Chapter 21 Marini Acute Coronary Syndromes

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SECTION II • Medical and Surgical Crises

heparin and Gp2b/3a receptor antagonists. This drug, though expensive, has become popular with interventional cardiologists. Fibrinolytic Therapy There is no proven benefit of fibrinolytic therapy in NSTE-ACS. This is probably because a completely occlusive coronary thrombus is present in fewer than 50% of patients, because platelet-rich thrombi, which predominate in coronary vessels of patients with NSTE-ACS, are resistant to dissolution with fibrinolytic therapy and because fibrinolytics pro- mote platelet aggregation. Fibrinolytic agents have not been demonstrated to be effective in reduc- ing the risk of MI or death in NSTE-ACS and in fact may be deleterious. This is in stark contrast to STEMI-ACS, where the effectiveness of fibrino- lytic therapy has been proven. Therefore, fibrino- lytics are contraindicated in NSTE-ACS, except in unusually high-risk and unstable patients as a tem- porizing measure during transport to a center where PCI is available. Invasive Strategy of Coronary Angiography and Percutaneous Coronary Intervention Several recent studies have demonstrated ben- efit with an early invasive strategy in patients with NSTE-ACS as compared to conservative treat- ment strategy. In the early invasive strategy, patients undergo coronary angiography and revascularization within 12 to 48 hours of presentation to the hospi- tal with ACS. In the conservative strategy, patients undergo coronary angiography only for significant recurrent ischemia or ischemia demonstrated by stress testing. The early invasive strategy results in lower short-, intermediate-, and long-term major cardiac event rates (death, MI, recurrent ischemia, and revascularization rates) and shorter lengths of stay in the hospital. This is particularly true in patients with high-risk characteristics like elevated serum cardiac biomarkers (like troponins), ongoing chest discomfort, and dynamic ST–T changes on ECG. In intermediate-risk patients, a conservative strategy may be as good as an early invasive strat- egy. In low-risk patients, a conservative strategy is preferred. It has been shown that use of aggressive medi- cal regimens including “upstream” use of Gp2b/3a receptor antagonist (e.g., tirofiban or eptifibatide) for 12 to 24 hours before PCI reduces the risk of MI or death after PCI by at least 30% to 40%.

The majority of patients with NSTE-ACS will be candidates for PCI after coronary angiography (70% to 80%). Compared to balloon angioplasty, coronary stenting appears to substantially reduce recurrent ischemia and infarction. Restenosis in 3 to 6 months is a major limitation with bare-metal stents and occurs because of an intimal hyperplasia reaction to the vessel wall injury. Widespread use of drug-eluting stents has reduced long-term restenosis and repeat revascularization rates by 50% to 70%. However, with current stents, these patients must remain on long- term clopidogrel and aspirin therapy. Emergent cardiac catheterization and revascu- larization in NSTE-ACS are needed less commonly. The indications include pulmonary edema, hypoten- sion, and malignant ischemic ventricular arrhyth- mias. Most of the other high-risk patients can be stabilized with medical management for 12 to 48 hours before angiography and revascularization. Coronary Bypass Graft Surgery Versus Stenting The mortality risk with urgent CABG in NSTE-ACS patients is around 4% to 5%. The other complica- tions of bypass surgery include stroke and cognitive abnormalities. This is mainly due to cross-clamping of the aorta and the use of cardiopulmonary bypass. These risks should be borne in mind, especially while operating on elderly patients. The complica- tions and recovery times have improved over the course of the two decades because of refinement in surgical techniques and postoperative care. The advent of left internal mammary artery (LIMA) graft- ing to the left anterior descending (LAD) artery was a major advance in bypass surgery since the 1980s. The use of off-pump bypass surgery may reduce the risk of stroke in elderly patients. The usual length of stay in the hospital is 5 to 7 days, but it may take up to 2 to 3 months for the patients to recover back to their usual pre-event baseline. Only 20% to 30% of NSTE-ACS patients need urgent CABG. The classical indications for CABG include (1) significant left main coronary stenosis, (2) multivessel CAD with left ventricular ejection fraction (LVEF) less than 40%, (3) CAD with sig- nificant valvular disease (aortic stenosis and mitral insufficiency), (4) diabetes mellitus with multi- vessel CAD, (5) coronary anatomy unsuitable for PCI, and (6) failed PCI. It is preferable to stabilize these patients with medical management prior to CABG. Sometimes, an intra-aortic balloon pump (IABP) may be needed for prior stabilization in