Chapter 21 Marini Acute Coronary Syndromes

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CHAPTER 21 • Acute Coronary Syndromes

• High-volume centers are those that performgreater than 200 to 300 PCI procedures per year. Data from the National Registry for MI (NRMI) show that there is a 37% reduction in death in STEMI patients treated with PCI at high-volume cent- ers and little change in mortality when treated at low-volume centers. However, a 64% reduction in risk of CVA was seen with PCI at both low- and high-volume centers. Therefore, primary PCI is the preferred mode of reperfusion for STEMI patients if access to a high-volume cardiac cath- eterization laboratory is available and if PCI can be performed in a timely fashion. The ideal door- to-balloon time should be less than 90 minutes. • On-site fibrinolytic therapy versus transfer of patients for PCI: When patients with STEMI arrive at a hospital without a cardiac catheteriza- tion laboratory, the question arises as to whether these patients are better off with on-site fibrino- lytic therapy or with transfer for PCI to a larger center with cardiac catheterization facilities. The DANAMI-2 and PRAGUE-2 trials have both shown benefit of transferring patients for primary PCI over on-site fibrinolytic therapy, if the trans- fer of patients can be achieved within 2 hours. In the DANAMI-2 trial, there was a 40% reduc- tion in reinfarction, death, and CVA at 30 days, compared to fibrinolytic therapy. The transferred patients have outcomes with PCI comparable to those who present directly to the invasive treat- ment center. Transfer of patients was found to be safe, with very few adverse events during transportation. Thus, establishment of primary PCI centers with 24/7 cardiac cath-lab facilities and efficient patient transfer protocols is key to improving outcomes in patients with STEMI. The door-to-balloon time is approximately 3 hours in the United States for patients with STEMI transferred for PCI (time of entry to the first emergency room to the time of balloon infla- tion at the PCI). Therefore, the prevailing guide- lines in the United States would favor the admin- istration of fibrinolytic therapy for lytic-eligible patients—if the door-to-balloon time is likely to exceed 90 minutes. These patients must be transported to a PCI center soon after adminis- tration of fibrinolytic therapy, so that if they fail to achieve reperfusion, then they could still undergo PCI and mechanical reperfusion in an expedi- tious manner. For patients with contraindications for fibrinolytics (lytic ineligible) and in situations

where the door-to-balloon time is likely to be less than 90 minutes, quick transfer to another hospi- tal for primary PCI is the best approach. • PTCA versus intracoronary stenting in AMI: Stents improve long term outcome from PTCA. Meta-analysis of all the stent-versus-balloon angioplasty trials shows 46% reduction in composite endpoint of death, reinfarction, and target vessel revascularization at 6 months using stents compared to PTCA alone. This difference was mainly due to reduced restenosis and recur- rent ischemia. • Drug-eluting versus bare-metal stents: Bare- metal stents have been in clinical practice in the United States since 1994. In 2003, the FDA approved sirolimus (Rapamune) and paclitaxel (Onxol, Taxol) DES for clinical use. Zotarolimus and everolimus-eluting stents have also been approved by the FDA. These stents are made of stainless steel and are covered with a poly- mer, which elutes an antiproliferative drug. The stents usually elute the drug for a period of 3 to 6 weeks from the time they are deployed in the artery. The main advantage of DES as compared with the older bare-metal stent is reduction of restenosis from excessive neointimal prolifera- tion. Neointimal proliferation occurs as a result of intimomedial injury caused by the stent. The antiproliferative agent eluted by the stent pre- vents neointimal proliferation in the artery. These devices are now used extensively in patients with CAD, including in those with AMI. The use of DES has reduced clinical restenosis rates quite dramatically compared to those receiving bare- metal stents (5% to 9% vs. 20% to 40%). DES has been shown to have superior clinical outcomes in all subsets of patients, including AMI. The major disadvantage of stents, particularly DES, is stent thrombosis, which can cause catastrophic MI or death. Patients who receive bare-metal stents should remain on dual antiplatelet therapy (e.g., clopidogrel and ASA) for a minimum of 1month. The recommendation is for aminimumof 12 months of dual antiplatelet therapy for patients with DES. However, over the course of the last few years, it has become apparent that a small group of patients with DES will suffer from the phenomenon of late stent thrombosis , especially with discontinuation of clopidogrel therapy. That is the reason why most patients who receive DES remain on dual antiplatelet indefinitely.