Studies of PCI with bare-metal stents vs CABG
The ARTS trial (Arterial Revascularization Therapy Study) compared PCI (with bare-metal stents) and CABG in 1,205 patients with multivessel coronary artery disease.23 The mortality rate did not differ significantly between two treatment groups overall or in the diabetic subgroup. However, the repeat revascularization rate was higher with PCI than with CABG.
The SoS trial (Stenting or Surgery)24 had similar results.
The ERACI II trial (Argentine Randomized Study: Coronary Angioplasty With Stenting Versus Coronary Bypass Surgery in Multi-Vessel Disease)25 found no difference in mortality rates at 5 years with CABG vs PCI.
These trials were criticized, as none of them routinely used glycoprotein IIb/IIIa inhibitors with PCI, which by then had been shown to reduce mortality rates.30 However, these trials made it clear that restenosis requiring repeat revascularization was a major disadvantage of PCI with bare-metal stents compared with CABG in patients with diabetes. Drug-eluting stents, which significantly reduced the rates of in-stent restenosis and target-lesion revascularization, were expected to overcome this major disadvantage.
Studies of PCI with drug-eluting stents vs CABG
ARTS II was the first trial to compare PCI with drug-eluting stents vs CABG. This was a nonrandomized single-arm study of 607 patients (including 159 with diabetes) who were treated with drug-eluting stents; the outcomes were compared with the CABG group from the earlier ARTS trial.31
At 3 years, in the diabetic subgroup, the rates of death, myocardial infarction, and stroke were not significantly different between treatments, although a trend favored PCI. However, this comparison was limited by selection bias, as ARTS II was a nonrandomized trial in which operators chose patients for drug-eluting stents in an attempt to match already known outcomes from the CABG cohort of ARTS.
SYNTAX (Synergy Between PCI With Taxus and Cardiac Surgery) was the first randomized trial comparing PCI with drug-eluting stents (in this trial, paclitaxel-eluting) vs CABG in patients with three-vessel or left main coronary artery disease.26,27 Subgroup analysis in patients with diabetes mellitus revealed a higher rate of major adverse cardiac and cerebrovascular events (death, myocardial infarction, stroke, or repeat revascularization) in the PCI group than in the CABG patients, largely driven by higher rates of repeat revascularization after PCI.32,33 SYNTAX was not designed to assess significant differences in rates of death.
The CARDIa trial (Coronary Artery Revascularization in Diabetes) randomized patients with diabetes and multivessel coronary artery disease to PCI (about one-third with bare-metal stents and two-thirds with drug-eluting stents) or CABG. Rates of major adverse cardiac and cerebrovascular events were higher in the PCI group, again largely driven by higher rates of repeat revascularization.4 CARDIa was stopped early because of a lack of enrollment and could not provide sufficient evidence to endorse one strategy over the other.
VA-CARDS (Veteran Affairs Coronary Artery Revascularization in Diabetes) randomized patients with diabetes and proximal left anterior descending artery or multivessel coronary artery disease to receive PCI with drug-eluting stents or CABG.28 Although the rate of death was lower with CABG than with PCI at 2 years, the trial was underpowered and was terminated at 25% of the initial intended patient enrollment. In addition, only 9% of diabetic patients screened were angiographically eligible for the study.29
Registry data. Analysis of a large data set from the National Cardiovascular Disease Registry and the Society of Thoracic Surgeons revealed a survival advantage of CABG over PCI for a follow-up period of 5 years.34 However, this was a nonrandomized study, so its conclusions were not definitive.
THE FREEDOM TRIAL
Given the limitations of the trials described above, the National Heart, Lung, and Blood Institute sponsored the FREEDOM trial—an appropriately powered, randomized comparison of PCI (with drug-eluting stents) and CABG (using arterial grafting) in patients with diabetes and multivessel coronary artery disease using contemporary techniques and concomitant optimal medical therapy.8
FREEDOM study design
The FREEDOM trial enrolled 1,900 patients with diabetes and angiographically confirmed multivessel coronary artery disease (83% with three-vessel disease) with stenosis of more than 70% in two or more major epicardial vessels involving at least two separate coronary-artery territories. The main exclusion criteria were severe left main coronary artery stenosis (≥ 50% stenosis), class III or IV congestive heart failure, and previous CABG or valve surgery. For CABG surgery, arterial revascularization was encouraged.
Dual antiplatelet therapy was recommended for at least 12 months in patients receiving a drug-eluting stent, and optimal medical management for diabetes, hypertension, and hyperlipidemia was strongly advocated.
Between April 2005 and April 2010, 32,966 patients were screened, of whom 3,309 were eligible for the trial and 1,900 consented and were randomized (953 to the PCI group and 947 to the CABG group). The patients were followed for a minimum of 2 years and had a median follow-up time of 3.8 years. Outcomes were measured with an intention-to-treat analysis.
Patients. The groups were comparable with regard to baseline demographics and cardiac risk factors.
The mean age was 63; 29% of the patients were women, and 83% had three-vessel coronary artery disease. The mean hemoglobin A1c was 7.8%, and the mean ejection fraction was 66%. The mean SYNTAX score, which defines the anatomic complexity of lesions, was 26 (≤ 22 is mild, 23–32 is intermediate, and ≥ 33 is high). The mean EURO score, which defines surgical risk, was 2.7 (a score ≥ 5 being associated with a lower rate of survival).
The primary composite outcome (death, nonfatal myocardial infarction, or nonfatal stroke) occurred less frequently in the CABG group than in the PCI group (Table 2). CABG was also associated with significantly lower rates of death from any cause and of myocardial infarction. Importantly, survival curves comparing the two groups diverged at 2-year follow-up. In contrast to other outcomes assessed, stroke occurred more often in the CABG group. The 5-year rates in the CABG group vs the PCI group were:
- Primary outcome—18.7% vs 26.6%, P = .005
- Death from any cause—10.9% vs 16.3%, P = .049
- Myocardial infarction—6% vs 13.9%, P < .0001
- Stroke—5.2% vs 2.4%, P = .03.
The secondary outcome (death, nonfatal myocardial infarction, nonfatal stroke, or repeat revascularization at 30 days or 12 months) had occurred significantly more often in the PCI group than in the CABG group at 1 year (16.8% vs 11.8%, P = .004), with most of the difference attributable to a higher repeat revascularization rate in the PCI group (12.6% vs 4.8%, P < .001).
Subgroup analysis. CABG was superior to PCI across all prespecified subgroups, covering the complexity of the coronary artery disease. Event rates with CABG vs PCI, by tertiles of the SYNTAX score:
- SYNTAX scores ≤ 22: 17.2% vs 23.2%
- SYNTAX scores 23–32: 17.7% vs 27.2%
- SYNTAX scores ≥ 33: 22.8% vs 30.6%.
Cost-effectiveness. Although up-front costs were higher with CABG, at $34,467 for the index hospitalization vs $25,845 for PCI (P < .001), when the in-trial results were extended to a lifetime horizon, CABG had an incremental cost-effectiveness ratio of $8,132 per quality-adjusted life-year gained vs PCI.35 Traditionally, therapies are considered costeffective if the incremental cost-effectiveness ratio is less than $50,000 per quality-adjusted life-year gained.
WHY MAY CABG BE SUPERIOR IN DIABETIC PATIENTS?
The major advantage of CABG over PCI is the ability to achieve complete revascularization. Diabetic patients with coronary artery disease tend to have diffuse, multifocal disease with several stenotic lesions in multiple coronary arteries. While stents only treat the focal area of most significant occlusion, CABG may bypass all proximal vulnerable plaques that could potentially develop into culprit lesions over time, truly bypassing the diseased segments (Figure 1).
In addition, heavy calcification may not allow optimal stenting in these patients.
Use of multiple stents increases the risk of restenosis, which could lead to a higher incidence of myocardial infarction and need for repeat revascularization. This was evident in the FREEDOM trial, in which the mean number of stents per patient was 4.2. Also, some lesions need to be left untreated because of the complexity involved.
The major improvement in outcomes after CABG has resulted from using arterial conduits such as the internal mammary artery rather than the saphenous vein.36 The patency rates of internal mammary artery grafts exceed 80% over 10 years.37 Internal mammary artery grafting was done in 94% of patients receiving CABG in the FREEDOM trial.