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Interact CardioVasc Thorac Surg 2009;8:325-329. doi:10.1510/icvts.2008.195511 © 2009 European Association of Cardio-Thoracic Surgery
Comparison of graft patency for off-pump and conventional coronary arterial bypass grafting using 64-slice multidetector spiral computed tomography angiography
a Department of Cardiovascular Surgery, PLA General Hospital, PLA Institute of Cardiac Surgery, China Received 30 September 2008; received in revised form 29 October 2008; accepted 3 November 2008
*Corresponding author. 28 Fuxing Rd, Haidian District, Beijing 100853, China. Tel.: +86 10 88626988; fax: +86 10 88626988.
Off-pump coronary artery bypass graft surgery (OPCAB) has been performed for many years and its use is increasing frequently, but it remains an open question whether OPCAB provides similar patency to conventional coronary artery bypass graft (CCABG) surgery with cardiopulmonary bypass. The present study assessed the graft patency in patients that had coronary arterial bypass grafting (CABG) performed on-pump and off-pump. A total of 237 patients with CABG performed by a single surgeon were retrospectively studied, in which 100 patients underwent CCABG and 137 patients underwent OPCAB; the two groups were well matched according to relative factors and no significant differences were found in both groups. Postoperatively, systematic assessment on the graft patency of all the patients was conducted with 64-slice multidetector spiral computed tomography angiography (MSCTA) at one month, 1 year, 2 years, 3 years and 4 years, respectively, to provide 641 grafts for analysis. Patency of left internal mammary artery (LIMA) was higher than that of saphenous vein (SVG) in both groups; no significant difference was seen in LIMA patency and SVG patency in both groups. Results of 64-slice MSCTA indicate that OPCAB provides similar patency to CCABG surgery with CPB.
Key Words: CABG; Graft patency; Multidetector spiral computed tomography
The success of coronary artery bypass grafting (CABG) is dependent on the long-term patency of the arterial and venous grafts [1]. Off-pump coronary artery bypass graft surgery (OPCAB) has been performed for many years and its use is increasing frequently, but it remains an open question whether OPCAB provides similar patency to conventional coronary artery bypass graft (CCABG) surgery with cardiopulmonary bypass (CPB). This is the most hotly debated and polarizing issue to date in cardiac surgery [2–5]. Recent studies showed that 64-slice multidetector spiral computed tomography (MSCT) provides high diagnostic accuracy, sensitivity and specificity for the assessment of graft patency and native coronary arteries for the presence of stenosis [6, 7]. Graft patency for OPCAB varied greatly with different surgeons [4]. Only a few researchers reported the graft patency for OPCAB vs. CCABG performed by the same surgeon [8, 9]. This study presents a retrospective comparison of graft patency of conventional versus off-pump CABG using MSCT in a single surgeon's experience.
2.1. Patients' characteristics From January 2002 to August 2006, a total of 779 patients underwent isolated primary CABG surgeries completed by a single experienced surgeon (Prof. Gao CQ) [9], who has performed more than 1000 cases of OPCAB surgery with a single surgical team at the Department of Cardiovascular Surgery, the PLA General Hospital, Beijing. In this study, 100 CCABG patients were randomized according to the operation years as control group; the 137 patients of the OPCAB group were matched with the CCABG group during the same periods. Clinical data of the patients are shown in Table 1. No significant differences were found in both groups.
2.2. Surgical techniques All patients were intubated with general anesthesia. Both an arterial line and central venous catheter were established routinely. The median sternotomy was performed in both groups in standardized fashion as previously described [9]. The pedicle left internal mammary artery (LIMA) was harvested regularly with extrapleural technique, and the great saphenous vein (SV) was prepared simultaneously under direct vision. CCABG and off-pump procedures were described in previous studies [9]. In patients of both groups, graft flow was measured intraoperatively using a Medi-Stim Butterfly Flowmeter (Medi-Stim ASA, Oslo, Norway). Postoperatively, antiplatelet therapy (aspirin, 100 mg daily) was received routinely for life by all CABG patients; aggressive lowering of cholesterol therapy was received by patients in need. 2.3. MSCT coronary angiography CT coronary angiography was performed with the latest 64-slice CT-scanner (Siemens Somatom Sensation Cardiac 64, Germany) using the following scan parameters: 330 ms gantry rotation time, detector collimation 0.6 mm. Electrocardiographic gated tube current modulation was applied in all patients. After region of interest placement in the ascending aorta, patient circulation time was determined using a test bolus of 20 ml contrast agent (Ultravist 370) at a flow rate of 4.5–5.0 ml/s and a saline chaser bolus of 40 ml at a flow rate of 4 ml/s using a dual-head power injector. For coronary angiography, 65–80 ml contrast agent was injected in an antecubital vein via an 18-gauge catheter at a flow rate of 5 ml/s, followed by 60 ml of saline. Image reconstructions of the raw data were performed and evaluated using 3 mm thin-slab maximum intensity projections (MIP), curved multiplanar reconstructions (cMPR), and volume-rendering techniques (VRT) on a post-processing workstation (Volume Wizard, Siemens Medical Solutions, Germany).Patency of each distal anastomosis was referred to Fitzgibbon et al. [10]. The duration of graft life was calculated from the operation time to last time when the graft showed patency or when the graft was found to be occluded. After the operation, all 237 patients, including the patients with recurrent symptoms, underwent systematic MSCT angiography at 1 month, 1 year, 2 years, 3 years and 4 years, respectively, several patients underwent multiple MSCT scans. MSCT data were analyzed by two radiologists and one cardiac surgeon together. The graft patency was assessed not only at the anastomotic site, but along the main body of the graft as well. SAS 8.2 was adopted for statistical analysis. Univariable comparisons in both groups were done with a standard Pearson 2-test, a non-paired t-test, rank-sum test, or a one-way analysis of variance as appropriate. P-value <0.05 was regarded as statistically significant. The data were presented as time-based occlusion rates in which occlusion was defined in two ways. Graft life was calculated by using interval-censored observations: If a patient had only one MSCT angiogram and this showed an occluded graft, the time between the date of the CABG and the date of angiography was used as the occlusion occurrence interval. If a patient had multiple angiograms, the time between the date of the most recent angiogram that showed a patent graft and the date of the angiogram that showed occlusion was used as the occlusion occurrence interval. The date of the latest angiogram was used as the right censored time for grafts, which remained patent. During follow-up, no patient died in this study.
3.1. Patients' characteristics and operative data Baseline clinical data were similar in patients of both OPCAB and CCABG groups, but fewer grafts per patient were performed in OPCAB group than in CCABG (2.47 vs. 3.01, P=0.0001), because fewer SVG per patient were performed in OPCAB than in CCABG (1.45 vs. 2.06, P=0.002) (Table 1). 3.2. MSCT angiographic outcomes After operation, overall 237 patients, including the patients with recurrent symptoms, underwent systematic MSCT angiography at 1 month, 1 year, 2 years, 3 years and 4 years, respectively, to provide 641 grafts for analysis. The number of occluded grafts is listed in parentheses in Table 2 right after the total number of grafts to each particular target coronary artery of the heart. In total, 32 of 304 (10.5%) grafts were occluded in the CCABG group, and 36 of 337 (10.7%) grafts were occluded in the OPCAB group.
3.3. Comparison of graft patency Sixty-eight grafts were occluded in 57 patients of the two groups, graft patency of LIMA and SVG were calculated respectively, and time-related graft patency curve was drawn by Life Table analysis. Radial artery patency was not calculated due to the few grafts. Thirty-six occluded grafts in OPCAB group were composed of seven LIMA, two radial arteries and 27 SVG. The patency of both LIMA and SVG decreased as postoperative time increased, but the latter decreased more quickly than the former, the significant difference was proved by two-sample log-rank test, QPH=4.408, P=0.036 (Fig. 1).
Thirty-two grafts were occluded in CCABG group (6 LIMA, 1 radial artery and 25 SVG). The time-related patency of the two grafts (LIMA and SVG) decreased as time went by, LIMA patency was higher than SVG patency, the results of two-sample log-rank test showed significant difference, QPH=3.776, P=0.048 (Fig. 2).
A two-sided log-rank test was used to compare LIMA patency for both OPCAB and CCABG groups: QPH=0.093, P=0.7603; the same method was used to compare SVG patency for both groups: QPH=0.313, P=0.5756. Both LIMA and SVG patencies were not significantly different in OPCAB and CCABG groups.
LIMA and SVG patencies after operation at five time-plots were calculated and a comparison analysis was done by
Further patency comparison between OPCAB and CCABG was carried out according to the target vessel territories: LAD, LCX and RCA. LAD comprised anastomoses on left anterior descending artery, diagonal branch and intermediate branch; LCX comprised anastomoses on left circumflex coronary and obtuse marginal artery; RCA was composed of anastomoses on right coronary, acute margin, posterior descending artery and left ventricular branch artery. 2-Test showed no significant difference between the two procedures (Figs. 3–5 ).
CABG is performed around the world as a means to treat myocardial ischemia. For evaluation of graft patency, conventional coronary angiography remains the gold standard; however, limitations of this procedure include a small but definable risk, the need for multiple staff members, and the cost related to the procedure itself and subsequent observational period. Because of this, alternative non-invasive methods have been investigated for imaging of venous and arterial graft patency. Many studies show that 64-slice MSCT provides high diagnostic accuracy, sensitivity and specificity for the assessment of graft patency and native coronary arteries for the presence of stenosis [6, 7]. Our study has found that 64-slice MSCT is compatible with conventional coronary angiography for the assessment of graft patency as well [6]. We retrospectively studied the graft patency of matched patients with CCABG and OPCAB which were performed by a single surgeon so that outcome could be least affected. One hundred and thirty-seven OPCAB patients and 100 CCABG patients were retrospectively studied, but the clinical characteristics were well matched for the two groups. In our study, patency of LIMA was higher than that of SVG in both OPCAB and CCABG groups. Four years after operation, LIMA patency in both groups remained higher than 94%. It is generally consented that arterial conduits have a better long-term patency [1, 11]. In fact, the LIMA has been proclaimed the graft of choice to bypass the LAD because of its excellent long-term patency [1].
Comparison of graft patency between the two groups showed similar patency rate not only for LIMA but also for SVG, results of log-rank test and In our study, LIMA patency was similar to those recorded in previous literatures [11], however, SVG patency was higher than those recorded in previous literatures in both groups [11]. The SVG patency for OPCAB was 98.5% at 1 month, 95.3% at 1 year, 93.3% at 2 years, 90.6% at 3 years, and 88.4% at 4 years, respectively. The SVG patency for CCABG was 99.5% at 1 month, 95.9% at 1 year, 94.1% at 2 years, 91.4% at 3 years, and 89.3% at 4 years, respectively (Table 3). We agree that surgeon experience may be the key to best outcome for OPCAB surgeries [13]. For example, we have never used silicon rubber tapes for the distal anastomoses to avoid injuring the target vessels. Our study showed that fewer grafts were performed in OPCAB group than in CCABG group (2.47 vs. 3.01, P=0.0001), because fewer SVG per patient were performed in OPCAB than in CCABG (1.45 vs. 2.06, P=0.002) (Table 1). Similar results were seen in two prospective randomized researches [14, 15]. Potential bias in patient selection and management has existed. This study was not a randomized controlled trial of patients for CABG; however, our findings are supported by many of the trials published to date and appear consistent over time. It is necessary to point out that the distal anastomosis of a graft is often obscured by stitches or clips causing substantial image noise on CTA. We assessed graft patency not only at the anastomotic site, but along the main body of the graft as well for the purpose of achieving an overall assessment. Although OPCAB surgery has not become the standard of care, it remains desirable for surgeons and trainees alike to continue to learn and maintain their skills to explore the role of OPCAB surgery in selected patients. An important limitation of our study is that 64-MSCT cardiac angiography was not accepted widely to assess the graft patency, but some previous studies had showed compellent evidences. Another potential limitation is that the surgeon performed more off-pump than on-pump surgeries; this may bias the patency results in favor of off-pump.In conclusion, our study shows that there is no significant difference in LIMA patency and SVG patency for CCABG and OPCAB groups. However, the number of grafts is smaller in OPCAB group than that in CCABG group. Results of 64-slice MSCT angiography indicate that OPCAB provides similar patency to CCABG surgery with CPB. Further studies need to be done on the assessment of bypass graft patency using 64-slice MSCT.
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Abstract
1. Introduction
