, posterior descending artery, and posterolateral branches) according to their location, the anastomotic proportions of territory in each group were similar between the two groups (anterior, 53.9% vs 54.2%; posterior, 24.1% vs 27.2%; inferior, 22.0% vs 18.8%; p
= ns).
During the study period, we changed revascularization strategies based on our early patency study after OPCAB [7]: (1) we tried to perform total arterial revascularization and avoided the use of vein graft if possible, (2) a skeletonized technique for harvesting the arterial graft was used, (3) protamine was not given at the end of the procedure, and (4) we revised the abnormal graft intraoperatively since the introduction of transit time flow measurement (BF1001, Medi-Stim AS, Oslo, Norway) [9].
The patients were given heparin with an initial dose of 1.5 mg/kg of heparin and periodically received supplemental doses to maintain an activated clotting time of more than 300 s.
All patients stopped taking aspirin the day before surgery and resumed aspirin (200–300 mg/day) beginning 1 day postoperatively. Ticlopidine hydrochloride (200 mg/day) was used simultaneously with aspirin for the early postoperative 2 months. If the patient had a high blood low-density lipoprotein cholesterol level (>100 mg/dl) postoperatively, drug therapy was started.
2.3 Angiographic evaluation
Early postoperative (postoperative day 1.6 ± 1.5) and 1-year (postoperative month 12.1 ± 4.2) angiographies were performed in 96.5% (804 of 833) and 80.6% (671 of 833) of the patients, respectively, regardless of the patient's anginal symptom. Patients who died, refused angiographic evaluation, or had renal function impairment (serum creatinine >1.5 mg/dl) were excluded from the angiographic follow-up. Patients with renal replacement therapy were included in the angiographic follow-up. Follow-up coronary angiography included four-plane selective coronary and bypass graft angiography. One physician initially reviewed all the coronary angiograms, and consensus was reached after review. Graft patency was graded as described by FitzGibbon et al. (grade A = excellent; grade B = fair; grade A + B = patent; grade O = occluded) [10]. Target vessel revascularization was defined as percutaneous coronary intervention of the target lesion or another segment within the same vessel because of the presence of 75% or greater stenosis, as measured by the follow-up angiography. The target lesion was defined as the surgically bypassed segment.
2.4 Statistical analysis
Statistical analysis was performed with the SPSS software package (version 11.0, SPSS Inc., Chicago, IL). Comparison between the two groups was performed using the unpaired Student's t-test for continuous variables, and using the 
2-test (Pearson
2 and Fisher exact tests) for categorical variables. Multivariate logistic regression analysis was carried out to define the predictors for graft failure. All results were expressed as mean ± standard deviation or as proportions, and a value of p
< 0.05 was considered as statistically significant.
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3. Results
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3.1 Clinical results
In-hospital mortalities were 2.2% (3 of 135) in group 1 and 1.6% (11 of 698) in group 2 (p
= 0.484). There were no significant differences in the incidence of postoperative morbidities such as atrial fibrillation, perioperative myocardial infarction, acute renal failure, reoperation for bleeding, mediastinitis, and stroke between the two groups (Table 2
).
3.2 Immediate postoperative and 1-year angiographies
Postoperative early angiographies demonstrated a 90.9% overall graft patency rate (FitzGibbon grade A + B) in group 1 and 99.1% in group 2 (p
< 0.001). The ITA graft showed an excellent patency rate in both groups 1 and 2, even though the ITA graft patency in group 1 was slightly lower than in group 2 (97.1% vs 99.1%, p
= 0.038). There was no significant difference in the right gastroepiploic artery graft patency rate between the two groups (90.9% vs 98.9%, p
= 0.132). The saphenous vein graft in group 1 showed an 86.4% patency rate (Table 3
).
Postoperative 1-year angiographies demonstrated a 78.8% overall graft patency rate in group 1 and 95.0% in group 2 (p
< 0.001). There was no significant difference in the internal thoracic artery graft patency rate between the two groups (94.3% vs 95.6%, p
= 0.402). The right gastroepiploic artery graft showed a 72.2% (8 of 11) patency rate in group 1 and 92.7% (332 of 358) in group 2 (p
= 0.047). The saphenous vein graft in group 1 showed a 67.9% patency rate (Table 4
).
The proportion of the FitzGibbon grade A and O patency rates of grafts was significantly different between the two groups (p
< 0.001); however, the proportion of the FitzGibbon grade B patency rates of grafts was not different between the two groups at both the early postoperative and 1-year follow-up angiographies (p
= ns). The patency rates of the arterial grafts were significantly higher than those of the vein grafts at both the early postoperative (86.4%, 210 of 243 vs 98.9%, 2081 of 2105; p
< 0.001) and 1-year follow-up angiographies (67.9%, 148 of 218 vs 94.9%, 1678 of 1769; p
< 0.001).
When the study patients were divided into two groups (early: 1998–1999, n
= 158 vs late: 2000–2003, n
= 675) based on the changes of revascularization strategy that happened between the latter half of 1999 and the first half of 2000, patency rates of overall grafts and ITA graft in the latter period were significantly improved in 1 year as well as early postoperatively (p
< 0.001). However, patency rate of saphenous vein was not improved even after the changes of revascularization strategy (85.7% vs 90.0% at early; 67.0% vs 73.3% at 1 year; p
= ns) (Table 5
).
3.3 Risk factor for graft occlusion
Of the 811 patients who underwent angiographies postoperatively (early postoperative or 1-year angiographies, or both), occlusion of more than one graft was observed in 132 patients (occluded group). Univariate analysis demonstrated higher saphenous vein graft use, lower right gastroepiploic artery graft use, and early experience (1998–1999) in the occluded group than in the patent group. Multivariate logistic regression analysis defined the use of vein graft (Odds ratio = 5.204, p
< 0.001) as an independent predictor of graft failure during the first postoperative year after OPCAB (Table 6
).
3.4 Target vessel revascularization
Twenty-four patients of 819 survivors underwent target vessel revascularization during the first postoperative year. The rate of target vessel revascularization in group 1 was significantly higher than in group 2 (7.4%, 10 of 135 vs 2.0%, 14 of 698; p
= 0.002). Four of 10 target vessel revascularizations in group 1 were related to vein graft occlusion, whereas 1 of 14 target vessel revascularizations in group 2 was related to arterial graft occlusion. The remaining revascularizations were related to progression of native coronary disease.
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4. Discussion
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The present study revealed four main findings. First, the group of OPCAB patients who received vein grafts demonstrated significantly lower overall graft patency rates than patients who received total arterial grafts in both the early and postoperative 1-year angiographies. Second, vein graft use was an independent predictor for graft failure during the first year after OPCAB. Third, the target vessel revascularization rate during the first postoperative year was significantly higher in patients who underwent OPCAB using vein grafts than in those who underwent total arterial OPCAB.
Patients undergoing OPCAB revealed a lower graft patency than did patients undergoing conventional CABG in a meta-analysis of seven randomized trials [4]. A significantly lowered patency for saphenous vein grafts than for internal thoracic artery grafts was suggested to result from the type of graft, presence of hyperlipidemia, the exposure and quality of stabilization, and increased procoagulant activity in OPCAB patients [6,11]. Although some studies demonstrated similar early vein graft patencies between OPCAB and conventional CABG [12–14], other meta-analysis using five randomized studies showed that OPCAB significantly increased the risk of graft failure, with the odds of graft occlusion 51% higher within the first postoperative year [5]. Those differences were mainly attributable to the lower saphenous vein or radial artery graft patency rate. When the use of vein grafts was minimized, OPCAB showed comparable early graft patency with on-pump CABG [15]. The present study demonstrated significantly lower overall graft patency rates in patients who received vein grafts than in patients who received total arterial grafts, which might be affected by the lower vein graft patency rates in the vein graft group. The arterial grafts showed excellent patency rates in both groups, even though the ITA graft patency in group 1 was a little lower than that in group 2 in the postoperative early angiographies (97.1% vs 99.1%, p
= 0.038). The difference of ITA graft patency in the postoperative early angiographies might be attributed to the retrospective study of non-concurrent group of patients who underwent operations at different points.
During the study period, we changed revascularization strategies based on our early patency study after OPCAB [7]: (1) since the latter half of 1999, we tried to perform total arterial revascularization and avoided the use of vein graft if possible; one hundred of the 135 patients who received vein grafts (74.1%) underwent OPCAB before 2000, while 91.7% (640 of 698) of the patients who received total arterial grafts underwent OPCAB after 2000, (2) a skeletonized technique for harvesting the arterial graft was used since September 1999, (3) protamine was not given at the end of the procedure since November 1999, and (4) we derived the criteria to predict abnormal grafts (occluded or competitive grafts) [9] and revised the abnormal graft intraoperatively since the introduction of transit time flow measurement at our institute in 2000. The revision rate was approximately 2% (2 of 100 anastomoses), and those revisions in the latter part of this study period would affect the small difference in early postoperative arterial graft patency rates between the groups 1 and 2. When the study patients were divided into two groups (1998–1999 vs 2000–2003) based on the major changes of revascularization strategy, patency rates of overall grafts and ITA graft in the latter period were significantly improved in 1 year as well as early postoperatively. The improved patency rates of the latter period might be affected by the significantly improved patency rates of the ITA graft. Although univariate analysis demonstrated early experience before the changes of revascularization strategy as a risk factor for graft occlusion, multivariate logistic regression analysis failed to demonstrate it as an independent predictor during the first postoperative year after OPCAB.
The present study demonstrated the vein graft use as an independent predictor of graft failure during the first postoperative year, which might be an important guideline to the grafting strategies in OPCAB. The internal thoracic artery graft demonstrated excellent patency rates similar to previous studies. Increased procoagulant activity in the first 24 h after OPCAB was demonstrated as a possible cause of decreased vein graft patency rates [6]. Aspirin resistance was suggested as another cause of early vein graft thrombosis after OPCAB. As many as 30% of patients have been shown to develop aspirin resistance by the third postoperative day, and only recovering to normal levels at 30 days after OPCAB [16]. Although we failed to define the exact timing of vein graft occlusion during the first postoperative year, the early postoperative period (<30 days) would be a critical period for vein graft occlusion after OPCAB. A meticulous harvesting technique to avoid endothelial damage and introduction of a potent antiplatelet agent were suggested to decrease early vein graft occlusion [16,17]. Combined use of another antiplatelet agent such as ticlopidine hydrochloride with aspirin was suggested to potentiate aspirin's effect and to prolong the bleeding time more than with either drug independently [18]. In the present study, ticlopidine hydrochloride (200 mg/day) was used simultaneously with aspirin for the early postoperative 2 months. We suggest the combination of a potent antiplatelet agent with aspirin in the early postoperative period when performing the OPCAB using vein grafts.
Along with the lower vein graft patency, the present study demonstrated that the target vessel revascularization rate after OPCAB increased with the use of saphenous vein grafts. The rate of target vessel revascularization was significantly higher in the vein graft group than in the total arterial graft group. Forty percent of the interventions in group 1 were related to the vein graft disease; however, only 1 of 14 target vessel revascularizations in group 2 was related to arterial graft occlusion. The majority of interventions in the total arterial graft group were performed for progressed native coronary disease rather than problems with the graft or anastomotic site.
There are limitations to the present study that must be recognized. First, the present study was not performed in a randomized manner with regard to the type of conduits and the target vessels, and the majority of vein grafts were used to revascularize the left circumflex artery or right coronary artery territories rather than the left anterior descending artery territory. These might serve as confounding variables. Second, we changed the revascularization strategies during the study period. A majority of patients who received vein grafts underwent OPCAB in the early study period and most patients who received total arterial grafts underwent OPCAB in the latter part of the study period, which would affect the difference between the two groups.
In conclusion, our study revealed that vein graft use independently predicted graft failure and increased the rate of target vessel revascularization during the first year after OPCAB. We suggest performing OPCAB using arterial graft exclusively to avoid the low patency rate and sequelae of vein graft occlusion.
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Abstract
1. Introduction
