Acute Myocardial Infarction

Question 1

AMI

Answer 1

Macroscopic death of myocardium due ti vascular insufficiency (VI)

Question 2

VI

Answer 2

Myocardial ischaemia, i.e. balance between supply/flow and demand for oxygenated blood

Question 3

Underlying cause of AMI

Answer 3

Atherosclerosis, spasm, drugs, trauma

Question 4

Coronary artery occlusion- sequence of events

Answer 4

• Sudden change in atheromatous plaque- intraplaque hemorrhage, erosion/ulceration, or rupture/fissuring
• Exposed to subendothelial collagen and necrotic plaque contents- platelets adhere, activate, release granule contents, aggregate to form microthrombi
• vasospasm (mediators from platelets)
• Tissue factor activates coagulation pathway-bulk
• Within minutes, thrombus completely occludes lumen of vessel

Question 5

Features afecting sverity and rate of development of cotanary obstruction

Answer 5

Size of the vascular bed perfused by obstructed vessel

• Extent of collateral blood vessels
• Duration of occlusion
• Metabolic/ oxygen needs of the myocardium at risk
• Heart rate, cardiac rhythm, blood oxygenation

Question 6

Describe atherosclerosis

Answer 6

A chronic inflammatory and healing response of the arterial wall to endothelial injury. Lesion progression occurs through the interaction of modified lipoproteins, macrophages and T-lymphocytes with the normal cellular constituents of the arterial wall

Question 7

Pathogenesis of Atherosclerosis in AMI

Answer 7

• Endothelial injury- increased vascular permeability, leukocyte adhesion, thrombosis
• Accumulation of lipoproteins (mainly LDL) in vessel wall
• Monocyte adhesion to endothelium, migration into intima and transform into foam cells
• platelet adhesion
• Factor release from activated platelets, macrophages and vascular wall cells, including smooth muscle cells recruitment (from media of circulating precursors)
• Smooth muscle cell proliferation and ECM production
• Lipid accumulation both extracellular and within cells (macrophages and smooth muscle cells)

Question 8

What do location and size of myocardial death depend on?

Answer 8

• Location/severity of plaque
• Duration of occlusion
• Collateral circulation
• Needs of myocardium

Question 9

AMI medical intervention

Answer 9

Restoration of coronary blood flow

• Thrombolysis-activate fibrinolytic system to dissolve thrombus
• Balloon angioplasty
• Coronary bypass graft

Question 10

Ehy a reperfusion injury?

Answer 10

• Ischemic myocytes, endothelial cells, neutrophils
• incomplete reduction of O2 by damaged mitochondria- ROS/ free radicals generated and the antioxidant mechanisms were damaged by ischaemia.

Question 11

Complicationf of AMI

Answer 11

• Contractile dysfunction
• Arrhythmia
• Rupture
• Pericarditis
• Infarct expansion