Arterial Thromboembolism Flashcards
What’s virchows triangle?
- Endothelial damage
- Blood stasis
- Hyper coagulable state
Which hormone contributes to the lack of collateral blood supply?
Serotonin
What are the clinicians signs of saddle thrombus?
Ischemic neuromyopathy
What’s the 2nd most common place for ATE in cats with heart disease?
R subclavian artery
Where does the serotonin and theomboxane come from?
Platelets
How is collateral blood supplied improved?
Clopidogrel: helps with vasodilation (reduces the effects of vasoconstriction)
- anti-thromboxane in cats
- anti- serotonin in cats
- good vasodilation
Aspirin- effective anti-serotonin in cats but need dose high enough that can cause toxicity
What other clinical signs can be noted based on different underlying conditions?
- generalized
- IMHA
- nephrotic syndrome
- Cushing’s
- heart disease
What are the treatment goals for ATE?
- Reduce thrombus formation
- Improve collateral blood supply
- Pain management
- Addressing underlying condition
- Supportive therapy
What can be used to reduce thrombi formation?
- Unfractionated heparin
- deactivates IIa, Xa, XIa, XIIa, also V & XIII
- can deactivate platelet function as well
- watch for thrombocytopenia
- should do baseline PT, PTT, TEG - Low molecular weight heparin is another option but less studied
What’s the likelihood of reperfusion injury in cats?
- 40-70%
- the risk of mortality is up to 40%
- not all ATE need thrombolytic treatment
- but its very important for cerebral, renal and splenic infarcts
Which drugs can be used to dissolve thrombus?
- Streptokinase
- forms complex with plasminogen to deactivate plasminogen, plasmin, fibrin, fibrinogen, and coagulation factors
- repeated dosing leads to antigenic stimulation
- not available in the states
- one study had high mortality rate in cats - Urokinase
- more specific plasmin activator than streptokinase (goes to the thrombus rather than circulation as well)
- high mortality in dogs in one study (100%)
- also not available in the states - Tissue plasminogen activator
- also more thrombus specific
- at high dose can lead to systemic effects and bleeding
- ok efficacy
- only one approved for human use on the states
What are some options for pain managemnet?
Opioids!
- buprenorphine
- hydromorphone
- fentanyl
What’s the survival of ATE in cats related to CE?
- there is no difference between conservative vs thrombolytic therapy (35-39%, vs 33%) for survival
- cause of death is similar for treatment vs euthanasia (28-40% natural vs 25-35% euth)
- prognosis is better for single pelvic (68-93%) vs bilateral pelvic (15-36%)
- long term survival after initial CE ranged from 50-345 days
How is ATE prevented in cats?
Primary preventions:
- cats with echo evidence of left atrial enlargement: L atrium > 1.7cm in diameter or the La/Aorta ratio is >2.
Secondary preventions:
- to prevent more ATE in the future –> clopidogrel
- 1 year recurrence rate (general) 25-50%
What is the goal of ATE prevention?
For patients with underlying disease such as heart disease or nephrotic syndrome, complete prevention of ATE is unrealistic.
Goal should be to prolong the time to the next ATE or to reduce the severity/ minimize the clinical signs
What are some anti-platelet agents used for prevention of ATE?
- aspirin
- clopidogrel
How does Aspirin work?
It’s the anti-thromboxane
- irreversibly acetylates platelet cyclo-oxygenase, preventing the formation of thromboxane A2
- Thromboxane A2 = potent pro-aggregation and vasoconstrictive properties
- aspirin prevents secondary platelet aggregation
- use in cats = watch for GI signs, low dose no less effective but less side effects. Recurrence rate = 17-75%
- less well established in dogs
How does clopidogrel work?
- it’s a potent and irreversible antagonist of ADP receptor
- inhibits both primary and secondary platelet activation
- the conformational change of the ADP complex inhibits binding of fibrinogen and von Willebrand factor
- also impairs platelet release reaction, decreasing the release of pro-aggregating and vasoconstrictive agents
- requires hepatic metabolism to be active
- no GI toxicity in cats
- very bitter
What are some anti-coagulants that can be used to prevent ATE?
- Warfarin
- low molecular weight heparin
- new anticoagulants (not as well studied right now, but not inferior to warfarin)
How does warfarin work?
- it antagonizes vitamin K dependent coagulation factors: II, VII, IX, X, as well as anti-coagulant proteins C & S
- so initially will be hypercoagulable (with inhibition of protein C), so administer heparin at the same time
- bleeding is possible
- needs dedication on monitoring and $
- recurrence rate in cats 42-53%
- bleeding risk 13-20%, 13% = fatal
How does low molecular weight heparin work as a preventative for ATE?
- it inhibits Xa, and not much IIa, so checking the PTT or TEG is not helpful –> need to monitor Xa levels
- comparable results with warfarin in cats with ATE due to heart issues
- but no bleeding noted
