These are papers from the July 2011 St. Louis AVMA conference. I’ve edited them to delete some of the vet only jargon and for space considerations. If you see (…) that means that information has been deleted due to these considerations. The ones listed here include HCM, and other heart related papers, treatments, papers on x-rays and echos, thrombosis, kidney disease, idiopathic cystitis, pain management, anesthesia and cardiac disease, supplements and other hazards for pets, and some other basic information I hope is helpful.
Feline Thromboembolic Disease
Meg M Sleeper VMD, DACVIM (Cardiology)
Associate Professor of Cardiology; University of Pennsylvania School of Veterinary Medicine
Introduction
Arterial thromboembolism (ATE) has long been associated with cardiomyopathy. The
syndrome is most often associated with hypertrophic cardiomyopathy (HCM), likely because
this is the most common type of heart disease in cats. Although a majority (89-92%) of cats
with ATE have cardiogenic emboli, neoplasia (in particular bronchogenic carcinoma), was the
cause of ATE in 5% of cats, and 3% of cats had no identifiable cause of the ATE. In cats, most
thromboembolisms involve the left heart and systemic arteries, which causes obstruction of the
affected artery.
History and Chief Complaint
The thromboembolic event is often the first overt sign of heart disease in a subset of
cats. The site of cardiogenic embolization varies, but the distal aorta (“saddle embolus”) is the
most common site, representing 71% of the cases in one large study. The right and/or left
forelegs or, less commonly, various abdominal organs can be embolized…Affected
cats can present in a variety of ways depending on the site of embolization, the duration of
occlusion, and the degree of functional collateral circulation. Distal arterial embolization
affecting the limb(s) usually results in peracute signs of paresis, vocalization and pain. Many
animals present with concurrent congestive heart failure (CHF) with typical clinical signs
(dyspnea, tachypnea, etc.)…
Unfortunately, most cats presenting with ATE display tachypnea because of pain,
making a definitive diagnosis of CHF impossible without thoracic radiographs. In addition to
clinical signs associated with CHF, clinical signs secondary to the specific tissue or organ
embolized are to be expected. Clinical signs that relate to the extremities have been
characterized by the “five Ps”: Paralysis, Pain, Pulselessness, Pallor and Poikilothermia. The
neuromuscular ischemia secondary to vascular occlusion causes severe pain and paresis…and the
distal limbs are cold…The nail beds and pads may appear pale to cyanotic
depending on the severity and duration of ischemia, often there is progression from pallor to
cyanosis over the first 12 hours of embolization. Most affected cats are clinically dehydrated
and/or hypothermic…
Acute case management
Acute therapy of ATE patients is directed toward managing pain, CHF or significant
arrhythmias when present, general patient support, and adjunctive therapies to limit thrombus
growth or future thrombus formation. In the acute phase, a 24-hour care facility is best suited
for these cases, as there may be acute life threatening deterioration at any time during the first
several days after ATE has occurred. If CHF is present, therapy should be initiated similarly to
in other cats with CHF. Analgesia is crucial in these patients, particularly for the first 24 to 48
hours, because after that time period, there is often lack of pain noted in cats with a saddle
embolus. Analgesia can be addressed with various medications…Hypothermia is a manifestation
of poor systemic perfusion and shock rather than just local blood flow changes due to a saddle thrombus; improving it is one of the most important goals in managing the acute crisis in ATE patients…Fluid therapy is warranted for dehydrated patients, as long as CHF is not present, but it must be cautious in cats with significant heart disease. Vigilant monitoring of respiratory rate, effort and auscultation for the development of a gallop is particularly important
in these patients. ..Excellent supportive care in the form of good nutritional support, manual voiding of the urinary bladder, if necessary, and maintaining clean and comfortable bedding is critical in this patient population. In some cats, a nasoesophageal feeding tube may be necessary …Self mutilation of devitalized limbs occurs in a subset of patients and is characterized by excessive licking or chewing of the toes or hock. Application of a loose fitting
bandage barrier is usually effective.
…Sudden hyperkalemia can result from reperfusion syndrome (ischemic rhabdomyolysis and
reperfusion), which occurs when arterial blood flow is re-established to a previously ischemic
region, resulting in acute catastrophic release of potassium into the systemic circulation (9.4%
of cases in one study). Continuous recording of the ECG is one way to screen for circulating
potassium increases…In addition to the detection of hyperkalemia, the development of
reperfusion syndrome can be identified on clinical laboratory results by elevated lactate and acidosis. It is a life threatening condition which usually occurs hours to several days after the embolic event due to systemic release of the metabolic byproducts associated with ischemia. Treatment should be aggressive and
immediate. Hyperkalemia can be addressed with calcium gluconate and/or insulin and glucose
to drive K+ intracellularly. If a secondary bradycardia is present, atropine may be indicated.
Fluid therapy with sodium bicarbonate is warranted to address metabolic acidosis.
Unfortunately, the prognosis in cats which develop reperfusion syndrome is poor, and many
cannot be rescued.
Anticoagulant therapy has no effect on established thrombi, however by retarding
clotting factor synthesis, or accelerating its inactivation, thrombosis from activated bloodclotting
pathways can be prevented. The theoretical aim of anti-coagulant therapy in the acute
phase is to prevent or reduce thrombus extension. ..Although heparin has proven effective
in human trials…it has never been evaluated in spontaneously occurring feline arterial thromboembolism and reported dosages vary widely. In spite of this limitation, heparin is part of the standard of care for hospitalized patients during the early, acute stage of ATE because of these theoretic benefits…aspirin therapy initially has little or no effect, but eventually the effect of prostaglandin predominates…
Long term management
In retrospective studies, the proportion of affected cats with recurrence of ATE has
ranged from 24 to 75 percent and was the ultimate cause of death or euthanasia in 20 to 50
percent of the cats. Subjectively, it appears that a large majority of cats suffering from ATE
have recurrent ATE, and a majority likely succumb to this disorder… it is important to keep in mind that
treating these patients can still be fulfilling and may result in good quality of life for an extended
period of time…Therapy directed at the underlying cause of thromboembolism (most often cardiomyopathy) and CHF
(when present) is crucial for these patients…most veterinary recommendations for anti-coagulant therapy come from anecdotal experience and limited experimental and clinical trials. Of the available options, low dose aspirin therapy is a low risk and inexpensive option with theoretic benefit. Clopidogrel is more costly, but also
appears to be low risk. Antiplatelet therapies focus on the principle that exposure of blood to
subendothelial connective tissue leads to rapid platelet activation, platelet plug formation and
subsequent thrombus. A clinical trial comparing efficacy of aspirin and clopidogrel in cats
which have experienced ATE is currently underway…the general consensus is that clopidogrel is likely more effective than aspirin for prevention of ATE…Clopidogrel is more expensive than aspirin and it should be given with food…but most cats tolerate the medication in pill pockets or gel caps. It must be given daily, so in
cats which are particularly difficult to pill, aspirin administration every third day may be more
reasonable for the owner. Transdermal administration of neither clopidogrel nor aspirin has
been studied and is not recommended. Some clinicians prefer to avoid aspirin in patients with
renal disease because of possible gastric acidity; clopidogrel may be superior in these patients
as long as it does not alter their appetites…Warfarin therapy does not appear
to reduce the risk of ATE recurrence over aspirin therapy. Considering the risk of complications
to warfarin therapy and the cost of therapeutic drug monitoring, warfarin is not typically
recommended for therapy of ATE cats. For chronic therapy, UF heparin has traditionally not been used commonly in veterinary medicine because it requires frequent parenteral administration every 6-8 hours…Moreover, whether
using UF heparin or LMWH, bleeding is a possible complication.
Prognosis and long term outcome
Although the diagnosis of cardiogenic ATE carries a poor prognosis, it is important to
keep in mind that treating these patients can still be fulfilling and may result in good quality of
life for an extended period of time. The short term prognosis depends largely on the nature and
responsiveness of the underlying heart disease and heart failure. Findings which suggest a
better survival rate are having a single limb rather than bilateral limb involvement and
continued motor function at presentation. However, a number of findings suggest a more grave
prognosis including: refractory CHF or development of malignant arrhythmias, acute
hyperkalemia (secondary to reperfusion injury), clinical evidence of multiorgan or multisystemic
embolization, presence of an LA or LV clot, rising BUN/creatinine values, disseminated
intravascular coagulation, and/or unresponsive hypothermia. The owners’ commitment to
therapy and nursing care is an important factor. Notably, having a lower rectal temperature
was a significant risk factor.
References available from author
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