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a Cardiopulmonary Research Science and Technology Institute, Dallas, Texas
b Cardiovascular Care Management Network, HCA, Inc., Nashville, Tennessee
Accepted for publication March 25, 2008.
* Address correspondence to Dr Mack, 7777 Forest Lane, Ste A-323, Dallas, TX 75230 (Email: slhill{at}csant.com).
Presented at the Forty-third Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Jan 29–31, 2007.
| Abstract |
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Methods: All patients undergoing isolated coronary revascularization in 8 community-based hospitals were enrolled. Preprocedural, intraprocedural, and postprocedural data were captured, with outcomes obtained at 18 months by patient and physician contact, and the Social Security Death Index.
Results: The study enrolled 4336 patients, 71.2% PCI and 28.8% CABG. DESs were used in 2249 PCIs (73.1%), and 596 CABG procedures (47.8%) were off-pump. Incidence of major adverse cardiac events at 18 months was 14.7% for CABG vs 23.3% for PCI (p < 0.001). Cardiac death and myocardial infarction had similar rates. The need for repeat revascularization was significantly less with CABG (6.2% vs 13.6%, p < 0.001). Hazard ratio of CABG to PCI was 0.76 (95% confidence interval, 0.571 to 0.872). CABG outcome was similar on-pump and off-pump, as was repeat revascularization with DES (12.1%) vs BMS (14.9%; p = 0.096). Overall event-free survival was 85.3% in CABG and 76.8% in PCI (p < 0.001).
Conclusions: Rates of repeat revascularization were significantly higher for PCI than for CABG, but mortality and myocardial infarction were the same. There were no significant differences in outcomes between DES and BMS or between on-pump and off-pump CABG.
| Introduction |
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Much of the evidence for determining procedural outcomes, and therefore selecting the proper revascularization strategy for an individual patient, comes from randomized controlled trials (RCTs) comparing approaches [3–6]. Although RCTs represent the highest level of evidence-based medicine (level A), they are subject to trial design bias by preferentially enrolling relatively low-risk patients, resulting in a high degree of selectability. Only about 4% of patients screened for inclusion in RCTs comparing CABG vs PCI have actually been enrolled in these trials [3–11]; however, the results in trials of these highly selective patients are frequently extrapolated or generalized to the population as a whole.
The validity of this "generalizability" of the results in these select patients to the population as a whole is questionable. This is particularly currently relevant as an estimated 60% to 70% of DES usage is now "off label," without RCT evidence of outcomes in these patients. In a similar manner, RCTs of CABG performed on-pump or off-pump are subject to the same limitations as are pivotal trials of BMSs vs DESs. Doubts about whether the outcomes in the "real world" for coronary revascularization by either catheter-based or surgical approaches correlate with the RCTs has been raised by analysis of large population outcomes databases [2, 12–14]. We hypothesize that the results of coronary revascularization as performed in routine clinical practice may differ from the outcomes of RCTs.
| Material and Methods |
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Exclusion criteria included patients undergoing any concomitant procedure (except transmyocardial laser revascularization) or undergoing "salvage" PCI or CABG.
Follow-up was performed at 6, 12, and 18 months and was obtained by direct patient contact and, when that was not possible, by physician contact. Additional mortality outcomes were obtained from the Social Security Death Index. The major clinical end point was major adverse cardiac events (MACE), which included death, myocardial infarction (MI), or the need for repeat revascularization by CABG or PCI. When the study was initiated, the issue of stent thrombosis was not paramount. During the follow-up period of this study, this complication has assumed significant clinical relevance. All clinical events were retrospectively adjudicated using current Academic Research Council (ARC) definitions. Stent thrombosis is reported as a composite of ARC definite and probable.
A quality of life analysis was also performed. The Medical Outcomes Study 12-Item Short-Form Health Survey (SF-12) was used to summarize the general physical and mental health status of patients. The 12 questions in the SF-12 are designed to measure an individual's perceived health across eight health dimensions: physical functioning, role-physical, bodily pain, general health, vitality, social functioning, role-emotional, and mental health. Answers to those questions are combined (weighted) into physical and mental component summary scales, both of which are transformed to have a mean of 50 and a standard deviation (SD) of 10 in the general population.
Statistical Analysis
All data were input into a customized database. For statistical analysis, data were exported to SAS 9.1.3 software (SAS Institute, Cary, NC). Continuous variables were compared using t tests. Categoric variables were analyzed using the
2 or the Fisher exact test when the number of expected responses in a cell was small. Kaplan-Meier analysis of time to events was used. Risk adjustment was performed using Cox proportional hazard analysis. Data from the SF-12 study are presented as mean ± SD and median scores, with the groups compared across procedures using Wilcoxon rank sums.
| Results |
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Because this was an observational study, treatment was at the discretion of the treating physician. However, controlling for variables that are significantly different between the CABG and PCI groups, including operative status, previous CABG, previous PCI, previous MI, valve operations, or stroke, presence of cerebral or peripheral vascular disease, or current smoker, the hazard ratio for MACE by Cox analysis of CABG to PCI was 0.76 (95% confidence interval, 0.571 to 0.872).
Analysis of the subgroup with diabetes mellitus demonstrated that in both CABG and PCI, the outcomes were worse for diabetic patients than for nondiabetic patients (Table 6). Neither off-pump CABG nor DESs offered any particular benefit compared with nondiabetic patients.
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| Comment |
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RCTs represent the highest order of evidence-based medicine (level A). The RCTs comparing CABG vs PCI have repeatedly shown no differences in mortality between the two treatment strategies but have shown an increased need for repeat revascularization by PCI [3–11]. The shortcomings of these trials, however, are that they include only relatively small patient cohorts that are underpowered to show a mortality difference and that the follow-up period is relatively short so that any potential survival advantage with CABG may not yet be detected. Outcomes from single-center and large population studies have shown a mortality benefit from CABG compared with PCI that appears to increase with longer follow-up of 3 to 5 years [2, 12–15].
Despite the relatively large number of patients in this study (> 4000) and high rate of follow-up (> 90%) supplemented by mortality data from the Social Security Death Index, we were unable to discern any mortality advantage at this relatively short 18-month period of follow-up with either therapy. Overall survival at 18 months was 92.4% in the CABG group and 91.5% in the PCI patients. This is significantly less than the Arterial Revascularization Therapies (ARTS) trial, the most recent RCT comparing the two treatments, in which survival at 1 year was 97.2% for CABG and 97.5% for PCI [3]. The reintervention rate in the ARTS trial, which used BMSs only, was 16.8% at 1 year and 13.6% in this observational series in which 76% of the PCI patients received DESs. This represents some improvement but is significantly less than recent single-digit restenosis rates reported by pivotal DES trials. Target vessel revascularization was 8.6% with sirolimus stents in the SIRIUS trial (SIRolImUS-coated stent in treatment of patients with de novo coronary artery lesions) [16] and 4.7% with the Taxus stent (Boston Scientific, Natick, MA) in the Taxus IV trial [17]. Most recently, the ARTS II trial reported repeat reintervention rates of 8.5% at 1 year, with an 89.5% event-free survival [18]. With an estimated 60% to 75% of DES usage now off label (ie, not in patients typically included in these randomized trials), we believe that the event rates reported in our observational study are more reflective of real world outcomes than those reported in the pivotal RCTs.
We also demonstrated that the outcomes by all treatment approaches were worse in diabetic patients compared with nondiabetic patients. However, the incidence of major adverse events was proportionately the same relative to each other by each revascularization approach.
We also compared the outcomes of patients treated with DESs with those with BMSs. The composition of the groups receiving both treatments was relatively uniform and again demonstrated no significant difference in mortality or MI, but did show a significantly less need for repeat revascularization (12.1% vs 14.9%, p = 0.096) in the patients receiving DES. Although stent thrombosis was not a major issue at the initiation of this study, all adverse events in the PCI group were retrospectively adjudicated to determine the incidence of stent thrombosis by current criteria [19]. We found no increase in stent thrombosis in the DES group compared with BMSs, but the overall incidence was higher (3.1%) than the lower incidence reported in the pivotal trials and equivalent to that found in industry registries (2.7% for Cypher [Cordis Corporation; Miami, FL] and 3.6% for Taxus at 1 year).
Likewise, numerous RCTs of off-pump vs on-pump CABG have been done, and 37 RCTs and three meta-analyses of these RCTs have been published [20–21]. No mortality difference was found between the two groups even in meta-analyses; however, these are still underpowered to show a difference. As with the DES trials, relatively low-risk patients are enrolled in surgery trials. The 1- or 2-year mortality in off-pump vs on-pump CABG was 2.3% and 2.6%, which is significantly lower than the 6.6% and 8.7% we observed in this study. As CABG is performed in the real world clinical setting, we also found no difference in death or major adverse events in on-pump vs off-pump CABG.
We found that quality of life was superior to an age-matched referenced population for physical well-being and equivalent for mental well-being but that CABG and PCI did not differ significantly from each other. Any potential adverse effects on quality of life from the two revascularization approaches, periprocedural invasiveness for CABG, and need for repeat revascularization by PCI appear to have largely resolved by 18 months.
Limitations
This study is limited because it is observational in nature and is therefore subject to treatment bias. Despite this limitation, demographic analysis of the study groups show that for the major demographic factors of age, sex, race, and presence of diabetes, the four treatment groups were relatively uniform. Despite the inclusion of more than 4000 patients in this study, it is still underpowered to detect any potential mortality benefit.
Another limitation is the ability to achieve only 90% follow-up. The Sunbelt has a mobile population, and higher rates of follow-up were not achievable. The relatively short period of follow-up is also a limitation. An observation period of 18 months is still too short to detect differences in major outcomes, as has been seen in observational studies with large populations. We intend to obtain additional funding for continued follow-up for at least a 5-year period.
Summary
Coronary revascularization, as currently practiced in the real world clinical setting, generally leads to good outcomes. Overall, however, the outcomes were inferior in both treatment groups from the standpoint of death and need for repeat revascularization at 18 months compared with RCT results. Although the results with each revascularization approach were inferior to those in RCTs and industry-sponsored registries, relative to each other, the outcomes were similar. RCTs are sufficient to demonstrate initial proof of concept of therapies in selective homogeneous populations, but observational studies demonstrate different results in the more heterogeneous real world of clinical use.
We found no differences in any outcomes between on-pump and off-pump CABG. Patients who received DESs had less need for repeat revascularization than patients who received BMSs, but this was not statistically significant. We also found no mortality difference between CABG and PCI; however, this potential benefit of CABG has only been apparent in larger population studies with longer follow-up.
| Appendix |
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| Discussion |
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Thank you.
DR MACK: Thank you for that very relevant question, Robert. What the audience may not know is that Robert and I have spent a lot of time the last couple of months looking at outcomes of CABG vs PCI, and I think both of us are very conversant with the field, and Robert's point is the absolute crucial one. I have two responses.
First, this study did not show exactly what I anticipated. On the front end, when I went to obtain funding, my preconceived surgical bias was there are a lot of adverse events with PCI that we never know about and I will bet that at the end of this, CABG outcomes are going to be much better. Indeed, they weren't, and the numbers are the numbers. This I think is as close to what the real world is as one can be, and we have looked at this every which way, and I am absolutely confident that these are the numbers.
Secondly, as I alluded to at the end, despite the fact that this is over 4000 patients with relatively complete follow-up, it is too small a study with too short a follow-up and therefore is underpowered to detect a difference in mortality, or stroke, between the two groups. If one wants to detect a mortality benefit with a 2% incidence and you are looking to detect a 20% difference, it would take 88,000 patients to be adequately powered. It takes almost that many patients to detect a difference for stroke. And as I said, in New York and Northern New England, it has taken 3 to 5 years to show that there is a mortality benefit, and I think 18 months is too short a period of time for us to be able to say that there is no difference in mortality between the two groups.
| Acknowledgments |
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| References |
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