Direct Angioplasty In Acute Myocardial Infarction: State of the Art and Current Controversies

Administration of glycoprotein IIb-IIIa inhibitors in patients with ST-segment elevation myocardial infarction

Patients with ST-segment elevation acute myocardial infarction require immediate reperfusion therapy. Reperfusion therapy can be provided by either pharmacologic or mechanical means. Pharmacologic reperfusion therapy consists of administering fibrinolytics, whereas mechanical reperfusion consists of performing percutaneous intervention, usually with stent placement. Each approach has been shown to decrease mortality, but each has disadvantages in establishing flow in the infarct-related artery. Regardless of the approach, during an acute myocardial infarction, activation and externalization of glycoprotein (GP) IIb-IIIa receptors occur on the surface of platelets. The GP IIb-IIIa inhibitors block the binding of fibrinogen to these platelet receptors. These inhibitors have been investigated in combination with both reperfusion strategies. The goal of adding GP IIb-IIIa inhibitor therapy to either reperfusion approach is to obtain better early, complete, and sustained reperfusion. Subsequently, this should lead to better clinical outcomes for patients with ST-segment elevation acute myocardial infarction. Although no mortality benefit has been seen with the addition of GP IIb-IIIa inhibitor therapy, ischemic complications have been reduced significantly.

Diabetes mellitus and cardiovascular disease

Diabetes is associated with a high incidence and poor prognosis of cardiovascular disease, and with high short- and long-term mortality. Adequate treatment of cardiovascular disorders and aggressive management of coexisting risk factors have proved to be at least as effective in diabetic as in nondiabetic patients in randomized, controlled studies. Indeed, treating diabetic patients with cardiovascular disease results in a larger absolute risk reduction than in nondiabetic subjects. Nevertheless, diabetic patients often receive inadequate therapy, which may, to a certain extent, explain their poor prognosis. Recommendations for the treatment of diabetic patients with acute myocardial infarction should include beta-blockers, aspirin, and ACE-inhibitors in all patients in whom no specific contraindications exist. Fibrinolysis should be administered when indicated, and the benefits of improving glycemic control should not be forgotten either. In patients with multi-vessel disease who need revascularization, when selecting the type of procedure, the superiority of surgical revascularization over angioplasty should be borne in mind. Even heart transplantation should be included as a therapeutic option since there are no data to support the exclusion of patients on account of their diabetes. Finally, coexisting risk factors should be intensively treated through lifestyle intervention, with or without drug therapy, in order to achieve secondary prevention goals.

Contrast-enhanced MRI for the assessment of myocardial viability after permanent coronary artery occlusion

Previous studies in a model of ischemia/reperfusion using a constant infusion of Gd-DTPA have shown that distribution volume (lambda) is increased in infarcted myocardial tissue. This study examined this technique in the setting of permanent coronary artery occlusion. Ten beagles underwent permanent occlusion of a coronary artery for 2 days (N = 3), 1 week (N = 4), or 3 weeks (N = 3). Imaging was performed at 2 days and, depending on the length of occlusion, 1 week, 2 weeks, and 3 weeks to follow changes in lambda in vivo. At sacrifice, (201)Tl was injected and the extent of the hyperenhanced region was compared to pathology. lambda was increased in infarcted tissue by 2 days post occlusion and this increase persisted for 3 weeks. At sacrifice, lambda correlated strongly with (201)Tl uptake (r = -0.86 to -0.95, P < 0.05; i.e., lambda increased in infarcted tissue) and the size of the hyperenhanced region was comparable to pathological infarct size (slope 1.006, r = 0.96, P < 0.0001). Thus, beyond 2 days after coronary occlusion, MRI, during a constant infusion of Gd-DTPA, can assess myocardial viability regardless of the success of reperfusion. Magn Reson Med 44:309-316, 2000.

Emerging concepts in the management of acute myocardial infarction in patients with diabetes mellitus

Although fibrinolysis has improved survival of patients after myocardial infarction (MI), such therapy is less likely to be administered to patients with diabetes. Furthermore, these patients present later (15 min) than nondiabetics. Moreover, even with the use of early potent fibrinolytic agents, patients with diabetes continued to suffer excessive morbidity and mortality. This finding is not related to the ability of fibrinolytic agents to restore complete reperfusion or increased risk of reocclusion of the infarct-related artery. Instead, the impaired ventricular performance at the noninfarct areas and metabolic derangements during the acute phase of MI may account for the adverse outcome. The efficacy of percutaneous coronary revascularization procedures for treatment of acute MI requires further evaluation. Therapeutic approaches should consider correcting these abnormalities to afford greater survival benefit for this subset of high-risk patients.

Primary stenting and glycoprotein IIb/IIIa inhibitors in acute myocardial infarction

Early patency of the infarct-related vessel improves in-hospital and long-term survival. Mechanical reopening is as effective as or superior to pharmacological therapy in the treatment of acute myocardial infarction. However, in patients treated with primary percutaneous transluminal coronary angioplasty, recurrent ischemia occurs in 10% to 15% before hospital discharge, and angiographic restenosis occurs in 30% to 50% of infarct-related vessel within 6 months. Primary stenting in acute myocardial infarction has been found to be safe and feasible and reduces early and late events. In particular, restenosis rate has been found to be lowered by stent implantation. Use of glycoprotein IIb/IIIa receptor inhibitors alone has resulted in infarct-related vessel patency rates approximately the same as with the use of thrombolytic therapy. Furthermore, glycoprotein IIb/IIIa receptor blockers reduce the occurrence of acute complications during percutaneous transluminal coronary angioplasty. Preliminary results of some ongoing trials showed that the combined therapeutic approach (ie, primary stenting plus glycoprotein IIb/IIIa inhibitors) in patients with acute myocardial infarction reduces both early and late complications of percutaneous transluminal coronary angioplasty. This finding supports the concept that optimal mechanical resolution of the plaque and the inhibition of platelet aggregation are the key of the treatment of the infarct-related vessel.

Thrombolytic therapy versus primary angioplasty in the treatment of acute myocardial infarction

The quest to identify the acute interventional approach that will achieve the lowest mortality rate with the fewest adverse events has led to a continued controversy surrounding the relative merits of thrombolytic therapy compared with primary angioplasty in the setting of acute myocardial infarction. This article summarizes the benefits and limitations of each reperfusion strategy and highlights adjunctive therapies that will enhance either treatment strategy.

Thrombolysis: the development of unit guidelines

A challenge remains to develop guidelines for practice which facilitate safer and effective administration of thrombolytic agents following acute myocardial infarction. Clinical trials have proven that early reperfusion of ischaemic myocardium following rapid diagnosis, aspirin administration, analgesia and the instigation of an appropriate thrombolytic regime reduces mortality rates. Accordingly, as thrombolysis becomes the buzzword of the 1990s, controversy has resulted in substantial variations in practice of thrombolytic strategies within the UK (FTTCC 1994). The purpose of this review article is to consider the importance of current research and its application to current practices. Topics under discussion include thrombolytic agents, antistreptokinase antibody, time delay, eligibility for thrombolytic treatment, and clinically proven therapeutic regimes; with a suggested admission protocol that facilitates bi-directional communication minimising time delay and preventing inappropriate, cost-inefficient admissions to critical care areas. The results of this provide a logistical basis to thrombolytic therapy, and the subsequent development of effective and safe algorithmic guidelines in a busy medical intensive care unit.