Unprotected Left Main Coronary Artery PCI in Acute Myocardial Infarction
The standard of care for patients with unprotected left main coronary artery (ULMCA) disease is coronary artery bypass grafting (CABG) based largely on older, outdated data which demonstrate improved survival as compared with medical therapy and poor outcomes with balloon angioplasty.(1-3) However, given the data which demonstrate that ULMCA percutaneous coronary intervention (PCI) with drug-eluting stents (DES) is safe and effective, the 2009 American College of Cardiology (ACC)/American Heart Association (AHA) focused guidelines for PCI state that ULMCA stenting may be considered in patients with anatomic conditions that are associated with a low risk of procedural complications and clinical conditions that predict an increased risk of adverse surgical outcomes.(4)
Acute thrombotic occlusion involving the ULMCA is uncommon, and can lead to abrupt and severe circulatory and arrhythmic dysfunction. Patients may die suddenly before reaching the hospital, while others who survive may present to the emergency room with acute myocardial infarction (MI). These patients are often in extremis, in cardiogenic shock, and have high mortality rates.
There is uncertainty regarding the optimal revascularization strategy in patients with acute MI due to acute thrombotic occlusion of the ULMCA. The guidelines do not clearly state whether CABG or PCI is preferred in these patients. Although the 2004 revised ACC/AHA ST-elevation MI guidelines indicate that PCI is a class IA indication in cardiogenic shock, CABG is also listed as a class IA indication if there is suitable coronary anatomy.(5) Interventionalists may feel reluctant to perform emergent PCI for thrombotic occlusion of the ULMCA, because of the fear of litigation for malpractice, especially if the patient is likely to die. However, in the most critically ill patients, many patients are likely to succumb regardless of the revascularization strategy. We review the current literature with emergent revascularization of the ULMCA and argue that primary PCI is the preferred revascularization in selected patients with thrombotic occlusion who are critically ill patients with hemodynamic instability, because PCI provides more rapid reperfusion compared with CABG.
There is a paucity of data for emergent CABG for ULMCA disease in patients with acute MI. Two small studies both reported in-hospital mortality rates of 46% after emergent CABG for ULMCA disease.(6,7)
Given the data from the SYNTAX trial and MAIN-COMPARE registry for non-emergent cases, which reported no significant differences in the outcomes of death or MI,(8,9) PCI has been considered a possible alternative to CABG in ULMCA thrombosis in patients who need emergent reperfusion. Comparative data on percutaneous ULMCA revascularization vs. CABG in patients with acute MI are limited and nonrandomized.(10–13)
Several studies have reported on the outcomes of ULMCA PCI in acute MI in the DES era. A retrospective, multicenter, international registry evaluated 62 patients with MI (23 ST-elevation MI) who underwent ULMCA PCI with DES.(14) In-hospital and long-term (586±431 days) major adverse cardiac events were 10% and 29%, respectively, and mortality was 8% and 29%, respectively. Target vessel revascularization was performed in 4 patients, all of whom had distal bifurcation involvement. In another multicenter, retrospective study of 28 patients who underwent primary PCI with either bare-metal stents or DES due to ULMCA disease, in-hospital and long-term mortality at a follow up of 26±12 months were 36% and 3.6%, respectively, with one patient (3.6%) requiring in-hospital target vessel revascularization and two others requiring revascularization at follow up.(15)
Because ULMCA thrombotic occlusion is rare, conducting a multicenter, randomized trial to determine the optimal revascularization strategy will be a difficult task. Although distal bifurcation disease is associated with a higher rate of target vessel revascularization compared with ostial or mid-shaft lesions,(16) primary PCI should still be considered a reasonable initial strategy, if there are signs of arrhythmic or hemodynamic instability or if there are severe co-morbidities in patients with thrombotic occlusion of the ULMCA. The higher risk of restenosis with PCI may be acceptable when patients with thrombotic occlusion of the ULMCA need emergent reperfusion that can be accomplished more quickly with PCI. Emergent CABG may lead to significant delays in reperfusion, with a minimum of an hour or longer during off-peak hours at night before patients are placed on cardiopulmonary bypass. The loss of valuable time before reperfusion is achieved may increase mortality, given that there is an 8% increase in the relative risk of dying at one year for every 30-minute delay from the onset of symptoms to primary angioplasty.(17)
Primary PCI of the ULMCA may also have a safety advantage as compared with CABG, especially for the elderly, who are at higher risk for stroke. Patients with ULMCA disease in the SYNTAX trial randomized to CABG had a 9-fold higher risk of stroke compared to the PCI arm (2.7% vs. 0.3%, p=0.009).(9) The GRACE registry also reported a higher risk of stroke in the CABG arm as compared with PCI (2.1% vs. 0.4%, p=0.02).(10)
Because incomplete revascularization is an independent predictor of in-hospital mortality in patients who undergo emergent ULMCA PCI, complete revascularization should be attempted for patients with multivessel disease and cardiogenic shock.(18) If complete revascularization cannot be achieved percutaneously, or a mechanical complication like severe mitral regurgitation or ventricular septal defect is present, then CABG may be preferred.
Stent thrombosis of the ULMCA can lead to devastating consequences, leading to either a large MI or death. To minimize the risk of stent thrombosis, it is imperative to ensure that patients continue dual antiplatelet therapy for at least one year if DES are used.(19) If prolonged dual antiplatelet therapy is contraindicated or if there is a foreseeable circumstance where it cannot be continued for one year (i.e. impending surgery, financial burdens, dental procedures, etc.), then bare-metal stents may be preferred.
In conclusion, primary PCI is a viable alternative to CABG for the high-risk subgroup of patients with ULMCA thrombosis and acute MI.(20) PCI is technically feasible and can provide faster reperfusion compared with CABG, with acceptable short-term and long-term outcomes. ULMCA PCI is associated with a higher risk of target vessel revascularization with ULCMA PCI, especially when the distal bifurcation disease is involved. However, target vessel revascularization may be acceptable in these clinically ill patients. A large-scale, multicenter trial utilizing contemporary revascularization techniques to evaluate fundamental clinical and angiographic end points may be difficult to conduct, because this condition is uncommon.
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