Disorders Flashcards
What is Virchow’s triad
- Endothelial dysfunction
- Hypercoagulability of blood
- Blood stasis / altered blood flow
Briefly describe the mechanisms of prothrombosis induced by endothelial damage
- Decreased anticoagulant molecules that are normally found in the endothelial glycocalyx (TFPI, thrombomodulin, heparan sulfate)
- Release of ultra-large multimers of vWF and fVIII
- Exposure of procoagulant substances (tissue factor)
What are the effects of neutrophil extra-cellular traps promoting immunothrombosis
- Cell-free DNA activates FXII and prekallikrein -> contact pathway
- Bind to clotting factors, TF, fibrin -> fortifie clots
- Histones activate platelets via platelet TLR-2 and TLR-4 and increase thrombin generation
- Histones inhibit activation of protein C
- Cell free DNA forms complexes with plasmin and fibrin, inhibit tPA ->inhibit fibrinolysis
- Neutrophil elastase degrades TFPI
How can microparticles have a procoagulant effect
- Expression of phosphatidylserine on their surface (external membrane)
- Expression of tissue factor
What are the 4 big factors contributing to a hypercoagulable state
- Endothelial disturbances (-> loss of anticoagulants + release of vWF + exposure of TF)
- Increased procoagulant elements (TF expressed on inflammatory cells, microparticles, NETs)
- Decreased endogenous anticoagulants (decreased hepatic production of AT / protein C / protein S, consumption, loss of endothelial anticoagulants)
- Decreased fibrinolysis (loss of endothelial tPA/uPA, increase in PAI-1, inhibition of fibrinolysis by NETs)
What are 2 types of tests that can be used for assessment of global coagulation and what parameters to they give
- Viscoelastic testing (thromboelastography, rotational thromboelastometry) -> time to initial fibrin crosslinking, rate of clot formation, viscoelastic properties of clot, time to clot lysis
- Calibrated automated thrombography (CAT) -> endogenous thrombin potential
Name a few potential laboratory markers of hypercoagulability
- Increased D-dimers
- Increased fibrin degradation products
- Increased fibrinogen
- Increased thrombin-antithrombin complexes
- Increased clotting factors activity
- Decreased protein C
- Decreased antithrombin
- Increased vWF multimers
- Increased thrombin generation on calibrated automated thrombography (CAT)
- Decreased fibrinolysis and/or increased clot formation on viscoelastic testing
In the CURATIVE guidelines, what are the conditions for which antithrombotic therapy is recommended? What are the conditions for which it is recommended only if other risk factor(s) are present?
- Recommended:
- IMHA in dogs
- PLN and PLE in dogs
- Cardiomyopathy in cats especially if prior ATE, spontaneous echocontrast, reduced LA flow velocity
- Necrotizing pancreatitis in dogs - If other risk factor(s):
- Neoplasia in dogs
- Hyperadrenocorticism or corticosteroid administration in dogs
- Sepsis in dogs
- Heartworm in cats and dogs
- PLN and PLE in cats
What are causes of procoagulant state found in PLN in dogs
- Urinary loss of AT
- Decreased fibrinolysis (higher alpha2-antiplasmin)
- Higher fibrinogen activity
- Increased fVIII activity
What are causes of procoagulant state found in IMHA in dogs
- Increased TF (due to microparticles and endothelial expression stimulated by free heme)
- Erythrocyte membrane becomes procoagulant +/- release microparticles
- NET formation due to hypoxia
What is the main mechanism suggested for hypercoagulability in neoplasia
Release of TF-bearing microparticles from neoplastic cells
What are possible causes of vitamin K deficiency
- Impaired intestinal absorption = impaired fat absorption (usually a consequence of failure of bile secretion = hepatic or post-hepatic issues)
- Impaired vitamin K recycling by vitamin K epoxide reductase (usually from rodenticide toxicity)
What is the overall survival to discharge for cats with FATE? What are negative prognostic factors
About 30-45% survival to discharge
Negative factors = lower rectal temperature, higher affected limb lactate, presence of CHF, both limbs affected, absence of motor function
What are the thromboprophylaxis recommendations for cats with FATE
- Clopidogrel 18,75 mg PO q24 (with suggested loading dose)
- OR UFH 250 U/kg SC QID
- OR Dalteparin 75 U/kg SC QID
- OR Rivaroxaban 0.5-1 mg/kg PO q24
What is the recurrence rate of FATE for cats on clopidogrel
About 50% (time to recurrence or cardiac death of 1 year)
What are autoantibodies directed against in ITP
Platelet integrin αIIbβ3 (fibrinogen receptor) or glycoprotein Ibα (vWF receptor)
What is a proposed mechanism for uremia-induced platelet dysfunction
Decreased platelet adhesion due to decreased vWF binding activity (similar to type II vWD)
What are the 3 types of von Willebrand diseases with their breed predispositions
- Type I = quantitative vWF deficiency, reduced quantity of all multimers (Doberman Pinschers, Corgis, Poodles, Irish Setters, Westies)
- Type II = qualitative vWF abnormalities, some multimers missing (German Wirehaired and Shorthaired Pointers)
- Type III = absence of vWF (Chesapeake Bay Retriever, Shetland Sheepdogs, Scottish Terriers)
What are mechanisms of platelet dysfunction induced by hydroxyethyl starch
- Binding to αIIbβ3 or glycoprotein Ibα inhibits platelet aggregation and adhesion
- Interference with fVIII-vWF complex
- Interference with intracellular signaling function
List some diagnostics available for evaluation of platelet disorders
- Tier 1 tests (rule out easy things):
- Platelet count with smear
- Platelet size and morphology
- Clotting times
- vWF concentration (Ag) or binding assay - Tier 2 tests (confirm platelet disorder)
- Buccal mucosal bleeding time
- Platelet function analyzer
- Clot retraction assay
- Viscoelastic testing - Tier 3 tests (definitive diagnosis)
- Flow cytometry
- Platelet aggregometry
- Western blot
- Genetic molecular testing
List causes of acquired platelet dysfunction
- Uremia (decreased vWF binding activity)
- Liver disease (unknown mechanism)
- Drug induced: anti-platelets, anticoagulants, NSAIDs (theoretically only salicylic acid, but COX-2 selective NSAIDs can decrease platelet activity in situations of increased thrombopoiesis), phosphodiesterase inhibitors, NO donors, beta-lactams
How long before a procedure should antiplatelet drugs be discontinued in low-to-moderate-risk patients? What is the recommendation for high risk patients?
- 5-7 days before for low-to-moderate risk
- For high risk patients, if on dual anti-platelets then one should be discontinued ; if only on one anti-platelet it should be continued
What are preventative treatment options for a dog with vWD undergoing surgery
- Cryoprecipitate 1 unit / 10-15kg
- FFP 6-10 mL/kg
- DDAVP (desmopressin) 1-3 ug/kg IV or SQ
(ONLY for type 1 or type 2 vWD)
What is the estimated platelet count in a unit of platelets derived from whole blood
8x10^10 platelets -> give 1 unit / 10kg
What is a normal BMBT in cats and dogs? What can affect the result?
Cats: < 2 min
Dogs: <3-4 min
Anemia will prolong BMBT
What is added to blood to measure prothrombin time (PT) / activated partial thromboplastin time (aPTT)
- PT: tissue factor + calcium (-> extrinsic + common pathway)
- PTT: kaolin + phospholipids + calcium (-> intrinsic + common pathway)
What are the 3 major characteristics of coagulation investigated with viscoelastic testing
- Kinetics of the clot = rate of clot formation (reaction time R / clot time CT, kinetics K / clot formation time CFT, alpha angle)
- Mechanical properties of the clot = clot strength (maximum amplitude MA / maximum clot firmness MCF, calculated elastic shear modulus G)
- Rate of fibrinolysis (lysis L30 and L60 / clot lysis CL 30 and CL60)
Name a few differentials for primary hemostasis disorders
See picture
Name a few differentials for secondary hemostasis disorders
See picture
What are the available tests for therapeutic monitoring of warfarin, clopidogrel, unfractionated heparin, low molecular weight heparin, and direct oral anticoagulants? Which ones are recommended by the CURATIVE guidelines?
- Warfarin: PT
*Warfarin use not recommended by CURATIVE, but if being used recommend PT) - Clopidogrel: PFA-100 (using ADP-collagen or PGE-1 activator), platelet aggregometry, TEG-platelet mapping (using ADP)
*Monitoring not recommended in CURATIVE - UFH: drug specific anti-Xa activity, ACT, aPTT, TF and kaolin activated TEG
*Anti-Xa activity in CURATIVE (0.35-0.7 U/mL) - LMWH: drug specific anti-Xa activity
*No recommendation in CURATIVE (but if using anti-Xa should target 0.5-1.0 U/mL 2-4h post-dose) - Direct oral anticoagulants: drug specific anti-Xa activity, PT
*No recommendation in CURATIVE
Name a few congenital platelet disorders in dogs
- Glanzmann thrombasthenia (abnormal αIIbβ3)
- Bernard-Soulier syndrome (abnormal GP1b)
- P2Y12 defect
- Canine Scott syndrome (deficient scrambling of phospholipids)
- Chediak-Higashi syndrome (abnormal platelet granules)
How decreased does a coagulation factor activity need to be to increase PT or PTT
By at least 60-70%
What diseases have been associated with hyperfibrinolysis
- DIC
- Trauma
- Spontaneous hemoperitoneum
- Snake envenomation
- Liver diseases
- SIRS / sepsis
- Neoplasia
- Greyhounds
What tests can be used to evaluate fibrinolysis
- D-dimers (but non specific)
- Viscoelastic testing (can do tPA augmented to be able to assess fibrinolysis within the test time frame)
- Assays measuring tPA, plasminogen, TAFI, alpha2-antiplasmin, PAI-1
What is the dose for protamine
1 mg per 100 units of UFH, decrease dose by 50% if administered more than 30 min ago ; can be repeated as needed
For LMWH, 1 mg per 100 units of anti-factor Xa activity (partial reversal)
Name 3 malignancies mostly associated with DIC
- Hemangiosarcoma
- Mammary gland carcinoma
- Pulmonary adenocarcinoma
What are the 2 big components of trauma-associated coagulopathy
- Resuscitation-associated coagulopathy (from worsening acidosis, hypothermia, hypocalcemia, hemodilution)
- Acute coagulopathy of trauma-shock (caused by tissue injury and shock)
What is the difference between acute coagulopathy of trauma-shock (ACOTS) and DIC
DIC starts as a hypercoagulable / hypofibrinolytic state and progresses to hypocoagulable due to a consumptive process. ACOTS presents initially as a hypocoagulable / hyperfibrinolytic process mostly due to the action of thrombomodulin
Explain the pathogenesis of acute coagulopathy of trauma shock (ACOTS)
- The combination of trauma, hypoperfusion, catecholamine release, and inflammation leads to endothelial activation:
->thrombomodulin release -> activation of protein C -> inhibition of fVa and fVIIIa, inhibition of PAI-1 and TAFI -> hypocoagulation and hyperfibrinolysis
-> tPA release -> hyperfibrinolysis
-> endothelial glycocalyx damage -> heparin release -> endogenous anticoagulation
- Platelet consumption also possible due to early activation and consumption
- Systemic activation of coagulation can also lead to consumption of coagulation factors and fibrinogen
What are the 2 factors required for development of acute coagulopathy of trauma shock (ACOTS)? What other phenotype can develop if they are not met?
- Tissue injury and shock (hypo perfusion) +/- inflammation
- In less severe trauma, a hypercoagulable phenotype can develop due to diffuse thrombin generation, leading to microvascular thrombosis and organ dysfunction
What is the principle of platelet function analyzers
Patient’s blood is placed in cartridge containing a membrane coated with platelet agonists. Blood is aspirated under high shear conditions through an aperture in the membrane. Platelets aggregate and close the aperture -> test measures the closing time (normal 1-3 min)
=> high shear-stress test (vs aggregometry)
What is the principle of platelet aggregometry
The formation of platelet aggregates in the sample is measured by light transmission or electrical impedance (following shear conditions / addition of agonists)
=> low shear-stress test (vs PFA)
What is the principle of TEG / ROTEM and the difference between them? What can be used as activators?
Blood is placed in a cup warmed at 37°C and a pin attached to a torsion wire is inserted in the sample.
In TEG, the cup oscillates around the pin vs. in ROTEM the pin oscillates (under low shear conditions).
In both cases, formation of the clot attaches the pin to the cup and causes more oscillations of the torsion wire which allows tracing of the clot strength (amplitude of oscillations) in time.
Several activators can be used - kaolin or ellagic acid for intrinsic pathway / tissue factor for extrinsic pathway are used most often, tPA can be used to investigate fibrinolysis
What are the 3 phases of a viscoelastic tracing
- Initiation: time to separation of the 2 curves (formation of the first strands of fibrin)
- Stabilization: time to maximum separation of the 2 curves (max clot strength)
- Lysis: progressive convergence of 2 curves
What are global coagulation indices calculated from viscoelastic testing
- MCE = maximum clot elasticity, calculated from maximum amplitude
- G = shear elastic modulus strength, calculated from MCE
- TPI = thrombodynamic potential index. calculated from MCE
- CI = coagulation index, calculated from R, K, MA, and alpha
What factors can influence viscoelastic testing results (other than coagulation profile)
- Hematocrit (anemia -> hypercoagulable profile)
- Age (older -> hypercoagulable profile)
- Fibrinogen (low fibrinogen -> hypocoagulable profile)
- Platelets (low platelets -> hypocoagulable profile)
What is the effect of DDAVP in coagulation? What is the receptor?
Release of vWF via V2 receptor on endothelium
Also increases platelet function
What is classically the recommendation for antithrombotic choice for venous vs. arterial thrombus
- Venous -> anti-coagulant (low-shear environment -> clot rich in fibrin and poor in platelets)
- Arterial -> anti-platelet
(In practice venous and arterial thrombosis often combined, and with cell-based model of coagulation everything happens together)
What are proposed mechanisms for hypercoagulability secondary to pancreatitis in dogs
- Decreased thrombomodulin expression
- Decreased antithrombin
- Decreased fibrinolysis
What are proposed mechanisms for hypercoagulability secondary to sepsis in dogs
- Decreased thrombomodulin expression
- Decreased antithrombin
- Decreased protein C
- Increases platelet activity
- Increased fibrinogen
According to the CURATIVE guidelines, what patients are considered at high risk of thrombosis vs at moderate risk of thrombosis
- High risk thrombosis:
- Dogs with IMHA, PLN, PLE, necrotizing pancreatitis
- Cats with cardiomyopathy with history of ATE, LA dilation, spontaneous echocontrast or reduced LA appendage flow velocity
- Dogs or cats with > 1 risk factor for thrombosis - Moderate risk thrombosis:
- Dogs or cats with a single risk factor (excluding the previous ones)
- Dogs or cats with known risk factor conditions which are likely to resolve in days to weeks with treatment
In the CURATIVE guidelines, what anticoagulant is preferably recommended among UFH, LMWH, direct oral anti-Xa
- LMWH is recommended over UFH (more predictable pharmacokinetics)
- Direct Xa inhibitors recommended over UFH
- No preference between direct Xa inhibitors and LMWH
What is the recommended dose for UFH
- Dogs:
- IV: 100 units/kg bolus followed by CRI 20-37.5 units/kg/h
- SQ: 150-300 units/kg q6 - Cats:
- 250 units/kg q6 SQ
What is the recommended dose for rivaroxaban
- Dogs: 1-2 mg/kg/ day
- Cats: 0.5-1 mg/kg/day
What are the differences between the 3 generations of thrombolytics (and give one example per generation)
- First generation = no fibrin specificity and easily inhibited by PAI-1 (urokinase = uPA, streptokinase) -> increased risk of hemorrhage
- Second generation = fibrin specificity but inhibited by PAI-1 (recombinant tPA = alteplase)
- Third generation = resistance to PAI-1 and still fibrin specific (reteplase)
What are indications for thrombolysis in cats and dogs
- Acute arterial thrombosis in dogs (best if < 1h) - catheter-guided, no recommendation on agent type but rtPA seems to be preferred
- Acute venous thrombosis only after assessment of risks and benefits (catheter-guided if possible)
- Acute arterial or venous thrombosis in cats (< 6h) only after assessment of risks and benefits - no recommendation on agent type but tPA seems to be preferred
What is the suggested tPA dose for thrombolysis
0.5-1 mg/kg over 60-90 min (systemically or catheter directed) ; some reports of giving 10% of the dose as a bolus over 1 min initially
What are the CURATIVE guidelines recommendations regarding combination of an anticoagulant / anti-platelet with thrombolytic
Combination with an anti-platelet or an anti-coagulant can be considered in cats and dogs with thrombosis and risk factors - no recommendations on timing
Should heparin therapy be discontinued prior to an invasive procedure
- In patients at high risk for thrombosis, it should not be discontinued. The procedure should be planned at nadir (6-8h after prior dose if intermittent dosing)
- In patients at low-to-moderate risk, it can be stopped in the 24h prior to the procedure
How quickly after surgery can anti-thrombotics be (re)started
- Immediately if patient develops thrombosis
- ASAP if no ongoing bleeding in high risk patients
- No recommendation in low-to-moderate risk patients (restart when no evidence of ongoing bleeding)
What anticoagulants should be tapered before discontinuation
UFH and oral Xa inhibitors (no need for LMWH)
When can anti-thrombotics be discontinued following resolution of a venous / arterial thrombus
- As soon as it is resolved if underlying risk factors have been resolved
- Never if ongoing high risk factors or unknown risk factors
- Weigh risk benefits for patients with ongoing low-to-moderate risk of thrombosis
What mutation could be responsible for clopidogrel resistance in cats
Mutation of gene for P2Y1 receptor (possibly due to gain of function of P2Y1 receptor which is not targeted by clopidogrel)
What is a characteristic of TEG studies in dogs with IMHA?
Increased MA (clot strength)
Mechanisms of ATE in cats with cardiomyopathy
- Structural changes associated with enlarged LA –> increased TF and vWF on areas of damaged endothelium
- Stasis through LA enlargement and shear stress reduction –> reduction of NO
% of cardiomyopathie cats with hyper coagulable state
45-50%
Results of BLASTT study
Overall discharge rate 37.5% (45% t-PA vs 30% placebo)
Improvement in limb score over the 1st 24h in both groups with no significant difference
Complications included AKI and repercussion injury with no statistical difference between 2 groups
Results fo the FAT CAT trial
- Recurrence rate for ATE of 49% (clopidogrel) vs 75% (aspirin)
- Longer MST in clopidogrel group (443 days vs 192 days)
Complications of thrombolysis
Hyperkalemia
AKI
Clinical bleeding
Coagulation abnormalities
Cats with cardiomyopathy with the following risk factors should receive antithrombotics
- LA dilation
- Spontaneous echocontrast
- Reduced LA appendage flow velocity
- Historical FATE
Elements of a viscoelastic tracing and their meaning
- R: reaction time
- K: clot kinetics = speed and strength of clot kinetics
- Alph angle: speed of clot formation as well as the kinetics of fibrin formation and cross-linkage
- MA: maximum amplitude
- LY: clot lysis = dissolution of the fibrin-platelet bonds
True or false: Anemia can creat artificial hypo coagulable tracings on TEG
False –> anemia can cause artifactual HYPER coagulable tracings
True or false: The presence of melon at the time of admission is associated with increased mortality and transfusion requirements in patients with ITP
True
7 causes of acquired clotting factor dysfunction
- Severe acidemia
- Severe hypothermia
- Consumption (e.g. DIC)
- Dilutional coagulopathy
- Vitamin K deficiency (rodenticides, liver dysfunction, intestinal malabsorption)
- Hypocalcemis from citrate toxicity
- Trauma induced coagulopathy
What enzyme is inhibited by anticoagulant rodenticides?
Vitamin K epoxide reductase
Which category of liver disease has been associated with a HYPERcoagulable state?
Congenital PSS
List 6 potential hemostatic abnormalities in patients with DIC
- Thrombocytopenia
- Prolonged PT/PTT
- Hypofibrinogenemia
- Elevation in D-dimers
- Reduced antithrombin activity
- Abnormal viscoelastic testing (hyper vs hypo)
- RBC fragmentation
- Dogs with hypo coagulable tendency associated with worse survival
3 reasons why the use of BMBT is questionnable
- Operator dependent variability
- Lack of ability to detect mild defects in platelet function
- Unreliable prediction of surgical bleeding
Why is ACT considered less sensitive than PTT?
- Less than 10% of factor activity necessary for ACT prolongation
- May be affected by sever thrombocytopenia (increased with plt < 10 000)
What is the mechanism of action of desmopressin?
Release of vWF and FVIII from Weibel-Palade bodies in the endothelial cells
Increases platelet adhesion potential
True or false: in dogs with PLN, the degree of hypercoagulability correlated with serum albumin level
False
Mechanisms of DIC
- TF expression in response to inflammatory cytokines (IL-6)
- Impairment of natural anticoagulant pathways (AT, protein C, TFPI)
- Inhibition of fibrinolysis (PAI-1 increases)
What is the INR
INR = international normalized ratio
INR = (PT patient / PT reference)^ISI
(ISI: international sensitivity index to standardize to thromboplastin reagent used)
What factor VIII coagulant activity is consistent with a diagnosis of hemophilia A
20% or less (severe when <2%)
List mechanisms explaining the relation ship between inflammation and coagulation
- Inflammation -> coagulation
- Inflammatory cytokines lead to tissue factor expression on endothelial cells and mononuclear cells ->activation of coagulation cascade
- LPS binds platelet TLR-4 ->platelet activation
- Endothelial injury -> exposure of tissue factor on endothelial cells + loss of thrombomodulin and TFPI and heparan sulfate (activator of antithrombin)
- Decreased antithrombin due to impaired synthesis and degradation by neutrophil elastase - Coagulation -> inflammation
- P-selectin expressed on activated platelets is bound by neutrophils (P-selectin glycoligand) -> NETosis
- Thrombin activates NF-kB pathway in leukocytes -> production of TNF-alpha, IL-6, IL-1
- Platelets secrete HMGB-1 (DAMP)
