The Lancet December 03, 2016

Percutaneous coronary angioplasty versus coronary artery bypass grafting in treatment of unprotected left main stenosis (NOBLE): a prospective, randomised, open-label, non-inferiority trial

Timo Mäkikallio, Niels R Holm, Mitchell Lindsay et al.

Bottom Line

In patients with unprotected left main coronary artery disease, CABG was superior to PCI with respect to the composite endpoint of major adverse cardiac or cerebrovascular events at 5 years, primarily driven by higher rates of non-procedural myocardial infarction and repeat revascularization in the PCI group.

Key Findings

1. At 5 years, the Kaplan-Meier estimate for the primary composite endpoint (MACCE) was 29% for PCI compared to 19% for CABG (HR 1.48; 95% CI 1.11–1.96, p=0.0066), demonstrating the superiority of CABG.

2. There was no significant difference in 5-year all-cause mortality between the PCI and CABG groups (12% vs. 9%; HR 1.07; 95% CI 0.67–1.72, p=0.77).

3. PCI was associated with a significantly higher rate of non-procedural myocardial infarction compared to CABG (7% vs. 2%; HR 2.88; 95% CI 1.40–5.90, p=0.0040).

4. The need for any repeat coronary revascularization was significantly higher in the PCI arm than in the CABG arm (16% vs. 10%; HR 1.50; 95% CI 1.04–2.17, p=0.032).

5. Stroke rates at 5 years trended higher with PCI compared to CABG (5% vs. 2%; HR 2.25; 95% CI 0.93–5.48, p=0.073), though this difference did not reach statistical significance.

Study Design

Design

RCT

Open-Label

Sample

1,201

Patients

Duration

3.1 yr

Median

Setting

Northern Europe

Population Patients with stable angina, unstable angina, or NSTEMI with a visually assessed left main coronary artery stenosis ≥50% or fractional flow reserve ≤0.80, and suitable anatomy for either PCI or CABG (no more than 3 additional non-complex lesions).

Intervention Percutaneous coronary intervention (PCI) using drug-eluting stents (predominantly biolimus-eluting).

Comparator Coronary artery bypass grafting (CABG).

Outcome Major adverse cardiac or cerebrovascular events (MACCE): a composite of all-cause mortality, non-procedural myocardial infarction, any repeat coronary revascularization, and stroke.

Study Limitations

• The open-label design could have influenced decision-making regarding the need for repeat revascularizations, potentially biasing a component of the primary endpoint.

• The primary endpoint evaluation timing was changed from 2 years to a median of 3 years due to lower-than-expected overall event rates.

• The trial utilized predominantly biolimus-eluting stents; results might differ with the use of newer generation ultra-thin strut drug-eluting stents.

• There was no routine angiographic follow-up mandated, so the true rates of silent graft or stent failure remain unknown.

• Patients with high SYNTAX scores (≥33) constituted less than 10% of the study population, limiting the generalizability of the findings to more anatomically complex cohorts.

Clinical Significance

The NOBLE trial provided critical evidence that CABG remains the gold standard for revascularization in unprotected left main coronary artery disease, offering superior freedom from major adverse cardiovascular and cerebrovascular events at 5 years compared to PCI. Although mortality was similar between the two strategies, the PCI group faced significantly higher risks of non-procedural myocardial infarction and repeat revascularization. These findings highlight the importance of Heart Team discussions to weigh the upfront procedural invasiveness of CABG against the longer-term recurrent ischemic morbidity associated with PCI.

Historical Context

Historically, surgical revascularization (CABG) was the uncontested standard of care for unprotected left main coronary artery (LMCA) disease. As percutaneous techniques and drug-eluting stents advanced, the SYNTAX trial (2009) established PCI as a feasible alternative for LMCA patients with low-to-intermediate anatomical complexity. The NOBLE trial was conducted concurrently with the EXCEL trial to definitively compare modern PCI against CABG in LMCA disease. While EXCEL (published simultaneously) reported non-inferiority for PCI at 3 years using a different composite endpoint, NOBLE demonstrated CABG superiority, largely because NOBLE excluded periprocedural MI and included repeat revascularization in its primary endpoint. This discordance has fueled ongoing debate regarding the optimal patient-centered revascularization strategy for LMCA disease.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

What does the term 'unprotected' mean in the context of left main coronary artery disease, and why does significant stenosis in this vessel traditionally mandate surgical bypass?

Key Response

'Unprotected' refers to the absence of prior patent bypass grafts to the left anterior descending or circumflex arteries. Because the left main supplies a massive portion of the left ventricular myocardium, an acute occlusion in an unprotected left main is frequently fatal, making definitive revascularization critical.

Resident

How do the findings of the NOBLE trial influence the shared decision-making process when evaluating a patient with unprotected left main disease for PCI versus CABG, particularly regarding specific complication risks?

Key Response

While PCI offers a less invasive option with faster recovery, NOBLE showed CABG provides a more durable result with lower 5-year rates of non-procedural MI and repeat revascularization. Mortality was similar, so residents must frame the discussion around the trade-off between procedural invasiveness and long-term durability.

Fellow

The NOBLE trial used a primary endpoint that specifically excluded periprocedural myocardial infarction, unlike the EXCEL trial. How does this endpoint definition impact the comparative efficacy of PCI versus CABG?

Key Response

CABG inherently causes more periprocedural enzyme leaks than PCI. By excluding periprocedural MIs, NOBLE's primary endpoint favored the long-term durability of CABG (fewer spontaneous MIs). In contrast, EXCEL included periprocedural MIs, which heavily penalized CABG early on and drove its initial non-inferiority finding for PCI.

Attending

Given the nuanced differences between NOBLE and EXCEL, how should practicing cardiologists synthesize these data to guide the Heart Team approach for an average-risk patient with isolated left main disease?

Key Response

Attendings must synthesize conflicting evidence. While EXCEL showed early non-inferiority, 5-year data from both trials demonstrate a late hazard with PCI for repeat revascularization and spontaneous MI. The Heart Team must weigh frailty and early surgical morbidity against the definitive long-term anatomical protection of CABG.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

The NOBLE trial was designed as a non-inferiority trial but ultimately concluded that CABG was superior. From a statistical perspective, what are the methodological requirements for testing superiority after failing non-inferiority?

Key Response

This probes closed testing procedures. Because the upper limit of the 95 percent CI for the hazard ratio exceeded the non-inferiority margin, non-inferiority failed. Since the hazard ratio significantly favored CABG, superiority could be declared. Researchers should understand how hierarchical testing allows switching between non-inferiority and superiority without inflating type I error.

Journal Editor

NOBLE utilized the biolimus-eluting BioMatrix Flex stent, which is less commonly used today. How does this choice affect the external validity of the study, and how should an editor weigh this limitation?

Key Response

Reviewers focus on generalizability. Critics argue that using a stent with thicker struts might have disadvantaged the PCI arm compared to best-in-class contemporary thin-strut stents. An editor must ensure the authors adequately address whether this specific stent choice limits the current clinical applicability of the findings.

Guideline Committee

How do the 5-year outcomes of the NOBLE trial inform the current ACC/AHA and ESC/EACTS guideline recommendations regarding the Class of indication for CABG versus PCI in patients with low-to-intermediate SYNTAX scores?

Key Response

Current guidelines strongly recommend CABG (Class 1) for left main disease. PCI is considered a reasonable alternative (Class 2a) for low anatomical complexity (SYNTAX score under 23). NOBLE's data reinforces the Class 1 recommendation for CABG due to its durability, emphasizing the need to explicitly warn patients about the higher risk of repeat revascularization and spontaneous MI with PCI.

Clinical Landscape

Noteworthy Related Trials

2009

SYNTAX Trial

n = 1,800 · NEJM

Tested

PCI with paclitaxel-eluting stents

Population

Patients with 3-vessel or left main coronary artery disease

Comparator

Coronary artery bypass grafting (CABG)

Endpoint

Major adverse cardiac or cerebrovascular events (MACCE) at 12 months

Key result: CABG remained the standard of care for patients with complex lesions, though PCI was an acceptable alternative for less complex disease.

2011

PRECOMBAT Trial

n = 600 · NEJM

Tested

PCI with sirolimus-eluting stents

Population

Patients with unprotected left main coronary artery stenosis

Comparator

Coronary artery bypass grafting (CABG)

Endpoint

Major adverse cardiac or cerebrovascular events (MACCE) at 1 year

Key result: PCI was non-inferior to CABG for the composite primary endpoint at 1 year.

2016

EXCEL Trial

n = 1,905 · NEJM

Tested

PCI with everolimus-eluting stents

Population

Patients with left main coronary artery disease and low or intermediate SYNTAX scores

Comparator

Coronary artery bypass grafting (CABG)

Endpoint

Composite of death, stroke, or myocardial infarction at 3 years

Key result: PCI was non-inferior to CABG with respect to the primary composite endpoint at 3 years.

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