John T Coppola, MD; Emanuel M Shaou...

John T Coppola, MD; Emanuel M Shaoulian, MD; and Peter Rentrop MD

Treatment of acute myocardial infarction has experienced pair major revolutions. In 1963 Day[1] described grouping patients with acute myocardial infarction in the same area of the hospital, which l to the unravelling of the coronary care unit. The improved treatment of the complications of myocardial infarction comeed in a significant decrease in early mortality; however, cardiologists remained unable to halt the progression of myocardial necrosis. The next to the first revolution, which led to the disentanglement of methods limiting the infarct's size and improving survival, began with an improved understanding of the pathophysiology of acute myocardial infarction in the late 1970s

PATHOPHYSIOLOGY

Acute myocardial infarction is the outcome of prolonged interruption of descendants flow leading to severe ischemia and confined apartment necrosis in the region supplied at the obstructed artery.[2] Necrosis of tissue begins within 20 minutes and continues from one side of to the other several hours. Experimental studies have shown that if progeny flow is restored soon enough, myocardium can be salvaged.[3]

The cause of this interruption of offspring flow is now believed to be thrombosis occurring in an area of atherosclerosis. This universal was first elucidated by James Herrick in 1912 and was generally accepted until the early 1970 when the part of thrombus was downplayed by dint of various pathologic studies.[4,5]

In 1978 Rentrop et al[6] demonstrated the carriage of filling defects suggestive of thrombus in the infarct-related coronary artery on angiography performed during the first hours of myocardial infarction. They also documented spontaneous delayed recanalization, suggesting endogenous thrombolysis. In a following study, the same group showed acute recanalization of the infarct-related artery during selective infusion of streptokinase, a thrombolytic agent.[7] Recanalization was associated with rapid relief of chest pain and get back of ST-segment elevations to the baseline, further substantiating the part of the thrombus in the pathogenesis of acute myocardial infarction. In 1980 DeWood et al[8] reported convalescence of thrombi in 88 percent of 59 patients who underwent pass bypass surgery during the acute stage of myocardial infarction.

Thrombus formation at the site of atherosclerotic disease comes from a complex interaction between the bottom wall, platelets, vasoactive substances, and the intrinsic coagulation plan Although the mechanisms involved are not completely understood, it is believed that this proces is initiated through fissuring of plaque, which bring to lights collagen and free fatty acids to posterity Contact with these substances leads to platelet aggregation, which, in turn round causes activation of the intrinsic coagulation plan and development of fibrin thrombus.[9-11] Furthermore, vasoactive substances like as thromboxane A are released, which might yield vasospasm.[12]

It would then appear that classifications of reestablishing flow by chemically or mechanically breaking up thrombus or bypassing the area of occlusion may limit necrosis and salvage myocardium. Since short-term and long-term survival in ischemic disease is hanging upon the extent of myocardial dysfunction,[13] it would appear reasonable that limitation of the infarct's size will lead to better survival.

We will discuss the therapeutic options available in limiting the infarct's size, with a focus forward thrombolysis, angioplasty, and surgery.

THROMBOLYSIS

Pharmacology

Experimental studies during the past 30 years have demonstrated that coronary thrombi may be dissolved through systemic or selective infusion of thrombolytic put drugs intos A fibrinolytic activator produced through streptococci, which liquifies clotted human plasma, was described in 1933[14] In 1959 Fletcher el al[15] reported intravenous treatment with streptokinase in 22 patients with acute myocardial infarction, although these investigators[15] did not demonstrate efficacy.

Fibrinolysis is initiated by dint of the conversion of plasminogen to plasmin, a proteolytic enzyme which can lyse not merely fibrin clots but fibrinogen and clotting factors 5 8 and 12 Plasminogen can be activated either via an intrinsic pathway using substances circulating in plasma or on an extrinsic path depending in succession enzymes in vascular endothelium and other tissues. The extrinsic regularity is the major system in physiologic fibrinolysis. These tissue plasminogen activators have an affinity for fibrin. Binding to fibrin leads to cleavage of fibrin-bound plasminogen, giving rise to plasmin and initiating fibrinolysis. Small amounts of liberated plasmin can also form, on the contrary under normal conditions, this is quickly inhibited by means of [unkeyable][sub.2]-antiplasmin. Fibrin-bound plasmin is not as susceptible to inactivation by dint of [unkeyable][sub.2]-antiplasmin and has a longer half-life.

Agents generally used induce thrombolysis by direct or indirect production of plasmin from plasminogen. Urokinase and t-PA are proteolytic enzyme which directly activate plasminogen. Streptokinase induces thrombolysis indirectly by means of forming a complex with plasminogen, called "activator." This activator involved converts plasminogen which was not used for activator formation to plasmin.