Long-Term Outcomes of Coronary-Artery Bypass Graft Surgery Versus Percutaneous Coronary Intervention for Multivessel Coronary Artery Disease in the Bare-Metal Stent Era
Background— Observational registries comparing coronary artery bypass graft (CABG) surgery and percutaneous coronary intervention (PCI) have reported long-term survival results that are discordant with those of randomized trials.
Methods and Results— We conducted a multicenter study in Japan enrolling consecutive patients undergoing first CABG or PCI between January 2000 and December 2002. Among 9877 patients enrolled, 5420 (PCI: 3712, CABG: 1708) had multivessel disease without left main involvement. Because age is an important determinant when choosing revascularization strategies, survival analysis was stratified by either age ≥75 or <75 years. Analyses were also performed in other relevant subgroups. Median follow-up interval was 1284 days with 95% follow-up rate at 2 years. At 3 years, unadjusted survival rates were 91.7% and 89.6% in the CABG and PCI groups, respectively (log rank P=0.26). After adjustment for baseline characteristics, survival outcome tended to be better after CABG (hazard ratio for death after PCI versus CABG [HR], 95% confidence interval [CI]: 1.23 [0.99-1.53], P=0.06). Adjusted survival outcomes also tended to be better for CABG among elderly patients (HR [95%CI]: 1.37 [0.98-1.92] P=0.07), but not among nonelderly patients (HR [95% CI]: 1.09 [0.82-1.46], P=0.55). Unadjusted and adjusted survival outcome for CABG and PCI were not significantly different in any subgroups when elderly patients were excluded from analysis.
Conclusions— In the CREDO-Kyoto registry, survival outcomes among patients <75 years of age were similar after PCI and CABG, a result that is consistent with those of randomized trials.
- coronary artery disease
- percutaneous coronary intervention
- coronary stent
- coronary artery bypass graft (CABG) surgery
- long-term outcome
Randomized controlled trials comparing coronary artery bypass graft (CABG) surgery and percutaneous coronary intervention (PCI) in the bare-metal stent era generally showed similar survival rates up to 5 years.1–7 However, a recent report from New York’s cardiac registries involving 59|314 patients demonstrated higher risk-adjusted survival rates at three years with CABG in all clinical and anatomic subgroups studied.8 Similarly, an analysis from the Northern New England Registry revealed better survival with CABG among patients with triple-vessel disease.9
These conflicting observations between randomized trials and registries have raised much controversy, and the reasons for this discrepancy have not yet been well addressed. To further understand relative survival outcomes of CABG and PCI, we evaluated long-term outcomes of patients undergoing coronary revascularization in a large-scale multicenter registry in Japan.
The CREDO-Kyoto (Coronary REvascularization Demonstrating Outcome Study in Kyoto) is a multicenter registry in Japan enrolling consecutive patients undergoing first PCI or CABG and excluding those patients with acute myocardial infarction within a week before index procedure. The relevant review boards or ethics committees in all 30 participating centers (Table 1⇓) approved the research protocol. Because of retrospective enrollment, written informed consent was not obtained from the patients; however, 73 patients were excluded because of their refusal to participate in the study when contacted for follow-up. This strategy is concordant with the guidelines for epidemiological studies issued by the Ministry of Health, Labor and Welfare of Japan.
Between January 2000 and December 2002, 9877 patients were identified to have undergone either CABG (2999 patients) or PCI (6878 patients) without prior history of coronary revascularization. Patients were enrolled from 21 centers for CABG (median number of patients from each center: 100 [19 to 550, interquartile range 57 to 199]), and from 30 centers for PCI (median number of patients from each center: 129 [16 to 1760, interquartile range 74 to 237]), respectively. Four hundred eighty-four patients undergoing concomitant valvular, left ventricular, or major vascular operation were excluded from the current analysis. Patients with disease of the left main coronary artery (PCI 165 patients, CABG 742 patients) and with single-vessel disease (PCI 3001 patients, CABG 65 patients) were excluded. Therefore, the study group comprised 5420 patients with multivessel coronary artery disease undergoing first coronary revascularization (PCI: 3712 patients, CABG: 1708 patients).
Data Collection and Definitions
Demographic, angiographic, and procedural data in both groups were collected from hospital charts or databases in each center by independent clinical research coordinators (Appendix) according to prespecified definitions. Follow-up data were obtained from hospital charts or by contacting patients or referring physicians.
Baseline clinical characteristics, such as myocardial infarction, heart failure, diabetes, hypertension, current smoker status, atrial fibrillation, chronic obstructive lung disease, and malignancy were regarded as present when these diagnoses were recorded in the hospital charts. Stroke at baseline included asymptomatic stroke detected by noninvasive imaging modalities. Peripheral vascular disease was regarded to be present when carotid, aortic, or other peripheral vascular disease were being treated or scheduled for surgical or endovascular interventions.
Elderly patients were defined as those patients ≥75 years of age. Left ventricular ejection fraction (LVEF) was measured either by contrast left ventriculography or echocardiography. Patients with LVEF ≤40% were regarded as having left ventricular dysfunction. Chronic kidney disease was regarded as present when creatinine clearance estimated by Cockcloft-Gould formula was less than 60 mL/min. Anemia was defined as blood hemoglobin level less than 12 g/dL.
An independent clinical events committee adjudicated events. Death was regarded as cardiovascular in origin unless obvious noncardiovascular causes could be identified. Any death during the index hospitalization was regarded as cardiovascular death. Myocardial infarction was adjudicated according to the definition in the Arterial Revascularization Therapy Study.1 Within 1 week of the index procedure, only Q-wave myocardial infarction was adjudicated as myocardial infarction. Stroke at follow-up was defined as symptomatic stroke.
After the descriptive statistics, we used Kaplan-Meier estimates to plot the percentage of patients in each group who died for any reason; data on patients who lost follow-up were censored. The log-rank test was used to identify significant differences in unadjusted survival rates. To determine the baseline risk factors for mortality, we conducted Log-rank tests for the following 30 potential variables: age, gender, body mass index, emergency procedure, prior myocardial infarction, congestive heart failure, stroke, peripheral arterial disease, atrial fibrillation, chronic obstructive pulmonary disease, malignancy, hypertension, diabetes without insulin therapy, diabetes with insulin therapy, hemodialysis, chronic kidney disease, anemia, current smoker status, LVEF, total occlusion, proximal LAD disease, triple vessel disease, and use of medications such as statins, aspirin, thienopyridines, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, beta blockers, calcium channel blockers, and nitrates. All continuous variables were dichotomized for fitting proportional assumption according to the predetermined clinical contexts. We plotted log (time) versus log [-log (survival)] stratified by each significant risk factor and evaluated whether the plotted lines were parallel.10 Those variables for which probability values were less than 0.05 in univariate analyses and proportional assumptions were generally fair were included in the multivariable analysis. We developed multivariable Cox proportional hazard models that controlled for significant risk factors while testing for significant differences in long-term survival between the 2 groups of patients undergoing CABG or PCI.
Analysis of treatment-related differences in long-term survival was stratified whether or not the patients have 5 prespecified risk factors, including triple vessel disease, diabetes, left ventricular dysfunction, proximal LAD disease, and elderly. The same factors used for analysis of the total cohort were incorporated in the multivariable models for subgroup analyses.
All analyses were conducted by the 2 physicians (Takeshi Kimura and Takeshi Morimoto) with the use of SAS software version 9.1 (SAS Institute Inc) and S-Plus version 7.0 (Insightful Corp) and all reported probability values were 2-sided. The authors had full access to the data and take responsibility for its integrity. All authors have read and agreed to the manuscript as written.
Baseline characteristics of the patients in the 2 groups are shown in Table 2. The PCI group included more elderly patients, particularly those ≥80 years of age. Although malignancy was more often found in the PCI group, the CABG group generally included more high-risk patients, such as those with left ventricular dysfunction, heart failure, prior myocardial infarction, diabetes, stroke, and anemia. However, mean EuroSCORE values were similar between the PCI and the CABG groups.
Regarding the complexity of coronary artery anatomy, the CABG group included more complex patients, such as those with triple-vessel disease, involvement of proximal LAD, and total occlusion. Patients in the CABG group underwent more complete revascularization as indicated by the number of vessels revascularized.
In the PCI group, bare-metal stents were used in 85% of patients. None of the patients received drug-eluting stents. Directional and rotational coronary atherectomy was used in 2% and 7% of patients, respectively. In the CABG group, internal mammary artery graft was used in 95% of patients. Forty-three percent of CABG operations were performed without cardiopulmonary bypass.
Medications such as statins, aspirin, thienopyridines, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, beta blockers, and nitrates were more frequently used in the PCI group than in the CABG group. Blood pressure and HbA1c level were significantly higher in the PCI group than in the CABG group.
Clinical follow-up were completed in 98% at 1 year, and 95% at 2 years. The median follow-up interval was 1319 days in the CABG group (interquartile range, 994 to 1642) and 1266 days in the PCI group (interquartile range, 933 to 1567).
In the total patient population, unadjusted survival outcomes were not different between the CABG and PCI groups (hazard ratio for death after PCI versus CABG [HR], 95% confidence interval [CI]: 1.11 [0.93-1.32], P=0.26; Table 3). Operative mortality in the CABG group evaluated at 30 days was only 1.1% as compared with 0.8% in the PCI group. At 3 years, unadjusted survival rates were 91.7% and 89.6% in the CABG and PCI groups, respectively (log rank P=0.26) (Figure 1).
Survival rates at 3 years were similar in patients with Euro SCORE below or equal to median (3 points; CABG 96.1% versus PCI 95.6%, log rank P=0.77). However, survival rates at 3 years tended to be better for CABG in patients with EuroSCORE above median (CABG 87.5% versus 83.1%, log rank P=0.06).
By multivariable analysis, 14 independent predictors of all-cause mortality were identified, including age ≥75 years, chronic kidney disease, hemodialysis, history of heart failure, chronic obstructive lung disease, malignancy, anemia, peripheral vascular disease, stroke, left ventricular dysfunction, body mass index ≤25.0, diabetes with insulin, absence of statin use, and use of angiotensin converting enzyme inhibitors.
When treatment modalities (CABG/PCI) were incorporated into this multivariable model, survival outcomes tended to be better after CABG (HR [95% CI]: 1.23 [0.99-1.53], P=0.06; Table 3).
Survival outcomes were compared in the prespecified high-risk subgroups. Even in high-risk patients, such as those with diabetes or triple-vessel disease, PCI was frequently chosen in this registry (66% and 51% of patients with diabetes and triple-vessel disease, respectively). CABG was associated with significantly better unadjusted-survival outcomes in patients with triple-vessel disease, diabetes, and left ventricular dysfunction (Table 3). After adjustment for baseline characteristics, the CABG group had significantly better survival outcomes in patients with diabetes, but not in patients with triple-vessel disease (Table 3).
Influence of Age on the Survival Outcome After PCI and CABG
Because age is an important determinant in coronary revascularization strategy choice, survival analyses were stratified by age with a prespecified cut-off value of 75 years.
Survival outcomes favored CABG in patients ≥75 years of age (adjusted HR [95% CI]: 1.37 [0.98-1.92], P=0.07), but not in patients <75 years of age (adjusted HR [95% CI]: 1.09 [0.82-1.46], P=0.55) (Tables 3 and 4⇓ and Figures 2 and 3⇓). The magnitudes of the differences in survival rates between the CABG and PCI groups in patients ≥75 years of age were greater in the high-risk subgroups of triple-vessel disease, diabetes and left ventricular dysfunction (Table 4 and Figures 4 and 5⇓).
In patients ≥75 years of age, unadjusted rates for all-cause mortality at 3 years were 13.3% and 20.7% in the CABG and PCI groups, respectively (log rank P=0.07). Rates of noncardiovascular and cardiovascular death tended to be higher in the PCI group. This trend for excessive noncardiovascular death rates in the PCI group was not observed in patients <75 years of age (Figures 2 and 3⇑).
In patients <75 years of age, no differences between the 2 treatment modalities were apparent in either unadjusted or adjusted survival outcomes in any of the high-risk subgroups of triple-vessel disease, diabetes and left ventricular dysfunction (Table 4 and Figures 4 and 5⇑).
Other Cardiovascular End Points
Event-free rates from other cardiovascular end points are shown in Figure 6. The rate of freedom from myocardial infarction was significantly higher after CABG as compared with that after PCI. The incidences of myocardial infarction were similar at 30 days in the 2 groups. The 2 event-free curves for myocardial infarction diverged between 30 days and 1 year (incidences of myocardial infarction: 0.3% and 1.6% in the CABG and PCI groups, respectively). On the other hand, the incidences of myocardial infarction between 1 year and 3 years were similar in both groups (1.4% and 1.5% in the CABG and PCI groups, respectively).
The rates of freedom from stroke were significantly higher after PCI versus CABG, a difference driven by a relatively higher rate of periprocedural stroke in the CABG group (1.8% and 0.2% in the CABG and PCI groups, respectively, at 30 days).
The rates of freedom from death, myocardial infarction, and stroke were similar between the 2 groups (87.8% and 86.8% in the CABG and PCI groups, respectively, at 3 years, log rank P=0.63).
The rate of freedom from any revascularization procedures was strikingly lower in the PCI group. At 3 years, only 51.7% of patients in the PCI group were free from any revascularization procedures as compared with 90.2% of patients in the CABG group. The rates of target-lesion revascularization in the PCI group were 33.4%, 35.9% and 37% at 1, 2, and 3 years, respectively. The rate of crossover to CABG in the PCI group was 7.2% at 3 years.
The discrepancy in outcomes between randomized controlled trials and registries comparing PCI with CABG is commonly ascribed to usual enrollment in the former of very selected low-risk patients with multi vessel coronary artery disease who are suitable for PCI, a feature that limits the ability to generalize conclusions to many high-risk patient categories in real-world clinical practice.
Our current analysis of CREDO-Kyoto registry data demonstrated both similar and discrepant results to those of other large-scale registries.8,9 Although we also observed trends for better survival outcomes after CABG among overall and diabetic patient populations, in contrast to prior registries, adjusted survival outcomes were not significantly different in patients with triple-vessel disease. Differences in the practice pattern might be related to this discrepancy. Only 14% and 10% of patients with triple vessel disease were treated by PCI in the New York’s cardiac registries and the Northern New England registry, respectively, an observation that is consistent with current guidelines that generally recommend CABG in patients with triple-vessel disease.11,12 However, when CABG is the preferred treatment choice for triple-vessel disease patients, it is possible that the proportion of patients who have comorbidities that preclude choice of CABG would increase in the PCI group. Therefore, the practice pattern in Japan, which is reflected by the choice in the CREDO-Kyoto registry of PCI in 51% of patients with triple-vessel disease, may provide a more appropriate environment to compare PCI with CABG in this subgroup.
Age is an important determinant when considering the choice between CABG and PCI. We observed better survival rate in the CABG group in patients ≥75 years of age, especially in the high risk subgroups such as triple vessel disease and diabetes. Excellent outcome could be achieved by contemporary CABG even in elderly patients. Complex coronary anatomy in elderly patients might be more adequately managed by CABG. However, one could argue this result could be attributable to patient selection bias. Consistent with the latter argument, although better survival after CABG in elderly patients was also reported in the APPROACH registry,13 the AWESOME randomized trial demonstrated similar survival outcomes in patients ≥70 years of age.14 In real-world clinical practice, it is likely that elderly patients with significant comorbidities tend to be more often referred for PCI because of its less invasive nature. The trend for excessive noncardiovascular mortality observed among elderly patients who underwent PCI in this study is suggestive of patient selection bias. This trend for excessive noncardiovascular mortality in the PCI group was not seen in patients <75 years of age. Considering the potential presence of profound patient selection bias in the elderly population, it would be appropriate to exclude elderly patients when attempting observational comparisons between CABG and PCI. In the current analyses, unadjusted and adjusted survival rates of CABG and PCI were not different in any of the anatomic and clinical subgroups when elderly patients were excluded from analyses.
In this study, diabetes did not influence survival among nonelderly patients with triple vessel disease, which is an important difference with current guideline and prior studies.8,9,11,12 This finding might relate to the characteristics of patients with diabetes in our population. Only a quarter of the diabetic patients in this study were insulin-treated diabetes. However, we could not find out any difference in terms of relative survival outcome for CABG as compared with PCI between diabetic patients with or without insulin use.
Another important issue regarding comparisons between CABG and PCI using observational study data are the fact that patients undergoing CABG are more likely to be subjected to extensive scrutiny for comorbidities. Underestimation of comorbidities in the PCI group could lead to results favoring CABG when multivariable analysis is performed to adjust for confounding factors.
Long-term follow-up studies to compare revascularization strategies have the inherent limitation that rapid technical and technological improvements often render the tested strategies obsolete by the time results are available. Although in the current study surgical practices and outcome rates (at least one internal mammary graft in 95% of patients, 43% off-pump procedures, and a 30-day survival rate of 98.8%) were comparable to contemporary ones, contemporary PCI procedures have already shifted from bare-metal to drug-eluting stenting with variable penetration rates. The striking efficacy of drug-eluting stents in preventing both clinical and angiographic restenosis15,16 has led to a rapid expansion of PCI use particularly for patients with complex multivessel disease; however, improvement of survival has not yet been reported with use of drug-eluting stents.17 In the ARTS-2 study, survival rates at 3 years were not significantly different among the 3 groups of ARTS-2, ARTS-1 CABG, and ARTS-1 PCI, initial advantage with sirolimus-eluting stent appeared to be diminished at 3 years of follow-up (Serruys PW, MD, unpublished data, 2007). Furthermore, the pooled analysis of the pivotal randomized trials of the sirolimus-eluting stents suggested excessive mortality in diabetic patients treated with the sirolimus-eluting stents as compared with those treated with bare-metal stents.18 These observations underscore the need for longer-term follow-up of patients with multivessel coronary artery disease treated with drug-eluting stents. When we expand the indications of PCI to more complex subsets of patients by using drug-eluting stents, we should at least confirm that PCI in high risk patients using bare metal stents did not impair the long-term survival as compared with CABG.
Results regarding cardiovascular endpoints other than mortality also deserve some discussion. Although incidences of myocardial infarction were clearly lower after CABG versus PCI, the excess of myocardial infarction in the PCI group was only seen within 1 year after the index procedure. Besides progression of new lesions, abrupt closure, stent thrombosis and restenosis are among the mechanisms of myocardial infarction in this particular time period. Myocardial infarction secondary to these causes might be largely preventable by future development of better drug-eluting stents and improved use and availability of existing and novel adjunctive pharmacology. It is noteworthy that the incidences of myocardial infarction beyond one year were similar in both groups, although this observation needs confirmation with longer-term follow-up.
Restenosis had been the major drawback of PCI using bare-metal stent. Extremely high rate of repeated revascularization procedures in this study might be largely attributable to expanded use of PCI for more complex subsets of patients and high rate of angiographic follow-up in the Japanese clinical practice. However, the advent of drug-eluting stents have already markedly ameliorated the problems related to restenosis in real world clinical practice.19
There are several important limitations of this study. As compared with prior observational studies,8,9 the sample size was not large enough to detect small differences in survival rates between the CABG and PCI groups. Although the definition of elderly patients was prespecified and seems clinically reasonable, the cut-off value of 75 years of age is arbitrary. Although variations in the frequencies of some anatomic factors such as numbers of diseased vessels, involvement of proximal LAD, and presence of total occlusions were adjusted for comparative analyses, our conclusions might not be applicable to those patients with other anatomic complexities, such as diffuse disease, heavy calcification or bifurcation that were not evaluated in this study. Furthermore, important medications, statins in particular, to prevent cardiovascular events are obviously underused. More optimal use of medications might have changed the long-term outcome of both CABG and PCI. Finally, the baseline characteristics such as age, body mass index, and prevalence of diabetes in the current population were markedly different from prior studies.8,9 Although it is beyond the scope of the current article to discuss on the contribution of these demographic features to the different outcome in comparison to prior studies, we should admit that differences in racial, cultural, and socioeconomic factors might hinder generalization of the conclusions of this study outside Japan. Relatively low rate of recurrent coronary events in the Japanese population demonstrated in the REACH registry might have favorable influence on survival outcome after PCI.20
Despite the abovementioned study limitations, we would conclude that for patients with multivessel coronary artery disease, survival outcomes were similar among those who underwent either CABG or PCI with bare-metal stents in real-world clinical practice in Japan, when elderly patients are excluded from analysis.
List of Clinical Research Coordinators
Kumiko Kitagawa, Hiromi Yoshida, Misato Yamauchi, Asuka Saeki, Chikako Hibi, Emi Takinami, Izumi Miki, Miya Hanazawa, Naoko Okamoto, Sachiko Maeda, Saeko Minematsu, Saori Tezuka, Yuki Sato, Yumika Fujino, Hitomi Sasae, Rei Fujita, Ayu Motofusa, Takami Hiraoka, Ayumi Yamamoto, Miho Hayashikawa, Yoko Fujiki.
We are indebted to the clinical research coordinators for data collection and to Yoko Kasakura for secretarial assistance.
Sources of Funding
This work was supported by an educational grant from the Research Institute for Production Development (Kyoto, Japan).
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