Unprotected Left Main PCI: Status Report 2013

Abstract: Unprotected left main coronary artery (ULMCA) disease is seen in 4% of patients who undergo angiography. Though coronary artery bypass graft surgery has traditionally been the preferred approach to revascularization, recent major society guidelines support the use of percutaneous coronary intervention (PCI) in properly selected patients. This article provides an overview of recent studies evaluating the efficacy of ULMCA PCI and looking at contemporary approaches to the evaluation and percutaneous treatment of ULMCA disease. The ongoing EXCEL trial will help elucidate the role of ULMCA PCI in the treatment of left main disease compared with coronary artery bypass graft surgery.

J INVASIVE CARDIOL 2013;25(9):478-482

Key words: high-risk PCI, left main disease, ULMCA PCI

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Unprotected left main coronary artery (ULMCA) disease is seen in approximately 4% of patients who undergo angiography.¹ Revascularization in these patients is recommended due to a significantly higher mortality rate in those treated medically.² While coronary artery bypass graft (CABG) surgery has traditionally been the preferred mode of revascularization, there are increasing data that percutaneous coronary intervention (PCI) is often a viable option, and recent guidelines now suggest that PCI be considered in appropriate patients.^3,4 The purpose of this article is to provide an updated overview of the current understanding of the evaluation and treatment of ULMCA disease, with a particular focus on what recent clinical studies have added to this body of data.

Major Society Guidelines

Recent major society guidelines are summarized in Table 1. The 2011 American College of Cardiology Foundation/American Heart Association/Society for Cardiovascular Angiography and Interventions (ACCF/AHA/SCAI) guidelines for PCI make a Class IIa recommendation for ULMCA PCI in patients with ostial or trunk left main disease, or in those with low SYNTAX scores (ie, <23), if they are also felt to be at increased risk for surgical revascularization. A Class IIa recommendation is also made for PCI for unstable angina (UA)/non-ST elevation myocardial infarction (NSTEMI) if a patient is not a candidate for CABG, or in the setting of ST-elevation myocardial infarction (STEMI) if coronary flow is compromised and PCI can be performed more rapidly and safely than CABG.³ Additionally, the guidelines make a Class IIb recommendation for PCI in patients with bifurcation disease, low-intermediate SYNTAX scores (ie, <33), and increased surgical risk. Though still not fully supportive of ULMCA PCI, this is a departure from the last full guideline update in 2005⁵ and focused update in 2007,⁶ which recommended against ULMCA PCI if a patient was eligible for CABG, except in the case of UA/NSTEMI with ongoing hemodynamic instability. CABG is still considered the gold standard and maintains a Class I indication in all of these scenarios.

The European Society of Cardiology (ESC) and European Association for Cardio-Thoracic Surgery (EACTS) released their first guideline statement for myocardial revascularization in 2010.⁴ These guidelines make a Class IIa recommendation for PCI in the setting of ostial or trunk left main disease, either in isolation or with single-vessel coronary artery disease (CAD). A Class IIb recommendation is made in the setting of left main bifurcation disease with single-vessel CAD, or in left main with 2- or 3-vessel CAD with a SYNTAX score of <33. CABG receives a Class I recommendation in all of these scenarios. Both the American and European guidelines recommend a Heart Team approach involving the input of both cardiologists and surgeons when determining the optimal revascularization strategy in patients with ULMCA disease.

Left Main Assessment

Angiographic assessment of the ULMCA, even using quantitative coronary angiography, is notoriously unreliable and can lead to improper evaluation of lesion severity.^7,8 Several invasive tools have been clinically validated for the hemodynamic and anatomic assessment of intermediate lesions involving the ULMCA to aid in decision-making regarding revascularization.

Fractional flow reserve (FFR) was first validated in decision-making for left main revascularization in 2001.⁹ Patients with FFR <0.75 underwent CABG and those with FFR ≥0.75 were treated medically, with similar clinical outcomes during 3 years of follow-up. The largest clinical validation of FFR use for left main stenosis used a cutoff of 0.80; survival estimates at 5 years were similar between the surgically-treated group with FFR <0.80 and the medically-treated group with FFR ≥0.80 (85.4% vs 89.8%, respectively; P=.48).⁷ Of note, the available studies looking at the use of FFR in ULMCA disease utilized CABG when revascularization was pursued, so it is uncertain whether the results would be similar following ULMCA PCI.

Intravascular ultrasound (IVUS) has also been used in this setting. The LITRO study was published in 2011 and prospectively validated a minimal luminal area (MLA) cutoff of 6 mm² to determine the need for left main revascularization.⁸ Outcomes in patients with MLAs <6 mm² who underwent revascularization (45% with PCI and 55% with CABG) were similar to those in patients with MLAs ≥6 mm² who were treated medically. Prior to this, a MLA of 6 mm² had been suggested based on Murray’s law using MLAs of 4 mm² in the left anterior descending and circumflex arteries. More recently, an MLA of 4.8 mm² has been proposed as a more specific cutoff and correlates with an FFR of 0.80; however, no clinical validation of this cutoff has yet been undertaken.¹⁰ In addition to helping determine the severity of left main stenosis, IVUS can also provide useful anatomic information to help guide PCI should this be pursued.

Optical coherence tomography (OCT) can also be used in this setting, though the large diameter of the vessel and need for adequate catheter engagement may limit OCT’s ability to image left main lesions, especially those involving the ostium. Fujino et al recently reported a comparison of OCT and IVUS assessment of left main lesions before and after PCI and found that MLA values were similar between the two modalities, suggesting that the use of OCT for deciding whether to revascularize a left main lesion may be feasible and comparable to the use of IVUS.¹¹ OCT was unable to completely image the left main more often, but was more sensitive in detecting stent malapposition and edge dissections following PCI.

Recently, Spoon et al presented data comparing three-dimensional (3D) quantitative coronary angiography (QCA) to IVUS.¹² 3D QCA utilizes data derived from various views obtained during angiography to create a 3D model of the left main. 3D QCA was found to correlate well with minimal luminal diameter and MLA values and may ultimately help to reduce the need for invasive assessment.

Non-invasive evaluation with coronary computed tomography (CT) angiography is an attractive approach given the large diameter and proximal nature of the left main. However, the use of coronary CT angiography for deciding whether or not to perform revascularization in ULMCA disease has not been well studied to date. Newer techniques such as CT-derived FFR are being refined, but are still lacking in diagnostic accuracy and have not yet been studied in the assessment of ULMCA disease.¹³ 

Comparison to Surgical Revascularization

The available randomized trials comparing CABG to PCI in ULMCA disease^14-17 are summarized in Table 2. They predominantly provide short-term follow-up, but appear to indicate that PCI may provide similar outcomes when compared to CABG, particularly in the setting of lower anatomic complexity. PCI is associated with a higher incidence of subsequent revascularization, but also comes at a lower cost of periprocedural morbidity. More recently, long-term follow-up data have emerged regarding the durability of ULMCA PCI in comparison to CABG.

The 5-year follow-up data of the SYNTAX trial reported an increased incidence of major adverse cardiac and cerebrovascular events (MACCE) in the PCI group compared with the CABG group, driven primarily by higher incidences of myocardial infarction and repeat revascularization.¹⁸ However, in the subset of patients with ULMCA disease, there was no significant difference in MACCE between treatment groups (31.0% in the CABG group vs 36.9% in the PCI group; P=.12). When stratified by score, the 5-year incidence of MACCE in patients with ULMCA disease was similar between groups with low (<23) and intermediate (23-33) SYNTAX scores, continuing the trend noted at 12 months within the ULMCA disease cohort¹⁵ (Table 2). In contrast, the cumulative event rate was higher in the overall cohort and in patients with 3-vessel disease who carried an intermediate SYNTAX score. Therefore, the SYNTAX score continues to be a useful tool in the assessment of ULMCA disease and suggests that patients with low or intermediate scores have similar long-term outcomes with PCI or CABG. In addition, the SYNTAX data demonstrate a significantly lower rate of stroke in the PCI group at 1 year (0.3% in PCI vs 2.7% in CABG; P=.009) and maintain a trend toward significance at 5 years (2.4% in PCI vs 3.7% in CABG; P=.09).^15,18

A recent propensity-matched observational study looking at off-pump CABG (OPCAB) versus PCI in ULMCA disease also found a lower incidence of MACCE at 8-year follow-up in the OPCAB group, driven by higher rates of target vessel revascularization and myocardial infarction in the PCI group.²⁰ However, there was no significant difference in mortality or stroke. 

Ali et al reported the long-term follow-up data in 158 patients who underwent PCI for ULMCA stenosis.²¹ Procedural success rate was 100% despite a high average SYNTAX score of 39.6. Mortality at 30 days was 4.4%, compared with a predicted surgical mortality rate of 10.6%. At a mean follow-up of 54 months, the incidence of cardiac death was 7.6% and target lesion revascularization was 3.8%.

Though PCI is technically feasible, these long-term follow-up studies raise questions regarding the long-term durability of stenting when compared to CABG, particularly with regard to the incidence of myocardial infarction in addition to the expected increase in revascularization rates. Nonetheless, the results of SYNTAX suggest that PCI can be an effective and durable treatment option in patients with low to intermediate anatomic complexity and is associated with a lower risk of stroke than CABG. The Evaluation of XIENCE PRIME Everolimus Eluting Stent System (EECSS) or XIENCE V EECSS Versus Coronary Artery Bypass Surgery for Effectiveness of Left Main Revascularization (EXCEL) trial is an ongoing randomized study with a projected enrollment of 2600 patients and will help to answer these questions.²² EXCEL is randomizing patients with ULMCA disease and low or intermediate SYNTAX scores to PCI or CABG, thereby excluding patients who should undergo CABG due to anatomic complexity. Additionally, the trial is using a primary outcome of death, myocardial infarction, and stroke, notably leaving out target vessel revascularization. December 2016 is the projected primary completion date, and patients will be followed for a median of 3 years.

The results of meta-analyses echo the above findings and demonstrate similar incidences of mortality and MACCE at 1 year, with increased rates of revascularization in patients who underwent PCI.^23,24 Continued improvements in device technology, techniques, and pharmacotherapy are expected to further improve outcomes with PCI in the future. The 5-year follow-up data from the MAIN-COMPARE (Revascularization for Unprotected Left Main Coronary Artery Stenosis: Comparison of Percutaneous Coronary Angioplasty Versus Surgical Revascularization) registry demonstrated similar outcomes with respect to death, MACCE, and even revascularization in patients who underwent PCI for ostial left main disease when compared to CABG.²⁵

Stent Selection

Because of the potentially catastrophic consequences of in-stent restenosis involving the left main, drug-eluting stents (DESs) are generally preferred over bare-metal stents (BMSs). A meta-analysis involving 44 studies and 10,342 patients demonstrated lower rates of mortality, myocardial infarction, and revascularization following DES use compared with BMS use.²⁶

The ISAR-LEFT MAIN (Drug-Eluting-Stents for Unprotected Left Main Stem Disease) trial randomized 607 patients to paclitaxel-eluting stent (PES) versus sirolimus eluting stent (SES) for the treatment of ULMCA disease.²⁷ The 1-year incidence of death, myocardial infarction, or target lesion revascularization was 13.6% in the PES group and 15.8% in the SES group (P=.44). Definite stent thrombosis occurred in 0.3% of patients in the PES group and 0.7% of patients in the SES group (P=.57). Angiographic restenosis occurred in 16.0% of patients in the PES group and 19.4% of patients in the SES group (P=.30). A more recent non-randomized trial by Song et al evaluated the use of SES versus PES in left main bifurcation stenting and found reduced rates of major adverse cardiac events (MACE) and late loss in the SES group.²⁸

ISAR-LEFT MAIN 2, which examined the use of second-generation DESs in treating left main disease, included 650 patients randomized to zotarolimus-eluting stent (ZES) or everolimus-eluting stent (EES).²⁹ The primary endpoint of MACE occurred in 17.5% of patients in the ZES group and 14.3% of patients in the EES group (P=.25). Angiographic restenosis occurred in 21% in the ZES group and 16% in the EES group. The results of this study suggest that the use of second-generation DESs is feasible, with similar outcomes to those noted with the use of first-generation DESs in ISAR-LEFT MAIN. Additionally, both stent types appear to provide similar results at 1-year follow-up.

Planned Versus Provisional Bifurcation Stenting

A strategy of provisional stenting for bifurcation left main disease has been preferred due to the results of bifurcation stenting trials. The Nordic Bifurcation Study randomized 413 patients to either a planned or provisional bifurcation stenting strategy and found no difference in MACE at 6 months, but noted longer procedure times, higher contrast volumes, and higher cardiac biomarker elevations with the planned 2-stent strategy.³⁰ However, only 2% of these patients were treated for left main bifurcation disease.

This issue has not been addressed in a randomized trial. However, Palmerini et al reported in an observational study that patients who underwent a 2-stent strategy had increased MACE at 2 years.³¹ More recent studies also note an association with increased MACE in patients who undergo a 2-stent strategy compared with those who receive a single stent for left main bifurcation disease.^32,33 However, as these are non-randomized studies, the use of 2 stents may simply reflect disease that is more difficult to treat, leading to this association with worse outcomes. Preprocedural coronary CT angiography may help identify patients at higher risk for branch vessel compromise who would be more likely to benefit from a planned 2-stent strategy.³⁴

Bifurcation Stenting Strategies

The ideal revascularization technique for distal bifurcation disease of the ULMCA requiring 2 stents is unknown. Unlike the “crush” technique or the culotte technique, simultaneous kissing stenting does not require rewiring the side branch for final kissing balloons. Simultaneous kissing stenting was performed in 150 consecutive unselected patients with ULMCA disease. The rate of ischemia-driven target lesion revascularization was 4.3% at 1 year and 6.2% at 2 years.³⁵ This represents a simple, feasible, effective, and durable option for patients with ULMCA disease that requires a 2-stent strategy.

The DKCRUSH (Double Kissing Crush Versus Culotte Stenting for the Treatment of Unprotected Distal Left Main Bifurcation Lesions)-III study compared culotte and double kissing (DK) crush techniques for the treatment of distal bifurcation disease and demonstrated a reduction in 1-year MACE in the crush group, driven primarily by a reduction in repeat revascularization.³⁶ The rate of MACE at 1 year was 6.2% in the DK crush group vs 16.3% in the culotte group (P=.001). The 1-year target lesion revascularization rate was 2.4% in the DK crush group compared with 6.7% in the culotte group (P=.04).

Surveillance Coronary Angiography

The 2005 ACC/AHA/SCAI guideline endorsed routine follow-up angiography between 2 and 6 months after ULMCA PCI (Class IIa recommendation).⁵ However, given that this strategy is unable to predict a situation where acute, sudden stent thrombosis might occur, in addition to the risk associated with angiography in a patient who underwent ULMCA PCI, the 2009 Focused Update no longer recommends routine surveillance angiography.³⁷

Conclusion

Data continue to accumulate regarding the optimal treatment for patients with left main CAD. While surgical revascularization has traditionally been the cornerstone of therapy for this entity, there is an increasing role for PCI, especially in patients who present an increased surgical risk. PCI appears to be associated with fewer periprocedural complications and lower rates of stroke, though at the cost of increased revascularization with time. Additionally, recent long-term data may suggest an increased rate of myocardial infarction with PCI compared to CABG, though similar rates of MACCE in those with low or intermediate SYNTAX scores. Nonetheless, the use of invasive and non-invasive diagnostic tools, appropriate stent selection, and PCI by experienced operators can continue to improve the outcomes seen with PCI. Ongoing studies such as the eagerly awaited EXCEL trial will help to further clarify the contemporary role of PCI in the treatment of ULMCA disease.

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From the Department of Medicine, Division of Interventional Cardiology, UCLA Medical Center, Los Angeles, California.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Lee reports associations with Abbott, Gilead, and Medtronic. Dr Oyama reports no disclosure.

Manuscript submitted April 11, 2013, provisional acceptance given May 28, 2013, final version accepted July 19, 2013.

Address for correspondence: Dr Michael S. Lee, 100 Medical Plaza, Suite 630, Los Angeles, CA 90095. Email: mslee@mednet.ucla.edu