Thrombosis. Definition Thrombosis is the process of formation of a solid mass from the blood...

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Transcript of Thrombosis. Definition Thrombosis is the process of formation of a solid mass from the blood...

  • Slide 1
  • Thrombosis
  • Slide 2
  • Definition Thrombosis is the process of formation of a solid mass from the blood constituents, within non-interrupted cardiovascular system during life
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  • A thrombus is a solid mass formed from blood constituents within the cardiovascular system during life. It is formed mainly of platelets and clotted blood( fibrin network entangling red and white blood cells)
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  • Aetiology of thrombosis Predisposing factors Virchow triad 1- Endothelial cell injury 2- Alteration in normal blood flow 3- Alteration in blood coagulability
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  • THROMBOSIS -Virchow triad
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  • I- Endothelial lining injury: Important in the formation of thrombi in the heart and arteries. Normally, the vascular endothelium inhibits thrombosis, but if it is injured, the exposed collagen will act as a potent thrombogenic factor.
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  • 1-Arteries: Degenerative diseases: e.g., arterial atherosclerosis Hemodynamic stresses of systemic hypertension (Mechanical trauma). Cigarette smoking and hyperlipidemia Immune-induced arteritis (S.L.E, P.A.N), radiation.
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  • 2-Veins: Mechanical trauma: e.g., presence of catheter, tight bandages. Chemical injury: e.g., infusion of certain compounds into the veins for treatment of varicose veins and hemorrhoid. Inflammation: e.g., vein drained septic focus
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  • 3- Endocardial injury: Over myocardial infarct Endocarditis: Rheumatic and infective endocarditis
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  • II- Alterations in the normal blood flow This may be in the form of stasis or turbulence.
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  • Slowing of the speed of blood flow (Stasis) It is the major factor in the development of venous thrombosis & caused by: Local causes: Pressure on the veins by bandages, tumours, gravid uterus. Lack of muscular pumping action as in bedridden patients, in postoperative period or after delivery. Dilatation of veins and vulvular incompetence e.g., in varicose veins. General factors: e.g., congestive heart failure
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  • Disturbance in the laminar blood flow (Turbulence) is seen in Major turbulence e.g., arterial aneurysm, and myocardial aneurysm
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  • Effects of Alterations in the normal blood flow: Endothelial injury or dysfunction Disrupting the laminar blood flow and bring platelets into contact with endothelium
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  • III- Alterations in blood coagulability (Hypercoagulability): might be primary or genetic; and secondary or acquired. Primary or genetic deficiency of protein C or antithrombin III
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  • B-acquired hypercoagulablility : Increased blood viscosity as in severe dehydration Postoperative and postpartum patients Oral contraceptives Tissue damage e.g., massive burn, fracture, surgery ( release of tissue thromboplastin). In association with some tumours as carcinoma of pancreas After splenectomy Hyperlipidemia ( platelet adhesiveness and aggregation).
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  • Morphology of thrombi a-Gross appearance: 1-Site and shape: Anywhere in the cardiovascular system: within the cardiac chambers; on valve cusps; or in arteries, veins, or capillaries. Cardiac or arterial thrombi begin at the site of endothelial injury (atherosclerotic plaque) or turbulence (aneurysms & vessel bifurcation). On the other hand, venous thrombi usually occur at sites of stasis.
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  • All thrombi are attached to the vessel wall or cardiac chamber at the point of their origin. Arterial thrombi tend to grow in a retrograde direction from the point of attachment (that is away from the heart), while venous thrombi extend in, the direction of blood flow (i.e. towards the heart). The propagating tail may detach leading to emboli especially found in veins.
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  • 2-The colour: Characteristic laminations (lines of Zahn) due to alternating layers of platelets (pale) and fibrin containing RBCS & leukocytes (red)are especially noticed in thrombi of the heart and large arteries as the aorta.
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  • These are "lines of Zahn" which are the alternating pale pink bands of platelets with fibrin and red bands of RBC's forming a true thrombus
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  • Red thrombus: It occurs when stasis plays a prominent role in its pathogenesis e.g., in veins. It is formed of platelets and fibrin entangling a large number of R.B.Cs. Pale thrombus: When there is no stasis and alteration of blood flow is prominent. It is composed predominantly of platelets and fibrin with few entrapped R.B.Cs
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  • 3- Type Mural thrombus: non-occlusive thrombus adherent to the vessel wall or cardiac wall. Occlusive thrombus: when it completely obstructs the vessel Propagating thrombus: with complete occlusion of the vessel, the static blood beyond may coagulate (tail of thrombus) that reach a tributary vessel in which there is flowing blood, and a fresh thrombus is initiated. This is common in venous thrombi.
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  • b- Microscopic appearance: Recent thromus show alternating layers of platelets and fibrin (lines of Zahn). Old thrombi show granulation tissue or fibrosis (organized thrombus)
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  • ThrombosisBlood clotting AntimortemAntimortem or postmortem It occurs inside the cardiovascular system (in vivo ) In vivo: inside the CVS: during life (as a tail of thrombus) and after death. outside CVS as in hematoma. In vitro (in test tube outside the body) It is formed while the blood is circulating It is formed while the blood is stagnant It is composed of alternating layers of aggregated platelets & fibrin (line of zahn) It is composed of randomly oriented fibrin with entrapped platelets & blood cells (no lines of zahn) It is firmly attached to the endothelium It is loosely attached to the endothelium It is firm & friableIt is jelly like Differences between:
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  • Fate of the thrombus 1- Dissolution (removed by fibrinolytic activity ) 2- Propagation (The thrombus may accumulate more platelets and fibrin (propagate), eventually leading to vessel obstruction). 3- Embolization (Thrombi may dislodge and travel to other sites in the vasculature ) 4- Organization & recanalization (Thrombi may induce inflammation and fibrosis (organization) and may eventually become recanalized ) 5- Calcification
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  • Occlusive coronary atherosclerosis. narrowed by 60 to 70% thrombus and recanalization.
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  • Effect of thrombus (complications): Infarction: occlusive thrombi of arterial supply with absence of collateral circulation lead to ischemic necrosis of area supplied by this artery (infarct) Oedema, congestion when there is obstruction of venous outflow. Embolism: part of the thrombus may be detached and carried along in the blood stream to impact in a distant vessel. Infection: thrombi are fertile soil for bacterial infection.
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  • Sites of thrombi Venous Thrombosis A-Phlebothrombosis (thrombosis without inflammation) 90% occur in lower extremities (deep vein thrombosis of the calf) B-Thrombophlebitis (on top of inflammation) In veins draining septic focus: Appendicular veins in acute appendicits Pelvic veins in puerperal sepsis
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  • Points of differences PhlebothrombosisThrombophlebitis CauseStasis Inflammation of vein wall. SizeSmall Larger, depending on the extent of phlebitis. Size of propagated clot Long & is poorly anchored to the vessel wall. Usually none & if present is short & well anchored to the vessel wall Emboli Common, massive & sterile infarct. Rare except in infective cases. Septic & pyemic abscesses. SiteUsually calf veinsAny where Clinical picture Silent or there are few signs & symptoms Pain & signs of acute inflammation
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  • Thrombosis In Arteries Less common than veins because of the rapid flow, and the thick elastic arterial wall which resists injury. Thrombosis in arteries is caused by: (endothelial injury & blood turbulence). Types of arterial thrombosis are: - Occluding thrombus in medium sized and small arteries, frequently in association with atherosclerosis. Mural thrombus: occurring in a large artery or aorta.
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  • Heart, coronary atherosclerosis with thrombosis - Gross
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  • Coronary thrombosis
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  • Heart, coronary artery thrombosis - Low power
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  • Heart, coronary artery thrombosis - High power
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  • Effects: occlusive thrombi of arterial supply with absence of collateral circulation lead to ischemic necrosis of area supplied by this artery (infarct)
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  • Thrombi In The Heart Mural thrombi occur in the heart chambers especially in the left ventricle at sites of myocardial infarction, and, in the left atrium in cases of mitral stenosis. It is usually associated with atrial fibrillation. Valvular thrombi or "vegetations" are found in rheumatic valvulitis and infective endocarditis. Agonal thrombi, which occur during the last hours of life when death oc