Clinical Outcomes After Percutaneous Coronary Intervention in Acute Myocardial Infarction Due to Unprotected Left Main Coronary Artery Disease

Abstract: Objective. Patients with acute myocardial infarction (AMI) with unprotected left main coronary artery (ULMCA) as culprit lesion are a high-risk subgroup with a substantial mortality. Percutaneous coronary intervention (PCI) has become an option for these patients, but the data are limited. We therefore analyzed the clinical characteristics and the short-term and long-term outcomes of this subgroup of patients. Methods. This is a retrospective, single-center, observational study with 30 AMI patients admitted between July 2005 and March 2013 and treated with emergency PCI to an ULMCA culprit lesion. Results. Twenty-four males and 6 females with an average age of 63 ± 17 years were enrolled. Nineteen patients (63.3%) presented with ST-segment elevation MI, while 11 patients presented with non-ST segment elevation MI. Cardiac shock was present in 8 patients, total occlusion of left main coronary artery was identified by coronary angiography in 13 patients, and coexisting right coronary artery disease was present in 10 patients. Angiographic procedural success was achieved in 93% of patients, with intraaortic balloon pump used in 9 patients. Overall in-hospital mortality was 20%, all secondary to refractory cardiogenic shock and multiorgan failure. During a follow-up period of 1099 ± 819 days, no deaths or MIs were detected. Probability of freedom from death at 3 years was 79.7 ± 7.4%. Conclusion. We demonstrate that in patients with LMCA disease in the setting of AMI, PCI is a feasible treatment option with an in-hospital survival of 80%. The long-term clinical outcome of patients surviving to hospital discharge is excellent. 

J INVASIVE CARDIOL 2015;27(8):E153-E157

Key words: coronary artery disease, ischemic cardiac disease, cardiogenic shock, percutaneous coronary intervention, acute myocardial infarction

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Acute myocardial infarction (AMI) caused by unprotected left main coronary artery (ULMCA) disease is often complicated by pump failure and malignant ventricular tachyarrhythmias, and thus results in high mortality.¹ Although guidelines recommend surgery as the treatment of choice in LMCA, percutaneous coronary intervention (PCI) is also feasible in patients with cardiogenic shock following AMI.² If surgery is impossible in an emergent situation or patients are at high surgical risk, PCI and mechanical support are considered the first treatment choice.^3,4 However, limited data are available on the outcomes of patients with ULMCA disease presenting with AMI. Therefore, we analyzed the clinical characteristics as well as short-term and long-term outcomes of patients undergoing emergency PCI for AMI due to ULMCA lesion.

Methods 

Patient population. A total of 1687 patients presenting with AMI to Zhongshan Hospital, Shanghai, China, from July 2005 to March 2013 underwent emergency PCI, from which we retrospectively analyzed 30 consecutive patients (1.8%) treated with PCI to a culprit ULMCA lesion. The indication for emergent PCI was based on the presence of prolonged (>30 minutes) or ongoing chest pain, coupled with electrocardiographic changes of acute ST-segment elevation myocardial infarction (STEMI), new/presumed left bundle branch block, or persistent widespread ST-segment depression refractory to medical therapy (non-ST segment elevation myocardial infarction [NSTEMI]), with or without cardiogenic shock. Of the 30 patients enrolled, 19 patients (63.3%) presented with STEMI and 11 patients (36.7%) presented with NSTEMI.

Percutaneous coronary intervention. Aspirin was administered as a 300 mg oral dose at the point of first medical contact in all patients, and clopidogrel was administered as a 300 mg oral loading dose at the first point of medical contact before the procedure. During the procedure, unfractionated heparin was administered at 100 IU/kg or 70I IU/kg when associated with glycoprotein (GP) IIb/IIIa inhibitors. GP IIb/IIIa inhibitors were administered at operator discretion. Lesions at the ostium or in the body of the ULMCA without distal bifurcation involvement were mostly treated with a single stent. Several techniques were used for the treatment of distal bifurcation disease, with a preference for a single stent from LMCA to left anterior descending (LAD) artery across the left circumflex (LCX) artery ostium. The choice of stent size and length were at operator discretion. Intraaortic balloon pump (IABP) was positioned during the procedure at operator discretion and was maintained for approximately 48 hours. Poststenting antiplatelet regimen included lifetime aspirin of 100 mg/day if no contraindications were present and clopidogrel 75 mg/day for at least 12 months after the procedure. 

Demographics and follow-up. Demographic, procedural, and outcome data were obtained from review of the catheterization laboratory database and hospital chart review. Clinical follow-up data were available on all 24 patients who were discharged alive through outpatient visits and telephone interviews.

Endpoints and study definitions. In-hospital complications included death, reinfarction, and emergency coronary artery bypass graft (CABG) surgery. Major adverse cardiac event (MACE) rate was assessed at follow-up and was defined as death from any cause, non-fatal MI, and target lesion revascularization.

Statistical analysis. Continuous variables were presented as mean ± standard deviation and were compared by Student’s t-test. Categorical variables were presented as counts and percentages, and were compared by c² test (or Fisher’s exact test when appropriate). The Kaplan-Meier method was used to show long-term event-free survival curves. All analyses were performed using SPSS 13 for Windows statistical software (IBM). Statistical significance was accepted at P<.05. 

Results

Baseline clinical data. Demographic and clinical characteristics of 30 consecutive patients undergoing PCI to ULMCA following STEMI/NSTEMI are presented in Table 1. The mean age of the cohort treated was 63 ± 17 years. Six patients (20%) had a prior history of diabetes mellitus, 14 patients (46.7%) had a history of smoking. A total of 8 patients (26.7%) were in cardiogenic shock upon arrival at the catheterization laboratory (4 in the mortality group and 4 in the survival group). The time from symptom onset to PCI was 6.4 ± 5.5 hours in all 30 patients, 5.1 ± 3.0 hours in STEMI patients, and 8.6 ± 8.0 hours in NSTEMI patients. 

Angiographic and procedural characteristics. The angiographic and procedural characteristics are presented in Table 2 and Table 3. LMCA was judged the culprit vessel in all patients and distal bifurcation involvement was the most common finding (56.7%) (Table 2). LMCA stenosis >70% was present in 26 patients, of whom 13 had totally occluded LMCA (5 out of 6 patients [83.3%] who died during hospital stay and 8 out of 24 patient [33.3%] in the long-term survival group). Fifteen patients suffered from LMCA complicated with single-vessel disease, which comprised one-half of the study population. Significant coexistent disease of the RCA was documented in 10 patients (33.3%) (2 patients [33.3%] in the in-hospital death group and 8 patients [33.3%] in the long-term survival group). 

As shown in Table 3, angiographic success was achieved in 28 patients (93.3%) and was similar in the survival and mortality groups. IABPs were placed in 9 patients (30%) and GP IIb/IIIa inhibitor was used in 17 patients (56.7%), according to operator discretion. Of 17 patients with distal LMCA disease and 5 patients with either diffuse LMCA lesion or shaft lesion complicated with proximal LAD stenosis, single-stent crossover technique was used with LM-LAD stenting in 18 cases and LM-LCX stenting in 4 cases. None of the study patients received complex bifurcation stenting. Coronary stents were used in 28 patients: 24 patients received drug-eluting stents, and 4 patients received bare-metal stents. In 1 patient, stent deployment was not possible because of hemodynamic instability. In another case, as the patient showed optimal angiographic result (stenosis <30%) and Thrombolysis in Myocardial Infarction (TIMI) grade-3 flow after thrombus suction, no stent was implanted. After PCI, TIMI grade-3 flow was achieved in 28 patients (93.3%).

In-hospital and long-term outcomes. In-hospital and long-term clinical outcomes are illustrated in Table 4. Six patients (20%) died in hospital, all secondary to refractory cardiogenic shock and multiorgan failure. The mean follow-up duration in this study was 1099 ± 819 days. From hospital discharge to long-term follow-up, no death or reinfarction was detected. One patient suffered from in-stent restenosis of the LMCA at 1 year post PCI and underwent CABG. A significant restenosis of stents implanted outside the ULMCA was found in another 2 patients and re-PCI was implemented. Thus, the long-term survival rate of in-hospital survivors was excellent. The probability of freedom from death at 3 years was 79.7 ± 7.4% (Figure 1).

Discussion 

The LM provides coronary perfusion to more than 75% of the left ventricular myocardium.¹ AMI caused by LMCA disease is often associated with extensive myocardial infarction, cardiogenic shock, and death because of the large amount of the myocardium affected. The prompt and complete reperfusion of the occluded coronary artery is crucial to satisfying clinical outcomes. PCI for ULMCA disease has been performed with increasing frequency over the past decade. However, it remains a significant challenge to the interventional cardiologist, especially in the setting of AMI. Here, we report 30 cases of patients with AMI treated with emergent PCI at our center. Our results indicate that emergent LM-PCI in the context of AMI has a good in-hospital survival rate (80%) and long-term survival rate, with no deaths recorded after hospital discharge.

The incidence of AMI due to LMCA culprit lesion is reported to be 0.9%-5.2%.^5-7 This subgroup of patients is more commonly complicated with hemodynamic instability, cardiogenic shock, and in-hospital death compared with patients with non-LMCA related AMI. The presentation of cardiogenic shock varies between 23.3%-78.0% for patients with AMI due to ULMCA disease;^6,8,9 however, it was reported to be as low as 12% by the AMIS Plus registry due to the more favorable risk profile in patients enrolled.⁵ As reported by large clinical trials, the percentage of shock is as low as 3.5%-12.1% in patients with non-LMCA related AMI.^5,6 Besides, the presentation with shock is independently associated with mortality.^10-12 According to a meta-analysis of 13 studies evaluating PCI in the treatment of ULMCA culprit lesion in AMI, 26% of patients presented in cardiogenic shock. The average estimated 30-day all-cause mortality was 15% in patients presenting without cardiogenic shock and 55% in patients presenting with cardiogenic shock.¹³ In our study, 26.7% of patients had shock on arrival, and 66.7% of the patients who died while in-hospital presented with shock. These data indicate that presentation with shock has a trend toward in-hospital mortality.

In our study, we observed a 20% in-hospital mortality rate, which compares favorably with those reported previously for similar patient cohorts ranging from 21%-55%.^7,8,12,14,15 This might be explained by our relatively low cardiogenic shock incidence (26.7%). Another potential explanation might be the proportion of patients with STEMI. Jensen et al showed that patients with LMCA-related STEMI had worse outcomes compared with NSTEMI patients;¹⁶ however, a study by Lee et al showed no difference.¹⁷ In the current study, there was a statistically non-significant trend toward more STEMI in the mortality group compared with the survival group. In addition, the symptom-onset to PCI interval in this study was 6.4 hours, which is longer than the previously reported interval of 2.2-3.4 hours,^18,19 due to patient delay and transfer delay, which reflects the reality in our country. Patients with AMI caused by ULMCA are prone to die at home or during transfer, before reaching the catheterization laboratory, and these high-risk patients were excluded from our study; this may partly explain the good prognosis of the patients in the current study.

We detected no late deaths during the long-term follow-up (1099 days), which indicates a promising long-term outcome in PCI-treated patients. The wide difference in the incidence of mortality between short-term, mid-term, or long-term outcomes has been reported by previous studies. A death rate of 2.1%-10.5% at 12-16 months after hospital discharge was reported.^6,7,10 Lee⁹ reported that none of the patients who survived to discharge died over the 39-month follow-up period. In another study, 1 late death was reported over the 26-month follow-up period.¹² Therefore, these results support our data that the majority of mortalities occurred in short-term and mid-term follow-up.    

Emergent CABG may be another choice for AMI due to ULMCA disease; however, it is time consuming, accompanied by procedural risks, and supported only by limited published data; thus, cardiothoracic surgeons are generally reluctant to undertake emergency CABG in this patient subgroup. One study of 21 patients reported a 19% in-hospital mortality rate in patients with acute coronary syndrome and significant LMCA disease who underwent emergency CABG. For the subgroup of patients with cardiogenic shock, the in-hospital mortality rate was much higher, at 75%.²⁰ In another report on a 13-patient cohort with acute LM thrombosis undergoing emergency CABG, the in-hospital mortality rates were 46% and 53% for the subgroup of patients with cardiogenic shock.²¹ The hemodynamic deterioration and electrical instability of AMI patients caused by ULMCA disease occurs rapidly, and demands a more prompt reperfusion strategy than CABG may offer. As a result, in the stent era, PCI may be preferred over emergency CABG in order to achieve prompt reperfusion.

Study limitations. This study has several limitations. First, this was a retrospective, non-randomized study. Second, it was a single-center experience with a small number of patients, which made further analysis of potential predictors impossible. Therefore, a larger series or controlled clinical trials may be required. Third, as AMI due to LMCA lesion is a life-threatening condition, quite a lot of patients may not survive to PCI. Furthermore, even patients who presented alive to hospitals with emergency PCI facilities received medical therapy instead of PCI for fear of high-risk operations. As a result, selection bias may exist in this study and lead to a relatively stable patient population enrolled in PCI therapy. Nonetheless, this study represents a real-world cohort of patients undergoing treatment for a relatively rare event.

Conclusion

AMI due to ULMCA lesion is a rare but serious condition. Emergent PCI is technically feasible, with an in-hospital survival of 80%. Patients surviving to discharge have excellent long-term prognosis.

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*Joint first authors.

From the Zhongshan Hospital, Fudan University, Shanghai Institute of Cardiovascular Disease, Shanghai, China.

Funding: This study was funded by National Natural Science Foundation of China, #81000044.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted March 5, 2014, provisional acceptance given May 2, 2014, final version accepted May 8, 2014.

Address for correspondence: Dr Junbo Ge, 180 Fenglin Road, Shanghai, China 200032. Email: ge.junbo163@163.com