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Common Congenital Heart Lesions - page 34 / 126





34 / 126

34 of 126

Acute Coronary Syndromes

Chapter 7, pp. 157-184

Definition : life-threatening conditions that punctuate the course of CAD at any time.

  • Encompass a continuum ranging from unstable angina (UA) to the most

severe form of acute MI (STEMI)

  • In >90% of the time they all have the same underlying pathophysiology:

Atherosclerotic plaque disruptionÆplatelet aggregationÆintracoronary thrombus formation

  • Thrombus formation is the result of interactions b/t the plaque, endothelium, circulating platelets, & vasomotor tone of the vessel wall

  • The thrombus transforms an original region of stenosis or narrowing into a region of complete coronary obstruction

  • The result is impaired blood flow through the coronary arteryÆimbalance b/t myocardial O2 supply and demand

  • The type of ACS that results is dependent upon the degree of obstruction

  • PartialÆUA & Non-ST elevation or non-Q wave MI (NSTEMI)

(These are distinguished based on the presence of myocardial necrosis)

  • Complete or near completeÆST elevation or Q wave MI (STEMI)

(Characterized by severe ischemia & myocardial necrosis)

Pathogenesis of Coronary Thrombosis

  • Normally, mechanisms are in place to prevent spontaneous thrombus formation…However, in the presence of atherosclerotic lesions, these may be overwhelmedÆcoronary thrombus formation

  • Atherosclerosis contributes to thrombus formation by:

    • Plaque ruptureÆexposure of prothrombotic substances

    • Endothelial dysfunctionÆloss of protective, antithrombotic & vasodilatory properties

Plaque Rupture

  • Considered the major trigger of coronary thrombosis

  • Underlying causes include:

    • Circulating chemical factors (inflammatory cytokines)Æincreased vulnerability of the plaque to rupture

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