28: Embolism and Infarction

Best outcome after thrombus formation

Fibrinolysis and complete dissolution

Enzyme that mediates fibrinolysis

Plasmin

If a thrombus becomes more permanent, what may happen

Organization and recanalization

Direction of thrombus propogation

Towards the heart

How bad is it if a thrombus embolizes

Not great…pretty dangerous

Embolus

A detached intravascular solid, liquid, or gas

Most common type of embolus

Thromboembolus

Why are emboli such a problem

They lodge somewhere and can completely occlude blood flow

What organ can sort of accommodate an embolus without guaranteed, immediate problems or death

Lungs (pulmonary thromboembolism)

Common things that embolize in the body

• Fibrin (thrombus)

• Fat

• Air

• Cartilage (IVD → fibrocartilage)

• Neoplasia

Common cause of thrombus formation in the heart due to endothelial injury

Endocarditis

Common cause of thrombus formation in the heart due to turbulent blood flow

HCM

Common cause of thrombus formation due to hypercoagulation

Loss of AT III through a protein-losing nephropathy

Condition that is a common (still rare) cause of fat embolus

Large bone fracture

Common veterinary cause of air embolism

Air in an IV line

Patient demographic for a fibrocartilage embolism

Adult large breed dog after jumping or other activity

Hypoxia

Low oxygen in the blood

Ischemia

Low blood flow (and so also low tissue oxygen)

Ischemic necrosis

Tissue death due to an ischemic event

Infarct

Area of ischemic necrosis

Typical morphology of an infarction

Sharply demarcated, often triangular with the apex nearest the site of occlusion

Morphology of acute infarction

Swollen and red (passive congestion)

Morphology of subacute infarction

Pale zone of ischemic necrosis surrounded by a line of hemorrhage

Morphology of chronic infarction

Depressed, fibrotic, and contracted

Conditions that allow reperfusion injury

Ischemic event that is short enough that an infarct doesn’t form and blood flow is restored

Why is sudden return of blood flow after an ischemic event bad

Tissue adapted to hypoxic conditions, and the rapid return of blood brings lots of inflammatory cells and lots of O₂ allowing for rapid consumption and high production of ROS, ultimately overwhelming the tissue area

How bad is a reperfusion injury

Often worse than the initial ischemic event