10.3 Left Main Disease: How to Assess and When to Intervene in Patients With Aortic Valve Disease

These proceedings summarize the educational activity of the 16th Biennial Meeting of the International Andreas Gruentzig Society held January 31-February 3, 2022 in Punta Cana, Dominican Republic

Faculty Disclosures     Vendor Acknowledgments

2022 IAGS Summary Document

Statement of the problem or issue

Left main coronary artery disease often presents a diagnostic dilemma, and the concomitant presence of aortic stenosis (AS) can make precise evaluation even more complicated. Intracoronary injection of nitroglycerin during diagnostic angiography often helps resolve the issue in assessing borderline left main lesions. In other patients, AS may create uncertainty that ultimately is due to anatomical and physiological changes in the left ventricle as the result of concentric hypertrophy (LVH). Coronary flow reserve (CFR) may be impaired when the effective orifice area of the left main is <1.0 cm². This is due to adaptive up-regulation of baseline flow to meet the oxygen demands of the hypertrophied ventricle, thereby diminishing any further up-regulation when hyperemia is induced, and giving an impaired CFR, which will often normalize upon relief of the AS. Moreover, endothelial dysfunction in these patients also impairs CFR. IVUS may be helpful though imprecise. Recent data have shown that a minimal lumen area (MLA) of >4.5 mm in the left main indicates a nonsignificant stenosis, however, approximately 25% of those patients will still have an ischemic FFR <0.8. While an MLA <6 mm has been suggested as a threshold to denote ischemia, still 36% will have an FFR >0.8. Recent observational data highlight significant limitations of physiological assessment using CFR in this setting due to a combination of LVH, increased ventricular cavity size, and decreased diastolic perfusion from external compression with subendocardial ischemia. Issues regarding the safety of using a vasodilator in these patients have turned attention to FFR and iFR as possible aids in the assessment of left main lesions in patients with AS. As described above, data have shown they may overestimate lesions and often they will improve after aortic valve replacement. Accordingly, it is currently suggested that more stringent criteria should be used such that an iFR <0.82 would denote ischemia while an iFR >0.93 implies no ischemia.

Gaps in knowledge

Once a significant left main stenosis is detected, decisions regarding the optimal mode of treatment become quite complex. Currently, TAVR has been shown in comparative trials to be at least as effective as surgery (SAVR) for AS alone, with reassuring long-term outcomes data. Consideration of percutaneous solutions to coexisting AS and left main disease entails ensuring an outcome similar to that achievable with surgery. Randomized controlled trials have shown narrowing of the gap between PCI and CABG, with some remaining issues to be considered. The EXCEL trial IVUS substudy analyzed the relationship between final achieved post-PCI minimal stent area (MSA) and clinical outcomes.¹ Three equal-sized groups were analyzed according to final MSA: Group 1 (MSA 4.4-8.7 mm), Group 2 (MSA 8.8-10.9 mm), and Group 3 (MSA 11-17.8 mm). Patients in Group 3 with the largest final MSA had the lowest event rates, with a 3-year stent thrombosis rate of 0% vs 3.1% in Group 1 (the smallest final MSA group). Cardiac mortality at 3 years was also significantly lower in Group 3 compared with Group 1 (1.9% vs 6.9%; P=.02).² The authors suggested that a cutoff value of 9.8 mm final MSA was the desired criterion to ensure optimal long-term outcomes. Although these data highlight the importance of achieving (an eagerly awaited) precise IVUS measurement during the PCI procedure rather than using the vague term “IVUS optimization,” they also warrant a deeper dive to explore why this criterion could not be achieved in a large percentage of these patients despite IVUS use in 77% of cases. Although no explanation was given, possible causes are: variations in size of the left main relative to body size, variations in vessel diameter even among similar-sized individuals, as well as variations in vessel geometry since some patients have a conical-shaped artery, a biconcave artery, or a tapered or funnel-shaped vessel, among others. Of note, recent data have shown that patients in whom post-PCI iFR >0.95 was achieved had the lowest long-term event rates. Hopefully, these intraprocedural criteria will help PCI close the gap vs surgery for these patients. A final question to ponder: patients live longer after CABG due to the superiority of the LIMA-LAD conduit even if vein grafts to the left circumflex and right coronary arteries close, which they often do. Accordingly, will we need to perform complex bifurcation stenting of the left circumflex, which may jeopardize the LM-LAD stent and hinder long-term outcomes?

Possible solutions and future directions

A critical factor in treating left main lesions will be optimal pre-stent lesion preparation using plain balloons, cutting balloons, atherectomy (rotational or orbital), and possibly lithotripsy which could, via deeper fractures of calcium, ensure abolition of resistance to optimal stent expansion, an issue which itself requires further studies. Imaging during these difficult left main PCI procedures will be critical to ensure optimal final outcomes.

References

1. Maehara A, Mintz G, Serruys P, et al. Impact of final minimal stent area by IVUS on 3-year outcome after PCI of left main coronary artery disease: the EXCEL trial. J Am Coll Cardiol 2017;69(11 Suppl):963. doi:10.1016/S0735-1097(17)34352-8

2. Maehara A. IVUS-guided left main and non-left main stenting in the EXCEL trial: lessons from the EXCEL-IVUS core laboratory. TCT 2016.