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Chapter 20: Arterial Thromboembolism 309

and other neoplasias, as well as fibrocartilaginous embo- gency treatment. Other factors that may contribute to
lism-induced infarction. Acute forelimb paresis can be these arrhythmias may include hypocalcemia and/or aci-
caused by trauma, foreign body, or brachial plexus avul- dosis (see Chapter 18, Figure 18.1). Approximately half
sion. Usually the diagnosis of arterial thromboembolism of affected cats had elevated BUN and serum creatinine
is fairly easy to confirm on physical examination. If the levels. Mild prerenal azotemia is common since many
cause is cardiogenic, thoracic radiographs will often cats are dehydrated. However, significant or progressive
demonstrate cardiomegaly. However, in some cats, par- azotemia suggests renal infarction may be playing a role.
ticularly those that are obese, this diagnosis can be dif- Elevations in alanine aminotransferase (ALT) and aspar-
ficult. Moreover, pulse identification can be challenging tate aminotransferase (AST) are common and indicate
in the forelimbs and partial occlusion of appendicular hepatic and hepatic or skeletal muscle inflammation and
arteries can cause limb paresis in the presence of pal- necrosis, respectively. These values usually peak by 36
pable femoral pulses. Doppler evaluation of blood flow hours. As already stated, skeletal muscle enzymes are
can be helpful to lend additional support to a diagnosis significantly elevated, consistent with cellular injury.
of ATE. Severe serum elevations in muscle enzymes (cre- Hyperglycemia, a mature leukocytosis, lymphopenia,
atine phosphokinase and aspartate aminotransferase) and hypocalcemia may also be present. Hyperthryoidism
are frequently present with ATE, as a result of muscle has historically been thought to be linked to ATE through
ischemia. One study showed that local venous glucose secondary cardiac remodeling. However, Smith’s retro-
was significantly lower than central venous glucose and spective study results (2003) suggest hyperthyroidism
local venous lactate was significantly higher than central may pose a risk factor for ATE independent of the cardiac
venous lactate in cats affected with appendicular ATE effects. Therefore, cats of the appropriate age should be
(McMichael et al. 1998). However, the value of these screened for hyperthyroidism. Coagulation abnormali-
diagnostic tests beyond the physical examination abnor- ties may also be detected, especially in cats without sig-
malities remains to be proven. When there are partial nificant cardiac disease, or findings may be normal. Arterial Thromboembolism
thrombi or equivocal findings, they may be supportive Urinalysis may show pigmenturia, (myoglobinuria),
of a diagnosis of ATE. which resolves over the first couple of days.
When echocardiography is available, it allows one to
rapidly and noninvasively evaluate the cardiac structure
DIAGNOSTIC TESTING
and function to choose the optimum chronic therapy
If thromboembolism is suspected, a minimum database for the underlying heart disease of the individual patient,
should include thoracic radiographs, electrocardiogra- once the acute crisis has resolved. An echocardiogram is
phy (ECG), echocardiography, biochemical profile, and not essential to diagnose ATE, and in the acute crisis,
urinalysis. Thoracic radiographs usually reveal cardio- management of thromboembolism and/or heart failure
megaly; however, a small percentage (11%) of cats with takes priority over chronic cardiac therapies. The sonog-
thromboembolism had normal cardiac silhouettes in rapher should search for possible intracardiac clots,
one study (Laste and Harpster 1995). Many affected cats which can be small and attached to the ventricular wall
have evidence of CHF (40–60%) (Smith and Tobias or in the left atrial appendage, large echogenic masses
2004; Schoeman 1999). Radiographs are particularly visible in the left atrium (Figure 20.5). In some patients,
important to definitively diagnose the presence of CHF, spontaneous echocardiographic contrast (SEC, “smoke”)
since some cats will manifest pain with tachypnea and can be visualized in the left atrium or ventricle. Often
medical treatment for CHF could worsen perfusion in an obliqued view results in optimal assessment of spon-
cats that are not truly in CHF. Electrocardiography was taneous contrast in the dilated appendage (Figure 20.6).
shown to be informative in a large retrospective study of This finding has been associated with blood stasis and
cats presenting with ATE, with 85% of affected cats is considered a marker for increased thromboembolic
having ECG changes in heart rate or rhythm (Laste and risk. The mechanism of SEC formation has been attrib-
Harpster 1995). The most common ECG abnormalities uted to erythrocyte or platelet aggregation at low blood
included a left ventricular enlargement pattern (39%), flow velocities. Left atrial enlargement is usually present
sinus tachycardia (28%), ventricular premature beats in ATE cats; however, a small subset of them do not have
(19%), supraventricular premature beats (19%), prolon- cardiac abnormalities detected on echocardiography.
gation of the QRS interval (16%), and a left atrial For example, one study of cats diagnosed with distal
enlargement pattern (16%) (Laste and Harpster 1995). aortic thromboembolism found the left atrium was
The presence of bradycardia or atrial standstill with a severely enlarged in 57%, moderately enlarged in 14%,
sinoventricular rhythm is suggestive of marked hyperka- and mildly enlarged in 22%, with only 5% of cats having
lemia, a dire consequence of reperfusion muscle injury a normal left atrial size (Laste and Harpster 1995). Other
and/or renal thromboembolism, which requires emer- etiologies of thromboembolism should be considered in