Treating Acute Myocardial Infarction in the Unprotected Left Main: Is PCI Better Than CABG?

The unprotected left main (UPLM) coronary stenosis is the last frontier for the interventionalist, and a continuing battleground between the interventionalist and the surgeon. At this time in the United States, for elective revascularization, surgery is favored for the patient with either isolated UPLM or UPLM and multivessel coronary artery disease (CAD), unless unusual circumstances dictate otherwise. The debate between the minimally invasive (percutaneous coronary intervention, PCI) and coronary artery bypass graft surgery (CABG) approaches was summarized well in 2009 by two of the top revascularization physicians.(1,2) Dr. Craig Smith, cardiothoracic (CT) surgeon from Columbia University, in New York City, New York, said that based on available PCI-CABG data, the limited follow up of the PCI studies to date, the poor outcomes with some of the more complex anatomy of the UPLM and the small incidence of stent thrombosis made the case that CABG should be chosen for revascularization.1 Taking the opposing view, Dr. Paul Teirstein, from the Scripps Institute in La Jolla, California, noted what types of lesions were best suited to surgery or PCI (see Table 1).(2) While the role of PCI for elective UPLM is still debatable, in this issue of CLD, Dr. Michael S. Lee, from the UCLA Medical Center in Los Angeles, California, summarizes his understanding of acute myocardial infarction (MI) with thrombotic occlusion of the UPLM, the most critical of coronary locations. The incidence of this unusual condition is unknown, since most of the UPLM PCI studies exclude these patients from analysis or meld them with all ST-elevation MIs (STEMIs) that underwent PCI. Dr. Lee’s review of the acute thrombotic UPLM appears to make a strong argument that PCI is likely the best, if not the only, choice for emergency life-saving revascularization under most acute circumstances.(3) We have long known that urgent PCI for STEMI is better than thrombolytics or surgery; better in terms of more patent arteries achieved and that restoration of flow occurs in a much shorter time than with either lysis or CABG. The same logic applies to the acutely thrombotic UPLM. From the work of Dr. Lee and others,(4) the outcomes of the UPLM PCI for AMI in the drug-eluting stent (DES) era are worse than STEMIs of other vessels, with increased early and late major adverse cardiac events (MACE) (10%, 29%, respectively) and death (8-36%, 4-29%, respectively) rates. It is of note that PCI for LM thrombosis is associated with in-hospital mortality rates of 36 to 55%.(4) SB Prasad et al(4) report the lowest mortality, 36%, in the current era with DES. Compared to 5 similar studies from 1996 to 2003, reviewed in their paper, Prasad et al also had fewer patients presenting in shock (63% vs. 93%) and more stent deployment (96% vs. 56%) in their patients from Melbourne, Australia. The reduced, albeit high, mortality is a testament to improved STEMI care from the onset of symptoms to arrival in the cath lab. While the mechanisms for the increased adverse events in this population are unknown, one can speculate that thrombotic occlusion involving the left main produces profound global ischemia and subsequent worse reperfusion salvage, with both early and late increased death rates. Likewise, distal LM thrombotic occlusion might produce unequal degrees of ischemia/infarction, but the technical challenge of treating the distal LM bifurcation may produce the complications of bifurcation LM stenting in the thrombotic milieu and also account for the increased late event rates. While a patient with a complete UPLM thrombotic occlusion might never come to the cath lab due to sudden death, there are patients who survive long enough to arrive in the cath lab. Their survival is likely due to the development of a collateral blood supply either from chronic CAD or from acute collateral recruitment sufficient to provide myocardial perfusion distal to a complete LM occlusion. These same patients may have a variety of presentations, ranging from progressive angina to acute STEMI with shock. If we focus on the acute STEMI, the quickest and least traumatic approach to revascularization is undoubtedly PCI. CABG, in this setting, must deal with a patient in shock, in which time to revascularization is critical. Dr. Lee points out that there is likely a safety advantage to PCI vs. CABG, especially in the elderly patient, supported by data from the SYNTAX trial, with a 9-fold increase in cerebrovascular accident (CVA) compared to PCI. Finally, Dr. Lee emphasizes that the type of stent for the acute thrombotic LM should be carefully considered. In patients who cannot tolerate or continue dual antiplatelet therapy for at least a year, bare-metal stents (BMS) may be an acceptable alternative. Some physicians advise 3-4 month angiographic follow up. I agree that close follow up is needed, but would not automatically proceed with angiography. Symptoms and change in activity level would certainly push for early angiography. I would just add that the technique of LM stenting requires use of intravascular ultrasound to ensure an adequately sized and fully deployed stent, and that if possible, the issues of medication compliance be addressed at the time of stent placement to select DES vs. BMS for your patient. Dr. Kern can be contacted at mortonkern005@hotmail.com Disclosure: Dr. Kern reports that he is a speaker for Volcano Therapeutics and St. Jude Medical, and is a consultant for Merit Medical and InfraReDx, Inc. References 1. Smith CR. Surgery, not percutaneous revascularization, is the preferred strategy for patients with significant left main coronary stenosis. Circulation 2009; 119: 1013–1020. 2. Teirstein PS. Percutaneous revascularization is the preferred strategy for patients with significant left main coronary stenosis. Circulation 2009; 119: 1021–1033. 3. Lee MS. Unprotected left main coronary artery PCI in acute myocardial infarction. Cath Lab Digest 2010 Sept;18(9):1. 4. Prasad SB, Whitbourn R, Malaiapan Y, et al. Primary percutaneous coronary intervention for acute myocardial infarction caused by unprotected left main stem thrombosis. Catheter Cardiovasc Interv 2009;73:301-307.

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