|
| HOME | SUBSCRIPTIONS | CURRENT ISSUE | PAST ISSUES | CARDIOSOURCE | SEARCH | HELP | FEEDBACK |
|
|
|
|||||||||
|
|||||||||||
|
J Am Coll Cardiol, 2004; 44:2149-2156, doi:10.1016/j.jacc.2004.08.064 © 2004 by the American College of Cardiology Foundation |
* Southern Arizona VA Health Care System and the University of Arizona Sarver Heart Center, Tucson, Arizona
VA Cooperative Studies Program Coordinating Center, Hines, Illinois
Manuscript received May 6, 2004; revised manuscript received August 16, 2004, accepted August 25, 2004.
* Reprint requests and correspondence: Dr. Steven Goldman, Cardiology Section (1-111C), Southern Arizona VA Health Care System, 3601 South 6th Avenue, Tucson, Arizona 85723 (Email: steven.goldman{at}med.va.gov).
 |
Abstract |
|---|
 Top Abstract MethodsResultsDiscussionAppendixReferences |
|---|
BACKGROUND: This VA Cooperative Studies Trial defined 10-year SVG patency in 1,074 patients and left IMA patency in 457 patients undergoing coronary artery bypass grafting (CABG).
METHODS: Patients underwent cardiac catheterizations at 1 week and 1, 3, 6, and 10 years after CABG.
RESULTS: Patency at 10 years was 61% for SVGs compared with 85% for IMA grafts (p < 0.001). If a SVG or IMA graft was patent at 1 week, that graft had a 68% and 88% chance, respectively, of being patent at 10 years. The SVG patency to the left anterior descending artery (LAD) (69%) was better (p < 0.001) than to the right coronary artery (56%), or circumflex (58%). Recipient vessel size was a significant predictor of graft patency, in vessels >2.0 mm in diameter SVG patency was 88% versus 55% in vessels 
2.0 mm (p < 0.001). Other positive significant predictors of graft patency were use of aspirin after bypass, older age, lower serum cholesterol, and lowest Canadian Functional Class (p < 0.001 to 0.058).
CONCLUSIONS: The 10-year patency of IMA grafts is better than SVGs. The 10-year patency for SVGs is better and the 10-year patency for IMA grafts is worse than expected. The 10-year patency of SVGs to the LAD is better than that to the right or circumflex. The best long-term predictors of SVG graft patency are grafting into the LAD and grafting into a vessel that is >2.0 mm in diameter.
| ||||||||
|
Methods |
|---|
|
TopAbstractMethodsResultsDiscussionAppendixReferences |
|---|
Surgery. Coronary artery bypass grafting was done in a standard fashion as previously described (8–12). The decision to use arterial or venous conduits was made by the attending surgeon. The patient was eligible for the trial only if the determination was made preoperatively to utilize at least one SVG.
Angiographic analysis. The angiographic analysis was identical to our earlier trials (8–12). Briefly, the left IMA and each aortic anastomosis were selectively engaged and injected. When the status of a vein graft could not be determined by graft or stump injection, an aortic root angiogram was performed. Selective angiography of the native coronary arteries was performed during the one-week and one-year catheterization only when a graft was occluded. Selective angiography of the native coronary arteries was routinely performed at the 3-year and 10-year catheterization. Graft patency and stenosis were defined in a central angiographic laboratory with a computer-based system (8–12). The data are presented as time-based occlusion rates where occlusion is defined in two ways. The primary event of interest is 100% stenosis (Figs. 1 to 4). The secondary event is 50% to 99% stenosis, not including vessels totally occluded (Fig. 5). Because of long-term follow-up and the study group being composed of middle-aged men with coronary artery disease, some patients died before the completion of the study. We obtained autopsies in as many patients as possible and included the autopsy patency data in our analysis.
|
|
The data from this study posed two major analytic problems. The first problem was that the exact time of graft occlusion could not be known. We addressed this by using interval-censored observations in the survival analysis (PROC LIFETEST in SAS [SAS Institute Inc. SAS/STAT Version 8, Cary, North Carolina]). This analysis requires identification of the time interval in which the occlusion occurred. If a patient had only one angiogram and this showed an occluded graft, the time between the date of the CABG and 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 graft was patent 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. For patients who had patency data from an autopsy, the date of death was used. If there was an intervention on a stenotic but still patent graft by either percutaneous coronary intervention or repeat surgical revascularization, the graft was right censored on the date of the angiogram and no further data were collected for that graft. Comparisons of Kaplan-Meier product-limit survival curves were made with the log-rank test.
Although time-related analyses of graft patency data used the exact date of each postoperative angiogram, for convenience of presentation, some information is presented in arbitrarily defined time frames. The 1-week data included catheterizations performed between 1 and 60 days post-operation, the 1-year included catheterizations performed between 61 days and 1.5 years post-operation, the 3-year included catheterizations after 1.5 to 4.5 years post-operation, the 6-year included catheterizations after 4.5 up to 8 years post-operation, and the 10-year included catheterizations after 8 to 12 years post-operation.
The second analytic problem was that there were multiple grafts (i.e., clustered observations, within a patient). We showed previously (14) that graft patency within a patient is not independent. This does not affect the estimates for patency rates, but it does cause the standard error terms to be underestimated. Recently, the SAS macro IWM (16) has become available for the analysis of clustered, interval-censored survival data (15,16). This approach produces robust estimates of the standard error terms by adjusting for the correlated nature of the clustered observations. Patient-related risk variables, graft-related risk variables, and CABG processes of care variables were used as candidate independent variables in the IWM macro to identify the set of variables that jointly predict 10-year graft patency. Variables that were significant at the p < 0.10 level were included in the final models. The Appendix gives a description on how to interpret the importance of the variables.
The t test and chi-square test were used to compare pre-CABG patient risk factors for patients who received a 10-year catheterization versus those who did not.
|
Results |
|---|
|
TopAbstractMethodsResultsDiscussionAppendixReferences |
|---|
|
|
|
|
|
2.0 mm (p < 0.001). For SVGs to the LAD, the 10-year patency was 90% for vessels >2.0 mm versus 52% for vessels 2.0 mm (p < 0.001). For the IMA, the 10-year patency was 100% for vessels >2.0 mm versus 82% for vessels 2.0 mm (p = 0.008). After controlling for hospital effects, other positive significant predictors of graft patency over the 10-year post-bypass period were older age, use of aspirin after CABG surgery, lower serum cholesterol, and lowest Canadian Functional Class (Table 4). If a graft was patent at one week, significant positive predictors of graft patency rates over the 10-year post-bypass period included IMA grafts to the LAD, larger diameters of the recipient vessel, older age, and lower serum cholesterol (Table 5). Lower platelet count was mildly predictive (p = 0.089) of graft patency. Interestingly, the presence of diabetes requiring insulin and cigarette smoking did not predict graft patency independent of whether the vein graft was patent early or not. Other variables that were tested in the model that were not predictive of vein graft patency included the following: race, number of diseased vessels, presence of peripheral edema, systemic emboli, hypertension, white blood cell count, prior myocardial infarction, proximal anastomotic site, temperature of cardioplegia solution, whether preservation solution given via graft or not, heart size, use of positive inotropic, vasodilator, antiarrhythmic agent perioperatively, use of an intraaortic balloon, lowest body temperature, and total volume of cardioplegia.
|
|
|
|
Discussion |
|---|
|
TopAbstractMethodsResultsDiscussionAppendixReferences |
|---|
The most often quoted results in published reports regarding graft patency after CABG are that at 10 years, SVGs have about a 40% to 50% patency and that IMA grafts have a 90% to 95% 10-year patency. The initial studies that are the basis of this information were not prospective and reported on selected patients operated upon in the 1970s (1–6). In these retrospective studies, graft patency was not determined on everyone in the initial cohort, but rather on those patients who received angiography most often because of symptoms. In 1996 there was a report from a larger database, which included a combination of first surgery and re-operation surgery (7). Even though that trial was designed to follow patients prospectively, the authors state that their plans "were thwarted by lack of funds" and their graft patency data, in the subset that underwent catheterization, were similar to the numbers cited above. When the present study was planned, the longest angiographic follow-up studies of IMA grafts were from the Cleveland Clinic (6,17,18), Karolinska Hospital (19), and the Montreal Heart Institute (3,20). At or past 10 years, each of these centers has reported studying 37, 39, and 20 patients, respectively. Although these reports are important and are obviously responsible for the enthusiasm for using IMA grafts today, they are relatively small retrospective studies. Perhaps the most telling criticism of these studies is that the type of patients operated on 10 to 15 years ago is not the same as patients undergoing CABG now. In the report from the Karolinska Hospital, the 37 patients studied at 11 years had an 88% IMA patency rate (19). The baseline characteristics of this patient population included an average ejection fraction of 64% and 42 of 99 (42%) of the original patients had only IMA grafts. This obviously does not represent the current cardiac surgical population. The patients in our study had average ejection fractions of 61%, but they received 2.9 vein grafts per patient. Another reason why the earlier data may not be applicable now is that the patient population operated on today has more extensive disease than those operated on in the 1970s because today surgeons must operate on patients who have been denied percutaneous coronary intervention or are having second and third revascularization procedures.
All of the studies from the 1970s were done prior to the widespread use of antiplatelet therapy after CABG, and it is now well established that aspirin helps to prevent SVG occlusion (8–12). In the 1970s, very little attention was paid to risk factor control and aggressive lowering of low-density lipoprotein cholesterol, which may alter SVG patency and improve clinical outcomes after CABG (21–23). Lastly, surgical techniques have been modified with regard to preparation of the vein graft before implantation; for instance, we know that cold vein graft preservation solution improves long-term vein graft patency (13).
Comparisons are often made between veins and arteries used as conduits, with the general belief that arterial conduits have a better long-term patency. In fact, the IMA has been proclaimed the graft of choice to bypass the LAD because of its presumed excellent long-term patency rate. A 1986 editorial in the New England Journal of Medicine (23) stated, "at 10 years internal mammary artery grafts remained in excellent condition; nearly 95% were patent, with no signs of deterioration." Although this suggests that the IMA is an ideal conduit, it is important to emphasize that there are no randomized prospectively controlled trials comparing IMA to SVGs. In the past surgeons tended to use IMA grafts in better candidates (i.e., the patient was clinically stable, without severe lung disease, diabetes, and so on). This clinical approach is borne out by our data and that of others, which show that patients receiving SVGs tend to have more severe disease initially than the patients receiving IMA grafts (9,10,13). This argument is probably not germane today, when the characteristics of patients have dramatically increased toward more complex disease as a result of percutaneous coronary intervention, and yet IMA grafts are still used in the majority of patients. In the present study, where patients were not randomized to different conduits, the 10-year patency of left IMA grafts to the LAD is 85%, as opposed to 69% for SVGs to the LAD. Another argument that is often used to support the IMA as the conduit of choice is that retrospective studies have shown that survival is improved in patients receiving IMA grafts as opposed to vein grafts (4,6,25,26). Even though these studies adjust for demographic and clinical differences, they are still retrospective nonrandomized analyses. Data from our study group have shown that use of the IMA is associated with a longer operative time as well as increased postoperative bleeding (27). Thus, the sicker, more complicated patients 10 to 15 years ago would have received vein grafts and not IMA grafts.
The data on predictors of graft patency are interesting. We and other investigators have previously shown that the size of the recipient vessel is an important predictor of graft patency (13). The simple explanation has been that the larger the recipient vessel, the better the flow and distal runoff. The size of the recipient vessel is also thought to be the explanation for why SVGs to the LAD do better than those to the right or CX (Tables 4 and 5, Fig. 3). The other significant patient specific predictors of graft patency are, for the most part, a reflection of the disease in the patient (i.e., there was worse SVG patency in younger patients, which probably is a reflection of worse native coronary disease in younger patients, and patients with elevated serum cholesterols). Interestingly, diabetes and cigarette smoking were not predictors of poor graft patency. We have previously reported on the beneficial effects of aspirin on SVG patency up to one year after surgery (11–13). That observation is consistent with our present data that show the use of aspirin is predictive when looking at all grafts (Table 4), but not in grafts that were patent originally at one week (Table 5). Our earlier work also showed that the temperature used to preserve the vein graft was important, with improved three-year SVG patency when colder temperatures were used (13). We hypothesized that the colder temperatures and the type of preservation fluid used in the vein might have preserved endothelial function and thus improved long-term graft patency.
We believe that the estimates of 10-year graft patency presented here are less biased than any results previously published. First, although it is generally believed that patients who die may have much higher occlusion rates than survivors, the patency rate from 71 autopsies in our study (13.6% of all deaths) was 76% (156 of 205 grafts). Therefore, the effect of lost observations due to death on long-term patency rates may be minimal. Second, although only 33% of the 10-year catheterizations were done strictly for the purposes of this study, this is a substantial proportion compared with previous reported 10-year data, which used retrospective data collection and based their results solely on symptomatic patients. The use of survival analysis techniques to estimate long-term patency is a third technique in fine-tuning the estimates of graft patency. Angiography at any time point can only tell that a graft has become occluded at that point in time, but it cannot determine when the occlusion occurred. Thus, to use the time of the angiography to estimate graft patency will overestimate the patency rate. The use of interval censoring is an attempt to more accurately estimate the time that the occlusion occurred. Lastly, as in all our previous reports, we acknowledge that graft patency within an individual is correlated and we have adjusted for this association.
It may be reasonable to assume that graft patency influenced survival. The data are only from the survivors who, by definition, may have had better graft patency than the nonsurvivors. We acknowledge that not being able to address whether graft patency influenced survival is a potential weakness in our study, but this would be true for any long-term study of graft patency after CABG. Owing to the long-term nature of the study and the fact that coronary artery disease is a progressive disease, we used data from clinically indicated angiograms, in part, for the 6- and 10-year follow-up. In this older patient population it is difficult to get patients to agree to repeat invasive procedures when they already have had a clinically indicated catheterization, are asymptomatic, or when the attending cardiologist would not consider any interventional procedure. Two notes of caution: the patients who did not undergo the 10-year catheterization had more diabetes and hypertension and, therefore, the current estimates of patency may be overestimated. Lastly, all patients were men and, therefore, long-term angiographic follow-up of CABG grafts is not available for a female cohort.
In conclusion, we report long-term analysis of SVG and IMA patency for 10 years after operation, showing that patency for IMA grafts is better than for SVGs, but the 10-year patency for SVGs is better and 10-year patency for left IMA grafts is worse than previously thought. The most important predictors of long-term graft patency are initial patency at one week after CABG and the diameter of the recipient vessel into which the graft is placed.
|
Appendix |
|---|
|
TopAbstractMethodsResultsDiscussionAppendixReferences |
|---|
|
Footnotes |
|---|
|
References |
|---|
|
TopAbstractMethodsResultsDiscussionAppendixReferences |
|---|
This article has been cited by other articles:
|
|
 |
|
  J. Kempfert, U. T. Opfermann, M. Richter, T. Bossert, F. W. Mohr, and J. F. Gummert Twelve-month patency with the PAS-port proximal connector device: a single center prospective randomized trial. Ann. Thorac. Surg., May 1, 2008; 85(5): 1579 - 1584. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. V. Ozcan, H. Evrengul, I. Goksin, S. Gur, and A. Kaftan 30-Year Patency of a Saphenous Vein Graft in Coronary Bypass Graft Surgery Ann. Thorac. Surg., April 1, 2008; 85(4): e23 - e23. [Full Text] [PDF]
|
|
|
|
|
|
N. S. Burris, E. N. Brown, M. Grant, Z. N. Kon, M. Gibber, J. Gu, K. Schwartz, S. Kallam, A. Joshi, R. Vitali, et al. Optical Coherence Tomography Imaging as a Quality Assurance Tool for Evaluating Endoscopic Harvest of the Radial Artery Ann. Thorac. Surg., April 1, 2008; 85(4): 1271 - 1277. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. B. Barner Operative Treatment of Coronary Atherosclerosis Ann. Thorac. Surg., April 1, 2008; 85(4): 1473 - 1482. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. J. Magee, J. H. Alexander, G. Hafley, T. B. Ferguson Jr, C. M. Gibson, R. A. Harrington, E. D. Peterson, R. M. Califf, N. T. Kouchoukos, M. A. Herbert, et al. Coronary Artery Bypass Graft Failure After On-Pump and Off-Pump Coronary Artery Bypass: Findings From PREVENT IV Ann. Thorac. Surg., February 1, 2008; 85(2): 494 - 500. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. A.R. Hayward and B. F. Buxton Contemporary Coronary Graft Patency: 5-Year Observational Data From a Randomized Trial of Conduits Ann. Thorac. Surg., September 1, 2007; 84(3): 795 - 799. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. J. Murphy, A. C. Newby, J. Y. Jeremy, A. Baumbach, and G. D. Angelini A randomized trial of an external Dacron sheath for the prevention of vein graft disease: The Extent study J. Thorac. Cardiovasc. Surg., August 1, 2007; 134(2): 504 - 505. [Full Text] [PDF]
|
|
|
|
|
|
E. J.W. Wallitt, M. Jevon, and P. I. Hornick Therapeutics of Vein Graft Intimal Hyperplasia: 100 Years On Ann. Thorac. Surg., July 1, 2007; 84(1): 317 - 323. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. J. Botman, J. Schonberger, S. Koolen, O. Penn, H. Botman, N. Dib, E. Eeckhout, and N. Pijls Does Stenosis Severity of Native Vessels Influence Bypass Graft Patency? A Prospective Fractional Flow Reserve-Guided Study Ann. Thorac. Surg., June 1, 2007; 83(6): 2093 - 2097. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Renda, R. Di Pillo, A. D'Alleva, A. Sciartilli, M. Zimarino, E. De Candia, R. Landolfi, G. Di Giammarco, A. Calafiore, and R. De Caterina Surgical bleeding after pre-operative unfractionated heparin and low molecular weight heparin for coronary bypass surgery Haematologica, March 1, 2007; 92(3): 366 - 373. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Burris, K. Schwartz, C.-M. Tang, M. S. Jafri, J. Schmitt, M. H. Kwon, O. Toshinaga, J. Gu, J. Brown, E. Brown, et al. Catheter-based infrared light scanner as a tool to assess conduit quality in coronary artery bypass surgery J. Thorac. Cardiovasc. Surg., February 1, 2007; 133(2): 419 - 427. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Schachner, G. Laufer, and J. Bonatti In vivo (animal) models of vein graft disease. Eur. J. Cardiothorac. Surg., September 1, 2006; 30(3): 451 - 463. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Rigatelli, M. Giordan, P. Cardaioli, L. Roncon, G. Faggian, G. Rigatelli, and P. Zonzin Subclavian artery angioplasty allows for implantation of the in situ internal thoracic artery graft in patients scheduled for surgical myocardial revascularization J. Thorac. Cardiovasc. Surg., June 1, 2006; 131(6): e9 - e10. [Full Text] [PDF]
|
|
|
|
|
|
T. Schachner Pharmacologic inhibition of vein graft neointimal hyperplasia J. Thorac. Cardiovasc. Surg., May 1, 2006; 131(5): 1065 - 1072. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Gossl and A. Lerman Endothelin: Beyond a Vasoconstrictor Circulation, March 7, 2006; 113(9): 1156 - 1158. [Full Text] [PDF]
|
|
|
|
|
|
J. P. Greelish, S. S. Eagle, D. X. Zhao, R. J. Deegan, M. H. Crenshaw, J. M. Balaguer, R. M. Ahmad, and J. G. Byrne Management of new-onset mitral regurgitation with intraoperative angiography and intraoperative percutaneous coronary intervention J. Thorac. Cardiovasc. Surg., January 1, 2006; 131(1): 239 - 240. [Full Text] [PDF]
|
|
|
|
 |
|
 PREVENT IV Investigators Efficacy and Safety of Edifoligide, an E2F Transcription Factor Decoy, for Prevention of Vein Graft Failure Following Coronary Artery Bypass Graft Surgery: PREVENT IV: A Randomized Controlled Trial JAMA, November 16, 2005; 294(19): 2446 - 2454. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Kitamura, H. Okabayashi, M. Hanyu, Y. Soga, T. Nomoto, H. Johno, J. Nakano, T. Matsuo, M. Kai, and E. Umehara Early and midterm patency of the proximal anastomoses of saphenous vein grafts made with a Symmetry Aortic Connector System J. Thorac. Cardiovasc. Surg., October 1, 2005; 130(4): 1028 - 1031. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. H. Jones The Year in Cardiovascular Surgery J. Am. Coll. Cardiol., May 3, 2005; 45(9): 1517 - 1528. [Full Text] [PDF]
|
|
|
|
|
|
PREVENT IV Investigators Efficacy and Safety of Edifoligide, an E2F Transcription Factor Decoy, for Prevention of Vein Graft Failure Following Coronary Artery Bypass Graft Surgery: PREVENT IV: A Randomized Controlled Trial JAMA, November 16, 2005; 294(19): 2446 - 2454. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | SUBSCRIPTIONS | CURRENT ISSUE | PAST ISSUES | CARDIOSOURCE | SEARCH |
