Chapter 21 Marini Acute Coronary Syndromes

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CHAPTER 21 • Acute Coronary Syndromes

ischemia, reinfarction, heart failure, or significant ventricular arrhythmias. With successful PCI, ventricular remodeling and LVEF are improved and these patients may tend to have fewer ven- tricular arrhythmias. Thus, it may be worthwhile attempting late revascularization (PCI or CABG surgery) in occluded coronary vessels if there is evidence of myocardial viability—especially if a large area of myocardium is in jeopardy. • Antithrombotic therapy in primary PCI: Patients undergoing primary PCI for STEMI should receive UFH (50 to 70 units/kg bolus fol- lowedby an infusion at rate of 12 to 15units/kg/h). Heparin should be started while the patient is waiting to be transferred to the cardiac catheter- ization laboratory. An infusion of heparin after the procedure is unnecessary, unless an IABP is used or if the result is unsatisfactory and there is ongoing ischemia postprocedure. The vascu- lar sheaths are generally removed 3 to 6 hours after heparin dosing (typically when the ACT is below 170 seconds). Enoxaparin can be used as an alternative to heparin in the dose of 1 mg/kg subcutaneously twice daily. There is no need to monitor ACT or for additional antithrombotic therapy if PCI is done within 8 hour of enoxapa- rin dose. The vascular sheaths can be removed 8 to 12 hours after the last dose of enoxaparin. • Bivalirudin in STEMI: The influential HORIZONS-AMI trial showed lower cardiac death and bleeding rates at 30 days with bivali- rudin (a DTI) compared to standard treatment of heparin combined with Gp2b/3a receptor antag- onists in STEMI patients undergoing emergent PCI. The drug although has become popular among interventional cardiologists despite its relatively high cost. • Gp2b/3a receptor antagonists in primary PCI: Gp2b/3a receptor antagonist agents have been routinely used in patients with AMI. Abciximab has been shown to be beneficial in STEMI patients and as a pharmacological adjunct for primary PCI, and many interven- tional cardiologists use this agent routinely in almost all STEMI patients. Given the efficacy of safer dual antiplatelet regimens, others prefer to use it selectively in those with large throm- bus burden, diabetic patients, and complications like distal embolization and dissections. Many hospitals are now using one or the other small- molecule agents (eptifibatide and tirofiban) for

patients with STEMI, because the incidence of dangerous bleeding, thrombocytopenia, and pul- monary hemorrhage is lower with these agents as compared with abciximab. For best results, the medications should be started prior to the PCI procedure. • Clopidogrel: This is given as a 300- to 600-mg bolus at the completion of the acute infarct PCI, particularly in those who receive intracoronary stents. The medication is generally continued for a minimum of 12 months in AMI patients receiving DES. The primacy of more potent and recently introduced alternatives (e.g., prasugrel and ticagrelor) has not yet been established. Indications for CABG in STEMI • Urgent or emergent CABGmay be necessary in 5% to 8% of patients with STEMI undergoing emer- gent PCI. The usual indication for emergent CABG is failure of reperfusion with PCI, a large area of jeopardized myocardium, in a patient with coronary anatomy suitable for CABG. That emergent rescue approach is especially attractive if the patient is within 6 to 12 hours of an acute infarction. • Patients with mechanical complications of an MI, such as acute MR, acute VSD, or wall ruptures, are also candidates for emergent surgery. Patients with certain coronary anatomies may benefit from emergent or urgent CABG: severe left main dis- ease (>70% stenosis) and severe proximal multi- vessel disease (especially those with CHF or car- diogenic shock). • Mortality is 10% to 15% in STEMI patients undergoing emergent CABG within the first few hours of infarction. However, this may be the only way to salvage myocardium in some patients with STEMI who fail PCI. Improvement in tech- niques for myocardial preservation (like use of blood cardioplegia) during CABG has certainly improved outcomes with emergent surgery. Also, it is important to keep bypass pump time short in these patients. In fairly stable patients, one should try to graft the LIMA to the LAD artery (wherever applicable), but in unstable patients, vein grafts are preferred, as this shortens the time on the bypass pump. • In patients with cardiogenic shock who are less than 75 years of age, emergent bypass surgery should be considered as soon as possible if they are not candidates for PCI or if they fail PCI. Stabilization with IABP counterpulsation and