Thrombosis: Principles in Clinical Practice

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Thrombosis Principles in Clinical Practice

• Matthew Bunte, MD
• Chief Resident
• Dept of Internal Medicine

2
Learning objectives

• Be able to explain risk factors for the
  development of deep vein thrombosis (DVT) and
  other types of thrombosis
• Recognize clinical conditions which are risk
  factors for thrombosis
• Recognize acquired and hereditary causes of
  hypercoagulability
• Review the diagnostic approach to suspected
  venous thromboembolism (VTE)
• Review the coagulation cascade and pharmacologic
  interventions against the hypercoagulable state
  and VTE

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Overview of VTE

• Most common presentations of venous thrombosis
  are
• Deep vein thrombosis (DVT) of the lower extremity
  
• Pulmonary embolism
• A clinical risk factor for thrombosis can be
  identified in gt 80 of patients with venous
  thrombosis
• Causes of venous thrombosis can be divided into
  two groups hereditary and acquired.

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Case Presentation

• A 35 y/o previously healthy F presented to the ED
  w/ 2 d hx of progressive swelling and pain in
  her L leg, without antecedent trauma or prolonged
  immobility. Her pain worsened acutely during the
  morning before her arrival. Associated symptoms
  included mild dyspnea during the previous day,
  with no associated chest discomfort. Her only
  medications were oral contraceptives and a
  multivitamin. She had no family history of heart
  disease, stroke or cancer. She never smoked and
  rarely used alcohol. She reported no illicit drug
  use.

What clinical characteristics in this case are
risk factors for VTE?
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Clinical risk factors in VTE

• Virchows triad
• Alterations in blood flow (i.e., stasis or
  turbulent flow)
• Disrupted laminar flow allows greater interaction
  between platelets and endothelial surface
• Prevents dilution of locally activated clotting
  factors
• Prevents inflow of clotting factor inhibitors
• Promotes endothelial cell damage and activation
• Vascular endothelial injury
• Causes exposure of sub-endothelium and release of
  tissue factor, thereby activating coagulation
  cascade
• Alterations in constituents of blood (i.e.,
  hypercoagulability)
• Acquired vs inherited coagulopathies
• Predisposing factors for thrombus formation

Rudolf Virchow, 1821-1902
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Clinical risk factors in VTE

• Acquired risk factors
• Prior thrombotic event
• Recent major surgery
• Especially orthopedic
• Presence of a central venous catheter
• Trauma
• Immobilization
• Malignancy

Bauer and Leung. UpToDate. Accessed online 7/08.
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Clinical risk factors in VTE

• Acquired risk factors
• Pregnancy
• Oral contraceptive or hormone replacement therapy
• Heparin use (and subsequent HITT)
• Antiphospholipid antibody syndrome
• Myeloproliferative disorders
• Polycythemia vera or essential thrombocythemia
• Hyperviscosity syndromes
• Multiple myeloma or Waldenstroms
  macroglobulinemia

Bauer and Leung. UpToDate. Accessed online 7/08.
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Clinical risk factors in VTE

• Inherited risk factors
• Factor V Leiden
• Prothrombin gene mutation 20210A
• Protein S deficiency
• Protein C deficiency
• Antithrombin deficiency
• Hyperhomocysteinemia
• As a group, the inherited thrombophilias have a
  prevalence of 10
• Total incidence of an inherited thrombophilia in
  subjects with DVT range from 24 37

Bauer and Leung. UpToDate. Accessed online 7/08.
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Factor V Leiden

• Activated Factor V (Factor Va)
• Activated by thrombin, accelerates conversion of
  prothrombin to thrombin
• Factor V Leiden
• Most common form of inherited thrombophilia (50
  of cases)
• Most common in those of northern European
  descent very rare in Asians and Africans
• Despite high prevalence, overall risk of
  thrombosis, even in homozygotes, is low (0.5-1
  per yr)

Thrombin (Factor IIa)
Conversion of fibrinogen to fibrin
Endothelial activation
Xa
Va
V
Ca2 PL VIIIa
Ca2 PL
Organized Fibrin/Platelet thrombus
TF/VIIa
Prothrombin (Factor II)
X
Leung. ACP Med, 2005. Accessed online 7/08.
10
Factor V Leiden

• Activated Protein C (APC) resistance
• Discovered in Leiden, the Netherlands (1993)
  amongst a group of subjects with unexplained VTE
  whose plasma responded poorly to APC in an aPTT
  assay
• Factor V Leiden gene mutation caused by a single
  nucleotide transition, leading to a subs of
  arginine to glutamine at position 506
• Mutant Leiden gene product is not susceptible to
  cleavage by APC and is thereby inactivated more
  slowly
• Dual hypercoagulable state of Factor Va Leiden
• Increased coagulation
• FVa Leidin inactivated more slowly, increasing
  generation of thrombin
• Decreased anticoagulation
• Reduced ability to facilitate inactivation of
  other procoagulant factors (e.g., FVIIIa)

Leung. ACP Med, 2005. Accessed online 7/08.
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Prothrombin gene mutation

• Normal prothrombin (Factor II) circulates as
  Vitamin K-dependent cofactor w/ ½ life of 3-5
  days
• Mutation discovered in 1996 as a transition (G?A)
  at nucleotide 20210, resulting in elevated plasma
  levels of Factor II (mutation thought to alter
  the mRNA processing and/or decay rate of
  prothrombin mRNA)
• Heterozygotes have a 30 higher plasma
  prothrombin level compared to normals
• Prothrombin 20210A mutation most common among
  those of southern European descent
• Study of 397 individuals from 21 Spanish families
  corroborated that G20210A is a functional
  polymorphism
• Like Factor V Leiden, Prothrombin 20210A mutation
  extremely rare in the non-white (Asian or
  African) population

Bauer and Leung. UpToDate. Accessed online 7/08.
12
Combined effect of inherited thrombophilias on
propensity for VTE

• Pooled analysis of 2310 cases and 3204 controls
  amongst 8 case-control studies (from UK, Denmark,
  France, Italy, Sweden, Brazil) evaluating the
  risks in patients with FVL and/or prothrombin
  20210A
• Of patients with VTE,
• 23 were heterozygous for prothrombin gene
  mutation
• 12 were heterozygous for Factor V Leiden
• 2.2 were double heterozygotes

Emmerich et al. Thromb Haemost. 2001 86(3)809.
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Protein C S deficiency

• Activated Protein C and S
• Are the 2 major cofactors responsible for
  regulating the amplification of the clotting
  cascade
• Inhibit activated cofactors Va and VIIIa,
  respectively
• Protein C is consumed and levels are low in DIC
  and liver disease
• Recombinant activated protein C (Xigris) given to
  prevent progression of DIC in septic shock
• Heterozygous protein C deficiency
• Prevalence of 1 per 100-200
• Clinical expression of hypercoagulability
  variable, and do not necessarily correspond with
  absolute concentration of Protein C
• Protein S deficiency may be induced by OCPs,
  pregnancy, or nephrotic syndrome

Leung. ACP Med, 2005. Accessed online 7/08.
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Activation of Protein C
Intrinsic Pathway
Extrinsic Pathway
X
IXa
TF/VIIa
Ca2PL
VIIIa
Xa
IIa
II
Ca2PL
Va
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Antithrombin deficiency

• AT is a potent inhibitor of thrombin and other
  serine proteases of the coagulation cascade
  (e.g., FXa, FIXa)
• AT slowly inactivates thrombin in the absence of
  heparin in the presence of heparin, AT rapidly
  inactivates FXa and thrombin
• AT deficiency typically occurs in a AD
  inheritance pattern, thereby affecting both sexes
  equally
• Overall incidence of AT deficiency is low
• Comparative analyses in 2132 consecutive
  individuals with VTE suggest a much lower
  incidence of VTE associated with AT deficiency at
  approximately 0.5
• Females with AT deficiency are at particularly
  high-risk for VTE during pregnancy
• DVT occurred in 18 of pts w/ AT deficiency, and
  in 33 in the postpartum period

Bauer and Leung. UpToDate. Accessed online 7/08.
16
Hyperhomocysteinemia

• Homocysteine is an intermediary amino acid
  formed by the conversion of methionine to
  cysteine
• Elevations may be caused by vitamin def (e.g.,
  Vit B12, Vib B6) or with chronic medial
  conditions or drugs

Adapted from www.med.uiuc.edu/hematology/PtHomocys
teinemia.htm. Accessed online 7/08.
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Hyperhomocysteinemia

• Homocysteinuria or severe hyperhomocysteinemia is
  a rare autosomal recessive disorder characterized
  by developmental delay, osteoporosis, ocular
  abnormalities, VTE, and severe premature CAD
• Less marked elevations of homocysteine are more
  common, occurring in 5-7 of the population, and
  are associated with a number of clinical factors
• Tobacco use
• Meds (i.e., fibrates, niacin)
• Chronic kidney disease
• Vitamin deficiencies (i.e., folate, Vit B6,
  and/or Vit B12)
• Homocysteine has primary atherogenic and
  prothrombotic properties
• Meta-analyses of case-control studies have found
  an odds ratio of 2.5-3 for VTE in pts with
  homocysteine levels gt 2 standard deviations above
  the mean value of control groups

Bauer and Leung. UpToDate. Accessed online 7/08.
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Role of inflammation coagulation in thrombosis
P-selectin
Oxidation of LDL
Activated microparticles stimulate enodthelial
cell cytokine release and promote adhesion with
platelets and endothelium
Circulating microparticle
Cytokine Release
Complement Activation
Tissue Factor
Circulating Monocyte
Phospha-tidylserine
Release of microparticles containing tissue
factor (TF), phosphotidylserine (PS), and
P-selectin glycoprotein ligand -1 (PSGL-1) aids
in leukocyte stasis, inflammation, coagulation
Endothelium
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Case Presentation

• In the ED, she was afebrile and in NAD. BP
  116/69 mmHg, pulse 96 bpm, and respiratory rate
  18 bpm. Pulse oximetry 99 on RA. Auscultation of
  the chest revealed no wheezes or crackles. Her
  heart sounds were normal, and there was no
  murmur, rub, or gallop. Her left leg showed no
  evidence of trauma but there was considerable
  swelling extending from her ankle to the upper
  thigh, and the area of the swelling was markedly
  tender to palpation. The leg was slightly pale
  with diminished but palpable pulses. She had
  normal strength and sensation in both legs. The
  remainder of the examination was normal.

What diagnostic studies should be performed to
evaluate for VTE?
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Diagnosis of VTE

• DVT and pulmonary embolism are the two most
  common manifestations of the same disease VTE
• 90 of cases of acute PE are due to emboli
  emanating from the proximal veins of the lower
  extremities proximal DVTs are clinically most
  significant due to high morbidity and mortality
• Consider the differential diagnosis of DVT
• Popliteal (Baker) cyst, superficial
  thrombophlebitis, muscle pulls/tears, chronic
  venous insufficiency, and others
• Consider pre-test probability for VTE before
  proceeding further in diagnostic evaluation
• Among those with suspected of DVT of the LE, a
  minority (17-32) actually have the disease

Grant and Leung. UpToDate. Accessed online 7/08.
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Wells Score System Clinically predicting DVT
pre-test probability
Wells PS, et al. Lancet. 1997350(9094)1795-8
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Diagnosis of VTE

• Clinical examination (non-specific)
• Physical findings may include a palpable cord
  over the calf, ipsilateral edema, warmth, and/or
  superficial venous dilatation
• Contrast venography
• Non-invasive testing
• Impedance plethysmography
• Compression ultrasonography
• Recommended in moderate to high pre-test
  probability
• D-dimer
• Useful in low pre-test probability to exclude
  diagnosis of VTE
• Sensitivity and negative predictive value are
  high (99)
• Magnetic resonance venography
• Computed tomography
• Echocardiography, ventilation-perfusion (V/Q)
  scanning, and pulmonary angiography

Grant and Leung. UpToDate. Accessed online 7/08.
23
Case Presentation

• The patient undergoes lower extremity compression
  ultrasonography, which reveals a unilateral DVT
  of the proximal L femoral vein. A
  contrast-enhanced chest CT is negative for
  pulmonary embolism. She is initiated on heparin
  infusion and transferred to the ward.

What duration of treatment should the patient
receive for her DVT?
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In vivo coagulation cascade
Endothelial damage or activation

• Extrinsic Pathway
• integral to thrombosis

Tissue Factor
FVIIa
Ca2 PL
FX
Thrombogenesis
FXa

• Intrinsic Pathway
• amplifies coagulation cascade

FVa FVIIIa
Fibrinogenesis, cross-linking of fibrin strands,
and thrombus formation
Fibrinogenesis
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Treatment of VTE

• Anticoagulation
• Unfractionated and low-molecular weight heparin
  (LMWH, ie, enoxaparin)
• Enable antithrombin to accelerate many-fold its
  inactivation of thrombin
• LMWH should be avoided in CKD contraindicated in
  Stage V CKD
• Vitamin K antagonists (warfarin)
• Heparin warfarin is more effective than
  warfarin alone all cases of VTE should be
  bridged with heparin
• Direct thrombin inhibitors (ximelagatran)
• Factor Xa inhibitors (fonduparinux)
• Thrombolysis
• Tissue plasminogen activators (t-PA, u-PA,
  urokinase, alteplase)
• Thrombectomy

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Sites of Vitamin K antagonism
Intrinsic Pathway
Extrinsic Pathway
Kallikrein
Prekallikrein
Endothelial activation or exposure of
subendothelium
HMWK
XII XIIa
X
XI XIa
Ca2PL
IX
IXa
Ca2
Tissue Factor
VIII VIIIa
VII
TF/VIIa
Xa
Va
V
Fibrinogen
IIa
II
Ca2PL
Cross-linked fibrin polymer
XIIIa
Fibrin
Ca2
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(No Transcript)
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Fibrinogenesis Fibrinolysis
Plasminogen
t-PA u-PA
Plasminogen activator inhibitor 1 (PAI-1)
Plasmin
Fibrin degradation
Alpha2 antiplasmin alpha2 macroglobulin
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Guidelines for management of VTE
Leung. ACP Med, 2005. Accessed online 7/08.
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Case Presentation

• Further laboratory evaluation reveals an elevated
  homocysteine level. As she is prepared for
  discharge, she recalls further family history.
  Two of her three sisters and her mother have all
  experienced miscarriages, and a brother had a
  post-operative DVT with pulmonary embolism after
  a knee surgery. She is initiated on warfarin
  therapy with a planned course of 6 months as she
  is considered moderate risk for recurrent VTE.

What acquired or hereditary causes of VTE should
be evaluated for?
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Clinical features suggestive of thrombophilia

• Age at onset of 1st thrombosis lt 50 yrs
• No identifiable risk factor
• gt 80 of VTE cases an identifiable risk factor is
  present
• Positive family history
• e.g., DVT, PE, miscarriages, etc
• Recurrent thrombosis
• Atypical site of thrombosis
• e.g., thrombus in mesenteric or cerebral vessels,
  great vessels, or arterial thrombus

Leung. ACP Med, 2005. Accessed online 7/08.
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Screening tests for suspected hypercoagulable
state

• Resistance to activated Protein C
• Factor V Leiden (genetic test)
• Clotting assay with APC
• Prothrombin mutation G20210A (genetic test)
• Antithrombin III (functional assay)
• Protein C (functional assay)
• Protein S
• Functional assay
• Antigenic assay for free Protein S

Leung. ACP Med, 2005. Accessed online 7/08.
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Summary

• One or more risk factors for VTE can be
  identified in most patients (gt 80)
• There is often gt 1 RF (acquired /- hereditary)
  at play in a given patient that precipitates VTE
• Most frequent hereditary cause of VTE is Factor V
  Leiden
• The strongest RF for recurrent VTE is prior
  thrombotic event

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Summary

• Consider pre-test probability when considering
  further evaluation
• The likelihood of VTE in a patient presenting
  with low pre-test probability based on clinical
  factors and a normal D-dimer is extremely low
• D-dimer sensitive and excellent negative
  predictive value in low pre-test probability
  states
• Non-invasive testing first line when pre-test
  probability intermediate or high