Background Several studies have compared the treatment effectsof coronary stenting and coronary-artery bypass grafting (CABG).However, there are limited data regarding the long-term outcomesof these two interventions for patients with unprotected leftmain coronary artery disease.
Methods We evaluated 1102 patients with unprotected left maincoronary artery disease who underwent stent implantation and1138 patients who underwent CABG in Korea between January 2000and June 2006. We compared adverse outcomes (death; a compositeoutcome of death, Q-wave myocardial infarction, or stroke; andtarget-vessel revascularization) with the use of propensity-scorematching in the overall cohort and in separate subgroups accordingto type of stent.
Results In the overall matched cohort, there was no significantdifference between the stenting and CABG groups in the riskof death (hazard ratio for the stenting group, 1.18; 95% confidenceinterval [CI], 0.77 to 1.80) or the risk of the composite outcome(hazard ratio for the stenting group, 1.10; 95% CI, 0.75 to1.62). The rates of target-vessel revascularization were significantlyhigher in the group that received stents than in the group thatunderwent CABG (hazard ratio, 4.76; 95% CI, 2.80 to 8.11). Comparisonsof the group that received bare-metal stents with the groupthat underwent CABG and of the group that received drug-elutingstents with the group that underwent CABG produced similar results,although there was a trend toward higher rates of death andthe composite end point in the group that received drug-elutingstents.
Conclusions In a cohort of patients with unprotected left maincoronary artery disease, we found no significant differencein rates of death or of the composite end point of death, Q-wavemyocardial infarction, or stroke between patients receivingstents and those undergoing CABG. However, stenting, even withdrug-eluting stents, was associated with higher rates of target-vesselrevascularization than was CABG.
Significant narrowing of the left main coronary artery putsa patient at high risk, since it can jeopardize the entire myocardiumof the left ventricle, and it has the worst prognosis of anyform of coronary artery disease.1 On the basis of clinical trialsthat show a survival benefit with bypass surgery as comparedwith medical treatment,1,2,3,4 coronary-artery bypass grafting(CABG) has been considered standard therapy for patients withleft main coronary artery disease and is recommended by currentpractice guidelines.5,6 Because of concern about proceduralrisk and long-term durability, percutaneous coronary intervention(PCI) usually has been restricted to patients who are poor candidatesfor surgery or have left main coronary artery disease that is"protected" by a patent bypass graft to the left anterior descendingor circumflex artery.
The development of coronary-artery stenting has led to a reevaluationof the role of PCI for left main coronary artery disease, andseveral studies have reported on the midterm safety and feasibilityof stenting.7,8,9 Interest in stenting of the left main coronaryartery has increased further with the availability of drug-elutingstents that significantly reduce the rates of restenosis andrepeat revascularization.10,11,12 However, there are limiteddata on the long-term safety and effectiveness of PCI with bare-metalor drug-eluting stents, as compared with CABG, in patients withunprotected left main coronary artery disease. We thereforecompared the long-term outcomes of the implantation of coronarystents and CABG among patients with unprotected left main coronaryartery disease in Korea, where stenting of the left main coronaryartery has been a more common practice than in Western countries,as recorded in the MAIN-COMPARE (Revascularization for UnprotectedLeft Main Coronary Artery Stenosis: Comparison of PercutaneousCoronary Angioplasty versus Surgical Revascularization) registry.
Methods
Study Population
The MAIN-COMPARE registry holds data on consecutive patientsfrom 12 major cardiac centers in Korea that performed PCI orCABG for unprotected left main coronary artery disease (definedas stenosis of more than 50%) between January 2000 and June2006. We excluded patients who had undergone previous CABG,those who underwent concomitant valvular or aortic surgery,and those who had myocardial infarction with ST-segment elevationor presented with cardiogenic shock. The registry is sponsoredby the Korean Society of Interventional Cardiology. There wasno industry involvement in the design, conduct, or analysisof the study. The local ethics committee at each hospital approvedthe use of clinical data for this study, and all patients providedwritten informed consent.
Patients underwent PCI, instead of CABG, because of either thepatient's or physician's preference or the high risk associatedwith CABG (see the Supplementary Appendix, available with thefull text of this article at www.nejm.org). From January 2000through May 2003, coronary stenting was performed exclusivelywith bare-metal stents, whereas from May 2003 through June 2006,exclusively drug-eluting stents were used. Methods of stentimplantation for patients with left main coronary artery diseasehave been described previously10,13,14 (see the Supplementary Appendix).Interventions for other clinically important types of coronaryartery disease were performed according to current practiceguidelines.6 All patients undergoing PCI were prescribed aspirinplus clopidogrel (loading dose, 300 mg or 600 mg) or ticlopidine(loading dose, 500 mg) before or during the coronary intervention.After the procedure, aspirin was continued indefinitely. Patientstreated with bare-metal stents were prescribed clopidogrel orticlopidine for at least 1 month, and patients treated withdrug-eluting stents were prescribed clopidogrel for at least6 months. Surgical revascularization was performed with theuse of standard bypass techniques.5 Whenever possible, the internalthoracic artery was used preferentially for revascularizationof the left anterior descending artery.
Follow-up and End Points
Clinical, angiographic, procedural or operative, and outcomedata were collected with the use of a dedicated Internet-basedreporting system. All outcomes of interest were confirmed bysource documentation collected at each hospital and were centrallyadjudicated by the local events committee at the Universityof Ulsan College of Medicine, Asan Medical Center, Seoul. Forvalidation of complete follow-up data, information about vitalstatus was obtained through July 15, 2007, from the NationalPopulation Registry of the Korea National Statistical Officewith the use of a unique personal identification number.
Clinical follow-up after PCI and after CABG was recommendedat 1 month, 6 months, and 1 year and then annually thereafter.Routine angiographic follow-up for all patients treated withPCI was recommended 6 to 10 months after the procedure. However,patients who were at high risk for procedural complicationsof angiography and had no symptoms or signs of ischemia, aswell as patients who declined the recommendation, did not undergoroutine follow-up angiography. For patients who underwent CABG,angiographic follow-up was recommended only if there were ischemicsymptoms or signs during follow-up.
The end points of the study were death; the composite of death,Q-wave myocardial infarction, or stroke; and target-vessel revascularization.All events were based on clinical diagnoses assigned by thepatient's physician and were centrally adjudicated by an independentgroup of clinicians. Death was defined as death from any cause.Q-wave myocardial infarction was defined as documentation ofa new abnormal Q wave after the index treatment. Stroke, asindicated by neurologic deficits, was confirmed by a neurologiston the basis of imaging studies. Target-vessel revascularizationwas defined as repeat revascularization of the treated vessel,including any segments of the left anterior descending arteryand the left circumflex artery.15
Statistical Analysis
Among patients who had unprotected left main coronary arterydisease, we compared long-term outcomes for those who underwentPCI, irrespective of stent type, with the outcomes for thosewho underwent CABG. In addition, we compared the long-term outcomesof patients who received bare-metal or drug-eluting stents withpatients who underwent CABG. Patients who received bare-metalstents were compared with patients who underwent CABG betweenJanuary 2000 and May 2003 (Wave 1 of the registry). Patientswho received drug-eluting stents were compared with patientswho underwent CABG between May 2003 and June 2006 (Wave 2 ofthe registry).
To reduce the effect of treatment-selection bias and potentialconfounding in this observational study, we performed rigorousadjustment for significant differences in the baseline characteristicsof patients with the use of propensity-score matching.16,17For each comparison (the entire cohort, Wave 1, and Wave 2),a separate propensity score for PCI versus CABG was derived.The details of the propensity-score method, with the resultingmodels and their predictive characteristics, are described inthe Supplementary Appendix.
After all the propensity-score matches were performed, we comparedthe baseline covariates between the two intervention groups.Continuous variables were compared with the use of the pairedt-test or the Wilcoxon signed-rank test, as appropriate, andcategorical variables were compared with the use of McNemar'stest. Statistical significance and the effect of treatment onoutcomes were estimated with the use of appropriate statisticalmethods for matched data.18,19 In the propensity-score–matchedcohort, the risks of each outcome were compared with the useof Cox regression models, with robust standard errors that accountedfor the clustering of matched pairs. Survival curves were constructedwith Kaplan–Meier estimates and compared with the useof methods described by Klein and Moeschberger.19
All reported P values are two-sided, and P values of less than0.05 were considered to indicate statistical significance. SASsoftware, version 9.1, and the R programming language were usedfor statistical analyses.
Results
Characteristics of the Study Population
Between January 2000 and June 2006, a total of 2240 patientswith unprotected left main coronary artery disease met the criteriafor inclusion. Of these, 1102 were treated with PCI and 1138with CABG. Of the patients who underwent PCI, 1073 (97.4%) hadclinical and angiographic conditions that made them eligiblefor either PCI or CABG, but they underwent PCI because of thepatient's or physician's preference. The remaining 29 patients(2.6%) had underlying conditions that made them poor candidatesfor surgery (8 were 80 years of age and had a poor performancestatus, 3 had limited life expectancy, 2 had a current malignantcondition, 12 had a concomitant severe medical illness, and4 had no suitable bypass conduits).
In the PCI group, 318 patients (28.9%) received bare-metal stentsand 784 (71.1%) received drug-eluting stents. Of the patientstreated with drug-eluting stents, 607 (77.4%) received sirolimus-elutingstents and 177 (22.6%) received paclitaxel-eluting stents. Themean (±SD) number of stents implanted in a patient'sleft main coronary lesions was 1.2±0.5, the mean totallength of the stents was 28.0±20.7 mm, and the mean stentdiameter was 3.5±0.4 mm. The mean total number of stentsimplanted in a patient (including left main and other vessels)was 1.9±1.1.
In the CABG group, 478 patients (42.0%) underwent off-pump surgeryand 1120 (98.4%) received at least one arterial conduit that,in 1096 patients (97.9%), was used in revascularization of theleft anterior descending artery. The mean number of grafts usedwas 2.9±1.0 (2.2±0.9 arterial grafts and 0.7±0.8venous grafts).
The baseline characteristics of the study patients accordingto the revascularization procedure are shown in Table 1. Patientsundergoing CABG were significantly older and had a higher prevalenceof diabetes, hyperlipidemia, smoking, and history of myocardialinfarction or peripheral vascular disease than those receivingstents. Patients undergoing CABG were also more likely to havelower ejection fractions, to present with unstable angina, andto have distal-bifurcation stenosis, three-vessel disease, andinvolvement of the right coronary artery. More patients in thePCI group than in the CABG group had undergone previous coronaryangioplasty and had restenotic left main coronary lesions.
Table 1. Baseline Characteristics of the Patients.
Follow-up
The median follow-up was 1017 days (interquartile range, 688to 1451) in the PCI group and 1152 days (interquartile range,681 to 1590) in the CABG group. Complete follow-up data formajor clinical events were obtained in 98.9% of the overallcohort. During follow-up, 187 patients (8.3%) died, of whom127 (67.9%, or 5.7% of the overall cohort) died of a cardiovascularcause. Twenty patients (0.9%) had a Q-wave myocardial infarction,and 35 (1.6%) had a stroke. Target-vessel revascularizationwas performed in 141 patients (6.3%).
Characteristics of Patients Matched for Propensity Scores
Details of the propensity-score analysis are provided in theSupplementary Appendix. After propensity-score matching wasperformed for the entire population, there were 542 matchedpairs of patients (Table 2). In this matched cohort, 25.5% ofthe PCI group received bare-metal stents and 74.5% receiveddrug-eluting stents. After propensity-score matching was performedseparately in the Wave 1 and Wave 2 cohorts, there were 207matched pairs of patients who received bare-metal stents andconcurrent control patients who underwent CABG, and 396 matchedpairs of patients who received drug-eluting stents and concurrentcontrol patients who underwent CABG. In the matched cohorts,there was no longer any significant difference between the PCIgroup and the CABG group for any covariate, according to theuse of statistical methods appropriate for matched data (Table 2).
Table 2. Baseline Characteristics of the Propensity-Matched Patients.
Outcomes for the Matched Cohorts
Figure 1 and Table 3 show the long-term rates of clinical outcomesaccording to the treatment approach in the overall matched cohort.For the 542 matched pairs, there was no significant differencebetween the PCI and CABG groups in the risk of death duringthe 3-year follow-up period. The rates of major adverse cardiovascularevents (death, Q-wave myocardial infarction, or stroke) werealso similar. However, the rate of target-vessel revascularizationwas significantly higher in the PCI group than in the CABG group.Of the patients with initial PCI treatment who underwent target-vesselrevascularization during the study period, 82.1% underwent repeatPCI (stenting or balloon angioplasty) and 17.9% underwent CABG.Of the patients with initial CABG treatment who underwent target-vesselrevascularization, all underwent PCI, not repeat CABG. The riskof target-lesion revascularization specifically for restenosisof the left main coronary artery was also significantly higherin the PCI group than in the CABG group (hazard ratio, 2.72;95% confidence interval [CI], 1.51 to 4.91).
Figure 1. Kaplan–Meier Curves for Outcomes in a Cohort of Patients Matched for Propensity Scores Who Underwent Stent Implantation or Bypass Surgery.
Propensity matching for the entire cohort created 542 matched pairs of patients. Panel A shows the outcomes for overall survival; Panel B, outcomes for freedom from death, Q-wave myocardial infarction, or stroke; and Panel C, outcomes for freedom from target-vessel revascularization. Event-free survival rates (at 1, 2, and 3 years) were derived from paired Kaplan–Meier curves. CABG denotes coronary-artery bypass grafting.
Table 3. Hazard Ratios for Clinical Outcomes after Stenting as Compared with after CABG among Propensity-Matched Patients.
The rates of death at 3 years of follow-up did not differ significantlybetween the group that received bare-metal stents and the CABGgroup (Figure 2 and Table 3). There was also no significantdifference between the two groups in the composite risk of death,Q-wave myocardial infarction, or stroke. However, the rate oftarget-vessel revascularization was significantly lower amongpatients who underwent CABG than among those who received bare-metalstents. Of patients with bare-metal stents who underwent target-vesselrevascularization, 60.5% underwent repeat PCI and 39.5% underwentCABG. All patients with initial CABG who required target-vesselrevascularization were treated with PCI. The risk of stenosisof the left main coronary artery that required target-lesionrevascularization was significantly higher for patients whoreceived bare-metal stents than for those who underwent CABG(hazard ratio, 5.86; 95% CI, 2.03 to 16.90).
Figure 2. Kaplan–Meier Curves for Outcomes in a Cohort of Patients Matched for Propensity Scores Who Received Bare-Metal Stents or Underwent Bypass Surgery.
Propensity matching for Wave 1 created 207 matched pairs of patients. Panel A shows the outcomes for overall survival; Panel B, outcomes for freedom from death, Q-wave myocardial infarction, or stroke; and Panel C, outcomes for freedom from target-vessel revascularization. Event-free survival rates (at 1, 2, and 3 years) were derived from paired Kaplan–Meier curves. CABG denotes coronary-artery bypass grafting.
No significant differences were noted for the rates of deathand the composite of death, Q-wave myocardial infarction, orstroke between the group that received drug-eluting stents andthe CABG group (Figure 3 and Table 3). However, the hazard ratiosfor each of these end points show a nonsignificant trend towardhigher risk among patients with stents. Despite the markedlysmaller hazard ratio in Wave 2 as compared with Wave 1, CABGcontinued to be associated with a lower rate of target-vesselrevascularization than did drug-eluting stents. Among patientswith drug-eluting stents who underwent target-vessel revascularization,90.9% underwent repeat PCI and 9.1% underwent CABG. All patientswith initial CABG who underwent target-vessel revascularizationwere treated with PCI, not repeat CABG. The risk of target-lesionrevascularization due to stenosis of the left main coronaryartery was higher among patients who received drug-eluting stentsthan among those who underwent CABG (hazard ratio, 2.98; 95%CI, 1.15 to 7.75).
Figure 3. Kaplan–Meier Curves for Outcomes in a Cohort of Patients Matched for Propensity Scores Who Received Drug-Eluting Stents or Underwent Bypass Surgery.
Propensity matching for Wave 2 created 396 matched pairs of patients. Panel A shows outcomes for overall survival; Panel B, outcomes for freedom from death, Q-wave myocardial infarction, or stroke; and Panel C, outcomes for freedom from target-vessel revascularization. Event-free survival rates (at 1, 2, and 3 years) were derived from paired Kaplan–Meier curves. CABG denotes coronary-artery bypass grafting.
Outcomes for the Unmatched Patients
Event-free survival in the unmatched cohort was consistent withthe lower-risk characteristics of the patients who underwentPCI and the higher-risk characteristics of the patients whounderwent CABG (see the Supplementary Appendix). Among the patientsnot included in the overall match, the 3-year rates of deathand the composite of death, Q-wave myocardial infarction, orstroke were significantly higher in the CABG group, whereasthe rate of target-vessel revascularization was higher in thePCI group. Among unmatched patients in Wave 1, the risks ofdeath and the composite of death, Q-wave myocardial infarction,or stroke did not differ significantly between the two groups.However, the risk of target-vessel revascularization was consistentlyhigher among patients who received bare-metal stents. Amongunmatched patients in Wave 2, CABG was associated with higherrisks of death and the composite of death, Q-wave myocardialinfarction, or stroke than was PCI with drug-eluting stents,whereas the risk of revascularization was higher among patientswho received stents.
Acute Complications
Acute complications occurred in 2.7% of patients undergoingPCI. The details of specific acute complications are providedin the Supplementary Appendix.
Discussion
We compared the long-term outcomes of coronary stenting andCABG in a large cohort of patients with unprotected left maincoronary artery disease. Our observational study showed thatthe risks of death and a composite of serious outcomes (death,Q-wave myocardial infarction, or stroke) were similar in thePCI and the CABG groups. These results were consistent whenbare-metal stents or drug-eluting stents were compared withCABG, although there was a nonsignificant trend toward higherrisk with drug-eluting stents. In contrast, the rate of target-vesselrevascularization was significantly lower in the CABG groupthan in the PCI group, although hazard ratios varied dependingon the type of stent.
Another large observational study, published before the developmentof drug-eluting stents, suggested that patients with left maincoronary artery disease did significantly better with CABG thanwith PCI.20 Although this was a risk-adjusted analysis, patient-selectionfactors probably contributed to the results. More recent observationalstudies have shown similar mortality rates and similar risksof major adverse cardiac and cerebrovascular events betweenpatients receiving drug-eluting stents and those undergoingCABG, although patients undergoing CABG have typically had significantlylower rates of repeat revascularization.15,21,22,23 These studieshave all been limited by small numbers of patients, a limitedduration of follow-up, and selective performance of PCI in patientsconsidered to be poor candidates for CABG.
In our study, despite the lower rates of repeat revascularizationwith drug-eluting stents than with bare-metal stents, CABG wasstill more effective than drug-eluting stents in reducing theneed for target-vessel revascularization. However, there wasa significantly higher rate of follow-up angiography in thePCI group than in the CABG group (73.0% vs. 14.6%, P<0.001).Therefore, the rate of asymptomatic graft stenosis or occlusionmay have been underestimated in the CABG group relative to thePCI group.
The major limitation of this study is that we evaluated observationaldata, and therefore the treatment strategy was not based onrandomized assignment. The choice of revascularization was atthe discretion of the treating physician or the patient. Inthe Supplementary Appendix we have attempted to provide as cleara description as possible of the factors that were likely tohave influenced the selection of a procedure for individualpatients. We acknowledge, however, that the particulars of clinicalpractice in the institutions in this trial, as well as the specificexpertise of the interventional cardiologists and cardiac surgeonswho performed the procedures, may differ from those of otherinstitutions and practitioners, potentially limiting the reproducibilityof these results in other settings.
From an analytical standpoint, our findings are subject to selectionbias and confounding with respect to the relative severity ofpreprocedural risks among patients who underwent PCI and thosewho underwent CABG. To minimize these biases, we used propensity-scorematching.16,17 Previous research has suggested that matchingaccording to the propensity score eliminates a greater proportionof baseline differences between two treatments than does stratificationor covariate adjustment.24 Nevertheless, hidden bias may remainbecause of the influence of unmeasured confounders. Given theseissues and the findings of our study, we believe that a randomizedtrial of PCI with drug-eluting stents as compared with CABGis warranted in patients with unprotected left main coronaryartery disease who are candidates for revascularization.
A final caveat is that our analysis was underpowered to detectsignificant differences in mortality, especially in the comparisonof drug-eluting stents with CABG. More than 5500 patients wouldhave been needed for such an analysis. Nonsignificant trendstoward higher event rates were seen in the group that receiveddrug-eluting stents; these trends might have been significantwith a larger cohort of patients.
In conclusion, we found that in matched cohorts of patientswith unprotected left main coronary artery disease, PCI withstenting and CABG were associated with similar long-term ratesof death and the composite end point of death, Q-wave myocardialinfarction, or stroke. Rates of target-vessel revascularizationwere higher among patients who underwent PCI than among thosewho underwent CABG.
Supported by the Korean Society of Interventional Cardiologyand the Cardiovascular Research Foundation, Seoul.
Drs. Seung, Hong, and Chung report receiving lecture fees fromCordis and Boston Scientific; Dr. Y.-H. Kim, receiving lecturefees from Cordis; Dr. C.W. Lee, receiving lecture fees fromMedtronic; Dr. Jeong, receiving lecture fees from Cordis, Medtronic,and Boston Scientific; Dr. Tahk, receiving lecture fees fromBoston Scientific; Dr. S.-W. Park, receiving research grantsupport from Medtronic; Dr. Seong, receiving grant support fromBoston Scientific; Dr. Gwon, receiving lecture fees from BostonScientific and Medtronic and research grant support from Medtronic;Dr. H.-S. Kim, receiving consulting fees from Abbott Vascular;and Dr. S.-J. Park. receiving consulting fees from Cordis, lecturefees from Cordis, Medtronic, and Boston Scientific, and researchgrant support from Cordis and Medtronic. No other potentialconflict of interest relevant to this article was reported.
We thank the staff members of the MAIN-COMPARE registry, theother members of the cardiac catheterization laboratories andthe cardiac surgery departments of the participating centers,and the study coordinators for their efforts to collect theclinical data that made this study possible and to ensure theaccuracy and completeness of the registry data.
Source Information
From the Catholic University of Korea, St. Mary's Hospital, Gangnam (K.B.S., P.J.K.) and Yeoido (W.-S.C.), Seoul; the Department of Cardiology (D.-W.P., Y.-H.K., S.-W.L., C.W.L., M.-K.H., S.-W.P., S.-J.P.) and Division of Biostatistics (S.-C.Y.), Center for Medical Research and Information, University of Ulsan College of Medicine, Asan Medical Center, Seoul; Samsung Medical Center, Seoul (H.-C.G.); Chonnam National University Hospital, Gwangju (M.-H.J.); Yonsei University Severance Hospital, Seoul (Y.J.); Seoul National University Hospital, Seoul (H.-S.K.) and Bundang (I.-H.C.); Chungnam National University Hospital, Daejeon (I.-W.S.); Kyung Pook National University Hospital, Daegu (H.S.P.); Gachon University Gil Medical Center, Incheon (T.A.); and Ajou University Medical Center, Suwon (S.-J.T.) — all in Korea. Drs. K.B. Seung and D.-W. Park contributed equally to this article. This article (10.1056/NEJMoa0801441) was published at www.nejm.org on March 31, 2008.
Address reprint requests to Dr. Seung-Jung Park at the Department of Cardiology, University of Ulsan College of Medicine, Cardiac Center, Asan Medical Center, 388-1 Poongnap-dong, Songpa-gu, Seoul, 138-736, Korea, or at sjpark{at}amc.seoul.kr.
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80 years of age and had a poor performance status, 3 had limited life expectancy, 2 had a current malignant condition, 12 had a concomitant severe medical illness, and 4 had no suitable bypass conduits). 
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