---start--- bbd 9/17 [note: The MYC-Donald question may not be on the exam] question: a 6 yr old male mixed breed dog presents to ES with acute onset dyspnea, cyanosis, painful abdomen, posterior paresis. dog had been on corticoisteroids for skin disease x 3 wks, and had bbeen recently dxd with severe protein losing nephropathy. renal bx one month ago - severe glomerular amyloidosis. dog died. necropsy: occlusive thrombi in pulmonary arteries, portal vein, aorta, and cranial vena cava; heart normal. attachment sites of thrombi showed acute fibrinous attachments in portal vein, and chronic granulation tissue at pulmonary artery, aorta, and vena cava attachment sites. briefly describe pathogenesis of thrombi in general, and explain why thrombi may have formed in this dog. --- Dr Van Winkle thromboembolic disease - dz of the blood vessels of heart, lung, and brain, will kill most of us. most people in the US who live past childhood die of thromboembolic disease. so, drink wine! :) it is a big problem in people. however, in veterinary medicine, is it important? well, remember when horses used to get it due to strongylus vulgaris - that was a problem. we don't see it anymore, thanks to Merck's ivermectin. :) in cat, we see it- due to aortic thromboembolism secondary to cardiomyopathy. in dogs and cats, we used to think (and if you read older books it will say) thromboembolic disease wasn't important. except with HW inn dogs, which we also do not see much. Today, we'll talk about what we do see, about clotting and thrombosis in general, and about a series of studies we have done to look at thromboembolic dz in dog. we found that it is way more common than we thought! much is probably subclinical. why is it so important in humans? what do people get? atherosclerosis. we get it b/c of genetics and diet. we see animal atherosclerosis rarely - in hypothyroid dogs, and also in aged pigs (aged pigs being somewhat of an oxymoron...) slide: thrombus in the spleen. splenic vein is thrombosed. one thing different now frm before is concept of fibrinolysis Fibrinolysis: this fits in nicely with human atherosclerotic dz as well as being key to primary thromboembolic dz in dog. remember - most people think of things as a balance between antithrombotic and prothrombotic factors. but, as a human, how would you like this to exist? Precariously, or more stable? [dr vw pulls out a bag of clotting factors (chocolate!)] i think we all agree it should be balanced - not to either side, but in the middle. well, Dr. VW says it should be OUT of balance. he doesn't want the entire blood stream to clot when he stubs his toe. only exceptional circumstances should lead to coagulation! ok that makes sense. Thrombus: a mass of clotted blood within an intact blood vessel system Embolus: any mass (thrombus or other - piece of wood, tumor, fat, whatever) lodged within a blood vessel. Clot: a mass of solid blood. clotting was first studied by people taking blood and putting it innto glass tubes. glass has a negative charge which activates the intrinsic clotting system, meaning you go from factor XII ---> thrombin --> fibrinogen ---> fibrin. so that is what happens in the tube. then you can spin it down and obtain serum. but when you have injury to blood vessels, platelets are involved - and those aren't even mentioned in the tube scenario. platelets are really important in vivo, though. normal hemostasis - what happens actually in the body normally? Injury --> reflex vasoconstriction turned on by local factors --> platelet adhesion and activation --> polymerization of fibrin, involving exposure of blood to tissue factor, activation of thrombin, etc --> fibrin deposition --> clot stabilization - cooperation b/w platelets and fibrin --> organization ---> eventual clot lysis/fibrinolysis this is what people usually talk about - everything up to fibrinolysis in normal situations, fibrinolyisis will occur and flow is restored. when you artificially produce thrombi in dogs, they are cleared within days by normal fibrinolytic systems. so, why don't all thrombi get cleared?? what does this have to do with thrombosis? around 1847, Virkow proposed 3 factors leading to thrombus formation: 1. endothelial injury 2. alterations in blood flow (stasis or turbulence) 3. hypercoagulability/hypothrombolysis this last one is really hypofibrinolysis Dr VW remarks he got to lecture in this class because he bid on the lecture slot in an auction...when he got it the question was what would he lecture on? and he was doing studies about thromboses in dogs. now they're pretty much done those studies. slide: someone looking at a waterfall we talked about the intrinsic system being activated by glass - not relevant in vivo; and extrinsic system involving endothelial injury. there are interconnections b/w the paths, though. so remember subendothelial collagen is negatively charged - so intrinsic system can be a bit involved in vivo btw, Mr Hageman had prolonged bleeding time, but didn't clinically have signs, but did die of thromboembolic dz... factors decreasing thrombosis- thrombomodulin on endothelial cell surface, and heparin like molecules that sit there too, which bind ATIII TPA - tissue plasminogen activator summary slide - diagram in handout. damaged vessel wall with organized thrombus on it - platelets and fibrin -this will grow and grow if fibrinolysis isn't present. when thrombus is formed - heparin, thrombin, plasmin, all get involved with the thrombus is formed. it's a local event. remember prostacyclin (PGI2) inhibits fibrin formatoin and platelet aggregation; also thrombin activates protein C and S to also stop thrombus formation. heparin works w/ATIII to stop formation of fibrinogen. the real action, though, is down on the left. plasminogen activator is locally made by endo cells - activates plasminogen to form plasmin, which is the only thing that breaks down fibrin. so this could be a single point of failure causing complete breakdown of the system. TPA is the thrombolytic drug of choice in humans but would be about $2000/dose in small animals.. things that feed into plasminogen activators - fluids, kallikreins, wbcs, bacteria...but the only thing that comes out if it is plasmin. how is fibrinolysis regulated? PAIs - plasminogen activator inhibitors - these inhibit TPA and other plasminogen activating factors. so we have found that many things elevate the level of PAI in animals. when you have elevated PAI levels, that decreases the amount of plasmin produced, decreasing fibrinolysis. also, if you decrease plasminogen activators, you also have the same effect. reduced availability of TPA can result in thrombus.... ok. questions? ok, when you deal with aortic thrombosis in the dog, textbooks say they are all emboli. that is not true. but why do thrombi form at the bifurcation? in cat, they are all emboli, they do all form in cardiomyopathic heart. but why in dog do they occur down there? endothelial injury? trauma, electrical, chemical, infection, toxin, inflammation, vasculitis, drugs, arteriosclerosis/atherosclerosis, neoplastic invasion, ischemia alteration in flow? immobilization (people in bed for a long time...), heart failure, vascular/cardiac anomaly, hypovolemia, compression of vessels, increased viscosity, preexisting thrombi. why is flow alteration important? ok, blood normally flows in laminar method. the fluid elements are near the endothelium, cells in center. during turbulent state, platelets bang against endothelium. also turbulence can cause more endothelial damage. two other things also happen - one, it brings coag factors into contact with endothelium in greater abundance than normal, andit is harder to get rid of them. hypercoagulability? elevated levels of coagulation cascade proteins (not proven), ATIII deficiency (used to think this was only problematic in congenital situation), decreased removal of activated coag factors, decreased fibrinolysis (decreased plasminogen activators, increased plasminogen activator inhibitors); platelet disorders (seen in patients with decreased albumen), dehydration/hyperviscosity chart p 2 of handout - antithrombotic and prothrombotic factors anti -inhibit platelet aggregation (intact endothelium, prostacyclin, NO, adpase) -anticoagulants - bind and inhibit thrombin (ATIII/heparin, thrombomodulin) -fibrinolysis - TPA pro -stimulate platelet aggregation (endo injury, vWF, PAF, ADP) -procoagulation factors (tissue factor, factor V, binding factors IX, X) -inhibitors of fibrinolysis (TPA inhibitor, antiplasmin) how does this affect dogs? it leads to death. THROMBOEMBOLIC DISEASE IN THE DOG: studies started in 1986 or 1987 when they noticed these cases going on. Why wasn't anyone seeing them before? Because they were poorly trained. Dr. VW was taught never to enter the lung with any other method other than going through bronchi. so he'd do that, then notice these things on the table that looked like emboli...lying on the table. so they changed technique- they go out through right heart and open the PA - one student found 4 dogs with massive emboli in his 2 wks on the service :) things classically associated with thromboembolic dz in dog: vegetative endocarditis - still exists, causes some heartworm dz - rare here; also seen in cats neoplasia - adrenal tumors in vena cava, etc catheterization heart dz vasculitis DIC arteriosclerosis "other" - primary thrombosis - this is the majority of cases Thromboembolic dz in dogs - Thromboembolism in dogs found in one or more of three main vascular beds (portal, pulmonary, systemic) without obvious cause included were dogs with: macroscopic thrombi attached to the vessel wall without other primary thrombi. So remember about the three vascular beds in the body - you inject into the jugular vein---> right atrium -->RV-->PA--->lung so if you put something big into the jugular or any part of vena cava, it will lodge in the lungs. you can't embolize something big from the right side/venous system into the arterial system, b/c it will get filtered in lungs. lung-->LA--->LV--->aorta-->body GI tract ---> portal vein --->liver sinusoidal bed -->hepatic vein -->vena cava so, what about dogs with jugular and anterior vena caval thrombi, PA thrombi, aortic thrombi, and portal vein thrombi? How do you explain this?? these dogs had no signs of endothelial injury, no signs of stasis or flow problem....how about hypercoagulability? pulmonary artery thromboemboli: # of dogs PA 46 PA and aorta 8 PA and portal vein 6 PA, portal, and aorta 1 total 61 well, how do you explain the 15 cases of multifocal thrombi? typical history - one of Dr Littman's wheaton terriers with protein losing enteropathy due to lymphoplasmacytic enteritis, was waiting to go home. it started to pant, then fell over and died. we didn't like this. but Dr VW came in to do the necropsy- there was a big thrombus in the PA. blood can't get into heart with that there, so, dog had to die. histologically, most of these thrombi were not acute, deep in lungs. in lungs, were well organized fibrotic thrombi, growing from periphery of lung back out. when dog gets a really big one, it falls over and dies. this was perplexing. oh, and the GI dz was cured. conditions assiated with the 61 dogs: # of dogs steroids 25 cushings 3 renal/protein losing dz many dogs pancreatic necrosis 4 AIHA 6 atherocsclerosi 3 pericarditis 1 Aortic thromboemboli: 24 with aortic and systemic 8 with aortic and PA 1 with aorta, PA, and vein again, interesting ones were the ones with right and left side thrombi. the disease isn't acute. the thrombi were associated iwth huge fibrous lesions. it looks acute b/c blood flow is suddenly totally cut off when thrombus finally fills the vessel associations: inflamamtory dz, vascular dz, steroids Aortic emboli in dogs: associated iwth endocarditis, endocardiosis, MI portal vein thrombi: in dogs with thrombi here and in other systems - we saw granulation tissue (indicating chronicity) in the portal vein, very chronic thrombus. these wre associated with steroids and local inflammatory disease. other studies done lately had similar results they have about 40 or 50 with brain infarcts, 1/3 associated with thrombi. this isn't seen anywhere as near as often as stroke in people, but it does occur. 44 dogs 1/3 thrombi/vascular dz 1/3 embolic dz 1/3 no clue back to the summary slide the question is why do you see infarcts in those vessels? a variety of reasons...not increased amount of thrombi being formed. we saw things that bothered us - chronicity. if chronic and slow growing, why were they not lysed by plasmin? another thing - if you decrease levels of TPA in dogs with experimentally induced thrombi, the thrombi persist. also in cushingoid dogs treated with steroids - all the catheterized dogs got longterm thrombi - but not the control dogs, though they got the same cath care. no increases in clotting factors was found. so we think the problem is with plasmin, lack or inhibition thereof. we've gathered a lot of evidence over past few years... animals and humans with hyperadrenocorticism (spontaneous or induced) have two problems with fibrinolytic system - decreased levels of TPA and elevated levels of PAI. Ken Bixel did a paper on this with someone. When you have elevated PAIs, you decrease plasminogen activation, so there is less plasmin, and less fibrinolysis. so again this supports the idea that when you ahve these conditions, the thrombi persist. not thatmore are formed, but the ones that do form will persist. another thing- AIHA - proposal here is hypoxic damage to endothelium --> we see animals come in with acute AIHA who are euthanized - they do not have thrombi. but after treatment they do get them - and they are always treated with steroids. so. one thing alone probably isn't enough. but when you take two things and put them together there is a lot of disease. glomerular disease --> decreased ATIII ---> increased PAI --> decreased albumen also leads to increased platelet adhesion. chronic interstitial nephritis ---> increased PAI older animals with cushings probably also have some DM or renal dz...these dogs are at increased risk. acute pancreatic necrosis --> direct endothelial damage many inflammatory diseases are associated iwth increased IL2 and TNF --> those cause increased PAI levels. why don't all dogs with these problems get thromboembolic disease? we had 158 animals with vessel thromboemboli then 108 with brain/other infarcts that's 266 animals how many necropsies were done? about 6000 cases to find these 266. so that's a low incidence. and we see about 20 cases per year. once every 2-3 wks we see an animal die of thromboembolic disease. how many necropsies do we do here? Only about 1/3 of the animals that die here. what about the ones we do not autopsy? it's generally the same population so making a big leap of faith, we guess maybe 1 animal a week dies of thromboembolic disease here. and how many animals have it, and do NOT die of it?? this is a chronic disease. there are probably a lot of animals with thromboembolic disease. treatment: heparin (works to inhibit thrombin by activating ATIII) coumarin (decreases platelet adhesion and K dependent factors) aspirin (not really in vetmed) (decreases prostaglandins and platelet adhesion) these three really prevent thrombus formation, don't help existing thrombi streptokinase- cheaper ($175/dog) but comes from streptococci, which are antigenic, and this stuff is antigenic, and you can only use it ONE time, after which there may be severe reactions. also it acts universally and can cause bleeding at catheter sites, etc. they are trying to make nonantigenic form. TPA and uPA- the real life savers. uPA is also globally acting. tPA acts locally, though. on fibrin that has already formed in thrombi. so TPA is drug of choice. these have been proposed as ways to lyse existing thrombi. they do it enzymatically, by similar mechanisms ICU patients- Dr Palmer's recent article in the July 15th 1998 JAVMA 213(2)- used TPA on some animals ----end----