Guidelines
While the results of the two major RCTs are still awaited, the European and American societies have both issued guidelines on revascularisation of patient with LMS disease (see Tables 1 and 2).28,29
CABG maintains a class 1 indication across all anatomical subgroups. It is interesting to note that PCI assumes a stronger position in the European Society of Cardiology (ESC) guidelines with a class 1 recommendation in patients with a low SYNTAX score and 2A for an intermediate score. By contrast, the US guidelines give only a 2A for low scores and a 2B for intermediate scores. Both societies are in agreement about the superiority of CABG for patients with a high SYNTAX score.
On-going Trials
Traditionally, patients with LMS disease as well as additional severe coronary disease elsewhere tend to be referred for CABG assuming decent distal targets are available for grafting. The class 1 recommendation of CABG in high Syntax scores is unlikely to be challenged in RCTs. However, the role in less-severe disease needs to be firmly established. In that respect, we look forward to the results of two trials that hopefully will settle the matter.
EXCEL (NCT01205776) is a multicentre study specifically looking at the treatment of patients with a low or intermediate SYNTAX score (<32). Use of the second generation Xience (Abbott Vascular, US) DES will make the results more relevant to current practice. The primary endpoint is the composite of death, MI and stroke at a mean of 3-year follow-up. It is worth noting that TVR is not included in the primary endpoint but is included as a secondary endpoint. While the original sample size was intended to be around 3,000 patients, recruitment was stopped early for financial reasons. Despite the curtailed sample size, it will still be the largest RCT covering the management of less complex LMS lesions and its findings will certainly influence the management of these patients. The use of IVUS guidance to perform PCI is strongly recommended both pre- and post-treatment.
The Nordic-Baltic-British Left Main Revascularization Study (NOBLE) trial (NCT01496651) is also a multicentre trial comparing the contemporary Biomatrix (Biosensors International Group, Singapore) stent versus CABG. Though the SYNTAX score is not being used for patient selection, the inclusion criteria will yield a population not dissimilar to that of Evaluation of XIENCE PRIME Everolimus Eluting Stent System or XIENCE V or XIENCE Xpedition or XIENCE PRO Versus Coronary Artery Bypass Surgery for Effectiveness of Left Main Revascularization (EXCEL) trial. In addition to the LMS lesions, there should be ≤3 additional non-complex lesions elsewhere to qualify for participation. The primary endpoint is MACE at 2 years.
While the overarching aim of the two trials is to compare PCI with CABG in less ‘complex’ anatomy, it is worth pointing out the subtle differences in inclusion criteria between the two trials. In the NOBLE trial, a significant LMS lesion is defined as having either a visually estimated diameter stenosis >50 % or FFR <0.8. In the EXCEL trial, it is defined as having either a visually estimated diameter of >70 % or 50–70 % with a FFR <0.8 or MLA <6 mm2. Results from both trials are expected in 2016.
The Future
Park et al. recently published a temporal analysis of their experience with ULM PCI over the past two decades.30 It illustrates the achievements in percutaneous treatment of coronary disease with progressively better outcomes as stent technology and profiles evolving over the past 2 decades.
There are other factors that may have contributed to the improvement in clinical outcomes. In addition to improvement in stent technology with the advent of not only DES but also better stent platforms with enhanced drug-delivery systems, the use of adjunctive intravascular imaging and increasing evidence on the efficacy of different bifurcation treatment strategies may have all helped in improving angiographic and clinical outcomes in LMS PCI. With the advent of more potent antiplatelet drugs, the incidence of stent thrombosis has improved. It is important to bear in mind that the techniques of CABG have evolved as well. There is now a greater use of off-pump CABG with associated lower complication rates compared with the traditional surgery as well as almost standard use of LIMA grafts with a better patency than vein grafts. All this means that trials to date are already ‘out of date’ in current real world practice.
The heterogeneity of LMS disease poses a particular difficulty in extrapolating results of clinical trials to the ‘real world’. In that sense, adequately powered RCTs are needed to firmly establish the role of PCI in an era where CABG still remains the gold standard for the treatment of LMS lesions.