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• Fibrinolysis

  The last stage of coagulation is fibrinolysis, which

  commences a few hours after fibrin polymerization.

  • Comprised of a systematic hydrolytic digestion of

  cross-linked fibrin polymers by bound plasmin.
• The Fibrinolytic System

  Fibrinolysis, the physiologic process of

  removing unwanted fibrin deposits ,

  represents a gradual progressive enzymatic

  cleavage of fibrin to soluble fragments.

  The fragments are then removed by the

  fixed macrophages of the MPS.

  (mononuclear phagocytic system).
• The Fibrinolytic System

  This action will re-establish blood flow in the damaged

  endothelium occluded by the thrombus and eventually facilitates

  healing and restores hemostasis.
• Components of Fibrinolysis

  1. Plasminogen - Plasmin

  2. Tissue plasminogen activator (TPA)

  3. Urokinase

  4. Streptokinase

  5. Plasminogen activator inhibitor-1 (PAI-1)

  6. A2- antiplasmin
• Plasminogen Plasma serine protease Liver 24-26 hrs

  TPA Serine protease Activated endothelium unknown

  Urokinase Serine protease Kidneys unknown

  Streptokinase Autocatalysis B-hemolytic strep 3 mins

  PAI- 1 Inhibits TPA Endothelium 1 hour

  A2-antiplasmin Inhibits plasmin Liver unknown
• PLASMINOGEN

  The fibrinolytic system is mediated mainly by the enzyme plasmin,

  which acts primarily on fibrin to produce lysis of the clot.

  Plasmin is generated from the inactive zymogen called

  plasminogen.

  Plasminogen is activated to plasmin by tPA and other substances.
• PLASMINOGEN

  Synthesized in the liver

  2 days half-life.

  20 mg/dL plasma concentration

  Has 2 forms :

  1. Lys- plasminogen - more readily converted to active plasmin.

  2. Glu- plasminogen
• ENDOGENOUS ACTIVATORS

  FACTOR XIa , XIIa and

  Kallikrein

  EXOGENOUS ACTIVATORS

  TIssue plasminogen

  activator, Urokinase ,

  Streptokinase
• PLASMINOGEN ACTIVATORS

  Regardless of the initiating mechanism , activation of plasminogen

  to yield plasmin proceed through the cleavage of the same “

  arginine 560-valine 561 bond “ in the Glu and Lys form of

  plasminogen.

  1. tPA - the main activator of plasmin in-vivo.

  2. Urokinase - minor role in in-vivo fibrinolysis.
• PLASMINOGEN ACTIVATORS

  Tissue Plasminogen Activator

  Endothelial cell product

  Potent fibrinolytic agent by activating plasminogen.

  Thrombin acts as the major release inducer.

  Urokinase

  Thrombin acts as the major release inducer

  Genitourinary system product

  • Lower affinity with fibrin
• PLASMINOGEN ACTIVATORS

  Streptokinase

  Produced by B-hemolytic streptococci

  NOT a serine protease

  • Indirectly activates plasminogen
• PLASMINOGEN ACTIVATOR INHIBITORS

  A group of substances referred to as Serpins , (Serine protease

  inhibitors).

  • Plasminogen activator inhibitor-1 : the primary inhibitor of tPA

  and Urokinase.
• PLASMIN : FIBRINOLYTIC MECHANISM

  Plasmin has the ability to proteolytically degrade both fibrin and

  fibrinogen in clots formed and native fibrinogen in the circulation.

  The degraded products of plasmin is collectively termed as

  Fibrin/fibrinogen degradation products.
• PLASMIN : FIBRINOLYTIC MECHANISM

  Proteolytically cleave and render inactive factors V and VIII and XII.

  • Proteolytically cleave GPIB complexes.
• FIBRIN / FIBRINOGEN DEGRADATION PRODUCTS (FDPs)

  The earliest recognizable unit is

  Fragment X, which is still capable of

  clotting.

  Fragment X gets cleaved further by

  plasmin to yield unclottable fragment Y

  and D.

  The Y fragment is further degraded to

  produce and additional D fragment and

  a single E fragment.

  • Crosslinked fibrin cleavage will produce

  the D-dimer.
• FIBRIN / FIBRINOGEN DEGRADATION PRODUCTS (FDPs)

  The breakdown products have specific inhibitory effects on the coagulation

  system.

  Fragment X - exhibits anticoagulant effect by competing with fibrinogen

  for thrombin.

  Fragment D - forms abnormal complexes with fibrin monomers as it

  polymerizes.

  Fragment E- no known anticoagulant effect.

  • In concentrations greater than 100 ug/mL the FDPs can inhibit platelet

  aggregation and secretion.
• PLASMIN INHIBITORS

  A2- plasmin inhibitor : the major in-vivo plasmin inhibitor.

  It rapidly binds irreversibly to plasmin binding site on a 1:1 ratio.

  Plasmin adsorbed to fibrin during the fibrinolytic process seems to be

  protected from this inhibitor because it binds to the same lysine-binding

  site.

  • THe overall effect is to make sure plasmin activity is limited to the are of

  fibrin deposition and prevent free plasmin from circulating.
• PLASMIN INHIBITORS

  A2- macroglobulin

  Has a role in plasmin inhibition during Normal hemostasis.

  Participates only when a2-antiplasmin inhibitor binding sites are

  saturated.

  Thrombin-activatable fibrinolysis inhibitor (TAFI)

  Inhibits fibrinolysis by hydrolyzing lysine from the carboxyl end of fibrin.

  • Activated by Thrombin-thrombomodulin complex
• Disorders involving the Fibrinolytic system : DIC

  Disseminated intravascular coagulation -

  Spontaneous activation of the coagulation system , leading to consumption of

  coagulation factors and platelets with subsequent thrombus formation not

  just on the site of endothelial damage but in a random manner throughout

  the miroccultion.
• Disseminated Intravascular Coagulation

   May be acute and uncompensated

  oThe more acutely ill the patient, the more dangerous the DIC's

  pathology

   Chronic DIC

  oLiver coagulation factor production and bone marrow platelet

  production incompletely compensate for consumption

   Trousseau syndrome

  oA term for tumor-induced DIC that generates DVT and migrating subepithelial thromboses causing ecchymosis and purpura fulminans
• Disseminated Intravascular Coagulation

   Also named defibrination syndrome or consumption coagulopathy

   Is the Black Death of the Middle Ages

   Is the generalized and uncontrolled hemostasis activation secondary to a

  systemic disorder

   Involves all hemostatic systems

   Is microangiopathic (a condition in which fibrin microthrombi form in

  and occlude small vessels where they consume platelets, coagulation

  factors, coagulation control proteins, and fibrinolytic enzymes
• Diagnostic Tests for DVT & PE

   Ultrasonography

  oeffective for most DVT cases

   Multislice or spiral chest computed tomography (CT) angiography

  oreference method for PE

   D-dimer assay

  ocan not be employed to "rule in" DVT or PE but a normal result

  reliably rules out either condition without the need for imaging

  oexpressed in D-dimer units (DDU) or fibrinogen equivalent units

  (FEU)
• DVT

   Cardinal symptoms:

  Edema

  Erythema

  Pain

  Sensation of heat

  Misidentified as muscle strain or a

  "charley horse"
• PE

   Symptoms:

  oDyspnea

  oShortness of breath

  oSyncope

  oTransient cyanosis

  oTachycardia

  oPleuritic pain

  oDistended neck veins
• Venous Thromboembolic Disease

   Comprises DVT and PE

  oDeep vein thrombosis (DVT): the most prevalent VTE; caused by

  clots that form in the iliac, popliteal, and femoral veins of the calves

  and upper legs

  oPulmonary embolism (PE): fragments of thrombi (called emboli) may

  separate from the proximal end of a venous thrombus, move swiftly

  through the right chambers of the heart, and lodge in the arterial

  pulmonary vasculature, causing ischemia and necrosis of lung tissue
• Venous Thromboembolic Disease

   Comprises DVT and PE

  oDeep vein thrombosis (DVT): the most prevalent VTE; caused by

  clots that form in the iliac, popliteal, and femoral veins of the calves

  and upper legs

  oPulmonary embolism (PE): fragments of thrombi (called emboli) may

  separate from the proximal end of a venous thrombus, move swiftly

  through the right chambers of the heart, and lodge in the arterial

  pulmonary vasculature, causing ischemia and necrosis of lung tissue
• Fibrinogen

   Fibrinogen becomes integrated into

  atherothrombotic lesions and

  contributes to their thrombotic

  potential

   High concentrations can be used to

  predict hypercholesterolemia and

  identify patients who are at high risk for

  new coronary events
• Plasma Homocysteine

  and Factor VIII

   Homocysteine: a naturally occurring

  sulfur-containing amino acid

  intermediate in the metabolism of

  dietary methionine

   Fasting homocysteinemia: an

  independent risk factor for arterial

  thrombosis

   Factor VIII: an acute phase reactant
• Lipoprotein A

   A low-density lipoprotein that may

  contribute to thrombosis by its

  antifibrinolytic property

   Competes with plasminogen for binding

  sites on newly formed fibrin polymer

  CRP

   An acute phase reactant whose plasma

  concentration rises 1000-fold 6 to 8

  hours after the onset of an

  inflammatory event

   Chronic plasma CRP concentrations

  that remain at 1.5 mg/L or greater

  indicate an atherosclerosis and lowgrade inflammatio
• Arterial Thrombosis Predictors

   Arterial thrombotic disease arises from atherosclerotic plaque

  (eruption of unstable plaque mediates platelet-driven

  thrombosis formation)

   The traditional predictors of arterial thrombosis are:

  oElevated total cholesterol

  oElevated LDL-C

  oElevated ratio of TC:HDL-C secondary to HDL-C deficiency
• Laboratory Evaluation of Thrombophilia

   Antiphospholipid antibodies (LAC, ACL, and Anti-B2

  -GPI)

   Activated protein C resistance and Factor V Leiden mutation

   Prothrombin G20210A

   Antithrombin

   Protein C control pathwa
• Protein C Assays:

  Clot-Based Assays

   Detects both quantitative and qualitative PC deficiencies

  Is based on the ability of APC to prolong the PTT

   Prolongation is proportional to PC activity
• Protein C Control Pathway

   Recurrent venous thrombosis:the consequence of PC or PS

  deficiency

   PS levels become proportionally decreased when acute phase

  reactants C4bBP level rises, binding additional PS

   PC or PS deficiency: defined as activity or concentration levels

  less than 65% of normal

   PC and PS activities are depressed in Coumadin therapy

  (Coumadin-induced skin necrosis), pregnancy, liver/renal

  disease, vitamin K deficiency, DIC, use of oral contraceptives,

  and neonatal purpura fulminans.
• Laboratory Evaluation of Thrombophilia

   Antiphospholipid antibodies (LAC, ACL, and Anti-B2

  -GPI)

   Activated protein C resistance and Factor V Leiden mutation

   Prothrombin G20210A

   Antithrombin

   Protein C control pathway
• Antithrombin Antigen Assay

  Is measured with a turbidometric microparticle immunoassay

   The AT concentration is directly proportional to the rate of

  light absorption change
• Degree of hemolysis is inversely proportional to the activity of test plasma AT

  Antithrombin

  Activity Assay

  A1. Chromogenic substrate

  method

  Detects quantitative and qualitative

  AT deficiencies

  • Detects mutations affecting the

  proteolytic site but NOTthe

  heparin binding site
• Antithrombin

  Is a serine protease inhibitor (SERPIN) that neutralizes factors

  IIa, IXa, Xa, XIa, XIIa, all of the coagulation system serine

  proteases except factor VIIa.

  Its activity is enhanced through binding to exogenous heparan

  sulfate (1000-fold by UFH, 400-fold by LMWH and synthetic

  pentasaccharide/fondaparinux therapies)

   AT deficiency is defined as AT activity levels less than 70% of

  normal or antigen concentration less than 22 mg/dL
• Prothrombin G20210A

   A guanine-to-adenine mutation at base 20210 of the 3'

  untranslated region of the prothrombin gene has been

  associated with mildly elevated plasma prothrombin levels

   Diagnosis of this mutation requires molecular genetic testing
• Activated Protein C Resistance and Factor V

  Leiden Mutation

  APC hydrolyzes activated factors V and VIII

  A mutation in the factor V gene substitutes glutamine for

  arginine at position 506 of the factor V molecule (FV

  R506Q)

  The factor V R506Q mutation is named for the city it,

  Leiden mutation (or APC resistance)
• Antiphospholipid Antibodies (anti-B2

  -GPI)

  An anti-B2-GPI result of greater than 20 IgG or IgM antiB2-GPI units correlates with thrombosis more closely

  than the presence of ACL antibodies