Calming the plaque to delay intervention for 24 hours in acute coronary syndromes

The role of low-molecular-weight heparins in cardiovascular medicine

Low-molecular-weight heparins (LMWHs) have been shown to be as effective and safe as unfractionated heparin (UFH) for acute phase treatment of acute coronary syndrome in the absence of ST-elevation [unstable angina/non-ST-elevation myocardial infarction (UA/NSTEMI)]. LMWHs have practical advantages over UFH, including usual lack of requirement for laboratory monitoring of the anticoagulant response because of their favourable pharmacokinetic properties, and thus represent a simpler and more cost-effective option in clinical practice. The LMWH dalteparin has been shown to provide extended therapy benefit to high-risk UA/NSTEMI patients and can provide a protective bridge until revascularization. While revascularization procedures are now an established intervention for patients with UA/NSTEMI, a new approach for patients who cannot undergo immediate catheter intervention is to continue with medical treatment until revascularization is possible. LMWHs are currently being investigated for use in the catheterization laboratory, in patients undergoing percutaneous coronary intervention procedures, and in conjunction with thrombolytics for treatment of acute myocardial infarction.

Pharmacologic plaque passivation for the reduction of recurrent cardiac events in acute coronary syndromes

Acute coronary syndrome (ACS) is often associated with the rupture of vulnerable atherosclerotic plaque, coronary thrombus formation, and abrupt limitation of blood flow, leading to adverse outcomes. Passivation of vulnerable plaque represents a therapeutic concept that has the potential to prevent or limit the magnitude of a new rupture in order to reduce the recurrence or severity of events. Plaque passivation can be defined as a process by which the structure or content of the atherosclerotic plaque is changed to reduce the risk of subsequent rupture and thrombosis. This may be achieved by using strategies that address different components of the plaque or the endothelium. The following factors can affect the susceptibility of plaque to rupture: macrophage infiltration; accumulation of inflammatory cells; paracrine secretion of enzymes that may cause degradation of the fibrous cap of coronary plaque; shear stress; circadian rhythm variation in stress hormone release; and infectious agents. The use of pharmacologic agents to reduce plaque vulnerability by passivation has been explored. Clinical studies demonstrate that lipid-modifying agents (e.g., statins), antiplatelet agents (acetylsalicylic acid, thienopyridines, thianopyridines, glycoprotein IIb/IIIa inhibitors), and antithrombotic agents (unfractionated heparin and low-molecular-weight heparin) can reduce the occurrence of acute coronary events in ACS patients. In addition, angiographic studies suggest that statins may also promote regression of atherosclerosis. Angiotensin-converting enzyme inhibitors, niacin, and calcium antagonists may also contribute to plaque passivation. This article reviews atherosclerotic plaque development and vulnerability and discusses some clinical studies highlighting the role of plaque passivation in the management of ACS patients.

The use of the glycoprotein IIb/IIIa receptor antagonists during percutaneous coronary intervention

Coronary thrombosis is the major cause of ischemic complications during percutaneous coronary interventions (PCI). The glycoprotein (GP) IIb/IIIa receptor plays a critical role in the process of platelet thrombus formation since it serves as the final common pathway for platelet aggregation. Presently, there are three commercially available intravenous GPIIb/IIIa inhibitors that block fibrinogen binding to its receptor. These agents significantly reduce the incidence of death and nonfatal myocardial infarction at 30 days in patients undergoing percutaneous coronary revascularization. In addition, the early benefits appear to be sustained at 6 months to 1 year. Increasing evidence shows that the predominant mechanism of benefit is due to a reduction in embolization to the microcirculation that occurs during PCI. While data regarding the comparative efficacy and cost-effectiveness of these agents are scarce, the magnitude of benefit appears to be greatest for abciximab. Furthermore, a mortality benefit has been demonstrated only for abciximab. Although high risk patients reap the greatest benefit from the use of these agents, it is clear that even patients who are classified as low-to-moderate risk still derive substantial benefit from their use. Finally, evidence indicates that the majority of patients with acute coronary syndromes without ST segment elevation who are scheduled to undergo PCI should be pretreated with a GPIIb/IIIa receptor antagonist.

Unstable angina pectoris and non-Q-wave myocardial infarction

Unstable angina pectoris and non-Q-wave myocardial infarction are clinical syndromes that share many pathophysiologic and clinical features. In the spectrum of coronary artery disease, these syndromes lie between chronic stable angina and Q-wave myocardial infarction. Although both conditions are associated with significant morbidity and mortality, patients presenting with these syndromes can be further risk stratified into higher and lower risk based on a number of readily available clinical features and biochemical parameters. Such risk stratification can allow for more tailored treatment and better resource allocation. Although routine early coronary angiography and revascularization has not been shown to be superior to conservative management, certain high-risk patients may benefit from a more aggressive strategy. Medical therapy with the use of antiplatelet, anticoagulant, and antiischemic agents remains the cornerstone of emergent treatment for patients presenting with these syndromes. The recent demonstration of a reduction in both morbidity and mortality with the glycoprotein IIb/IIIa antagonists has further expanded the armamentarium of available agents. Following initial stabilization, risk stratification with stress testing can help identify patients with a large residual ischemic burden who may benefit from coronary angiography with revascularization if feasible.