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Tex Heart Inst J. 2007; 34(4): 479–484.
PMCID: PMC2170495

Unprotected Left Main Coronary Artery Intervention for Acute Myocardial Infarction and Cardiogenic Shock

Abstract

Medical therapy alone often insufficiently alters the clinical course of patients who have experienced acute myocardial infarction and concomitant cardiogenic shock, and in whom the left main coronary artery is the culprit vessel. Emergency coronary artery bypass grafting is an effective yet time-consuming approach that entails the risk of extensive, irreversible myocardial damage. Percutaneous coronary intervention in the unprotected left main coronary artery can enable initial revascularization and rapid stabilization even in high-risk patients, but outcomes from the procedure since the recent advent of drug-eluting stents are still being determined.

Herein, we report the successful deployment of a sirolimus-eluting stent in a 65-year-old man who had experienced acute myocardial infarction and cardiogenic shock consequent to an occluded left main coronary artery. The patient recovered rapidly and completely. We review the medical literature and compare percutaneous coronary intervention with other methods of treatment.

Key words: Angioplasty, transluminal, percutaneous coronary; coronary angiography; coronary disease/complications/mortality/radiography; coronary restenosis/prevention & control; drug implants; myocardial infarction/complications/therapy; myocardial revascularization/methods; prognosis; shock, cardiogenic/diagnosis/etiology/therapy/ultrasonography; stents; treatment outcome

In patients who have experienced acute myocardial infarction and concomitant cardiogenic shock, medical therapy alone is often insufficient in altering the clinical course when the left main coronary artery (LMCA) is the culprit vessel. Emergency coronary artery bypass grafting (CABG) is effective but time-consuming and carries the risk of extensive, irreversible myocardial damage. Emergency percutaneous coronary intervention (PCI) has been shown to enable initial revascularization and rapid stabilization of these patients. However, definitive outcomes from combined PCI and the use of drug-eluting stents are still being determined. Herein, we report our deployment of a sirolimus-eluting stent into the unprotected LMCA of a 65-year-old man who had experienced acute myocardial infarction and cardiogenic shock, and we discuss the advantages and drawbacks of various methods of treatment.

Case Report

In January 2006, a 65-year-old man presented at our emergency department with a 2-week history of anginal chest pain and progressive dyspnea. He had no relevant medical history. Physical, laboratory, and radiologic examinations led to a diagnosis of non-ST-elevation myocardial infarction with heart failure and pulmonary edema. The patient was admitted to the coronary care unit for management and stabilization. His clinical status deteriorated within 24 hours: hypotension and cardiogenic shock did not respond to intravenous vasopressors. He developed respiratory failure and required intubation and mechanical ventilation. At the outset of emergent cardiac catheterization, we placed an intra-aortic balloon pump through a left femoral artery sheath. The patient was given bivalirudin in a 0.75-mg/kg bolus, followed by infusions at 1.75 mg/(kg·hr). Selective coronary angiography revealed a subtotal occlusion of the LMCA (Fig. 1). The right coronary artery was totally occluded at the ostium, filling retrogradely through collateral vessels from the left coronary arterial system.

figure 22FF1
Fig. 1 Before intervention: Coronary angiography (20° right anterior oblique view) shows the left main coronary lesion (arrow).

We decided to perform emergency PCI on the unprotected LMCA, although the patient was in cardiogenic shock. A 600-mg loading dose of clopidogrel was administered via a nasogastric tube. A Judkins left (JL4) 7F guiding catheter (Cordis Corporation, a Johnson & Johnson company; Miami Lakes, Fla) was used to engage the left coronary ostium. A Maverick® Over-The-Wire 2.5 × 15-mm compliant balloon catheter (Boston Scientific Corporation/scimed; Maple Grove, Minn) was advanced over a 0.014-in × 300-cm Asahi Prowater guidewire (Abbott Vascular, a unit of Abbott Laboratories; Abbott Park, Ill) into the distal left anterior descending coronary artery (LAD) across the LMCA lesion. Partial dilation of this lesion was performed by inflating the balloon to 12 atm for 13 sec and again for 21 sec. A 3.5 × 13-mm sirolimus-eluting Cypher® stent (Cordis) was then deployed in the LMCA across the lesion and across the ostium of the left circumflex coronary artery (LCx). Transient bradycardia developed, requiring intravenous atropine and temporary transvenous pacing. The bradycardia resolved. After the stent was deployed, the LAD and the LCx both remained patent. Subsequent dilation of the LMCA was achieved by inflating an NC Ranger 3.75 × 9-mm noncompliant balloon (Boston Scientific/scimed) to 22 atm for 23 sec and again for 27 sec. The angiographic results were excellent and included TIMI-3 flow and no residual stenosis in the LMCA segment (Fig. 2).

figure 22FF2
Fig. 2 After intervention: Coronary angiography (20° right anterior oblique view) shows the left main coronary artery.

In the intensive care unit, the patient's clinical status improved rapidly. He was weaned from vasopressors and inotropic agents, the intra-aortic balloon pump was removed, and he was extubated within 48 hours after the procedure. A 2-dimensional echocardiogram showed a left ventricular ejection fraction of 0.30 and moderate global hypokinesis. After 2 weeks, the patient was discharged from the hospital in stable condition, free of chest pain and other cardiac symptoms. He continued to do well and remained under close follow-up.

Two months later, a sestamibi myocardial perfusion stress test revealed a reversible inferolateral defect consistent with ischemia. The patient's left ventricular ejection fraction was 0.37. Coronary angiography showed a patent LMCA stent without in-stent restenosis, a 90% occlusion of the ostial LCx (Fig. 3), and a subtotal occlusion at the level of the mid LCx.

figure 22FF3
Fig. 3 Before intervention: Coronary angiography (left anterior oblique caudal view) shows the left circumflex coronary ostial lesion (arrow).

The ostial and mid LCx lesions were treated by means of PCI, with excellent results (Fig. 4). To ensure the adequate apposition of the LMCA stent, we performed intravascular ultrasonography (IVUS) by use of a 2.5F Atlantis SR Pro 40 MHz (Boston Scientific/scimed). The IVUS catheter was advanced into the LAD, and imaging was performed retrograde to the proximal reference point at an automatic transducer pullback speed of 0.5 mm/sec. The IVUS catheter was then advanced into the LCx and pulled back into the LMCA. Images of the LMCA segment revealed a well-apposed stent with a luminal and external elastic membrane cross-sectional area of 11 mm2, maximal luminal diameter of 3.8 mm, and minimal luminal diameter of 3.6 mm (Fig. 5). The proximal LAD segment had an external elastic membrane area of 11.6 mm2, a luminal cross-sectional area of 7.7 mm2, maximal luminal diameter of 3.5 mm, minimal luminal diameter of 2.5 mm, and a 34% stenosis (Fig. 6). On the basis of a reference vessel area of 13 mm2, the LCx ostium was 71% occluded before intervention, because the luminal cross-sectional area was 3.8 mm2 (Fig. 7), the maximal luminal diameter was 2.4 mm, and the minimal luminal diameter was 1.8 mm.

figure 22FF4
Fig. 4 After intervention: Coronary angiography (left anterior oblique caudal view) shows the ostium of the left circumflex coronary artery.
figure 22FF5
Fig. 5 After intervention: Intravascular ultrasonography of the left main coronary artery. The external elastic membrane and luminal cross-sectional area is 11 mm2.
figure 22FF6
Fig. 6 After intervention: Intravascular ultrasonography of the proximal segment of the left anterior descending coronary artery. The external elastic membrane area is 11.6 mm2; the luminal cross-sectional area is 7.7 mm2.
figure 22FF7
Fig. 7 Before intervention: Intravascular ultrasonography of the left circumflex ostial lesion. The luminal cross-sectional area is 3.8 mm2. The left main–left anterior descending coronary artery stent is partially visible (arrows).

One day after this intervention, the patient was discharged from the hospital in excellent condition. At his last follow-up visit—21 months after his initial presentation—he was doing very well and remained asymptomatic.

Discussion

Percutaneous interventional techniques and stents have been developed and refined over the past 25 years. Multiple investigators have reported successful and safe unprotected-LMCA interventions with the use of stents. It is still being determined whether the same success rates will hold true when the newer drug-eluting stents are deployed in patients who are in cardiogenic shock and have unprotected-LMCA disease.

Significant LMCA disease is found in 5% to 7% of patients who undergo coronary angiography.1,2 The 3-year mortality rate of medically treated patients who have unprotected-LMCA disease is approximately 50%.3,4 Results of clinical trials conducted in the late 1970s indicated that CABG reduces the substantial 3-year mortality rate that ensues from medical therapy alone5–7 in patients who have significant narrowing of the left main trunk. Chaitman and colleagues8 reported a mortality rate of 31% in association with medical therapy alone, versus 9% with surgery. The results after unprotected-LMCA balloon angioplasty alone were poor: the 1-year mortality rate was 30%.9

Patients who present with both acute myocardial infarction and cardiogenic shock have a very high mortality rate. The SHOCK trial10 studied patients who were in shock due to left ventricular dysfunction that complicated acute myocardial infarction. The results showed that early revascularization, via either surgery or PCI (at the option of the treating cardiologist), increased 1-year survival to 47%, in comparison with 34% survival after aggressive initial medical stabilization.

Early reperfusion of an infarct-related artery is associated with improved outcome in cases of shock.11–13 Thrombolysis alone results in relatively low rates of reperfusion in patients in whom shock is already established14,15; sustained reperfusion is more likely when PCI is performed.16–19 Survival after PCI is strongly correlated with the subsequent patency of the infarcted artery, the completeness of revascularization, and the age of the patient.20,21 Moreover, the benefits of early revascularization appear to extend beyond the conventional 12-hour window.20 As a stabilizing measure for revascularization, placement of an intra-aortic balloon pump is a class I recommendation from the American College of Cardiology/American Heart Association guidelines for management of acute myocardial infarction in the presence of cardiogenic shock.22 Other percutaneous ventricular assist devices are being considered as bridges to transplant or recovery. The TandemHeart® percutaneous ventricular assist device (pVAD™)system (CardiacAssist, Inc.; Pittsburgh, Pa) has proved safe and effective in cases of cardiogenic shock and during high-risk PCI.23

Park and colleagues24 reported that the treatment of unprotected LMCAs with sirolimus-eluting stents in 102 consecutive patients was safe and effective when compared with bare-metal stents that had been deployed earlier in a group of 121 patients. The procedural success rate in both groups was 100%, with no in-hospital death, Q-wave myocardial infarction, emergency bypass surgery, or stent thrombosis. At 6 months, the patients with drug-eluting stents had an angiographic restenosis rate of 7.0%, versus 30.3% in the bare-metal stent group. At 1-year follow-up, 98.0% ± 1.4% of patients in the drug-eluted group had not experienced death, myocardial infarction, or target-lesion revascularization, versus 81.4% ± 3.7% in the bare-metal group.

Valgimigli and associates25 monitored 2 consecutive groups of patients who had undergone LMCA interventions: 86 who received bare-metal stents, and 95 (15 with protected LMCA) in whom drug-eluting stents were deployed. The baseline characteristics of both groups were similar. At a median follow-up of 503 days (range, 331–873 days), 24% of the patients in the drug-eluting stent group had experienced major adverse coronary events, versus 45% in the bare-metal stent group. Although mortality rates between the groups were similar, the drug-eluting stent group experienced significantly fewer myocardial infarctions (4% of patients vs 12%) and underwent less target-vessel revascularization (6% vs 23%). As determined by multivariate analysis, independent predictors of major adverse cardiovascular events were Parsonnet classification, cardiac troponin T elevation at entry to the hospital, the deployment of drug-eluting stents, distal location of the lesion within the LMCA, and the diameter of reference vessels.

Chieffo and coworkers26 studied 2 groups: 85 consecutive patients who had drug-eluting stents deployed against new unprotected-LMCA lesions, and 64 consecutive patients who had received bare-metal stents earlier. In comparison with the patients in the bare-metal stent group, the patients with drug-eluting stents had lower left ventricular ejection fractions, more often had diabetes mellitus, were more frequently found to have distal LMCA lesions, had smaller vessels with more lesions, and had more vessels that were treated with longer stents. Despite their higher-risk health and lesion profiles, the patients with drug-eluting stents experienced fewer major cardiac events after 6 months than did patients with bare-metal stents. Three patients who had drug-eluting stents and 6 patients who had bare-metal stents died of cardiac events.

Price and associates27 performed a serial angiographic follow-up study of 50 patients who had undergone unprotected-LMCA interventions with sirolimus-eluting stents. In-lesion stenosis, which was chiefly focal, recurred in 21 patients. In most instances, the restenosis affected the branch ostium but not the LMCA itself. Over a mean follow-up period of 276 ± 57 days, target-lesion revascularization occurred in 19 patients and was driven by ischemia in 7 of those cases. Significantly greater late loss of vascular patency occurred in the LCx ostium than in the parent vessel of the LMCA bifurcation. Late loss of patency increased from the 3rd through the 9th month. The final minimal luminal diameters and maximal balloon pressures were determined to be the independent predictors of restenosis of the parent vessel. The high rate of target-lesion revascularization was thought to be due to the predominantly bifurcated lesions in 47 of those 50 patients, the bifurcation stenting techniques used, and angiographic follow-up that was routine rather than symptom-driven.28,29

Lee and co-authors30 recently reported 1-year unprotected-LMCA PCI outcomes that were equivalent to outcomes from CABG, despite a higher percentage of high-risk patients in their PCI group. In that observational study, 50 patients with drug-eluting stents deployed in the unprotected LMCA were compared with 123 patients who had undergone CABG. Patients with a Parsonnet score >15 constituted 64% of the PCI group and 46% of the CABG group. After 30 days, the rate of major adverse cardiac and cerebrovascular events was 2% in PCI patients and 17% in CABG patients. At 6 and 12 months, the respective event-free survival rates were 89% and 83% in the PCI group versus 83% and 75% in the CABG group. The researchers determined that the independent predictors of major adverse events were Parsonnet score, diabetes mellitus, and CABG.

These studies illustrate the great variability of outcomes among patients who undergo PCI for the treatment of LMCA disease. Depending on patient selection, combined in-hospital and 1-year mortality rates varied greatly—from as high as 78% in patients with poor left ventricular function and acute ischemic syndromes to as low as 3.4% in patients without high-risk markers.29 Another factor was lesion location: restenosis occurred rarely in cases of ostial and mid-segment lesions, and most often (8%–17%) in cases of lesions of the distal LMCA bifurcation.29 Also playing roles were stenting technique (T, V, culotte, or crush), and whether multiple stents were used.23–26,29,30 Stenting from the LMCA into the LAD ostium and jailing of the LCx ostium, with rescue balloon angioplasty of the LCx only if needed, was thought to offer adequate results.31

Conclusion

As PCI evolves and as additional studies are conducted, more cardiologists are undertaking unprotected-LMCA PCI. Emergency PCI of a culprit LMCA lesion may prove valuable in the initial revascularization and rapid stabilization of the patient who experiences acute myocardial infarction and concomitant cardiogenic shock. In our patient, deployment of a sirolimus-eluting stent in the LMCA enabled prompt restoration of coronary blood flow before extensive myocardial necrosis occurred. The result was a substantial improvement in the patient's hemodynamic status.

Footnotes

Address for reprints: Bernardo Treistman, MD, 6624 Fannin, Suite 2390, Houston, TX 77030. E-mail: ten.traeh-saxet@hsc

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